Antibody-mediated rejection (AMR) trigger the allograft rejection and impair renal transplant survival. Non-HLA antibodies are classified into alloantibodies directed against polymorphic antigens and antibodies that recognize self-antigens — autoantibodies. Angiotensin type 1 receptor ( AT1R ) antibody provoke AMR lead to inferior graft survival by increased tissue factor expression and thrombotic occlusions in renal allograft. Perlecan is a large heparan sulfate proteoglycan at vessel wall with anti-angiogenic properties. Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan. LG3 levels in renal transplant recipients associated with allograft vascular injury and dysfunction. Besides, the development of autoantibodies to collagen IV and fibronectin has been associated with transplant glomerulopathy. The collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels which play a vital role in chronic renal allograft rejection.
On the other hand, ischaemia reperfusion injury trigger cascade of inflammatory responses which contributing to the stimulation of the autoimmune responses to the renal allograft. Apoptosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) which can interact with pattern recognition receptors including Toll-like receptor (TLR) 2 and TLR4 expressed on myeloid cells, dendritic cells, vascular endothelial cells and tubular epithelial cells. The Ligation of TLRs results in the recruitment of MYD88 and the production of NF-κB. This process in turn promote the activation of immunological reaction which cause allograft dysfunction.
The immune responses to the transplanted organ occur through the direct, indirect and semi-direct allo sensitive mechanism. This expansion of alloreactive T cells to donor-derived MHC antigens is associated with chronic allograft rejection and DSA production which lead to poor graft survival. The autoreactive memory T cells are generated lead to epitope spreading and the generation of autoantibody. The intermolecular epitope spreading is considered the indirect pathway responses to donor antigens.
Cell-to-cell communication through extracellular vesicles is associated with stimulation of autoimmune and alloimmune responses. Depending on the cellular source, extracellular vesicles can be categorized into three classes exosomes, microparticles and apoptotic bodies which contain autoantigens which increase severity of allograft rejection.
Th17 cells activated by IL-23 lead to chronic tissue inflammation and stimulation of autoimmunity. The development of TLT stimulate chronic allograft rejection of kidney and compromise allograft function.
In conclusion, failure of efficient clearance of extracellular vesicles, particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and interplay between innate and adaptive immunity lead to autoantibody production. The treatment strategies for AMR due to autoantibodies are similar to HLA antibodies. This including antibody depletion, B-cell depletion, IVIG , proteosome inhibitors and complement inhibitors. IL-6 inhibitor tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney transplant recipients. Therapeutic strategies targeting IL-17 pathways, miRNA regulation and exosomes may treat autoantibody-mediated AMR and improve graft survival. The knowledge of the autoantigens that elicit immune responses during transplantation are essential for the diagnosis and treatment of AMR.
Jamila Elamouri
2 years ago
Antibodies against polymorphic HLA antigens is the main cause AMR. Although, they are not the only contributor as many studies have also demonstrated antibodies directed against non-HLA antigens in the process of AMR. These non-HLA antibodies play important role in chronic rejection and reduce long-term allograft survival.
There are two types of non-HLA antibodies:
1- Alloantibodies which are antibodies directed against polymorphic antigens that differ between the recipient and donor.
2- Autoantibodies: antibodies that recognize self-antigens.
Transplanted organ vasculature is the first line to face the recipient immune system, autoantigens expressed by endothelial cells are recognized by nonHLA antibodies leading to renal rejection. Anti-endothelial cell antibodies (AECA) in the recipient before transplantation was first reported by Brasile et al, which was associated with hyperacute rejection.
These recipients displayed negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injury.
The AECA are present in a higher level in renal recipients with graft failure than in those with functioning graft at one-year post-transplantation. Also, they are higher in HLA sensitized candidate than non-sensitized one. Prospective multicenter trial show that recipient with pretransplant AECA had increased episodes of early acute rejection and higher creatinine levels than those without AECA. When comparing living donor and deceased donor, organs from deceased donor exhibit higher levels of non-HLA ligands than those from living donors, explaining the lower association of AECA with acute rejection and with inferior renal graft function in the living donor renal transplant.
Although; ACEA can activate complement results in C4d or C3d deposition in the graft, C4d staining in renal biopsy can be absent in some cases. This could be explained by the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. However, ACEA positive biopsy shows histological findings consistent with AMR, even in absence of complement deposition. The effect of the autoantibodies on the allograft depends on many factors such as ligand expression, ischaemic injury and/or the inflammation within the microenvironment of the allograft.
Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation: AT1R is a G protein coupled receptors, expressed on the endothelial cell surface. It is site of action of angiotensin II, which binds to it, and regulates water-salt balance and blood pressure. AT1R hyperactivity is associated with hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
In renal transplantation, high levels of AT1R antibodies were associated with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA. Biopsy from anti-AT1R positive patients with vascular rejection does not show evidence of complement deposition, even though the AT1R antibodies are of IgG1 and IgG3.
Use of losartan in combination with plasmapheresis and intravenous immunoglobulin (IVIG) for treatment of AT1R antibody positive recipients results in significant improvement of allograft survival compared with those receiving standard anti-rejection therapy with no losartan.
Studies revealed that, AT1R antibody correlated with an increased incidence of AMR and inferior graft survival, and as only minority show positive C4d staining, possibly complement-independent mechanisms contributed to graft injury. The presence and the strength of AT1R antibodies correlate with AMR and also found to be associated with recurrence of FSGS in allograft. Pre-transplant and post-transplant AT1R antibodies were
studied in 351 consecutive kidney transplant recipients using a cut-off value of 15 U/ml44. Presence of DSA adds synergistic effect, and recipient with DSA and AT1R antibodies has lower graft survival.
AT1R antibodies were found to be linked to FSGS recurrence in the allograft, as AT1R are expressed on the podocytes. Many studies support the feasibility of developing an autoantibody panel that might serve as biomarker for risk of FSGS recurrence.
Clinical studies in heart transplantation:
AT1R antibodies level pre-transplantation is associated with ACR and AMR as well as early onset micro-vasculopathy specially in the presence of DSA that add synergistic effect to AT1R antibodies.
AT1R antibodies also develop after LVAD implantation, but this has no impact on the later occurrence of rejection post- heart transplant. Absence of C4d staining in a biopsy of allograft rejection suggest that complement independent pathway is responsible for AR1R antibody mediated rejection. Autoantibodies to AT1R mimic the action of angiotensin. Therefore, cause hypertension and induced vascular changes in the renal transplant.
Perlecan
Clinical studies in renal transplantation:
Perlecan is large heparin sulfate proteoglycan and it’s a major component of the vessel wall. The endorepellin that is the C-terminal of perlecan has anti-angiogenic properties. Perlecan contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)-like repeats. Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. pre-transplant and post-transplant levels of LG3 antibodies of the IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection. LG3 causes vascular
injury and neointimal formation by stimulating autoantibody production and/or by
promoting the migration of vascular smooth muscle cells and/or MSCs.
Collagen
Clinical studies in lung transplantation
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury. Graft injury releases collagen fragments that serve as a major target for autoantibody production. Development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients.
In kidney transplantation:
Kidney recipients diagnosed with transplant glomerulopathy have been shown to develop autoantibodies to collagen IV and fibronectin. These patients have increased collagen IV-specific and fibronectin-specific CD4+T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection.
In heart transplantation
Development of HLA DSA in recipients diagnosed with AMR correlated with the development of autoantibodies to collagen. This had been associated with increased frequencies of collagen V specific CD4+Th cells secreting IL-17 and higher risk of CAV.
Autoantibody production in transplantation
Graft damage mediated through ischemia reperfusion injury, alloimmunity, and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, so these cells act as an autoantigen reservoir which subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
Ischaemia reperfusion injury (IRI)
Organ transplantation associated with varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft. The pathophysiological process involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. IRI causes apoptosis and necrosis with release of damage associated molecular patterns (DAMPAs) which interact with recognition receptors such as Toll-like receptor 2 &4 that expressed on the vascular endothelial and tubular cells ultimately causes downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity:
Alloimmune responses to the transplanted organ occur through direct, indirect and semi-direct allorecognition pathways. The indirect response can spread to more determinants within the primary target antigen, which called intramolecular epitope. This indirect pathway is associated with chronic rejection and linked to the generation of DSAs.
Extracellular vesicles
Cell-to-cell communication can occur through extracellular vesicles. A mechanism that elicits autoimmune and alloimmune responses. The extracellular vesicles contain mRNAs,miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
They are three classes — exosomes, microparticles and apoptotic bodies — all of
which contain numerous autoantigens. Extracellular vesicles released by APCs also carry surface MHC class I and II molecules plus bound peptides that can activate T cell.
TH17 cells and tertiary lymphoid tissue
TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity. IL-17 associated with solid organ transplant rejection and generation of autoimmune responses.
The development of TLT has been reported in chronic allograft rejection of kidney.
lung and heart transplants. TLT is an ectopic accumulation of lymphoid cells, with
characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis. This support maturation and proliferation of B cells and formation of germinal center with production of pathogens autoantibodies.
Conclusion:
To improve long-term transplant out-comes we need to understand the mechanism and pathogenesis of autoantibodies that will help us to develop strategies to diagnose and treat AMR.
Ramy Elshahat
2 years ago
The immune system is considered a major barrier to organ transplantations. There is what is called HLA antigens which are highly polymorphic and act like personal fingerprint recognized by the immune system. If the immune system recognized the allo-HLA antigens expressed on the graft, it will be rejected.
All other antigens are called non-HLA antigens and most of them are monomorphic and cause no antigenic stimulation to the immune system but reports of ABMR in HLA-identical siblings highlight the presence and the importance of non-HLA antibodies.
In general, non-HLA antibodies are classified into:
Alloantibodies: formed only for polymorphic antigens.
Autoantibodies: recognize self-antigens.
Non-HLA antigens most of them not expressed on lymphocytes so, it’s difficult to be evaluated by routine crossmatch
Also, usually not expressed and recognized by the immune system unless there is severe tissue injury like prolonged ischemia time, CNI toxicity, and rejection so it more common with deceased kidneys caused by this prolonged ischemia time.
Its role in inducing ABMR by itself is not been fully proven and is still not recommended to do screening pretransplant and mostly it has a synergetic effect when HLA DSA are there.
Non-HLA Ab mediated rejection can be caused by complement fixing pathway or non-complement fixing pathway so it may cause c4d-ve ABMR and also chronic transplant glomerulopathy
There are several non-HLA antibodies but the most important ones which were generously studied include (Angiotensin II Type 1 Receptor (AT1R-Ab), anti-endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs, and anti-collagen)
Angiotensin type I receptor (AT1R) Ab:
expressed in the endothelial cell surface, binds to angiotensin, and causes salt and water retention and hypertension
if autoantibodies are present in native kidneys it can cause accelerated hypertension, systemic sclerosis, and pre-eclampsia
In renal transplantation, it was reported in patients with severe ABMR, and malignant hypertension and usually respond to treatment with ARBs and plasmapheresis + IVIG
pathogenesis:
complement dependent (C4d +ve) and complement independent process (C4D -v). Perlecan:
It’s a component of the blood vessel wall, the C-terminal domain contains three laminin-like globular domains (LG) separated by 2 sets of epidermal growth factor-like repeats.
Studies showed patients with pre-transplant DSA if patients developed post-transplant LG3 antibodies, patients had significantly reduced one-year graft survival.
Mechanism of injury:
it causes vascular damage and intimal proliferation and/or humoral immune responses that accelerate immune-mediated vascular injury. Collagen:
The development of autoantibodies to collagen IV and fibronectin has been associated with the development of chronic antibody-mediated rejection and transplant glomerulopathy.
The immune system is considered a major barrier to organ transplantations. There is what is called HLA antigens which are highly polymorphic and act like personal fingerprint recognized by the immune system. If the immune system recognized the allo-HLA antigens expressed on the graft, it will be rejected.
All other antigens are called non-HLA antigens and most of them are monomorphic and cause no antigenic stimulation to the immune system but reports of ABMR in HLA-identical siblings highlight the presence and the importance of non-HLA antibodies.
In general, non-HLA antibodies are classified into:
Alloantibodies: formed only for polymorphic antigens.
Autoantibodies: recognize self-antigens.
Non-HLA antigens most of them not expressed on lymphocytes so, it’s difficult to be evaluated by routine crossmatch
Also, usually not expressed and recognized by the immune system unless there is severe tissue injury like prolonged ischemia time, CNI toxicity, and rejection so it more common with deceased kidneys caused by this prolonged ischemia time.
Its role in inducing ABMR by itself is not been fully proven and is still not recommended to do screening pretransplant and mostly it has a synergetic effect when HLA DSA are there.
Non-HLA Ab mediated rejection can be caused by complement fixing pathway or non-complement fixing pathway so it may cause c4d-ve ABMR and also chronic transplant glomerulopathy
There are several non-HLA antibodies but the most important ones which were generously studied include (Angiotensin II Type 1 Receptor (AT1R-Ab), anti-endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs, and anti-collagen)
Angiotensin type I receptor (AT1R) Ab:
expressed in the endothelial cell surface, binds to angiotensin, and causes salt and water retention and hypertension
if autoantibodies are present in native kidneys it can cause accelerated hypertension, systemic sclerosis, and pre-eclampsia
In renal transplantation, it was reported in patients with severe ABMR, and malignant hypertension and usually respond to treatment with ARBs and plasmapheresis + IVIG
pathogenesis:
complement dependent (C4d +ve) and complement independent process (C4D -v). Perlecan:
It’s a component of the blood vessel wall, the C-terminal domain contains three laminin-like globular domains (LG) separated by 2 sets of epidermal growth factor-like repeats.
Studies showed patients with pre-transplant DSA if patients developed post-transplant LG3 antibodies, patients had significantly reduced one-year graft survival.
Mechanism of injury:
it causes vascular damage and intimal proliferation and/or humoral immune responses that accelerate immune-mediated vascular injury. Collagen:
The development of autoantibodies to collagen IV and fibronectin has been associated with the development of chronic antibody-mediated rejection and transplant glomerulopathy.
Wael Jebur
2 years ago
It was recognized in HLA identical twins and 100% donor/ recipient matched matched ,that they might develop progressive ABMR , underscoring the importance of non-HLA antibodies in mounting the reaction.
2 types of antibodies are recognized :
Allo-antibodies, antibodies directed against donor HLA antigens
Auto-antibodies , directed against self-antigens.
As the vasculature represents the inter-phase between the donor and the recipient,it might elucidate the auto-antibody reaction with auto-antigens expressed on the vascular endothelial cells. Anti-Endothelial cell antibodies AECA: Most of the allograft rejections mediated by non anti-HLA antibodies were attributed to AECA that recognize autoantigens on the vascular endothelial cells.
several case reports of acute and hyper-acute rejections inflicted by AECA in the setting of identical HLA haplotypes
Those antibodies are detectable pre-transplantation.
AECA were detected in patients with
1) failed allograft than in those with functioning allograft .
2)HLA sensitized then HLA compatible patients
3)complement is normal in AECA mediated rejection,therfore its considered cellular rejection. C4d was arquably reported in similar cases.
4)AECA are usually non complement fixing IgG2 and IgG4
5)Despite the fact that its non compliment fixing AECA, ALLOGRAFT BIOPSY is usually featuring full house ABMR characteristics including glomerulitis , ptc, margination of monocytes and neutrophils.
Nandita Sugumar
2 years ago
Summary
Antibodies against non HLA antigens are associated with rejection and lower rates of graft survival in the long run. These antibodies can be produced in response to ischemia reperfusion injury, surgical trauma and alloimuune response to antigen. Targeted therapy is needed to fight against these autoantibodies in order to sustain graft survival at good rates.
Current therapy with regards to this issue is antibody depletion, B cell depletion, IVIG, proteasome inhibitors and complement inhibitors. These drugs are given in combination to achieve maximum benefit. However, these are not sufficient in many cases which can be refractory to such therapy and lead to bad graft survival outcomes. A recent therapy includes IL-6 inhibitor tocilizumab. This drug reduces the production of HLA DSA in kidney transplant recipients who are resistant to desensitization protocols and therapy.
Further studies are needed to advance in the knowledge of autoantigens eliciting immune response to transplant. This will help to garner the diagnosis and treatment of AMR.
Manal Malik
3 years ago
summary of The importance of non-HLA antibodies in transplantationintroduction
de novo anti donor HLA (DSA) is associated with poor out come in kidney transplantation
the clinical implication of de novo DSA and the pathogenic role of DSA it self remain unclear.
antibody production usually require T cell help so presence of DSA include the presence of mature cellular alloimmune response.
literature is discrepancy as.to the incidence,timing and impact in term of graft survival of TCMR in patient with DSA .postive.
study is prospective single centre study screen at time of transplant patient with DSA and correlate with acute rejection, severity of rejection and graft out come comparing patients with no DSA or TCMR.DSA alone,TCMR alone or DSA plus TCMR.
we correlate DSA and TCMR to non adherence . Result
study population
among 378 patients kidney transplant between jan 2011-nov 2014
15 excluded death and graft loss with 3 month.
363 patients -294 at least 1 allograft biopsy with first year of transplant were include with study.
276 biopsy early 0 to 5 month .
244 biopsy late 6 to 12 month
total 209 of 294 had paired biopsy (early &late).and those group of patients were used to analyze histological proprieties. post transplant DSA detection
all patients were negative at time of transplant determined by luminex and negative flow-cross match.
294 patients 67 develop DSA in the first year so 40% transplant DSA
60% persistence DSA and 61% de novo DSA, Auto antibody production in transplant
auto antibody production in transplant depend on many factors
:
1-graft damage.
2-alloimmunity
3-chronic inflammation.
auto antigens can present to auto reactive Tcells and B cells either by recipient or donor antigen presenting cells(APCs) in the extra vesicles tissue TLT
Ischemic re perfusion injury
apoptosis and necrosis caused by IRI result in the release of damage associated molecules pattern (DAMPs) including self nucleic ,histone and high mobility group protein B1.
DAMPs interact with receptor include TOLL- like recptor or (TLR) and TLR4 expressed on dentirtic cell vascular endothelial cells and tubular cells.
this process cause down stream production of pro inflammatory cytokines. interplay between alloimmunity and autoimmunity
alloimmune response to the transplant oragan or tissue occur through the direct ,indirect and semi- direct allo recogenazation pathway.contribute to the rejection process..
tissue damage trigger an autoimmune process at the site of the graft.
information might guide to formulation and development of therapeutic intervention to prevent chronic rejection. extracellular vesicles
cell to cell communication through cellular vescles is increasing as a mechanism that elicit autoimmune and alloimmune response.
based on biogensis extracellular vescles classify into 3 classes
1-exosomes
2- micro particles
3- Apoptotic bodies all of them contain memory autoantigens.
TH 17 cells and tertiary lymphoid tissue
TH 17 cells are the major producer of IL-17 and implicated in many autoimmune disease
TH 17 cells have greater capacity to provide B cell help to TH1 by higher clonal expansion conculsion.
evidence support of immunity to self Ag in both acute and chronic rejection of solid organ transplant
auto antibody production via several mechanism:
1- extracellular vesicles insufficient clearance.
2- cross reactivity between self and foreign antigens
3-interplay between innate and a adaptive immunity.
clinical presentation and response to desensitization therapy of non HLA antibodies have not been clearly established.
a need clearly exist for further investigation into the pathogen mechanism of auto antibodies and identification of more effective therapies.
incomplete knowledge of the auto antigens that elicit immune response during transplant hamper the diagnosis and treatment of AMR.
ahmed saleeh
3 years ago
*Target of humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies also showed antibodies directed against non-HLA antigens in the process of AMR.
*Non HLA antibodies are divided into alloantibodies and autoimmune antibodies
*when to suspected Non HLA antibodies : negative lymphocyte crossmatches and tested negative for donorspecific HLA antibodies (DSAs), so AECA as the mediator of graft injury.
*AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates
* deceased donors might exhibit higher levels of non-HLA antibody ligands than those from living donors
*Angiotensin type 1 receptor (AT1R) : (IgG1 and IgG3 isotypes)
Causes ; hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
N.B Over 60% of heart transplant candidates who were AT1R negative prior to LVAD implantation developed de novo AT1R antibodies after the procedure . Development of AT1R antibodies postLVAD did not impact incidence of rejection or transplant survival .
* Perlecan : IgG1 and IgG3 isotypes
vascular rejection and elevated LG3 levels were associated with heightened neointima formation.
HLADSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
* Collagen: first assessed during Lung Tx
Transplant glomerulopathy is characterized by duplication of the glomerular basement membrane
type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity
**Autoantibody production in transplantation:
¥ Ischaemia reperfusion injury : generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment
¥ Interplay between alloimmunity and autoimmunity
Major efforts to define their targets is targeted to understand the mechanism and pathogenesis of autoantibodies and to develop strategies to improve long-term transplant outcomes.
Nasrin Esfandiar
3 years ago
Nowadays, antibodies against auto antibodies have known contribution in ABMR and chronic rejection. Unexpectedly low allograft long-term survival of TX between HLA- matched sibling donors confirms this subject.
Two categories of non-HLA Abs:
1- Allo-abs against polymorphic Ags (different between donor and recipient)
2-Abs against self-Ags (Auto abs) anti-endothelial cell Abs(AECA) are involved in accelerated AMR in many cases with negative XM and negative DSA.
HLA –sensitized TX candidates showed higher frequency of these Abs pre-transplantation. These patients had higher rate of early acute rejection but not for living donor. Many were negative for CD4 for CD4d, because they had subclasses IgG2 and IgG4. But they showed histologic finding of AMR without C4d staining. Using proteomics, a broad array of these auto-abs are known. But these are dependent on other factor such as IRI, ligand expression and inflammation of TX.
AT1R:
AT1R is a G-protein receptor first discovered in pre-eclampsia and its activation causes HTN, proliferation of vascular smooth muscles. In a study 20 Pts with vascular rejection were DSA negative and 16 had AT1R Abs (IgG1 and IgG3) with evidence of complement activation. Treatment consisted a combination of plasmapheresis, IVIG and losartan.
In a cohort of 97 TXs without DSA or M1CA-Abs, six of seven Pts with AMR had AT1R Ab>17IU/ml with no contribution of complement. AT1R-Abs were associated with 2.6- fold risk of chronic rejection. AT1R-Ab positivity had a synergistic effect with HLA-DSA.
In recurrence of FSGS post-TX, plasma exchange combined with losartan were effective in treatment of these Pts with reduction AT1R –Abs. In heart TXs: ACR and AMR were associated with presence of AT1R-Ab and DSA.
Perlecan:
It is a hepran sulfate proteoglycan. Its C-terminal domain two sets of EGF-like repeats. Its angiogenic activity depends on LG3 subdomain, which was increased in patients with Banff grade II or III of AR. LG3 also behave as a neo Ag causing LG3-Ab. Abs especially when they were associated with DSA. There are two different mechanism of vascular injury for perlecan:
1-Direct injury 2-humoral immune responses.
Collagen:
Expression of matrix metalloproteases can modify collagen and release its fragments that causes auto Ab formation.
In kidney TXs, transplant glomerulopathy was associated with collagen IV and fibronectin auto-abs. Collagen V Abs in lung TXs is associated with BOS. TH17-mediated immunity to collagen V caused BOS in lung TXs and IL-17 A and IL-17F secretion by CD4+ TH17 are mediators that lead to the BOS.
Ab production in treatment:
Understanding mechanism of graft damage is important. IRI and chronic inflammation cause auto-abs presented to T or B cell by APC in the form of EV or TLT. IRI cause tissue damage, apoptosis and necrosis and releases DAMPs which can interact with TLR2 and TLR4 on myeloid cell, dendritic cells VECs and TECs. Allo-immune responses against TX occurs through the direct, indirect and semi-direct pathways. Indirect pathway can spread and this process is called epitope spreading and leads to chronic rejection.
EV:
Extracellular vesicles cause cell-to-cell communication and auto-immune and allo-immune responses. EVs contain mRNA, mi RNA, DNA and protein, lipid and CHOs that modulate immunity. They have three classes: exosomes, micro particle and apoptotic bodies containing auto-abs or activate T cells. T H17 cells are activated by TGF-β and IL-6 where Th17 cells are activated by IL-23 causing chronic inflammation.TH 17 can produce IL-17 which has an important role in rejection and autoimmune responses.
TLT:
It is similar to GC but in setting of chronic inflammation through lymphoid neo-genesis. It supports maturation of autoreactive B cells and is modulated by IL-17 secreted from TH17.
Conclusion: Ab formation against self-Ag is important in acute and chronic rejection. Treatment option for AMR caused by auto Abs is similar to AMR caused by DSAs. But more investigation is needed for more effective therapies. For example, IL-6 inhibitor (Tocilizumab) or IL-17 inhibitors are other treatment options.
Ahmed Omran
3 years ago
Non HLA antibodies are involved in antibody mediated rejection leading to decreased graft survival . There are few Non- HLA antibodies and their features typically include positive FCXM in the absence of donor specific DSA on Luminex SAB .They are classified as allo- and auto- antibodies ;including
– AT1R- Angiotensin Type 1 Receptor
Present on endothelial cell surface and antibodies to AT1R are usually IgG1 & 3. and they are risk factor for malignant hypertension graft rejection.
-Preclan
Present on blood vessel wall and having antiangiogenic characters . Lamilin like globulin LG3 is highly antigenic and related to direct vascular injury.
– Collagen
Essentially important in Lung transplant Mechanism of Non HLA Antibodies production involve Ischemic reperfusion injuries(IRI),allo immunity and Chronic inflammation
In summary, non HLA antibody production is multifactorial and result in AMR. Different approaches can be undertaken to manage AMR including IVIG , antibody and B cell depletion and protease inhibitors. More studies are required for better understanding of pathogenesis of rejection to make long term graft survival much better.
MOHAMED Elnafadi
3 years ago
The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival. Although our knowledge of non-HLA antibodies is incomplete, recent studies provide compelling experimental and clinical findings demonstrating that antibodies directed against autoantigens contribute to the process of antibody-mediated acute and chronic rejection. Important areas for investigation remain understanding the mechanisms underlying the production of autoantibodies in the setting of organ transplantation. Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organ-derived autoantigens in the form of soluble antigens, extracellular vesicles or apoptotic bodies that are presented in context of the transplant recipient’s antigen presenting cells to stimulate autoantibody production. Th17 cells are essential in the orchestrating autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promoteallograft rejection. Identification of the immunologic phenotypes of transplant recipients at risk of non-HLA antibody-mediated rejection and the development of targeted therapies to treat these rejections are sorely needed to improve both transplant and patient survival.
Mohammed Sobair
3 years ago
Principal targets of the humoral immune response to the renal allograft are the
highly polymorphic HLA antigens, but studies have also implicated antibodies
directed against non-HLA antigens in the process of AMR.
Non-HLA antibodies are classified into two main categories:
Alloantibodies: directed against polymorphic antigens that differ between the
recipient and donor, autoantibodies: and antibodies that recognize self-antigens.
AECA:
Higher:
In failed transplants than in those with functioning grafts at 1 year post.
In HLA-sensitized renal transplant candidates than in non-sensitized candidates.
Despite generating autoantibodies following transplantation, the majority of patients
did not experience rejection or graft dysfunction. This finding suggests that the
pathogenicity of the autoantibodies is conditional upon other factors such as ligand
expression, ischemic injury and/or the state of inflammation within the
microenvironment of the allograft.
Angiotensin type 1 receptor (AT1R)
AT1R is a G protein receptor that is expressed at the endothelial cell surface, binds
to angiotensin II and regulates water–salt balance and blood pressure.
Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth
muscle migration and proliferation.
AT1R antibody correlated with an increased incidence of AMR and inferior graft
survival.
Significantly higher levels of AT1R antibodies were observed in recipients with
FSGS recurrence.
Clinical studies in heart transplantation:
Increased Pretransplant levels of AT1R antibodies are associated with heart
transplant ACR and AMR as well as early onset of microvasculopathy.
A study showed that elevated pretransplant AT1R antibody levels alone were not
associated with increased risk of rejection, but when both HLA-DSA and AT1R
antibodies were present, the risk of AMR and ACR increased significantly,
suggesting a synergism .
AT1R negative prior to LVAD implantation developed de novo AT1R after LVAD.
Mechanisms of injury:
AB identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a
subset of patients.
Biopsy shows increased tissue factor expression and thrombotic occlusions.
Perlecan:
Heparan sulfate proteoglycan — is a major component of the vessel wall.
The C-terminal domain of perlecan, endorepellin, is best known for its anti-
angiogenic properties68 and contains three laminin-like globular (LG) domains
separated by two sets of epidermal growth factor (EGF) – like repeats. Most of the
antiangiogenic activity of endorepellin resides in the LG3 subdomain.
Studies have shown increased serum LG3 levels in renal transplant recipients with
immune-mediated vascular injury and renal dysfunction.
Similar to AT1R antibodies, HLADSA and LG3 autoantibodies can synergize to elicit
endothelial cell and graft damage.
Mechanisms of injury:
Perlecan cause vascular injury and neointimal formation directly by promoting
migration of donor vascular smooth muscle and/or recipient-derived mesenchymal
cells, and/or elicit humoral immune responses that accelerate immune-mediated
vascular injury and remodelling.
Collagen:
Clinical studies in lung transplantation:
Graft injury is thought to induce the expression of matrix metalloproteases that
modify collagen and release collagen fragments that serve as a major target for
autoantibody production.
Clinical studies in renal and heart transplantation:
Autoantibodies to collagen IV and fibronectin has been reported in renal transplant
recipients diagnosed with transplant glomerulopathy.
In heart transplantation, development of HLA DSA in recipients diagnosed with
AMR correlated with the development of autoantibodies to collagen V.
Mechanisms of injury:
Type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant
vasculopathy in the absence of alloimmunity.
Autoantibody production in transplantation:
Autoantibody production in the transplant setting depends on multiple factors:
Graft damage mediated through IRI.
Alloimmunity.
Chronic inflammation.
Can cause intracellular proteins to be expressed on the surface of apoptotic cells,
raising the possibility that these cells act as an autoantigen reservoirs.
Autoantigens can be subsequently presented to autoreactive T cells and B cells
either by recipient or donor antigen presenting cells (APCs), in the context of
extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT).
Conclusion:
Patterns of clinical presentation and response to desensitization therapy of non-
HLA antibodies have not been clearly established.
Current treatment strategies for AMR due to autoantibodies are similar to that
reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG,
Proteosome inhibitor sand complement inhibitor.
However, it is not clear whether these regimens are effective either alone or in
combination.
Mohamed Essmat
3 years ago
The importance of non-HLA antibodies in transplantation:
The antibodies causing AMR can be either against HLA or non-HLA antibodies . Non-HLA antibodies are said to be a cause of AMR in patients with absence of donor specific HLA antibodies.
Some of these antibodies act against autoantigens like angiotensin type 1 receptor (AT1R), perlecan and collagen. Most of them show C4d negative AMR due to involvement of non-complement dependent pathways.
IRI, allo-immunity and chronic inflammation lead to increased expression of intracellular proteins on surface of apoptotic cells, acting as autoantigen presenting to autoreactive T and B cells by APCs in extracellular vesicles and tertiary lymphoid tissue (TLT). Indirect allo-recognition leads to intramolecular epitope spreading causing formation of allo-antibodies.. Th17 cells give rise to IL-17 which cause tertiary lymphoid tissue (TLT) formation and leukocyte recruitment, release of autoantigens and graft damage. Then B cell differentiation and plasma cell with antibody formation. This autoantibody graft injury can trigger DSA’s.
Last edited 3 years ago by Mohamed Essmat
nawaf yehia
3 years ago
Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and impedes long-term renal transplant survival . The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR. The most convincing evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings .
Non-HLA antibodies are classified into two main categories: alloantibodies & autoantibodies. As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the nonHLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. Brasile et al. were the first to report a patient with pretransplant antiendothelial cell antibodies (AECA) . AECA has been reported to be higher in renal recipients with failed transplants than in those with functioning grafts at 1 year posttransplant. AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates. Interestingly, many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection. Although AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patient and in animal models , others have reported the absence of C4d staining in biopsy samples from patients with AECA. This discrepancy could result from the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. Even in the absence of complement deposition, however, AECA+ biopsy samples exhibit histologic findings consistent with AMR, including glomerulitis, transplant glomerulopathy, focal interstitial haemorrhage, focal capillary thrombosis, and margination of neutrophils, monocytes and macrophages in the peritubular capillaries. ●Angiotensin type 1 receptor (AT1R)
Clinical studies in renal transplantation—Angiotensin type 1 receptor (AT1R) is is expressed at the endothelial cell surface, binds to angiotensin II , its Hyperactivity causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation .. In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA . Even though the AT1R antibodies were IgG1 and IgG3, graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition ( suggesting that complement-independent mechanisms contributed to graft injury)
. Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy. These results indicate that agonistic antibodies targeting AT1R can mediate vascular injury. Subsequent studies confirmed these initial findings and showed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival .
AT1R autoantibody positivity was associated with a higher risk of acute rejection within the first 4 months after transplantation and a higher risk of graft failure beyond 3 years post-transplantation.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement
The presence of AT1R autoantibodies prior to renal transplantation is a risk factor for vascular rejection and malignant hypertension. Not all renal recipients with AT1R antibodies reject their grafts, however, indicating that additional co-factors or environmental conditions might be needed to promote rejection.
●Perlecan
Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties. and contains three laminin-like globular (LG) domains , Most of the antiangiogenic activity resides in the LG3 subdomain . Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction .
●Collagen
Clinical studies in renal and heart transplantation—Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Transplant glomerulopathy is characterized by duplication of the glomerular basement membrane and is associated with chronic renal allograft rejection. Autoantibody production in transplantation
Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs .
Ischaemia reperfusion injury—Organ transplantation inevitably involves varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft. Although the immune system has a number of checkpoints to preserve tolerance to self-antigens, defects in these checkpoints coupled with the constant presence of autoantigen leads to chronic inflammation. Interplay between alloimmunity and autoimmunity
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways. Once initiated, the indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading. This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs . Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process. Conclusion ●The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival.
●Ischaemiareperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organderived autoantigens in the form of soluble antigens, extracellular vesicles or apoptotic bodies that are presented in context of the transplant recipient’s antigen presenting cells to stimulate autoantibody production
●Th17 cells are essential in the orchestrating autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promoteallograft rejection
Dalia Ali
3 years ago
The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
immunity to nonHLA antigens also portends poorer long-term allograft outcome. Two large multicenter studies using independent registry data unexpectedly showed reduced long-term survival of renal transplants performed between HLA-haplotype-matched sibling donors, underscoring the importance of non-HLA immunity to the allograft in chronic rejection
Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies
Angiotensin type 1 receptor (AT1R)
Clinical studies in renal transplantation—Angiotensin type 1 receptor (AT1R) is a Gprotein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure
. Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation
Subsequent studies confirmed these initial findings and showed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival
only one of 6 AT1R+ recipients with AMR had C4d staining in their biopsy sample, again suggesting that complement-independent mechanisms contributed to graft injury.
patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone, suggesting a synergistic effect of these autoantibodies
overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype
Mechanisms of injury
—Although AT1R antibodies implicated in renal rejection were identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of patients, suggesting the involvement of complement-independent pathogenesis of these antibodies
Although angiotensin II binds to several sites in the extracellular loops and transmembrane helices of AT1R58, AT1R antibodies implicated in renal allograft rejection have been mapped to the AFJYESQ and ENTNIT epitopes present in the second extracellular loop (ECL2) of AT1R
Perlecan
Clinical studies in renal transplantation—Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)like repeats.
Mechanisms of injury
First, they showed that passive transfer of anti-LG3 IgG in a murine model of vascular rejection significantly increased infiltration of T cells and natural killer cells, C4d deposition and obliterative vascular remodelling in recipients of ischaemic aortic allografts, but not in adjacent non-ischaemic native aortas70. Second, they showed that escalating serum LG3 levels in murine aortic allograft recipients significantly increased neointima formation
Collagen
Clinical studies in lung transplantation—
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IRI
. Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production
Clinical studies in renal and heart transplantation
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy
These patients displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection
Mechanisms of injury
The role of IL-17-dependent cell-mediated immunity to collagen V in the development of BOS was first demonstrated in a study of lung transplant recipients who were monitored over a period of 7 years following transplantation. Strong collagen V responses correlated with both the frequency and severity of BOS
Autoantibody production in transplantation
alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs
The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs), in the context of extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT)
Ischaemia reperfusion injury—
The tissue damage caused by IRI can lead to acute kidney injury and delayed graft Author Manuscript Author Manuscript Author Manuscript function, which can impair graft survival88. Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1
Interplay between alloimmunity and autoimmunity—
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways
indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading
Extracellular vesicles
Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses
Conclusions and future perspectives
Current treatment strategies for AMR due to autoantibodies are similar to that reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG proteosome inhibitors and complement inhibitors
However, it is not clear whether these regimens are effective either alone or in combination. This issue was highlighted in a case report of renal artery thrombosis, accelerated rejection and graft loss associated with AT1R antibody that was refractory to AT1R blockade, plasmapheresis, IVIG, corticosteroids and eculizumab
A need clearly exists for further investigation into the pathogenic mechanisms of autoantibodies and the identification of more effective therapies.
saja Mohammed
3 years ago
IMPORTANCE OF NON-HLA ABS:
This Review focus on the clinical significance of a selected group of well-characterized autoantibodies and discuss current theories concerning their pathogens and production in renal transplantation.
Introduction:
Antibody mediated rejection can contribute to acute and chronic allograft dysfunction and lead to progressive graft loss. still the effect of non-HLA antibodies on kidney transplant not completely understood, based on evidence from few studies and registry reports which shows that non-HLA antigens associated with increased risk of acute and chronic AMR and accelerated AMR in recipients of renal transplants from HLA-identical siblings. With unexpectedly reduced long-term survival of renal transplants (11,12).
Classification of non-HLA abs
1- Alloantibodies directed against polymorphic antigens
2-Autoantibodies against recognize self-antigens in the endothelial cells
endothelial injury can be triggered by ischemic reperfusion injury, post-surgical trauma and/or alloimmune responses.
AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patients and in animal models with negative C4D staining mimicking cellular rejection this can be explained by the fact that the endothelial-cell-reactive antibodies are enriched for non-complement-fixing subclasses IgG2 and IgG4(31), and still histologically its look like AMR.
The frequency of the AECA was found higher in kidney transplant recipient with previous history of failed graft or presensitization. And organs from deceased donors might have higher levels of non-HLA antibody compared to organs from LD.
Angiotensin type 1 receptor (AT1R):
G-protein coupled receptor that expressed in the endothelial cell surface combined to angiotensin 11 , It regulate the water -salt balance and BP control . increased activity of AR1R lead to hypertension and vasoconstriction with smooth muscle migration and proliferation. also associated with preeclampsia and malignant HTN Prevalence of AT1R vary from 17-59% this variation in prevalence may be explained by the different methods and different cutoff value used for its detection.
In renal transplant elevated levels of AT1R antibodies were first reported in recipients with severe steroid-resistant vascular rejection and malignant hypertension in the absence of HLA-DSA .
AT1R antibodies were IgG1 and IgG3, associated with complement independent endovascular injury and malignant HTN. correlated with an increased incidence of AMR and inferior graft survival. Studies shows combination of HLA-ABS with AT1R have synergistic effect and increase the risk of AMR and graft loss. Renal biopsy specimens from transplant recipients with AT1R-mediated rejection also had increased tissue factor expression and thrombotic occlusions.
Experimental studies address the role of AT1R expression in podocytes with the increase rate of FSGS recurrence post kidney transplant. Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement (52).
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy and also reduced the podocyte injury ().
AT1R might serve as a biomarker for risk of FSGS recurrence.
In heart transplant Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of micro vasculopathy (5). DenovoAT1R found in 60% of the patients with ACD insertion. Combination of AT1R, HLA DSAs increased the risk of both cellular and antibody rejection rate. Perlecan :
a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties. Most of the antiangiogenic activity of endorepellin resides in the LG3, LG3 important regulator of vascular remodeling. Its mainly cuase vascular injury and neointimal formation by stimulating autoantibody production and/or by
promoting the migration of vascular smooth muscle cells and/or MSCs. Few case based studies confirm that renal transplant recipient with high LG3 level have more immune-mediated vascular injury, higher incidence of Banff grade II or III acute vascular rejection and renal dysfunction.LG3 level consider prognostic marker as its associated with higher Risk of acute vascular rejection and reduced 1 years graft survival. collagen:
collagen autoantibodies effect is mainly assessed in lung transplantation.
Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients, triggers by IRI , ischemic immune injury
While in renal transplant recipients diagnosed with transplant glomerulopathy due to the development of autoantibodies to collagen IV and fibronectin. increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection.
In heart transplantation both the production of DSA to HLA and autoantibodies to collagen V was accompanied by increased frequencies of collagen V specific CD4+Th cells secreting IL-17 and higher risk of CAV. Autoantibody production in transplantation:
many factors affect the production of autoantibodies Like IRI ischemic reperfusion injury All immunity with chronic inflammation. Understanding of the mechanisms that lead to autoantibody formation will help in identification of target therapeutic agents to prevent and control vascular remodeling and rejection
Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity(70).defect in the immune check points after IRI in the presence of autoantigens can lead to chronic inflammation and damage .,many autoantigens during IRI can be released , processed and presented to autoreactive T cells by recruited APC . Circulating B cells bind these autoantigens and become activated by autoreactive T cells, resulting in the secretion of autoantibodies. In addition, complement activation can potentiate autoantibody production.
TH17 cells have a greater capacity to provide cognate B cell help than do TH1 cell populations by higher clonal expansion, production. Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.1L17 important for in solid organ transplant rejection and generation of autoimmune responses. Conclusions remarks:
————————————
Autoantibody production might occur via several mechanisms, including failure of efficient clearance of extracellular vesicles, particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and interplay between innate and adaptive immunity.
A lot of debates regarding the main clinical characteristics and response to desensitization protocols in non-HLA autoantibodies and they just follow the same available treatment protocols for AMR targeting Abs depletion, B cells depletion, IVIG, proteosome inhibitors, Complement inhibitors, 1L-6 Tocilizumab,
Still evidence lacking for the effectiveness of the current use of above treatment regimens alone we need further studies to address the main pathogenic mechanisms of autoantibodies and the use of more effective targeted therapies. Like 1L17 Pathways, miRNA regulation148–150 and exosomes.
Last edited 3 years ago by saja Mohammed
manal jamid
3 years ago
Non HLA Anti body
recent studies provide compelling experimental and clinical findings demonstrating that antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival in post renal transplantion.
The evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings.
Many factors lead to auto antibodies formation such as
Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses , extracellular vesicles or apoptotic bodies .
Th17 cells are essential in the regulating autoantibody production by thier effect in proliferation and maturation of autoreactive B cells .
Non-HLA antibodies are classified into two main categories: alloantibodies directed against difference between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the non HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. Brasile et al. were the first to report a patient with pretransplant anti endothelial cell antibodies (AECA) that caused hyperacute rejection, Notably, these
recipients displayed negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injure
Sensitized patient have higher frequency in devoloping AECA.
kidney transplant recipients with pretransplant AECA had increased episodes of early acute rejection and higher creatinine levels than those without AECA.
deceased donors might exhibit higher levels of non-HLA antibody ,because patients AECA and received live kidney not associated with acute rejection or with inferior renal graft function. They were negative for the complement degradation product C4d and graded as cellular rejection.
Angiotensin type I receptor ( AT1R):
Is a G- protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II, and regulates the water-salt balance and BP.
In renal transplantation, elevated level were reported in patients with severe steroid resistance vascular rejection, and malignant hypertension in the absence of HLA-DSA. The main stay of treatment for these patients is by a combination of plasmapheresis, IVIG and losartan.resulted in improved allograft survival compered to patients recovering standard anti rejection therapy.
Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and
FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
Perclean
is a major component of the vessel wall ,known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains.
LG3 regulates vascular remodelling.
Mechanism of injury ,the current paradigm of perlecan-mediated graft injury considers two interdependent mechanisms as follows the perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
Collagen V is present on airway epithelial cells and it increases following immune-mediated injury and/or IRI
Mechanism of injury ; in renal transplant recipients :development of autoantibodies to collagen IV and fibronectin has been detected
In renal transplantation recipients diagnosed with transplant glomerulopathy.
Reem Younis
3 years ago
-Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and long-term graft survival.
-The targets of the humoral immune response to the renal allograft are HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
– The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival.
-Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
– Pretransplant anti-endothelial cell antibodies (AECA) caused the hyperacute rejection.
-The frequency of AECA has been reported to be higher in renal recipients with failed transplants than in those with functioning grafts at 1-year post-transplant and in HLA-sensitized renal transplant candidates than in non-sensitized patients.
-Many of the renal rejections that were reported to be associated with AECA were negative for C4d and graded as cellular rejection.
-The endothelial-cell-reactive antibodies are enriched for non-complement-fixing subclasses IgG2 and IgG431.
-Despite generating AECA following transplantation, the majority of patients did not experience rejection or graft dysfunction.
-The pathogenicity of the autoantibodies depends on ligand expression, ischaemic injury, and/or the state of inflammation within the microenvironment of the allograft.
–Angiotensin type 1 receptor (AT1R):
-It is a G-protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water-salt balance and blood pressure.
– In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA .
-Graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition.
-Treatment of AT1R antibody-positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
– AT1R antibody correlated with an increased incidence of AMR and inferior graft survival.
-AT1R autoantibody positivity was associated with a higher risk of acute rejection within the first 4 months after transplantation and a 2.6-fold higher risk of graft failure beyond 3 years post-transplantation.
-Patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
– Studies suggest a role for AT1R in FSGS; overexpression of human AT1R in podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
-Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
-Significantly higher levels of AT1R antibodies were observed in recipients with FSGS recurrence.
– Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
-A study showed that with elevated pretransplant AT1R antibody levels and the presence of HLA-DSA, the risk of AMR and ACR increased significantly. Mechanisms of injury:
-Although AT1R antibodies implicated in renal rejection were identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of patients.
-Renal biopsy specimens from transplant recipients with AT1R-mediated rejection also had increased tissue factor expression and thrombotic occlusions.
-These occlusions decreased following treatment with losartan and this effect was accompanied by improved renal function and graft outcome.
-Binding of autoantibody binding to AT1R contributes to rejection by mimicking the action of angiotensin II. Perlecan:
-It is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic .
-Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction
-LG3 is a regulator of vascular remodelling.
-Pre-transplant and post-transplant levels of LG3 antibodies of the IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection.
-Patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival. Mechanisms of injury:
-Perlecan-mediated graft injury by two differentmechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodeling. Collagen
-The clinical significance of collagen autoantibodies has mainly been assessed in the setting of lung transplantation.
-Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production.
-Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients.
-Patients with idiopathic pulmonary fibrosis and cystic fibrosis reportedly have the highest prevalence of antibodies to collagen V and Kα-tubulin and are at increased risk of developing primary graft dysfunction, HLA-DSA, and BOS79.
-Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
-In heart transplantation, development of HLA DSA in recipients diagnosed with AMR correlated with the development of autoantibodies to collagen V. Mechanisms of injury:
-The role of IL-17-dependent cell-mediated immunity to collagen V in the development of BOS was first demonstrated in a study of lung transplant recipients who were monitored over a period of 7 years following transplantation. Strong collagen V responses correlated with both the frequency and severity of BOS77.
-Type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity.
-Treatment with neutralizing IL-17 prevented BOS in orthotopic lung transplantation and chronic corneal allograft rejection in experimental mouse models.
-IL-17A and IL-17F secreted by CD4+ TH17 cells specific to lung self-antigens are critical mediators of autoimmunity leading to the pathogenesis of BOS. Autoantibody production in transplantation
-Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated , alloimmunity and chronic inflammation.
-The autoantigens can be subsequently presented to autoreactive T cells and B cells either by the recipient or donor antigen-presenting cells (APCs). -Ischaemia reperfusion injury (IRI)is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation, and leukocyte recruitment .
-The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival.
– Apoptosis and necrosis caused by IRI result in the release of damage-associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1.
-This process in turn causes downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
-Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
– IRI, natural antibodies, HLA-DSA and complement can damage the vascular endothelium leading to release of autoantigens from necrotic and apoptotic cells . Interplay between alloimmunity and autoimmunity:
-Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways. Extracellular vesicles :
-Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
-Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
– Based on their biogenesis, extracellular vesicles can be categorized into three classes — exosomes, microparticles and apoptotic bodies — all of which contain numerous autoantigens.
-Although high concentrations of exosomes can directly activate T cells, the activatory effect of this type of antigen presentation is much weaker than that of antigen presentation by professional APCs owing to the lack of co-stimulatory molecules .
-Exosomes efficiently activate T cells when they interact with dendritic cells. TH17 cells and tertiary lymphoid tissue:
-TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases.
-It is activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.
manal jamid
3 years ago
About the question
Positive FCXM with negative Flowcymetry cPRA
The importance of non-HLA antibodies in transplantation
The development of post-transplant antibodies against non-HLA autoantigens is associated with
rejection and decreased long-term graft survival.
Studies have also implicated antibodies directed against non-HLA antigens in the process of antibody mediated rejection.The most convincing evidence comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings
Non-HLA antibodies are classified into two main categories: alloantibodies directed against
polymorphic antigens that differ between the recipient and donor, and antibodies that
recognize self-antigens — autoantibodies
Antiendothelial cells antibodies (AECA) are non HLA antibodies that were found a cause of AMR.
Interestingly, many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection. Although AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patients and in animal models others have reported the absence of C4d staining in biopsy samples from patients with AECA. This discrepancy could result from the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. Even in the absence of complement deposition, however, AECA+ biopsy samples exhibit histologic
findings consistent with AMR, including glomerulitis, transplant glomerulopathy, focal
interstitial haemorrhage, focal capillary thrombosis, and margination of neutrophils, monocytes and macrophages in the peritubular capillaries
In this article, a selected group of well-characterized autoantibodies are discussed and the current
theories concerning their pathogens and production in renal transplantation.
1-Angiotensin type 1 receptor (AT1R)
Although the AT1R antibodies were IgG1 and IgG3, graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition. Instead, the samples displayed increased expression of tissue factor, which was reduced following treatment with the angiotensin II receptor antagonist losartan. Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
These results indicate that agonistic antibodies targeting AT1R can mediate vascular injury.
Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and
FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
2- Perlecan
a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)- like repeats. Most of the antiangiogenic activity of endorepellin resides in the LG3
subdomain.Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
3-Collagen
Development of autoantibodies to collagen IV and fibronectin has been reported in
renal transplant recipients diagnosed with transplant glomerulopathy
Conclusion
Mounting evidence supports the importance of immunity to self-antigens in both acute and
chronic rejection of solid-organ transplants. Autoantibody production might occur via
several mechanisms, including failure of efficient clearance of extracellular vesicles,
particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and
interplay between innate and adaptive immunity.
The patterns of clinical presentation and response to desensitization therapy of non-HLA
antibodies have not been clearly established.
Current treatment strategies for AMR due to autoantibodies are similar to that reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG proteosome inhibitors and complement inhibitors.
However, it is not clear whether these regimens are effective either alone or in combination. Accelerated rejection and graft loss associated with AT1R antibody that was refractory to
AT1R blockade, plasmapheresis, IVIG, corticosteroids and eculizumab . A need clearly
exists for further investigation into the pathogenic mechanisms of autoantibodies and the
identification of more effective therapies. A potential candidate is the IL-6 inhibitor
tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney
transplant recipients in a small pilot study. Therapeutic strategies targeting IL-17
pathways, miRNA regulation and exosomes might also become viable options to treat
autoantibody-mediated AMR and improve graft survival
Weam Elnazer
3 years ago
The purpose of this paper is to shed light on the significance of non-HLA antibodies in renal transplantation.
In the initial study of AMR, it was shown that the production of post-transplant antibodies against non-HLA autoantigens is related to rejection and lower long-term graft survival. This was discovered in a sibling with matched HLA antigens and negative DSA who developed AMR.
Despite the fact that antibodies directed against non-HLA antigens have been involved in the process of AMR, the primary targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, which are the most common targets of AMR.
Generally speaking, non-HLA antibodies may be divided into two categories: alloantibodies, which are directed against polymorphic antigens that vary between the recipient’s and donor’s immune systems, and autoantibodies, which are antibodies that identify self-antigens.
In part, because the vasculature serves as an interface between the recipient immune system and the transplanted organ, a significant fraction of the non-HLA antibodies that have been found to drive renal rejection to identify autoantigens generated by the endothelial cells in the kidney. It has been shown that patients who have AECA prior to transplantation are more susceptible to hyperacute rejection, despite the fact that they have a negative lymphocyte cross-match and do not have DSA.
Despite the fact that C4 d is usually negative, the histology results are consistent with AMR.
Angiotensin type 1 receptor: This receptor is found in vascular endothelial cells and has been observed in certain individuals with severe steroid-resistant hypertension.
Two, perlecan, is a significant component of blood vessel walls.
3- Collagen type IV and fibronectin are two important proteins.
The processes that underlie the development and pathogenicity of non-HLA antibodies are currently poorly understood, and more research is needed. Examples of mechanisms include the ones listed below:
-Ischemia-reperfusion injury is the first kind of injury.
– a surgical complication
– An alloimmune response occurs.
– the significance of Th17 cells. Their involvement in the generation of autoantibodies by B cells in ectopic secondary lymphoid organs is critical.
– alloimmunity produced by autoantibodies graft injury and the development of DSA of different HLA types
Patients who are at risk of non-HLA antibody-mediated rejection will be identified, and tailored medications will be administered to such patients, resulting in improved graft survival.
The current therapy for AMR caused by autoantibodies is quite similar to the treatment for HLA-related AMR.
Sahar elkharraz
3 years ago
This article focus on importance of non HLA antibody in transplant.
Antibody mediated rejection (AMA) are responsible for both acute & chronic allograft rejection and decrease log term survival transplant.
Case series study who discovered by Brasile shows formation of pre transplant anti endothelial cell antibody (AECA) in patient develops hyperacute rejection in twice renal transplant despite negative lymphocytes cross match & negative DSA.
Many multicenter study discover increase level of AECA in sensitised patients develops acute kidney transplant rejection and noticed that it is not associated with complement activation (Cd40),
AECA is riched with non complement fixing sub class IgG2 & IgG4.
Histological feature of patients with AMR & high level of AECA includes glomerulitis / transplant glomerulopathy / focal interstitial haemorrhage/ focal capillary thrombosis/ migration of neutrophils and monocytes & macrophage in peri tubular capillaries.
Majority of patients who have generation of autoantibodies following transplant not develops rejection and graft dysfunction and this may related to many factors such as ligand expression and ischemic injury and inflammation within graft.
Angiotensin type 1 receptor (AT1R) : it’s G protein responsible for regulating water & salt balance and blood pressure.
In renal transplant shows who have high level of AT1R antibodies even in absence of DSA associated with malignant hypertension & severe steroid refractory vascular injury. it’s can treated by Losartan / Plasmapheresis and IV IG results in significant improvement of allograft.
AT1R also complement independent and associated with AMR especially if patients have DSA.
Recurrence of FSGS after kidney transplant accelerate allograft failure.
FSGS may be idiopathic or hereditary and manifested by proteinuria & affeciment & damage of podocytes. there’s relation between recurrence of FSCG and level of AT1R.
clinical study in heart transplant: presence of both AT1R & DSA associated with develops Acute cellular rejection (ACR) & AMR in comparison of high level AT1R alone. they reported increase level of AT1R in patients with left ventricle assist device but no evidence of rejection post transplant and it’s mechanism unknown. Presence of AT1R autoantibodies prior to transplant is a risk for vascular rejection and malignant hypertension but not all patients develop rejection and there’s another factors contribute to rejection which is ischemic reperfusion injury.
Perlecan : large heparan sulfate proteoglycan. it’s major component of blood vessel. it’s called antiangiogenic properties. it’s contain 3 laminin like globular domin separated by 2 set of epidermal growth factor. most of endorepellin resides LG3. Apoptolic endothelial cell liberate cathpsin L which cleave LG3. they show increase level of LG3 in rejected patients with Banff grade II & III. study found that pre- post transplant level of LG3 antibodies of IgG1, IgG2 isotype were significant higher in patients with acute vascular rejection. Also they show relation of LG3 & DSA together against graft.
Collagen : Release of collegen fragments can lead to autoantibodies production and accelerate graft injury in lung transplant.
Post transplant formation of collagen antibody associated with development of bronchitis obliterance syndrome in lung transplant recipients. it’s also high level of collagen in patients with idiopathic pulmonary fibrosis & cystic fibrosis and contributes to graft rejection.
Clinical study in renal & heart transplant: Formation of autoantibodies to collagen IV & fibrorectin associated with chronic allograft nephropathy and increase risk of transplant glomerulopathy, Those patients with chronic rejection shows increase level of collagen IV specific & fibronectin specific CD4 T cell that secret INF-gamma & IL-17 & reduction of IL-10.
Experimental study on rate which are immunized with collagen V induce up regulation IL17 & IL23, mRNA expression T cell and adaptive transfer of Th17 will induce BOS lesion in lung isograft.
they hardly discover drug targeting against Th17 may improve long term survival graft.
Intrabronchial administration of anti- MHC class 1 control IL-17 may reduce cellular infiltration and decrease fibrosis and reduce collagen V antibody level.
So IL-17 A, IL17F are secreted by CD4 Th17 cell are specific to lung specific antigen and have roles in autoimmunity in developing BOS in lung transplant.
Autoantibody production in treatment:
it’s important to understand mechanism of autoantibodies by production to identify new therapies to prevent and control transplant rejection.
Ischemic reperfusion injury (IRI):
it’s has many factors like surgical trauma and tissue damage can induce innate inflammatory response which lead to generation alloimmune and autoimmune on graft.
IRI is complex pathophysiology mechanism which lead to generation of reactive oxygen species/ complement activation / coagulation / endothelial activation and leukocyte recruitment.
Tissue damage due to IRI lead to acute kidney injury and delay graft function and improve graft survival.
IRI can lead to release of pro-inflammatory mediators which lead to activation of adaptive immune response that lead to exacerbate allograft damage.
Interplay between alloimmunity and autoimmunity: alloimmune response in transplant organ can related to direct/ indirect and semi direct allorecoganise pathway.
Extra cellular vesicles are responsible for communication between cells. it’s categories to exosome and micro particles and apotopic bodies; these contain many antigens and it’s role regulating autoantibodies.
Th17 cells & tertiary lymphoid tissue involved in many autoimmune disease and lead to produce IL17 which responsible to promote chronic tissue inflammation & anti immunity.
Conclusion;
Autoantibodies production may occur by several mechanisms.
Patterns of clinical presentation and response to desensitisation therapy of non HLA Ab still not clear.
Current treatment strategy of AMR due to antibodies are similar to HLA antibodies including antibodies depletion and B cell depletion and IV Ig / complement inhibitors and it’s still not clear if it’s effective alone or combination.
· Many non -HLA antibodies are formed against released Ag from the graft upon exposure to traumatic events like (ischemia-reperfusion injury and surgery itself), those antibodies were corelated to both active and chronic AMR and eventually worse graft outcome.
· The evidence of the role of non-HLA antibodies in rejection comes from rejection in HLA identically transplant couples.
· Non-HLA antibodies are either directed against:
o Polymorphicallogenic antigens in graft.
o Autoantibodies: directed against own Ag (as endothelial Ag- anti-endothelial cell antibodies) after their exposure to traumatic event.
· These anti-endothelial auto-antibodies characterized by:
§ Higher among sensitized than non-sensitized patients and correlated to the graft outcome.
§ Cause hyperacute AR that occurred on table and reoccurred in 2nd transplant.
§ Occur in cases that had negative cross match and no detected DSA before transplantation.
§ Pathology of acute rejection here not exclusive AMR, but commonly presented with TCMR and C4d negative.
· Not all cases with non-HLA antibodies develop AR as many coexisting factors like cold ischemia time, ischemic reperfusion injury and state of microvascular inflammation.
Examples of non-HLA antibodies with significant impact on graft outcome:
o Angiotensin II, type 1 receptor antibodies:
§ Characterized by severe steroid resistant vascular rejection, no detected DSA and malignant hypertension which was treated by combined plasma exchange, IvIg and losartan.
§ Persistent positive antibodies post transplant and denovo antibodies carry worse outcome than those with positive antibodies pretransplant and turned negative after transplant.
§ Combined presence of those antibodies and DSA carry worse outcome than DSA alone.
§ Patients with recurrent FSGS post transplant demonstrated higher levels of those antibodies, which can be related to their role in podocyte injury and foot processes effacement. Treatment with PEX and losartan improved their outcome.
§ The pathogenesis related to effect of AII receptor effect and the pathology shows marked vascular injury (endarteritis and intravascular inflammatory infiltrate).
§ In heart transplantation, only their coexistence with DSA (rather than isolated anti AII receptor type 1 antibodies) carry worse outcome and increased risk of AMR and TCMR.
o Anti LG 3 (laminin like globular, component of perlecan present in structure of blood vessel).
o Anti collagen V antibodies: associated with increased IL17
§ Especially in lung transplantation in cystic fibrosis with marked injury of bronchioles basement membrane and bronchiolitis obliterans syndrome.
§ Renal transplant: may be responsible for transplant glomerulopathy (GBM multilayering).
§ Heart: associated with increased DSA and coexistence carry worse prognosis of the graft.
Factors increase risk of autoantibodies:
o Release and processing of self antigens on apoptotic cells and its presentation by either donor or recipient APC to auto-reactive B and T cells.
o Ischemic reperfusion injury which release reactive oxygen species and other inflammatory mediators that lead to endothelial injury and leukocyte recruitment.
o Alloimmune-autoimmune interaction: Alloimmune recognition occurs either direct ( by donor APC), indirect (by recipient APC) and semidirect (by allo-peptides bound to donor Ag).
o Cell to cell communication through extracellular vesicle as apoptotic bodies. Failure of clearance of those extracellular vesicles lead to recognition by APC and B, T cells activation with immune mediated graft damage.
Treatment of non-HLA antibodies mediated vascular rejection;
o Yet, not clear.
o It may be resistant to current ttt for AMR including steroids, PEX, IvIg, rituximab, ecluzimab. A need clearly exists for further investigation into the pathogenic mechanisms of autoantibodies and the identification of more effective therapies.
o IL-6 inhibitor tocilizumab may be beneficial.
o New therapeutic options targeting IL-17 pathways, miRNA may be future target.
Amit Sharma
3 years ago
The importance of non-HLA antibodies in transplantation
The long-term graft survival gets affected by antibody mediated rejection (AMR). The antibodies causing AMR can be either against HLA or non-HLA antibodies which can be further divided into alloantibody against polymorphic antigens differing between the recipient and the donor or autoantibodies that recognize self-antigens. Non-HLA antibodies have been incriminated as cause of AMR in patients with absence of donor specific HLA antibodies (DSA). especially in deceased donor transplants.
A substantial number of these antibodies act against autoantigens like angiotensin type 1 receptor (AT1R), perlecan and collagen. Most of these show C4d negative AMR due to involvement of non-complement dependent pathways. AT1R antibodies act on AT1R (especially ECL2 loop) leading to phosphorylation of ERK kinase stimulating AP-1 and NFKB in endothelial cells and smooth muscle cells. This gets aggravated in presence of cofactors like ischemia (ischemia-reperfusion injury, IRI). Perlecan is found in vessel wall and its C terminal domain called endorepellin has anti-angiogenic properties due to its LG3 subdomain. Serum LG3 levels have been found to be high in acute vascular rejection and are associated with poor graft survival. Bioactive forms of perlecan can cause direct vascular injury as well as antibody mediated vascular injury and remodelling. Antibodies to Collagen IV and fibronectin in kidneys have been shown to be associated with rejection with specific CD4+ T cells secreting interferon gamma and IL-17 and decreased levels of IL-10.
IRI, alloimmunity and chronic inflammation lead to increased expression of intracellular proteins on surface of apoptotic cells, acting as autoantigen presenting to autoreactive T and B cells by APCs in extracellular vesicles and tertiary lymphoid tissue (TLT). Indirect allorecognition leads to intramolecular epitope spreading causing formation of alloantibodies. Extracellular vesicles including exosomes, microparticles and apoptotic bodies contain autoantigens which can activate T cells, although weakly due to absence of co-stimulation. Th17 cells give rise to IL-17 which cause tertiary lymphoid tissue (TLT) formation and leukocyte recruitment, release of autoantigens and graft damage. Il-21 released by them cause B cell differentiation and plasma cell with antibody formation. This autoantibody mediated graft injury can trigger DSA development and further graft deterioration.
Professor Ahmed Halawa
Admin
3 years ago
Dear All
Non-HLA is expected when the crossmatch is positive (CDC/FCXM) in the absence of DSA.
There are 10 winners
Last edited 3 years ago by Professor Ahmed Halawa
AMAL Anan
3 years ago
-Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and impedes long-term renal transplant survival.
-Non-HLA antibodies are classified into two main categories: alloantibodies directed against
polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens autoantibodies.
-Brasile et al. were the first to report a patient with pretransplant antiendothelial cell antibodies (AECA) that caused hyperacute rejection of a maternal renal allograft.
-At the population level, the frequency of AECA has been reported to be higher in renal
recipients with failed transplants than in those with functioning grafts at 1 year posttransplant.
-The specificity of the autoantibodies developed during the immune response to the allograft
is diverse.
** Angiotensin type 1 receptor (AT1R):
-Clinical studies in renal transplantation Angiotensin type 1 receptor (AT1R) is a Gprotein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin
II and regulates water–salt balance and blood pressure37. Hyperactivity of AT1R causes
hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
-In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA.
-Subsequent studies confirmed these initial findings and showed that AT1R antibody
correlated with an increased incidence of AMR and inferior graft survival.
-Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation
causes accelerated allograft loss in approximately 30% of recipients.
-Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause
podocyte damage and foot process effacement consistent with a FSGS phenotype.
-Depletion of AT1R antibodies by plasma
exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in
this patient.
*Clinical studies in heart transplantation Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
* Mechanisms of injury—Although AT1R antibodies implicated in renal rejection were
identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of
patients, suggesting the involvement of complement-independent pathogenesis of these
antibodies.
-the presence of AT1R autoantibodies prior to renal transplantation is a
risk factor for vascular rejection and malignant hypertension.
** Perlecan:
*Clinical studies in renal transplantation—Perlecan a large heparan sulfate .proteoglycan is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties.
* Mechanisms of injury:
-The current paradigm of perlecan-mediated graft injury considers two different, but interdependent mechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
** Collagen:
*Clinical studies in lung transplantation:
-The clinical significance of collagen
autoantibodies has mainly been assessed in the setting of lung transplantation . Collagen V is present on airway epithelial cells and its
expression increases following immune-mediated injury and/or IRI.
*Mechanisms of injury:
-Administration of collagen-V-specific CD4+ T cells or antibodies to collagen V can induce BOS in experimental models of lung transplantation.
*Autoantibody production in transplantation:
-Autoantibody production in the transplant setting depends on multiple factors. Graft damage
mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs.
*Ischaemia reperfusion injury:
-Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in
the absence of alloimmunity. For example, adoptive transfer of collagen-V-reactive
lymphocytes to Wistar Kyoto rats induced grade 2 rejection in fresh isografts and collagen V
expression (detected using immunhistochemistry) in fresh and well-healed isografts, but not
in native lungs.
-In a murine chronic lung transplant model, C3a increased IL-17 production by collagen-Vreactive T cells, suggesting an important role of
complement in the development of autoantibody responses.
*Interplay between alloimmunity and autoimmunity:
-Alloimmune responses to the
transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition
pathways.
-Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process.The indirect alloresponse triggers autoimmunity after transplantation presumably via antigen mimicry between autoantigen peptides and donor MHC peptides.
-Once autoreactive T cells are generated, chronic stimulation of these cells can lead to epitope spreading, which has been reported to contribute to the generation of autoantibodies.
* Extracellular vesicles :
-Cell to cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and
alloimmune responses.
-Extracellular vesicles released by APCs also carry
surface MHC class I and II molecules plus bound peptides that can activate T cells.Although high concentrations of exosomes can directly activate T cells.
* TH17 cells and tertiary lymphoid tissue:
-TH17 cells are the major producers of IL-17
and have been implicated in many autoimmune diseases. TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and
autoimmunity.
-The development of TLT has been reported in chronic allograft rejection of kidney. lung and heart transplants .TLT is an ectopic accumulation of lymphoid cells, with characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis.
References:
1. Stegall MD, et al. Terminal complement inhibition decreases antibody-mediated rejection in sensitized renal transplant recipients. Am J Transplant. 2011; 11:2405–13. [PubMed: 21942930] .
2. Amico P, et al. Clinical relevance of pretransplant donor-specific HLA antibodies detected by singleantigen flow-beads. Transplantation. 2009; 87:1681–8. [PubMed: 19502960] .
3. Gloor JM, et al. Baseline donor-specific antibody levels and outcomes in positive crossmatch kidney transplantation. Am J Transplant. 2010; 10:582–9. [PubMed: 20121740] .
4. Everly MJ. Incidence and hazards of alloantibodies in renal transplantation. Clin Transpl. 2013:313–7. [PubMed: 25095523] .
5. Wiebe C, et al. Evolution and clinical pathologic correlations of de novo donor-specific HLA
antibody post kidney transplant. Am J Transplant. 2012; 12:1157–67. [PubMed: 22429309] .
6. Lefaucheur C, et al. Preexisting donor-specific HLA antibodies predict outcome in kidney
transplantation. J Am Soc Nephrol. 2010; 21:1398–406. [PubMed: 20634297] .
7. Gourishankar S, et al. Pathological and clinical characterization of the ‘troubled transplant’: data
from the DeKAF study. Am J Transplant. 2010; 10:324–30. [PubMed: 20055809] .
8. Grafft CA, et al. Antibody-mediated rejection following transplantation from an HLA-identical
sibling. Nephrol Dial Transplant. 2010; 25:307–10. [PubMed: 19846396] .
9. Kalil J, et al. Humoral rejection in two HLA identical living related donor kidney transplants.
Transplant Proc. 1989; 21:711–3. [PubMed: 2650236] .
10. Montoliu J, et al. Delayed hyperacute rejection in recipients of kidney transplants from HLA
identical sibling donors. Am J Med. 1979; 67:590–6. [PubMed: 386793] .
11. Terasaki PI. Deduction of the fraction of immunologic and non-immunologic failure in cadaver donor transplants. Clin Transpl.2003:449–52. [PubMed: 15387129].
CARLOS TADEU LEONIDIO
3 years ago
This article resume studies about non-HLA autoantigens directed against autoantigens contributing to the process of antibody-mediated acute and chronic rejection. The most convincing evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings.
Non-HLA antibodies are classified into two main categories:
1 – alloantibodies directed against polymorphic antigens that differ between the recipient and donor;
2 – antibodies that recognize self-antigens — autoantibodies;
ANTI – ENDOTHELIAL CELL ANTIBODIES
A substantial proportion of the non-HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells (AECA). This kind of recipients displayed negative lymphocyte crossmatches and tested negative for donor-specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injury.
ANGIOTENSIN TYPE 1 RECEPTOR (AT1R)
Antibodies to angiotensin type 1 receptor (AT1R), are others kind of antibody no-HLA involved with antibody-mediated rejection (AMR) and inferior graft survival. A study showed that elevated pretransplant AT1R antibody levels alone were not associated with increased risk of rejection, but when both HLA-DSA and AT1R antibodies were present, the risk of AMR and ACR increased significantly, suggesting a synergism between AT1R and HLA antibodies in promoting rejection.
PERLECAN
Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG). Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
COLAGENN
Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
AUTOANTIBODY PRODUCTION IN TRANSPLANTATION
Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated through ischaemia reperfusion injury (IRI), alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs. The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs), in the context of extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT).
INTERPLAY BETWEEN ALLOIMMUNITY AND AUTOIMMUNITY
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways. Once initiated, the indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs
Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process. The indirect alloresponse triggers autoimmunity after transplantation presumably via antigen mimicry between autoantigen peptides and donor MHC peptides108. Several studies have shown that autoreactive proinflammatory T cells specific for collagen V and cardiac myosin are detected after lung and heart transplantation, respectively. Clonal expansion of these T cells occurs only after an alloresponse, and once stimulated they can induce rejection of allogeneic transplants.
EXTRACELLULAR VESICLES
Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses. Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
TH17 CELLS AND TERTIARY LYMPHOID TISSUE
TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases. TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity. A large body of data demonstrates the importance of IL-17 in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection
Filipe prohaska Batista
3 years ago
Humoral immunity may find different pathways for antibody production, either primarily (autoantibodies) or by exposing donor antigens outside the HLA complex (alloantibodies), inducing antibody-mediated rejection. This response is quite heterogeneous and multifactorial, involving increased or decreased expressions, ischemic injury, and inflammatory state of the allograft.
Angiotensin type 1 receptor (AT1R)
– Triggers apparently vascular lesion refractory to the use of corticosteroids
– Malignant hypertension
– Major vascular rejection
– Usually does not use complement to trigger the lesion
– May trigger acute rejection in the first 4 months or late after 3 years of transplantation
– Appears to be related to recurrent focal and segmental glomerulosclerosis
– When associated with DSA/HLA, the prognosis worsens
– Treatment is based on a combination of plasmapheresis, intravenous immunoglobulin, and losartan
Perlecan
– Important component of vascular endothelium
– Predominant activity in the LG3 subdomain
– LG3 suggests being a regulator of vascular remodeling
– May lead to vascular lesions and synergize with HLA-DSA, similar to what occurs with AT1R antibodies
Collagen
– Expresses metalloproteases that modify collagen and lead to the production of autoantibodies
– In lung transplantation, it is common to trigger bronchiolitis obliterans syndrome
– In kidney transplantation, it is common to cause transplantation glomerulopathy
– Uses the Th17 axis and interleukins can lead to direct graft injury (IL17) or autoantibody production (IL23)
Autoantibody production in transplantation
– Ischaemia reperfusion injury
– Alloimmunity x Autoimmunity
– Extracellular vesicles
– Th17 cells and tertiary lymphoid tissues
All of these paths can occur autoantibody production might occur via several mechanisms, including extracellular vesicles, apoptotic bodies, cross-reactivity between self and foreign antigens, and the interplay between innate and adaptive immunity induced by the Th17 IL 12-17-23 path.
Conclusion
Depending on the interleukins involved and the antibodies produced, new strategies such as antibody depletion, B cell depletion, IVIG, proteasome inhibitors, and complement inhibitors may be used with better results in the treatment of classical immunosuppression.
Theepa Mariamutu
3 years ago
The importance of non-HLA antibodies in transplantation
Acute and chronic antibody mediated rejection known to affects long term graft survival
HLA and Non- HLA antibodies have a role in pathogenesis of AMR
Non-HLA antibodies consists of:
· Alloantibodies -directed against polymorphic antigens that differ between the recipient and donor
· Autoantibodies: antibodies that recognize self-antigens
Antiendothelial cell antibody (AECA):
Directed against kidney are found more common in deceased donor transplants and in highly sensitized recipients
As endothelium is the most common tissue exposed to the circulating blood- directed against the endothelium cause hyperacute rejection in the renal transplant recipients
Usually negative for DSA and cross matches
Features of glomerulitis, capillary thrombosis, transplant glomerulopathy with or without c4d deposition are found
not activated by complement due to AECA being IgG2 or IgG4 antibodies in nature
Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation revealed:
Antibodies to AT1R are associated with severe resistant vascular rejection and malignant hypertension
The combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy
Its complement-independent mechanisms graft injury – HLA -DSA negative and no C4d in renal biopsy
Positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
Some studies revealed that AT1R has a role in recurrence of FSGS in post-transplant recipients as it found mostly in recurrence than first occurrence
Perlecan:
The C-terminal domain of Perlecan, endorepellin- known for its anti-angiogenic properties which resides in the LG3 subdomain
High LG3 level associated with poor graft outcome
HLA-DSA positive with high LG3 level were associated with vascular rejection and more graft failure comparison to HLA-DSA positive alone
Collagen:
autoantibodies to collagen IV and fibronectin have been reported in renal transplant recipients diagnosed with transplant glomerulopathy (TG)
displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection
Autoantibody production in transplant:
Depends on multiple factors including graft damage due to ischemia reperfusion injury, alloimmunity and chronic inflammation
Ischemia reperfusion injury (IRI):
Can induce innate inflammatory response resulting in alloimmune and autoimmune response to the graft – cause graft damage and delayed graft function
studies showed that it may induce autoimmune response in absence of alloimmunity
Interplay between autoimmunity and alloimmunity:
Indirect alloimmune response can trigger autoimmunity after transplant via antigen mimicry between autoantigen peptides and donor MHC peptides
Tissue damage due to alloresponse to donor HLA antigens may cause release of sequestrated autoantigens leading to triggering of autoimmune response at site of the graft
Extracellular vesicles:
Cell to cell communication via extracellular vesicles can elicit autoimmune and alloimmune response as they contain numerous autoantigens.
Th17 cells and tertiary lymphoid tissue (TLT):
Th17 cells secrete IL-17 that has a role in solid organ transplant rejection and in generation of autoimmune response
Development of TLT was reported in chronic allograft rejection, it is an ectopic accumulation of lymphoid cells similar to germinal centre in a secondary lymphoid organ which occur in chronic inflammation through lymphoid neogenesis
Conclusion:
Non HLA antibody production is multifactorial and leads to AMR. Multiple strategies can be adopted to treat AMR. These include IVIG , antibody and B cell depletion and protease inhibitors. More efforts are required to understand more the pathogenies to as to improve long term graft survival
ZAHID NABI
3 years ago
This article throw light on importance of non HLA antibodies in renal transplantation.
The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival, this was shown first in sibling with matching HLA antigens and negative DSA who developed AMR.
The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
Anti-endothelial cell antibodies (AECA): As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the non- HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. It has been seen that patients having AECA prior to transplant are more prone to hyper acute rejection though having negative Lymphocyte cross match and absence of DSA.
The histological findings are consistent with AMR though C4 d is negative most of times.
Angiotensin type 1 receptor antibody (AT1R )– can cause steroid resistant vascular rejection, malignant hypertension and will be HLA-DSA negative.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury.
Perlecan a large heparan sulfate proteoglycan is a major component of the vessel wall.
The current paradigm of perlecan-mediated graft injury considers two different, but interdependent mechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
Collagen
Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
Autoantibody production in transplantation.
Autoantibody production in the transplant setting depends on multiple factors. The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
Ischaemia reperfusion injury—Organ transplantation inevitably involves varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft.
Interplay between alloimmunity and autoimmunity. This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs.
Extracellular vesicles—Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
TH17 cells and tertiary lymphoid tissue.
A large body of data demonstrates the importance of IL-17 in solid organ transplant rejection and generation of autoimmune responses.
Innocent lule segamwenge
3 years ago
The importance of non-HLA antibodies in transplantation
This is a review article highlighting the different non-HLA antibodies, their mechanism and role in transplant rejection.
Rejection due to non- HLA antibodies was first described in sibling with matching HLA antigens and negative DSA who developed AMR.
Two types of non- HLA antibodies- Antibodies against polymorphic antigens and autoantibodies. Anti-endothelial cell antibodies (AECA) cause hyperacute rejection, non- complement fixing and may be C4d negative. The biopsy features are similar to those found in AMR.
Mechanism of action- activating endothelial cells and dependent on presence of other factors like inflammation and ischaemic injury to be full pathogenic.
Angiotensin type 1 receptor antibody (AT1R )– can cause steroid resistant vascular rejection, malignant hypertension and will be HLA-DSA negative.
Treatment is largely plasmapheresis, IV ig and Losartan.
Development of denovo ATIR antibodies leads to graft loss.
Presence of pretransplant antibodies has variable outcomes.
Could also have a role in initiating FSGS recurrence.
Have synergistic activity in the presence of HLA- DSA.
Mechanism of action is through activating the angiotensin type 1 receptor and mimic the action of angiotensin II.
Hence causing hypertension and vascular damage like endarteritis and increasing tissue factor leading to thrombotic occlusions.
Not all patients with AT1R antibodies develop rejection other additional factors may be needed.
Prelecan- Has c terminal domain called endorepellin which contains LG3 domains.
LG3 antibodies may associated with chronic rejection.
Cause vascular injury and neointimal formation.
Have synergistic activity with HLA- DSA.
Collagen
Collagen V antibodies in lung transplant are associated with development of bronchiolitis obliterans syndrome.
Collagen type IV antibodies may be associated with development of transplant glomerulopathy.
Auto-antibody production
May be due to ischaemia reperfusion injury
TH17 cells which produce IL17 may have a role in autoimmune pathogenesis.
Mohamed Mohamed
3 years ago
Week 1
Journal club
V.The importance of non-HLA antibodies in transplantation
Introduction Anti–HLA DSAs are involved in the majority of patients with ABMR, however rejection can also occur in those who are negative for DSA. Non-HLA auto-antibodies have been associated with rejection in kidney, heart, & lung transplant recipients. The evidence comes from reports of accelerated AMR among recipients from HLA identical siblings. Reduced long-term outcomes was also shown in transplant between HLA-haplotype-matched siblings.
Classification of non-HLA antibodies: (i) Alloantibodies: -target polymorphic antigens that differ between the recipient & donor (ii) Autoantibodies: -recognize self antigens Unlike HLAs, which are expressed on the cell surface of the allograft endothelium, auto-antigens are cryptic & become exposed after tissue damage due to ischemia-reperfusion or allograft injury. Thus non-HLA antibodies that mediate rejection recognize auto-antigens that expressed by endothelial cells. Auto-antibodies can, in turn, accelerate &/or enhance renal allograft damage. Anti-endothelial cell antibodies (AECA): Kidney transplant recipients with pre-transplant AECA had increased events of early acute rejection & higher creatinine levels than those without AECA. Angiotensin type 1 receptor (AT1R): -is a G-protein coupled receptor -expressed at the endothelial cell surface -binds to angiotensin II -regulates water–salt balance & BP. –AT1R antibodies associated with severe steroid-refractory vascular rejection & malignant hypertension. -AT1R antibody correlated with an increased incidence of AMR & inferior graft survival Perlecan (a large heparan sulfate proteoglycan): – A major component of the vessel wall. – It contains 3 laminin-like globular (LG) domains, the LG3 domain is the most anti-angiogenic one. – Increased serum LG3 levels seen in renal transplant recipients with immune-mediated vascular injury & renal dysfunction. Auto-antibodies to collagen IV & fibronectin:
– reported in renal transplant recipients diagnosed with transplant glomerulopathy; implicating collagen IV in the pathogenesis of chronic rejection. Autoantibody production in transplantation: Depends on multiple factors that lead to exposure of intracellular proteins: – Graft damage mediated through IRI – Alloimmunity – Chronic inflammation – Auto-antigens can then be presented to auto-reactive T cells & B cells either by recipient or donor APCs. Ischaemia reperfusion injury(IRI): – SOT involves surgical trauma, tissue damage & IRI. – All of the above can elicit innate inflammatory reactions leading to the generation of alloimmune & autoimmune responses to the graft. – Immune system has a number of checkpoints to keep tolerance to self- antigens, but defects in these checkpoints coupled with the constant presence of autoantigen leads to chronic inflammation. – This process in turn causes downstream production of pro-inflammatory cytokines( e.g. IL-1β, IL-6, & TNF), which activation adaptive immune responses that can exacerbate allograft damage & exposure to autoantigens. – Autoantigens released from the injured graft are processed & presented to autoreactive T cells by APC recruited during IRI – Circulating B cells bind these autoantigens & become activated by auto- reactive T cells, resulting in the secretion of autoantibodies.
– In addition, complement activation can potentiate autoantibody production in the transplant setting. Interplay between alloimmunity & autoimmunity: – Alloimmune responses to the transplanted organ occur through the direct, indirect & semi-direct allorecognition pathways. – The expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection & linked to the generation of DSAs. – Cell-to-cell communication via extracellular vesicles is known to elicit autoimmune & alloimmune responses.
– IL-17 plays important role in SOT rejection & generation of autoimmune responses, particularly in lung allograft rejection. Conclusions & future perspectives – Autoantibody production to self-antigens is seen in both acute & chronic rejection of SOTs – Responsible mechanisms include: -failure to clear apoptotic bodies -cross-reactivity between self & foreign antigens -interaction between innate & adaptive immunity. The clinical presentation & response to desensitization therapy of non- HLA antibodies have not been clearly established. Treatment of AMR due to auto-antibodies doesn’t differ from that used for HLA antibodies. There is a need for further investigation to delineate pathogenic mechanisms of autoantibodies & to identify more effective therapies. Tocilizumab, an IL-6 inhibitor was promising in a small pilot study. Targeting IL-17, miRNA & exosomes are some possible options to treat autoantibody-mediated AMR & improve graft life. Modern genomics & proteomics platforms provide new chances to improve our understanding of the mechanism, pathogenesis & therapeutic options of auto-antibodies.
Murad Hemadneh
3 years ago
The importance of non-HLA antibodies in transplantation.
Introduction
Antibody-mediated rejection AMR could be from antibodies against HLA and Non-HLA autoantigens. Our knowledge of non-HLA antibodies is limited but recent studies showed increased long-term graft failure of renal transplants between HLA-matched sibling donors which showed the importance of non-HLA antibodies especially in chronic allograft rejection.
Non-HLA antibodies are divided into two groups. First is Alloantibodies against polymorphic antigen that differ between the recipient and donor. Second is autoantibodies against various antigens in the body which may cause cytokine activation and tissue injury. One of the important Non-HLA autoantibodies is anti-endothelial cell antibodies (AECA) that was reported to cause hyperacute rejection of a maternal renal allograft which suggests a role for AECA in the pathogenesis of accelerated AMR.
AECA were found to be significantly higher in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates and correlated with AMR in heart transplantation. AECA can cause renal rejections through activation of the complement pathway resulting in C4d and C3d deposition. However, many rejections associated with AECA were negative for C4d deposition and was graded as cellular rejection which could be explained by the fact that AECA are enriched for the non-complement fixing subclasses IgG2 and IgG4 although the biopsy samples showed histologic features suggestive of AMR.
Auto-antibodies specificity developed during the immune response to allograft varies and depends on many conditions such as ligand expression, ischemic injury and inflammation of the allograft. The expression of autoantigens on the endothelium is diverse and depending on anatomic location, vessel type and inflammation. All of these factors contribute to the challenges in determining the clinical relevance of non-HLA autoantibodies.
Here, the summary of discussion of non-HLA clinical significant autoantibodies.
Angiotensin type 1 receptor (AT1R).
AT1R is a G-protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. Increased activity of this receptor leads to hypertension, vasoconstriction and vascular smooth muscle migration and proliferation. Initially Antibodies to AT1R (IgG1 and IgG3 isotypes) were found to be associated in pre-eclampsia with increased maternal and fetal morbidity and mortality. Now AT1R antibody is recognized to be associated with increased risk of AMR and graft failure as a result of vascular injury. AMR antibodies can induce vascular injury with complement independent mechanisms (without C4d deposition in a biopsy) in most cases. In fact biopsy samples showed increased expression of tissue factor which was reduced after treatment with angiotensin II receptor blockers (ARBS). These findings are consistent with the hypothesis that AT1R antibodies contribute to rejection by mimicking the action of angiotensin II. Using plasmapheresis, IVIG and losartan for these patients improved allograft survival in comparison to standard anti-rejection therapy.
Presence of pretransplant AT1R auto-antibody is associated with high risk of acute rejection within the first four months as well as increased graft failure after 3 years post-transplantation. Strength of the AT1R antibody positivity level correlates with the time of rejection. AT1R auto-antibody can occur after transplantation -de novo- and can be associated with positive HLA-DSA and might have a synergistic effect. Studies showed that the level of AT1R antibody is significantly high in recipient patients with recurrent focal segmental glomerulosclerosis (FSGS) after transplantation. In heart transplantation, high levels of pre-transplant levels of AT1R antibody was associated with ACR, AMR and early onset of microvasculopathy especially when HLA-DSA was also positive which implies AT1R antibody synergistic effect. De novo AT1R antibody was noticed in patients with left ventricular assist device LVAD as a bridge to transplantation but didn’t affect the incidence of rejection or transplant survival.
AT1R antibodies were not involved in rejection for all renal transplant grafts which indicated the presence of other factors which may contribute and promote the rejection. Many studies supported that ischemic reperfusion injury (IRI) mediated damage of the endothelium increased AT1R expression which facilitated the interactions with AT1R antibodies.
Perlecan.
Perlecan is considered a major component of cell wall which is large heparan sulfate proteoglycan and has C terminal domain (endorepellin). Endorepellin has antiangiogenic properties which reside mostly in the laminin-like globular third subdomain (LG3). Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan. High levels of LG3 is associated with vascular rejection and neointima formation by stimulating autoantibody production or/and promoting the migration of the vascular smooth muscle cells and mesenchymal stem cells. As AT1R antibodies, LG3 antibodies have a synergistic effect with HLA-DSA to induce graft damage.
Collagen.
Collagen V is presented on the airway lining which increases following immune-mediated injury or IRI. Its clinical significance is related to autoantibodies formation in lung transplantation as these antibodies are associated with bronchitis obliterans syndrome (BOS). Patients with idiopathic pulmonary fibrosis and cystic fibrosis have the highest prevalence of antibodies to collagen V and Kα-tubulin and are at increased risk of developing primary graft dysfunction, HLA-DSA and BOS. Autoantibodies to collagen IV and fibronectin have been reported in patients with transplant glomerulopathy which is characterized by duplication of glomerular basement membrane leading to chronic renal allograft rejection.
Autoantibody production in transplantation
Many factors can lead to autoantibody production in the transplant settings which leads to graft damage. This graft damage occurred because IRI, alloimmunity and chronic inflammation causes cells to present antigens on their surface as autoantigens. These autoantigens will be presented to T and B cells by different ways and forms but will eventually lead to formation of autoantibodies.
Ischemic reperfusion injury (IRI)
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. IRI can cause tissue damage which can lead to AKI and delayed graft function and can impair graft survival. Apoptosis and necrosis caused by IRI eventually decreases with production of proinflammatory cytokines and promotes activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity
There are three ways for alloimmune response to occur in transplanted tissue which are direct, indirect and semi-direct allorecognition pathways. Intermolecular epitope spreading is when indirect alloimmune response can spread to additional determinants within the primary target antigen which is associated with chronic rejection and linked to formation of DSAs. The indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process. Intermolecular epitope spreading has been described for indirect pathway responses to donor alloantigen.
Extracellular vesicles
extracellular vesicles is a way for cell-to-cell communication that can elicits autoimmune and alloimmune responses as they contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses. There are categorized into three classes based on their biogenesis: exosomes, microparticles and apoptotic bodies. Extracellular vesicles released by APCs also carry surface MHC class I and II molecules plus bound peptides that can activate T cells.
TH17 cells and tertiary lymphoid tissue
TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases. They are activated by IL-23 to promote chronic tissue inflammation and autoimmunity. IL-17 is important in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection. IL-17 plays an important role in the formation of Tertiary Lymphoid Tissue (TLT). TLT is an ectopic accumulation of lymphoid cells, with characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis. Under pro-inflammatory conditions, TLT is constantly fed neo-antigens released by tissue injury and trapped by defective lymphatic drainage leading to the production of pathogenic autoantibodies
Conclusion
Immunity to self-antigens plays an important role in both acute and chronic rejection of solid organ transplantation. Autoantibodies can be produced in many ways. Further studying is needed to establish a better knowledge of clinical presentation patterns and response to the desensitization therapy for non-HLA antibodies which can improve graft survival. Necrosis caused by IRI eventually decreases with production of proinflammatory cytokines and promotes activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
amiri elaf
3 years ago
*Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection dueto the implicated antibodies directed against HLA antigens and non-HLA antigens .
* Non-HLA antibodies are two types -Alloantibodies directed against HLA that are not identical.
-Antibodies that recognize self-antigens (autoantibodies).
* Non HLA antibodies mediate renal rejection by recognize autoantigens expressed by endothelial cells in vasculatur tissue, so presence of pretransplant antiendothelial cell antibodies (AECA) can cause hyperacute rejection.
* Organs from deceased donors might exhibit higher levels of non-HLA antibody ligands than hose from living donors. *Many of the rejections associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection, although AECA have been shown to activate complement
resulting in C4d or C3d deposition in the graft ,this discrepancy could result from the fact that endothelial-cell-reactive
antibodies are enriched for non complement-fixing subclasses IgG2 and IgG4.
* clinical significance of a selected group of well-characterized autoantibodies :-
* Angiotensin type 1 receptor (AT1R)
—AT1R is a Gprotein coupled receptor expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. *Hyperactivity of AT1R causes
hypertension, vasoconstriction and vascular smooth muscle migration and proliferation
* Antibodies to AT1R( IgG1 , IgG3) were reported in recipients with severe steroid refractory vascular rejection and malignant hypertension in the absence of HLA DSA, biopsy did not show evidence of complement deposition.
* Treatment of AT1R antibody positive patients with (plasmapheresis, IVIG and losartan )improved allograft survival compared to patients receiving standard anti-rejection therapy indicate that it mediated vascular injury.
* AT1R autoantibodies might impact long-term graft survival.
* patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
* Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation causes accelerated allograft loss due to podocyte damage resulting in proteinuria and loss of graft function.
*Causes of FSGS can be hereditary or idiopathic, autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.
* using plasma exchange and losartan therapy improving AMR and reduced podocyte injury.
*Clinical studies in heart transplantation Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
* Elevated AT1R antibody levels were also reported in patients witha left ventricular assist device LVDA , were AT1R negative prior to LVAD implantation developed de novo AT1R antibodies after the procedure.
.
*Perlecan
Is a large heparan sulfate proteoglycan (major component of the vessel wall).
The C-terminal domain of perlecan, endorepellin is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) Most of the antiangiogenic activity of endorepellin resides in the LG3
subdomain.
* Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction, and also associated with increasedd neointima formation.
* The IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection.
* patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival.
* Collagen
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IRI.
* Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production.
* Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome in lung transplantation.
* Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
*Ischaemia reperfusion injury can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft.
* Alloimmune responses to the
transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathway
* The indirect alloimmune response can spread to determinants within the antigen, this proces intramolecular epitope spreading, this expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs.
*The indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process and triggers autoimmunity after transplantation via antigen mimicry between autoantigen peptides and donor MHC peptides.
*TH17 cells are the major producers of IL-17 have been implicated in many autoimmune diseases and it play an important role in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection.
Mohamed Saad
3 years ago
The importance of non-HLA antibodies in transplantation.
Acute and chronic antibody mediated rejection (AMR) affects long term graft survival.
HLA and Non- HLA antibodies have a role in pathogenesis of antibody mediated rejection. Non-HLA antibodies are classified to :
1-Alloantibodies directed against polymorphic antigens that differ between the recipient and donor.
2-Autoantibodies : antibodies that recognize self-antigens. Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation reveled the following:
Antibodies to AT1R are associated with severe resistant vascular rejection and malignant hypertension and combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
Most of the patients are HLA -DSA negative and no C4d in renal biopsy as its complement-independent mechanisms graft injury.
Patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
Some studies reveled that AT1R has a role in recurrence of FSGS in post-transplant recipients. Perlecan:
The C-terminal domain of Perlecan, endorepellin, is best known for its anti-angiogenic properties which resides in the LG3 subdomain, high LG3 level associated with poor graft outcome.
Again patient with HLA-DSA positive with high LG3 level were associated with vascular rejection and more graft failure comparison to HLA-DSA positive alone. Collagen:
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
These patients displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection. Causes of Autoantibody production in transplantation:
1- Ischemia reperfusion injury: induced damage to vascular endothelial and tubular epithelial cells triggers the release of damage associated molecular patterns (DAMPs), which interact with recognition receptors on APC and led to production of proinflammatory cytokines, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
2- Interplay between alloimmunity and autoimmunity:
Alloimmune responses to the transplanted organ occur through the direct, indirect and semi-direct all recognition pathways.
Indirect recognition pathway can promote the development of autoimmune T and B cells that contribute to the rejection process.
3- Extracellular vesicles: released by APCs also carry surface MHC class I and II molecules that can activate T cells.
4-TH17 cells and tertiary lymphoid tissue: which produce IL-
17 that has major role in solid organ transplant rejection and generation of autoimmune responses. Conclusions:
Desensitization therapy has no role in Non-HLA DSA yet.
AMR due to autoantibodies is similar to HLA antibodies
Which are antibody depletion, B-cell depletion, IVIG , proteasome inhibitors, and complement inhibitors which used alone or combination.
IL-6 inhibitor tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney transplant recipients in a small pilot study.
Therapeutic strategies targeting IL-17 pathways, miRNA regulation and exosomes might also become viable options to treat autoantibody-mediated AMR and improve graft survival.
Professor Ahmed Halawa
Admin
3 years ago
Dear All How do you know that the crossmatch is positive due to non-HLA antibodies?
There is a reward (Kidney Transplantation 2021 – picture is below) for the correct answer (one sentence is required).
I think typical picture of non-HLA antibodies is to found FCXM positive for T and B cells
with no DSA(repeated many times) and auto cross match is negative.
Hello Professor Ahmed.
I think a positive crossmatch due to non HLA antibodies occur:
1. When here is no history of sensitization to anti HLA antibodies ( pregnancy, previous transplant and post transfusion) .
3. When is no history of desensitization protocols such as rituximab, antithymocyte globulin, or intravenous immunoglobulins
3. The recipient serum is tested negative for DSA on many occasions.
4. Negative autocrossmatch.
5. Crossmatch after serum treatment with heating or DDT( for IgM class antibodies) is negative.
Crossmatch would be positive due to non-HLA antibodies in case of:
1- Negative Lymphocyte cross match.
2- Confirmation of absence DSA on recipient serum and absence history of sensitization to HLA-antibodies.
3- No history of desensitization prior to organ transplantation using therapeutic antibody such as rituximab.
by detection of different types of non-HLA antibodies such as MICA (MICA-Ab) or MICB, or angiotensin II type 1 receptor (AT1R-Ab), endothelin-1 type A receptor (ETAR-Ab), perlecan, agrin or vimentin, and other non-HLA antibodies performing crossmatches with primary aortic endothelial cells (EC-XM).
positive B cell / T cell crossmatch with negative DSA testing, no history of desensitization, and negative auto-crossmatching is mostly due to the presence of Non-HLA antibodies.
Positive T cell with negative B cell crossmatch with negative DSA usually indicates non-HLA antibody.
Detection of donor-specific anti-endothelial cell antibodies in a flow cytometric crossmatch by using donor endothelial precursor cells (EPCs) as target cells has been to improve the sensitivity in detecting non-HLA antibody.
This technique is able to detect a non-HLA specific antibody population not detected by lymphocyte crossmatches
-Flowcytometry crossmatch positive for T and B cells.
– Negative DSA.
– Negative Autocrossmatch.
– No history of desensitisation prior to transplantation.
How do you know that the crossmatch is positive due to non-HLA antibodies?
As mentioned by my colleagues, I will suspect Non-HLA antibodies in the case of positive CDC and FCXM in the absence of detectable DSA by Luminex SAB (Negative virtual crossmatch)
Balaji Kirushnan
3 years ago
Antibody mediated rejection is an important cause of acute and chronic graft loss. The occurrence of antibody mediated rejection even in identical twins with good HLA match pointd to the occurence of Non-HLA antibodies causing graft rejection.
They are classified into 2 categories: Alloantibodies against different HLA polymorphic antigens between donor and recipient. Autoantibodies directed against various antigens in the body which may cause cytokine activation and tissue injury.
Antiendothelial cell antibody (AECA): Substantial portion of the non HLA antibodies directed against kidney are found more common in deceased donor transplants and in highly sensitized recipients. As endothelium is the most common tissue exposed to the circulating blood, AECA directed against the endothelium cause hyperacute rejection in the renal transplant recipients. These patients have tested negative for DSA and cross matches also. AECA cause features of glomerulitis, capillary thrombosis, transplant glomerulopathy with or without c4d deposition. Ideally AECA are not activated by complement due to AECA being IgG2 or IgG4 antibodies in nature.
Angiotension receptor Type 1 antibody: (ATR1 antibody). ATR1 are g protein coupled receptors that are expressed on the vasculature of the system. Activation of these receptors cause vasoconstriction, hypertension and salt and water reabsorption. Activation of these receptors are known to cause pre eclampsia in pregnant women as per animal studies. In renal transplant patients, ATR1 antibodies cause steroid resistant vascular rejection, malignant hypertension and graft failure. It is controlled with plasmapheresis, IVIG and losartan. They are reported to cause AMR in HLA DSA negative and MICA antibody negative transplant individuals. Complement independent mechanisms have been suggested for ATR1 receptor antibody. Presence of HLA DSA and ATR1 antibody are known to have synergistic inferior graft outcomes. They have a role in FSGS post transplant recurrence as patients with FSGS recurrence demonstrate higher levels of ATR1 receptor antibody.
Perlecan: It is the major component of the vessel wall which has a large heparan sulfate proteoglycan. It has a C terminal domain (endorepellin) which has antiangiogenic properties. Apoptotic endothelial cells liberate cathepsin L which cleaves the LG3 domain from the C terminal fragment of perlecan. Infact higher levels of LG3 are reported in patients with immune mediated vascular injury and vascular rejection. They are associated with neointima formation in the vessel walls. LG3 may also serve as a neoantigen and it causes anti LG3 antibodies which are reported to be higher in transplant patients with vascular or AMR. Patients with anti LG3 or anti perlecan antibodies are reported to have overall inferior graft outcomes and the outcomes are correlated with elevated elevels of anti LG 3 antibodies.
Collagen. Collagen V is normally present in the airway basement membrane and their expression is increased after IRI or airway injury after viral infections. It is most commonly seen in the lung transplant scenario. Post transplant Autoantibody to collagen has been implicated to cause BOOP in lung transplant patients. Transplant glomerulopathy is characterized by duplication of the glomerular basement membrane and is associated with chronic renal allograft rejection. Those patients with transplant glomerulopathy have been shown to have basement membrane duplication, and development of antibodies to collagen V and fibronectin have been reported.
Autoantibodies in renal transplant are produced in number of ways. There is constant interaction between autoimmunity and alloimmunity in transplant setting and this is known to aggravate the cytokine mediated injury in the graft. Ischemia reperfusion injury is the most common in the initial week after trauma to the endothelium after surgery. This leads to release of DAMP (damage asscociated molecular patterns) which contain self antigens as exosomes, apoptotic bodies and lysosomes. Integration of DAMP with Toll Like receptor which inturn cause downstream activation of cytokines. Tissue damage during episodes of rejection can cause exposure of cryptic neoantigens which are hidden beneath the cell surface. antibodies can get produced to these new antigens. The generation of auto reactive T cells are known to activate areas of epitope spreading and expose newer antigens to cause antibody production. Extracellular vesicles released by APCs also carry surface MHC class I and II molecules plus bound peptides that can activate T cells. TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases. Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity. IL 17 induces the formation of Tertiary Lymphoid Tissue (TLT) in many autoimmune diseases. These TLT serve as constant source of auto antibodies as those neoantigens which are escape the autoimmune check are trapped by them leading to production of autoantibodies.
Non-HLA antibodies can contribute in AMR and are associated with poor graft survival.
They are alloantibodies against polymorphic antigens which are different between donor and recipient or autoantibodies that recognize self antigens.
Several autoantibodies are generated after transplant, the pathogenicity is conditioned upon ligand expression, ischemic injury and/or state of inflammation in the graft. Anti-endothelia cell antibodies (AECA):
proportion of non-HLA antibodies that recognizes autoantigens expressed by endothelial cells in vasculature at interface between transplanted organ and immune system.
More common in patients with failed transplant and HLA-sensitized recipients.
include non complement fixing subclasses IgG2 and IgG4, graft biopsy show histologic findings of AMR without complement deposition
several reports showed that pretransplant AECA caused hyperacute rejection and/or accelerated AMR in transplant recipients with negative crossmatch and no DSA. Angiotensin type1 receptor (AT1R) antibodies:
A receptor expressed on endothelial surface, regulates water and salt balance.
AT1R antibodies were first reported in recipients with steroid resistant vascular rejection, malignant hypertension and negative HLA-DSA, treatment with IVIG, plasmaphereses and losartan significantly improved graft survival compared to standard anti rejection treatment.
Studies showed that AT1R antibodies correlated with increased incidence of AMR and suggested complement independent mechanisms.
AT1R antibodies and HLA-DSA have synergistic effect and are associated with lower graft survival.
They may have a role in FSGS recurrence post transplant, a study showed that recipient with FSGS recurrence had significantly higher levels of AT1R antibodies. Perlecan:
A major component of vessel wall, endorepellin is the C-terminal domain of perlecan which has anti-angiogenic activity mainly in the LG3 subdomains.
Studies showed that serum LG3 antibodies were higher in recipients with acute vascular rejection than in those without rejection, also recipients with Banff grade II or III acute vascular rejection had significantly higher levels of serum LG3 antibodies than those with tubulointerstitial rejection.
High pre transplant LG3 antibodies were associated with higher risk of vascular rejection.
HLA-DSA and LG3 autoantibodies had synergistic effect in graft failure. Collagen:
Autoantibodies to collagen IV and fibronectin were detected in recipients with transplant glomerulopathy that is associated with chronic allograft rejection. Autoantibody production in transplant:
Depends on multiple factors including graft damage due to ischemia reperfusion injury, alloimmunity and chronic inflammation. Ischemia reperfusion injury:
Can induce innate inflammatory response resulting in alloimmune and autoimmune response to the graft which can cause graft damage and delayed graft function.
studies showed that it may induce autoimmune response in absence of alloimmunity. Interplay between autoimmunity and alloimmunity:
Indirect alloimmune response can trigger autoimmunity after transplant via antigen mimcry between autoantigen peptides and donor MHC peptides.
Tissue damage due to alloresponse to donor HLA antigens may cause release of sequestrated autoantigens leading to triggering of autoimmune response at site of the graft. Extracellular vesicles:
Cell to cell communication via extracellular vesicles can elicit autoimmune and alloimmune response as they contain numerous autoantigens. Th17 cells and tertiary lymphoid tissue (TLT):
Th17 cells secrete IL-17 that has a role in solid organ transplant rejection and in generation of autoimmune response.
Development of TLT was reported in chronic allograft rejection, it is an ectopic accumulation of lymphoid cells similar to germinal center in a secondary lymphoid organ which occur in chronic inflammation through lymphoid neogenesis. Conclusion:
Immunity to self antigen may contribute in acute and chronic rejection of transplanted organ. Effect of desensitization on non-HLA antibodies is not clearly established.
Current strategies for treatment of AMR due to autoantibodies are similar to those used in treatment of AMR due to HLA antibodies and include antibody depletion, B cell depletion, IVIG, proteosome inhibitors and complement inhibitor.
The efficiency of these regimens is not clear.
*The importance of non HLA antibodies in renal transplantation:
A cute and chronic allograft rejection post kiney transplantation can be caused by antibody mediated rejection (AMR).These antibodies are mainly HLA antibodies. But, non-HLA antibodies was reported in recipients from identical siblings.
* Non-HLA antibodies are classified into two main categories:
1.Alloantibodies: directed against
polymorphic antigens.
2.Autoantibodies that recognize self-
antigenss.
* Non-HLA include anti endothelial cell antibodies ( AECA) which were reported by Brasile et al., these antibodies are enriched for noncomplement- fixing subclasses IgG2 and IgG4.
■Examples of Non HLA antibodies:
1- Angiotensin type I receptor ( AT1R):
Is a G- protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II, and regulates the water-salt balance and BP.
In renal transplantation, elevated level were reported in patients with severe steroid resistance vascular rejection, and malignant hypertension in the absence of HLA-DSA. The main stay of treatment for these patients is by a combination of plasmapheresis, IVIG and losartan.
– AT1R autoantibodies might
impact long-term graft survival because they are associated with a higher risk of
acute rejection within the first 4 months after transplantation and a 2.6-fold higher risk of graft failure beyond 3 years post-transplantation,
Patients who were positive for both AT1R
antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
– Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation causes accelerated allograft loss in approximately 30% of recipients.
Causes of FSGS and studies in an experimental rat model suggest a role
for AT1R in FSGS
– Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement. Treatment of these pts depends on Depletion of AT1R antibodies by plasma
exchange + losartan.
▪︎Mechanisms of injury:
– AT1R antibodies of IgG1 and IgG3 isotypes were identified in patients with transplant rejection. But, C4d deposition was only detected in a subset of
patients, suggesting the involvement of complement-independent pathogenesis of these antibodies.
-Renal biopsy specimens from transplant recipients with AT1R-mediated rejection
had increased tissue factor expression and thrombotic occlusions.
– Additional co-factors or environmental conditions might be needed to promote rejection by AT1R antibodies. For example, Ischemia.
2- Perlecan:
– Is a major component of the vessel wall composed of a large heparan sulfate
proteoglycan . It’s C-terminal domain
(endorepellin) has anti-angiogenic properties.
– Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain
from the C-terminal fragment of perlecan. – – Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal
dysfunction.
– Vascular rejection and elevated LG3 levels were associated with heightened neointima formation.
– LG3 behaves as a neoantigen capable of
driving the production of LG3 antibodies that can enhance the process of chronic rejection.
– Higher pretransplant levels of LG3 antibodies predicted recipients at risk of
vascular rejection.
– Patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival
– HLA-DSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
▪︎Mechanisms of injury:
– The bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of
donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
3- Collagen:
– Autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy. These patients
displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells implicating collagen IV in the pathogenesis of chronic rejection
■Autoantibody production in transplantation:
– Graft damage mediated through Ischemic reperfusion injury, alloimmunity and chronic inflammation can cause intracellular
proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen which can be subsequently presented to
autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
▪︎Ischaemia reperfusion injury:
– An innate inflammatory responses with generation of alloimmune and autoimmune responses to the graft can be elicited in organ transplantation due to surgical trauma, tissue damage and IRI.
– Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1.
– Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
– IRI can damage the vascular endothelium
leading to release of autoantigens from necrotic and apoptotic cells.
– Autoantigens such as vimentin, perlecan, and collagen V released from the injured allograft are processed and presented to autoreactive T cells by APC recruited during IRI.
– Circulating B cells bind these autoantigens and become activated by autoreactive T cells, resulting in the secretion of autoantibodies. In addition, complement activation can potentiate autoantibody
production in the transplant setting.
This article highlights the importance of Non HLA antibodies which are involved in antibody mediated rejection ultimately leading to decreased graft survival . There a quite a few Non HLA antbodies and typical features include positive FCXM in the absence of donor specific antibodies on Luminex SAB..Mainly classified as allo and auto antibodies
These include:
1- AT1R- Angiotensin Type 1 Receptor
Present on endothelial cell surface and antibodies to AT1R are usually IgG1 and 3. and are risk factor for graft rejection and malignant hypertension
2-Preclan
Present on blood vessel wall with antiangiogenic properties. Lamilin like globulin LG3 is highly antigenic and associated with direct vascular insult
In conclusion the Non HLA antibody production is multifactorial and leads to AMR. Mutiple strategies can be adopted to treat AMR.these include IVIG , antibody and B cell depletion and protease inhibitors. More efforts are required to understand more the pathogenis to as to imrove long term graft survival
Non-HLA antibodies are involved in both acute and chronic antibody mediated rejection (AMR), resulting in a decrease in long-term graft survival.
examples of these non-HLA antibodies are the following :
1- Angiotensin type 1 receptor : expressed in vascular endothelial cells and reported in some patients with severe steroid resistant AMR.
2- Perlecan : amajor component of blood vessel walls.
3- Collagen type IV and Fibronectin
The underlying mechanisms for production and pathogenesis of Non-HLA antibodies are still poorly-understood. the following mechanisms are examples :
1- ischemia-reperfusion injury.
2- surgical trauma.
3- allo-immune reaction.
4- the role of Th17 cells. they are essential in auto-antibody production by B-cells within ectopic tertiary lymphoid tissues.
5- auto-antibody graft damage-induced alloimmunity and development of DSA of HLA types.
identification of kidney graft recipients who are at risk of non-HLA antibody mediated rejection and the targeted therapies to treat those patients will improve graft survival.
the current treatment for AMR due to auto-antibodies is similar to that of HLA antibodies. However, it is not clear whether the used regimens are effective alone or in combinations.
non HLA antibodies were observed to play a role in ABMR,this was aboserved to some extent in kidney transplanted patient from HLA Identical twin.
non HLA antibodies are classifed into main categories ,
1-ALLOANTIBODIES
which is dirceted aganist polymorphic antigens that is different between recipent and donor .
2-AUTOANIBODIES
which is recognized as self antigens.
WHAT IS (AECA)?
Antibodies are directed against endothelial cells which are expressed mainly on graft tissue and not on lymphocytes
AECA was found to be higher in patients with graft failure when compared to patient with functioning graft at 1 year, also in sensitized recipients compared to non sensitized and may be more clinically significant in deceased donor than in living donor kidney transplantation.
kidney transplant patient with pretransplant AECA was found to haveepisodes of early acute rejections and higher creatinine levels than witout AECA.
WHAT IS ANGIOTENSINOGEN TYPE 1 RECEPTOR(AT1R)ANTIBODIES?
g coupled prtiens expressed on endocthelial receptor.
antibodies aganist ATR1 was first implicted in maternal and fetal morbidity and mortality.
in kidney transplantion , noted that patients with elevated levels of ATR1 was found in patients with severe refractory vascular rejection anad malignant hypertension in abasence of DSA.
tratment was succeful with plex and angiostesion blockers and iv igg.
some studis showed rcepients with ATR1 antibodies correlated with incres incidence of AMR and inferior graft survival
some studies found acorrelation between FSGS recurrence and ATR1 antibodies.
WHAT IS PERLECAN?
major component of vessel wall, c treminal domain of perlecan endorpellin ,has angiogenic proprties , contains three luminal like globular domain(LG)
studies showed incres level of LG3 in the recipents with rejcetions especially BANF CLASS 2 OR 3.
receipents with higher levels of LG3 pre transplant were found to have more rejection episodes ,
rcipents with LG3 positive pre or post transplant waere found to have poorer grfat outcome and decrease graft survival after one year of transplantion.
WHAT IS ANTI COLLAGEN ANTIBODIES?
collagen antibodies were more studied in lung transplantion
collagen 5 is found on ariway epithelial cells of lung tissue ,
collagen fragments ar realsed post lung btransplant which induce antibody production.
post transplant collagen 5 is assoicated with (bos)
in kidney transplant, collagen 4 was found to have autoantibiodies that causes chronic allograft nephropathy due to transplant glomerulopathy.
CAUSES OF AUTANTIBODIES PRODUCTION
ischemic reperfusion injury(IRI)
surgical trauma and tissue dadmge during transplant procees induces innate immunity .
studies had showen that (IRI) is ssufecient to induce an autoimmune responce in absence of alloimmunity.
alloimmunity and autoimmunity,
threee basic mechanisms of alloimmune responses e.g direct, indirect, and semi-direct.
extracelluar vesicles ,
cell to cell commuication through extracellular vesicles can elicit autoimmune and allloimmiune respons.
AMR is important cause of acute and chronic allograft rejection. New data suggesting that non-HLA antibodies play key role in accelerated AMR 8-10. They are two types ; 1) alloantibodies 2) auto-antibodies 13-14
Risk factors for AECA are failed graft, sensitized patients and these correlated with AMR 22-23
-ve C4d in the biopsy suggest complement independent process 31.
Factors associated with pathogenesis of non- HLA auto-antibodies are ; ligand expression, ischemia, & inflammation.
Angiotensin type1 receptor(AT1R) ;
G protein on the endothelial cells that regulate water& salt 37.
Stimulation will lead to hypertension, vasoconstriction, & smooth muscle proliferation 38.
Antibodies to AT1R has resulted in severe vascular rejection,accelerated HTN in absence of DSA 33. They are IgG1,IgG3 sub-types but not associated with C4d deposition.
Those with both HLA -DSA & AT1R antibodies had inferior graft outcomes compared to those with HLA-DSA = synergistic effects 44.
AT1R antibodies were detected in patients with AMR and FSGS 52. Pre-transplant AT1R was also defected in patients with idiopathic FSGS.
Plasma exchange and losartan therapy modified the course of the disease in this patients.
High levels of AT1R were seen in patients with LVAD and two-third of those who were negative before LVAD became +Ve for AT1RA after transplantation 57.
The relationship between ATR1 and LVAD is not clear.
Perlecan ; A very big heparin sulfate and the main component of the vessel wall. The C-terminal is made up of 3 laminin-like globular domains( LG3) which is highly anti-antiogenic 68.
LG3 is separated from the C terminal by cathepsin-L released from apoptotic endothelial cells 69.
Data confirmed increased levels of LG3 antibodies in kidney recipient with immunologic vascular injury 70-72.
The presence of both HLA-DSA and LG3 antibodies indicates poor prognosis due synergistic effect.
LG3 antibodies causes either direct vascular injury and neo-intimal formation or through initiation of humoral responses.
Collagen ;
Collagen V is found in airway epithelial cells and it is expression increases in setting of immunologic injury and/or Ischemia-reperfusion injury 74-75.
Anti-bodies against collagen V in the post-transplant period is linked to diagnosis of bronchiolitis Obliteran Syndrome(BOS)76-79.
This associated with CD4 and monocytes which produces IL17,TNF-alfa, IL-B1.
Auto-antibodies to collagen V & Fibronection are also reported in kidney recipients with transplants glomerulopathy 80.
The same anti-bodies to collagen V is seen in heart recipient with HLA-DSA 81
Auto-antibodies ; Factors involved are ;
Ischemia-reperfusion inkjury(IRI)
Alloimmunity
Chronic inflammation
This leads to expression of proteins on the surface of the apoptotic cells= auto-antigens 86. This is then presented to auto-reaction T and B cells by recipient or donor APC in the setting of extracellular vesicles or in tertiary lymphoid tissue.
Ischemia-reperfusion injury ; Complex patho-physiological process
Reactive oxygen species
Complement activation
Coagulation
Endothelial activation
Leukocyte recruitment
Tissue damage by IRI can lead to AKI, DGF which has impact on graft survival 88. Apoptosis & necrosis induced by IRI leads to release of DAMP e.g self-nucleic acids, histones, and high mobility group protein B1. DMAPs reacts with pattern recognition receptors e.g TLR2 & TLR4 express on myeloid cells,dendritic cells, vascular endothelial cells, and tubular epithelial cells 88-92. Ligation of TLRs leads to recuritment of MYD88 and the production of NF-kB. This results in productions of pro-infammatory cytokines IL-1B,IL-6 and TNF which prime adaptive immnue responses and causes allograft damages and exposure to auto-antigens.
Interplay between alloimmunity and autoimmunity ; 3 basic mechanisms of alloimmune responses e.g direct, indirect, and semi-direct. The indirect pathway causes expansion of the auto-reactive T cells to D-drive MHC antigen and associated with chronic rejections. Indirect pathway also causes autoimmunity either through antigen mimicry or release of cryptic antigens following tissue damage 108.
Extracellular Vesicles ; They can can cause autoimmune or alloimmune responses through cell to cell communications by the vesicles 115-116. They can modulate the immune system either positively or negatively 116. 3 Categories ;
Exosomes 2. Micro-particles 3. Apoptotic bodies
Exosomes are weaker than APC in activating T cells but it has great efficiency to active T cells if they interact with dendritic cells 117-120
TH17 cells and Tertiary Lymphoid Tissue(TLT) ;
TH17 secrets IL-17 which plays role in autoimmune diseases 124-125. TH17 activated by TGF-B & IL-6 leads to protective response against foreign antigens TH17 activated by IL-23 leads chronic tissue inflammation & autoimmunity specially in lung allograft rejection 76-77-78-81-112
TLT represent ectopic aggregates of lymphoid tissue which is identical to that of a germinal center present in the secondary lypmoid organ. It is develop in situations of chronic inflammation by the process of lymphoid neo-genesis. Studies reported TLT in Chronic allograft rejection of the kidney 128-131 and lung 132.
Conclusion & future perspectives ;
Auto-antibodies are important players in the pathology of graft rejection
pathogenesis ; apoptotic bodies, cross-reactive antigen, interactions between innate & adaptive immune systems
Up to now the treatment is not clear but people are using the regimens for HLA-DSA treatment
IL-6 inhibitor is a potential useful treatment in small cohorts
Therapies targeting IL-17 pathways, extra-cellular vesicles may be important in future to to treat non-HLA antibodies.
ABMR has 2 forms: acute and chronic form, both forms affect the long-term outcome of the graft. The principal target of the immune system is the HLA antigens, but reports of ABMR in HLA-identical siblings highlight the presence and the importance of Non-HLA antibodies.
In general, Non-HLA antibodies are classified into:
Alloantibodies: directed against polymorphic antigens.
Autoantibodies: recognize self-antigens.
Below are some types of Non-HLA antibodies:
Angiotensin type I receptor ( AT1R):
expressed in the endothelial cell surface, binds to angiotensin II, and regulates the water-salt balance and BP.
In renal transplantation, it was reported in patients with severe steroid resistance vascular rejection, and malignant hypertension in the absence of HLA-DSA. Treatment of these patients with losartan and plasmapheresis + IVIG significantly improved graft survival. Subsequent studies confirmed these findings.
Studies in the rat model suggest a role of AT1R in FSGS as overexpression of this antibody causes podocyte injury.
Mechanism of injury:
The 2 implicated isotypes are: IgG1 & IgG3, C4d deposition is noted in some subsets, so it is a complement independent process. There will be a process that is similar to the act of angiotensin II, so phosphorylation of ERK Kinase and activation of the transcription factors AP-1 & NF-kB in the endothelial and smooth muscle cells. clinical data are consistent with the hypothesis that binding of autoantibodies to AT1R contributes to rejection. So it is not only the AT1R that causes the rejection but a co-factor is needed which may be an autoantibody or environmental factor.
Perlecan:
Is a major component of the blood vessel wall, the C-terminal domain ( endorepellin) has antiangiogenic properties and contains three laminin-like globular domains ( LG) separated by 2 sets of epidermal growth factor-like repeats. The most angiogenic properties of endorepellin reside in the LG3 subdomain.
Studies showed that higher pretransplant levels of LG3 antibodies predicted the risk of vascular rejection. patients with pre-transplant DSA and higher posttransplant levels of LG3 antibodies had significantly reduced one-year graft survival.
Mechanism of injury:
Two interdependent mechanisms are implicated as the bioactive form of perlecan cause vascular injury and neointimal formation by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury.
Collagen:
The development of autoantibodies to collagen IV and fibronectin has been associated with the development of transplant glomerulopathy.
Autoantibody production in transplantation:
Many events that happened during the process of transplantation such as ischemia-reperfusion, surgical trauma, and alloimmunity lead to the formation of autoantibodies in the form of soluble antigens, extracellular vesicles, or apoptotic bodies. these are presented to the APC and induce an immune response.
Th17 cells are essential for autoantibody production by supporting the proliferation and maturation of autoreactive B cells within the tertiary lymphoid tissues.
Allograft antigens have been classically studied as the target of antibodies in the course of antibody mediated and acute cellular rejection. Classically antibodies against HLA classes I and II expressed on the allograft have been the target of immunosuppression. Also pretransplant screening tests aim to identify the presence of anti-HLA antibodies.
However a lot of reports demonstrated the development of hyperacute and acute antibody mediated rejection in matched receipient/donor with negative cross match and negative DSA.
Studies showed that antibodies directed against non-HLA antigens are implicated in the process of AMR.Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
Several studies reported non-HLA antibodies to mediate renal rejection by attacking self antigens expressed by endothelial cells.
Anti-endothelial cells antibodies have been reported to be higher in recipients with failed transplants than in those with functioning grafts at 1 year posttransplant.
AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates and have been reported to correlate with AMR in heart transplantation.
The expression of antigens on the endothelium depends widely upon the type of injury, anatomical location, vessel type and inflammatory milieu.
Angiotensin type 1 receptor (AT1R) is another target of autoantibodies. Angiotensin type 1 receptor is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
Elevated levels of AT1R antibodies were first reported in recipients with severe vascular rejection and malignant hypertension in the absence of HLA-DSA.
The IgG subtypes of AT1R antibodies involved in acute allograft rejection were IgG1 and IgG3, and graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition, although IgG1 and IgG 3 are complement fixing.
In patients with elevated AT1R 1 antibodies and biopsy proven antibody mediated rejection, treatment with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan significantly improved allograft survival. Subsequent studies confirmed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival.
AT1R antibodies have shown to be also implicated in the recurrence of focal segmental glomerulosclerosis after kidney transplantation. Studies in an experimental rat model suggest a role for AT1R in FSGS.Treatment aiming to deplete AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
High levels of AT1R antibodies in the pretransplant period are associated with increased risk of heart transplant ACR and AMR as well as early onset of microvasculopathy. Elevated AT1R antibody levels were also reported in patients with a left ventricular assist device as a bridge to transplantation.
Another type of antibidides that have been evaluated , is Perlecan which is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG). High levels of serum LG3 levels were detected in recipients diagnosed with Banff grade II or III acute vascular rejection. High pretransplant levels of LG3 antibodies predict high risk of vascular rejection.
Collagen was evaluated for immunogenicity in patients with lung transplantation.. Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IR. Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrom in lung transplant recipients
Autoantibody production in transplantation
Organ transplantation involves varying levels of surgical trauma, tissue hypoxia ,ischemia, damage and IRI, all of which can initiate and potentiate the inflammatory responses resulting in the generation of alloimmune and autoimmune responses to the graft.
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival. Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
Non-HLA antibodies are either alloantibodies directed against polymorphic antigens, and antibodies that recognize autoantibodies.
Brasile et al. notice pretransplant antiendothelial cell antibodies (AECA) that lead to hyperacute rejection of a maternal renal allograft.
Multiple studies demonstrated multiple successive hyperacute renal rejections and/or accelerated AMR due to pretransplant AECA meanwhile those recipients had negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs).
AECA were detected in failed renal transplants and in highly sensitised candidates, it was suggested that organs from deceased donors might exhibit higher levels of non-HLA antibody ligands than those from living donors.
Antiendothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4.
Concerning AT1R ,it’s hyperactivity causes hypertension, vasoconstriction and vascular smooth muscle migration .
AT1R antibodies were detected in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA.
AT1R antibody correlated with an increased incidence of AMR and inferior graft survival
AT1R autoantibody positivity was accompanied with a higher risk of acute rejection within the first 4 months after transplantation and higher risk of graft failure 3 years post-transplantation.
overexpression of human AT1R in rat podocytes was consistent with a FSGS phenotype.
In heart transplantation the Increased pretransplant levels of AT1R antibodies are associated with heart transplant AMR specialy if associated with HLA DSA
Development of AT1R antibodies post LVAD did not impact incidence of rejection or transplant survival.
Mechanism of injury through binding of autoantibody to AT1R contributes to rejection by mimicking the action of angiotensin II.
additional co-factors or environmental conditions to AT1R antibody might be needed to promote rejection. Perclean
is a major component of the vessel wall ,known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains.
LG3 regulates vascular remodelling.
Mechanism of injury ,the current paradigm of perlecan-mediated graft injury considers two interdependent mechanisms as follows the perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling. Collagen V is present on airway epithelial cells and it increases following immune-mediated injury and/or IRI7
Mechanism of injury ; in renal transplant recipients diagnosed with transplant glomerulopathy autoantibodies to collagen IV and fibronectin has been detected
In lung transplantation Strong collagen V responses reflects severity of Bronchiolitis obliterans syndrome.
17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity Autoantibody production in transplantation depends on multiple factors. Graft damage mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, acting as as a autoantigen reservoirs Interplay between alloimmunity and autoimmunity Alloimmune responses to the transplanted organ occur by direct, indirect and semi-direct allorecognition pathways
-Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
-TH17 cells are the major producers of IL-17 involved in many autoimmune diseases.
Non-HLA antigens are antigens expressed on the surface of graft tissue and sometimes on circulating lymphocytes, those which are expressed on the surface of lymphocytes can cause unexplained positive cross match
Several non-HLA antibodies were discovered , the most reported are Angiotensin II Type 1 Receptor (AT1R-Ab), anti endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs and anti-collagen
Non HLA antibodies are either autoantibodies directed to self-antigens or alloantibodies directed to donor non HLA polymorphic antigens.
Risk factors for development of pathogenic non-HLA antibodies includes
Tissue injury due to hypo perfusion or ischemia reperfusion injury, rejection, CNI toxicity, infections and recurrent disease, all these may lead to exposure of neo antigens with subsequent formation of non HLA antibodies or increase the expression of these antigens
Previous sensitization due to previous transplant, blood transfusion and pregnancy
Evidence of the significance of non-HLA Abs
Acute rejection can occur in patients receiving kidney from his/her HLA identical siblings.
Antiendothelial cell antibodies ( AECA)
Antibodies are directed against endothelial cells which are expressed mainly on graft tissue and not on lymphocytes so cross match is usually negative
AECR are either complement fixing (cause C4d positive ABMR) or non-complement fixing
The incidence of AECA was found to be higher in patients with graft failure when compared to patient with functioning graft at 1 year, also in sensitized recipients compared to non sensitized and may be more clinically significant in deceased donor than in living donor kidney transplantation.
AECR antibodies was found to be strongly associated with AR and lower GFR by some but not all studies.
Anti-Angiotensin II Type 1 Receptor (AT1R) Abs
AT1R gene is not polymorphic like HLA
AT1R antibodies are produced due to either inflammation or ischemic injury that can occur in pre or post transplantation; this may lead to more expression of AT1R in the endothelium with subsequent formation of either preformed or denovo AT1R Abs.
AT1R Abs are autoantibodies that can bind to receptors located on graft tissue of the recipients
AT1R was found by some studies to produce positive cross match
Once they bind to AT1R, they produce severe vasoconstriction and smooth muscle proliferation leading to severe hypertension and graft dysfunction
AT1R Abs are implicated in the pathogensis of systemnic sclerosuis and preeclampsia
AT1R Abs is either complement fixing (cause C4d positive ABMR) or non complement fixing, in one study including 16 patients with angiotensin II receptor antibodies presented by malignant hypertension and acute refractory vascular rejection, 5 out of 16 patients were positive for C4d indicating that the main mechanism of injury produced by AT1R antibodies is non-complement dependent cytotoxicity
The significance of preformed T1R Abs is debatable several studies demonstrated an association between detection of preformed AT1R Abs and increased incidence of acute rejection including ABMR, ACMR, and mixed rejection, with subsequent lower graft survival
Moreover, it was found that pre-transplant anti-AT1R Abs >10 U/ml , and in another study > 15 U/ml is an independent risk factor for graft failure.
A strong relation was found between AT1R Ab and HLA DSA, the presence of both HLA DSA and AT1R Abs is associated with higher incidence of graft failure than if HLA DSAs are present alone especially in patients with denovo AT1R Abs, 58 % of patients who developed graft loss had combined HLA DSA and AT1R Abs , Moreover the presence of AT1R Abs was found to accelerate graft loss due to HLA DSA mediated ABMR and higher level of AT1R ABS is associated with earlier development of HLA DSA (57),
On the other hand positive AT1R abs alone was not associated with increased risk of rejection or decreased graft survival. This may postulate a synergistic dose dependent effect of anti-HLA DSA and anti-AT1R on graft loss.
Treatment of rejection induced by AT1R antibodies should include RAAS system inhibition by ARBS in addition to plasmapharesis and IVIG
Anti-Perlecan (LG3) Abs
Perlecan, is a vessels wall component responsible for cell growth, differentiation and apoptosis
The LG3 or endorepellin domain is a fragment of perlecan that can be released during endothelial cell apoptosis due to either inflammation or ischemia which increase the expression of these antigens with subsequent production of ABS
It was found that pre formed or denovo Anti-Perlecan (LG3) Abs are significantly higher in patients with vascular rejection and may be a risk factor for development of this type of rejection, moreover patients with preformed anti-Perlecan (LG3) Abs are at higher risk of DGF and graft dysfunction at 1 year post transplantation which was unrelated to episodes of AR
Anti-Collagen Abs
There may be a correlation between the development of these antibodies post transplantation and the occurrence of transplant glomerulopathy
Professor Ahmed Halawa
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3 years ago
Thank you All I’m still waiting for all colleagues to complete their logging
The importance of non-HLA antibodies in transplantation
Non-HLA antibodies are classified into two main categories:
alloantibodies directed against polymorphic antigens that differ between the recipient and donor
antibodies that recognize self-antigens — autoantibodies
many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d.
Angiotensin type 1 receptor (AT1R)
In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA .
AT1R antibodies were IgG1 and IgG3,graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition.
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.
Mechanisms of injury
action of angiotensin II and triggered phosphorylation of ERK kinase and activation of the transcription factors AP-1 and NF-κB in endothelial and smooth muscle cells-increased tissue factor expression and thrombotic occlusions.
Perlecan
a large heparan sulfate proteoglycan — is a major component of the vessel wall.
Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan.
increased serum LG3 levels are seen in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
similar to AT1R antibodies, HLA- DSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
Mechanisms of injury
significantly increased infiltration of T cells and natural killer cells, C4d
deposition and obliterative vascular remodelling.
significantly increased neointima formation.
Collagen
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
Autoantibody production in transplantation
Ischaemia reperfusion injury
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment . The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival.
Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs)- interact with pattern recognition receptors including Toll-like receptor (TLR) 2 and TLR4 expressed on myeloid cells,dendritic cells, vascular endothelial cells, and tubular epithelial cells- downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF- promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity
tissue damage caused by the alloresponse to donor HLA antigens can cause the release of sequestered autoantigens resulting in the presentation of cryptic self-determinants and thereby triggering an autoimmune process at the site of the graft.
Extracellular vesicles
High concentrations of exosomes can directly activate T cells, the activatory effect of this type of antigen presentation is much weaker than that of antigen presentation by professional APCs owing to the lack of co-stimulatory molecules . Exosomes efficiently activate T cells when they interact with dendritic cell.
TH17 cells and tertiary lymphoid tissue
TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.
Antibody-mediated rejection (AMR) trigger the allograft rejection and impair renal transplant survival. Non-HLA antibodies are classified into alloantibodies directed against polymorphic antigens and antibodies that recognize self-antigens — autoantibodies. Angiotensin type 1 receptor ( AT1R ) antibody provoke AMR lead to inferior graft survival by increased tissue factor expression and thrombotic occlusions in renal allograft. Perlecan is a large heparan sulfate proteoglycan at vessel wall with anti-angiogenic properties. Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan. LG3 levels in renal transplant recipients associated with allograft vascular injury and dysfunction. Besides, the development of autoantibodies to collagen IV and fibronectin has been associated with transplant glomerulopathy. The collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels which play a vital role in chronic renal allograft rejection.
On the other hand, ischaemia reperfusion injury trigger cascade of inflammatory responses which contributing to the stimulation of the autoimmune responses to the renal allograft. Apoptosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) which can interact with pattern recognition receptors including Toll-like receptor (TLR) 2 and TLR4 expressed on myeloid cells, dendritic cells, vascular endothelial cells and tubular epithelial cells. The Ligation of TLRs results in the recruitment of MYD88 and the production of NF-κB. This process in turn promote the activation of immunological reaction which cause allograft dysfunction.
The immune responses to the transplanted organ occur through the direct, indirect and semi-direct allo sensitive mechanism. This expansion of alloreactive T cells to donor-derived MHC antigens is associated with chronic allograft rejection and DSA production which lead to poor graft survival. The autoreactive memory T cells are generated lead to epitope spreading and the generation of autoantibody. The intermolecular epitope spreading is considered the indirect pathway responses to donor antigens.
Cell-to-cell communication through extracellular vesicles is associated with stimulation of autoimmune and alloimmune responses. Depending on the cellular source, extracellular vesicles can be categorized into three classes exosomes, microparticles and apoptotic bodies which contain autoantigens which increase severity of allograft rejection.
Th17 cells activated by IL-23 lead to chronic tissue inflammation and stimulation of autoimmunity. The development of TLT stimulate chronic allograft rejection of kidney and compromise allograft function.
In conclusion, failure of efficient clearance of extracellular vesicles, particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and interplay between innate and adaptive immunity lead to autoantibody production. The treatment strategies for AMR due to autoantibodies are similar to HLA antibodies. This including antibody depletion, B-cell depletion, IVIG , proteosome inhibitors and complement inhibitors. IL-6 inhibitor tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney transplant recipients. Therapeutic strategies targeting IL-17 pathways, miRNA regulation and exosomes may treat autoantibody-mediated AMR and improve graft survival. The knowledge of the autoantigens that elicit immune responses during transplantation are essential for the diagnosis and treatment of AMR.
Antibodies against polymorphic HLA antigens is the main cause AMR. Although, they are not the only contributor as many studies have also demonstrated antibodies directed against non-HLA antigens in the process of AMR. These non-HLA antibodies play important role in chronic rejection and reduce long-term allograft survival.
There are two types of non-HLA antibodies:
1- Alloantibodies which are antibodies directed against polymorphic antigens that differ between the recipient and donor.
2- Autoantibodies: antibodies that recognize self-antigens.
Transplanted organ vasculature is the first line to face the recipient immune system, autoantigens expressed by endothelial cells are recognized by nonHLA antibodies leading to renal rejection. Anti-endothelial cell antibodies (AECA) in the recipient before transplantation was first reported by Brasile et al, which was associated with hyperacute rejection.
These recipients displayed negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injury.
The AECA are present in a higher level in renal recipients with graft failure than in those with functioning graft at one-year post-transplantation. Also, they are higher in HLA sensitized candidate than non-sensitized one. Prospective multicenter trial show that recipient with pretransplant AECA had increased episodes of early acute rejection and higher creatinine levels than those without AECA. When comparing living donor and deceased donor, organs from deceased donor exhibit higher levels of non-HLA ligands than those from living donors, explaining the lower association of AECA with acute rejection and with inferior renal graft function in the living donor renal transplant.
Although; ACEA can activate complement results in C4d or C3d deposition in the graft, C4d staining in renal biopsy can be absent in some cases. This could be explained by the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. However, ACEA positive biopsy shows histological findings consistent with AMR, even in absence of complement deposition. The effect of the autoantibodies on the allograft depends on many factors such as ligand expression, ischaemic injury and/or the inflammation within the microenvironment of the allograft.
Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation: AT1R is a G protein coupled receptors, expressed on the endothelial cell surface. It is site of action of angiotensin II, which binds to it, and regulates water-salt balance and blood pressure. AT1R hyperactivity is associated with hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
In renal transplantation, high levels of AT1R antibodies were associated with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA. Biopsy from anti-AT1R positive patients with vascular rejection does not show evidence of complement deposition, even though the AT1R antibodies are of IgG1 and IgG3.
Use of losartan in combination with plasmapheresis and intravenous immunoglobulin (IVIG) for treatment of AT1R antibody positive recipients results in significant improvement of allograft survival compared with those receiving standard anti-rejection therapy with no losartan.
Studies revealed that, AT1R antibody correlated with an increased incidence of AMR and inferior graft survival, and as only minority show positive C4d staining, possibly complement-independent mechanisms contributed to graft injury. The presence and the strength of AT1R antibodies correlate with AMR and also found to be associated with recurrence of FSGS in allograft. Pre-transplant and post-transplant AT1R antibodies were
studied in 351 consecutive kidney transplant recipients using a cut-off value of 15 U/ml44. Presence of DSA adds synergistic effect, and recipient with DSA and AT1R antibodies has lower graft survival.
AT1R antibodies were found to be linked to FSGS recurrence in the allograft, as AT1R are expressed on the podocytes. Many studies support the feasibility of developing an autoantibody panel that might serve as biomarker for risk of FSGS recurrence.
Clinical studies in heart transplantation:
AT1R antibodies level pre-transplantation is associated with ACR and AMR as well as early onset micro-vasculopathy specially in the presence of DSA that add synergistic effect to AT1R antibodies.
AT1R antibodies also develop after LVAD implantation, but this has no impact on the later occurrence of rejection post- heart transplant. Absence of C4d staining in a biopsy of allograft rejection suggest that complement independent pathway is responsible for AR1R antibody mediated rejection. Autoantibodies to AT1R mimic the action of angiotensin. Therefore, cause hypertension and induced vascular changes in the renal transplant.
Perlecan
Clinical studies in renal transplantation:
Perlecan is large heparin sulfate proteoglycan and it’s a major component of the vessel wall. The endorepellin that is the C-terminal of perlecan has anti-angiogenic properties. Perlecan contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)-like repeats. Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. pre-transplant and post-transplant levels of LG3 antibodies of the IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection. LG3 causes vascular
injury and neointimal formation by stimulating autoantibody production and/or by
promoting the migration of vascular smooth muscle cells and/or MSCs.
Collagen
Clinical studies in lung transplantation
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury. Graft injury releases collagen fragments that serve as a major target for autoantibody production. Development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients.
In kidney transplantation:
Kidney recipients diagnosed with transplant glomerulopathy have been shown to develop autoantibodies to collagen IV and fibronectin. These patients have increased collagen IV-specific and fibronectin-specific CD4+T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection.
In heart transplantation
Development of HLA DSA in recipients diagnosed with AMR correlated with the development of autoantibodies to collagen. This had been associated with increased frequencies of collagen V specific CD4+Th cells secreting IL-17 and higher risk of CAV.
Autoantibody production in transplantation
Graft damage mediated through ischemia reperfusion injury, alloimmunity, and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, so these cells act as an autoantigen reservoir which subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
Ischaemia reperfusion injury (IRI)
Organ transplantation associated with varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft. The pathophysiological process involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. IRI causes apoptosis and necrosis with release of damage associated molecular patterns (DAMPAs) which interact with recognition receptors such as Toll-like receptor 2 &4 that expressed on the vascular endothelial and tubular cells ultimately causes downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity:
Alloimmune responses to the transplanted organ occur through direct, indirect and semi-direct allorecognition pathways. The indirect response can spread to more determinants within the primary target antigen, which called intramolecular epitope. This indirect pathway is associated with chronic rejection and linked to the generation of DSAs.
Extracellular vesicles
Cell-to-cell communication can occur through extracellular vesicles. A mechanism that elicits autoimmune and alloimmune responses. The extracellular vesicles contain mRNAs,miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
They are three classes — exosomes, microparticles and apoptotic bodies — all of
which contain numerous autoantigens. Extracellular vesicles released by APCs also carry surface MHC class I and II molecules plus bound peptides that can activate T cell.
TH17 cells and tertiary lymphoid tissue
TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity. IL-17 associated with solid organ transplant rejection and generation of autoimmune responses.
The development of TLT has been reported in chronic allograft rejection of kidney.
lung and heart transplants. TLT is an ectopic accumulation of lymphoid cells, with
characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis. This support maturation and proliferation of B cells and formation of germinal center with production of pathogens autoantibodies.
Conclusion:
To improve long-term transplant out-comes we need to understand the mechanism and pathogenesis of autoantibodies that will help us to develop strategies to diagnose and treat AMR.
The immune system is considered a major barrier to organ transplantations. There is what is called HLA antigens which are highly polymorphic and act like personal fingerprint recognized by the immune system. If the immune system recognized the allo-HLA antigens expressed on the graft, it will be rejected.
All other antigens are called non-HLA antigens and most of them are monomorphic and cause no antigenic stimulation to the immune system but reports of ABMR in HLA-identical siblings highlight the presence and the importance of non-HLA antibodies.
In general, non-HLA antibodies are classified into:
Non-HLA antigens most of them not expressed on lymphocytes so, it’s difficult to be evaluated by routine crossmatch
Also, usually not expressed and recognized by the immune system unless there is severe tissue injury like prolonged ischemia time, CNI toxicity, and rejection so it more common with deceased kidneys caused by this prolonged ischemia time.
Its role in inducing ABMR by itself is not been fully proven and is still not recommended to do screening pretransplant and mostly it has a synergetic effect when HLA DSA are there.
Non-HLA Ab mediated rejection can be caused by complement fixing pathway or non-complement fixing pathway so it may cause c4d-ve ABMR and also chronic transplant glomerulopathy
There are several non-HLA antibodies but the most important ones which were generously studied include (Angiotensin II Type 1 Receptor (AT1R-Ab), anti-endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs, and anti-collagen)
Angiotensin type I receptor (AT1R) Ab:
pathogenesis:
complement dependent (C4d +ve) and complement independent process (C4D -v).
Perlecan:
Mechanism of injury:
it causes vascular damage and intimal proliferation and/or humoral immune responses that accelerate immune-mediated vascular injury.
Collagen:
The immune system is considered a major barrier to organ transplantations. There is what is called HLA antigens which are highly polymorphic and act like personal fingerprint recognized by the immune system. If the immune system recognized the allo-HLA antigens expressed on the graft, it will be rejected.
All other antigens are called non-HLA antigens and most of them are monomorphic and cause no antigenic stimulation to the immune system but reports of ABMR in HLA-identical siblings highlight the presence and the importance of non-HLA antibodies.
In general, non-HLA antibodies are classified into:
Non-HLA antigens most of them not expressed on lymphocytes so, it’s difficult to be evaluated by routine crossmatch
Also, usually not expressed and recognized by the immune system unless there is severe tissue injury like prolonged ischemia time, CNI toxicity, and rejection so it more common with deceased kidneys caused by this prolonged ischemia time.
Its role in inducing ABMR by itself is not been fully proven and is still not recommended to do screening pretransplant and mostly it has a synergetic effect when HLA DSA are there.
Non-HLA Ab mediated rejection can be caused by complement fixing pathway or non-complement fixing pathway so it may cause c4d-ve ABMR and also chronic transplant glomerulopathy
There are several non-HLA antibodies but the most important ones which were generously studied include (Angiotensin II Type 1 Receptor (AT1R-Ab), anti-endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs, and anti-collagen)
Angiotensin type I receptor (AT1R) Ab:
pathogenesis:
complement dependent (C4d +ve) and complement independent process (C4D -v).
Perlecan:
Mechanism of injury:
it causes vascular damage and intimal proliferation and/or humoral immune responses that accelerate immune-mediated vascular injury.
Collagen:
It was recognized in HLA identical twins and 100% donor/ recipient matched matched ,that they might develop progressive ABMR , underscoring the importance of non-HLA antibodies in mounting the reaction.
2 types of antibodies are recognized :
Allo-antibodies, antibodies directed against donor HLA antigens
Auto-antibodies , directed against self-antigens.
As the vasculature represents the inter-phase between the donor and the recipient,it might elucidate the auto-antibody reaction with auto-antigens expressed on the vascular endothelial cells.
Anti-Endothelial cell antibodies AECA:
Most of the allograft rejections mediated by non anti-HLA antibodies were attributed to AECA that recognize autoantigens on the vascular endothelial cells.
several case reports of acute and hyper-acute rejections inflicted by AECA in the setting of identical HLA haplotypes
Those antibodies are detectable pre-transplantation.
AECA were detected in patients with
1) failed allograft than in those with functioning allograft .
2)HLA sensitized then HLA compatible patients
3)complement is normal in AECA mediated rejection,therfore its considered cellular rejection. C4d was arquably reported in similar cases.
4)AECA are usually non complement fixing IgG2 and IgG4
5)Despite the fact that its non compliment fixing AECA, ALLOGRAFT BIOPSY is usually featuring full house ABMR characteristics including glomerulitis , ptc, margination of monocytes and neutrophils.
Summary
Antibodies against non HLA antigens are associated with rejection and lower rates of graft survival in the long run. These antibodies can be produced in response to ischemia reperfusion injury, surgical trauma and alloimuune response to antigen. Targeted therapy is needed to fight against these autoantibodies in order to sustain graft survival at good rates.
Current therapy with regards to this issue is antibody depletion, B cell depletion, IVIG, proteasome inhibitors and complement inhibitors. These drugs are given in combination to achieve maximum benefit. However, these are not sufficient in many cases which can be refractory to such therapy and lead to bad graft survival outcomes. A recent therapy includes IL-6 inhibitor tocilizumab. This drug reduces the production of HLA DSA in kidney transplant recipients who are resistant to desensitization protocols and therapy.
Further studies are needed to advance in the knowledge of autoantigens eliciting immune response to transplant. This will help to garner the diagnosis and treatment of AMR.
summary of The importance of non-HLA antibodies in transplantationintroduction
de novo anti donor HLA (DSA) is associated with poor out come in kidney transplantation
the clinical implication of de novo DSA and the pathogenic role of DSA it self remain unclear.
antibody production usually require T cell help so presence of DSA include the presence of mature cellular alloimmune response.
literature is discrepancy as.to the incidence,timing and impact in term of graft survival of TCMR in patient with DSA .postive.
study is prospective single centre study screen at time of transplant patient with DSA and correlate with acute rejection, severity of rejection and graft out come comparing patients with no DSA or TCMR.DSA alone,TCMR alone or DSA plus TCMR.
we correlate DSA and TCMR to non adherence .
Result
study population
among 378 patients kidney transplant between jan 2011-nov 2014
15 excluded death and graft loss with 3 month.
363 patients -294 at least 1 allograft biopsy with first year of transplant were include with study.
276 biopsy early 0 to 5 month .
244 biopsy late 6 to 12 month
total 209 of 294 had paired biopsy (early &late).and those group of patients were used to analyze histological proprieties.
post transplant DSA detection
all patients were negative at time of transplant determined by luminex and negative flow-cross match.
294 patients 67 develop DSA in the first year so 40% transplant DSA
60% persistence DSA and 61% de novo DSA,
Auto antibody production in transplant
auto antibody production in transplant depend on many factors
:
1-graft damage.
2-alloimmunity
3-chronic inflammation.
auto antigens can present to auto reactive Tcells and B cells either by recipient or donor antigen presenting cells(APCs) in the extra vesicles tissue TLT
Ischemic re perfusion injury
apoptosis and necrosis caused by IRI result in the release of damage associated molecules pattern (DAMPs) including self nucleic ,histone and high mobility group protein B1.
DAMPs interact with receptor include TOLL- like recptor or (TLR) and TLR4 expressed on dentirtic cell vascular endothelial cells and tubular cells.
this process cause down stream production of pro inflammatory cytokines.
interplay between alloimmunity and autoimmunity
alloimmune response to the transplant oragan or tissue occur through the direct ,indirect and semi- direct allo recogenazation pathway.contribute to the rejection process..
tissue damage trigger an autoimmune process at the site of the graft.
information might guide to formulation and development of therapeutic intervention to prevent chronic rejection.
extracellular vesicles
cell to cell communication through cellular vescles is increasing as a mechanism that elicit autoimmune and alloimmune response.
based on biogensis extracellular vescles classify into 3 classes
1-exosomes
2- micro particles
3- Apoptotic bodies all of them contain memory autoantigens.
TH 17 cells and tertiary lymphoid tissue
TH 17 cells are the major producer of IL-17 and implicated in many autoimmune disease
TH 17 cells have greater capacity to provide B cell help to TH1 by higher clonal expansion
conculsion.
evidence support of immunity to self Ag in both acute and chronic rejection of solid organ transplant
auto antibody production via several mechanism:
1- extracellular vesicles insufficient clearance.
2- cross reactivity between self and foreign antigens
3-interplay between innate and a adaptive immunity.
clinical presentation and response to desensitization therapy of non HLA antibodies have not been clearly established.
a need clearly exist for further investigation into the pathogen mechanism of auto antibodies and identification of more effective therapies.
incomplete knowledge of the auto antigens that elicit immune response during transplant hamper the diagnosis and treatment of AMR.
*Target of humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies also showed antibodies directed against non-HLA antigens in the process of AMR.
*Non HLA antibodies are divided into alloantibodies and autoimmune antibodies
*when to suspected Non HLA antibodies : negative lymphocyte crossmatches and tested negative for donorspecific HLA antibodies (DSAs), so AECA as the mediator of graft injury.
*AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates
* deceased donors might exhibit higher levels of non-HLA antibody ligands than those from living donors
*Angiotensin type 1 receptor (AT1R) : (IgG1 and IgG3 isotypes)
Causes ; hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
N.B Over 60% of heart transplant candidates who were AT1R negative prior to LVAD implantation developed de novo AT1R antibodies after the procedure . Development of AT1R antibodies postLVAD did not impact incidence of rejection or transplant survival .
* Perlecan : IgG1 and IgG3 isotypes
vascular rejection and elevated LG3 levels were associated with heightened neointima formation.
HLADSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
* Collagen: first assessed during Lung Tx
Transplant glomerulopathy is characterized by duplication of the glomerular basement membrane
type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity
**Autoantibody production in transplantation:
¥ Ischaemia reperfusion injury : generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment
¥ Interplay between alloimmunity and autoimmunity
Major efforts to define their targets is targeted to understand the mechanism and pathogenesis of autoantibodies and to develop strategies to improve long-term transplant outcomes.
Nowadays, antibodies against auto antibodies have known contribution in ABMR and chronic rejection. Unexpectedly low allograft long-term survival of TX between HLA- matched sibling donors confirms this subject.
Two categories of non-HLA Abs:
1- Allo-abs against polymorphic Ags (different between donor and recipient)
2-Abs against self-Ags (Auto abs) anti-endothelial cell Abs(AECA) are involved in accelerated AMR in many cases with negative XM and negative DSA.
HLA –sensitized TX candidates showed higher frequency of these Abs pre-transplantation. These patients had higher rate of early acute rejection but not for living donor. Many were negative for CD4 for CD4d, because they had subclasses IgG2 and IgG4. But they showed histologic finding of AMR without C4d staining. Using proteomics, a broad array of these auto-abs are known. But these are dependent on other factor such as IRI, ligand expression and inflammation of TX.
AT1R:
AT1R is a G-protein receptor first discovered in pre-eclampsia and its activation causes HTN, proliferation of vascular smooth muscles. In a study 20 Pts with vascular rejection were DSA negative and 16 had AT1R Abs (IgG1 and IgG3) with evidence of complement activation. Treatment consisted a combination of plasmapheresis, IVIG and losartan.
In a cohort of 97 TXs without DSA or M1CA-Abs, six of seven Pts with AMR had AT1R Ab>17IU/ml with no contribution of complement. AT1R-Abs were associated with 2.6- fold risk of chronic rejection. AT1R-Ab positivity had a synergistic effect with HLA-DSA.
In recurrence of FSGS post-TX, plasma exchange combined with losartan were effective in treatment of these Pts with reduction AT1R –Abs. In heart TXs: ACR and AMR were associated with presence of AT1R-Ab and DSA.
Perlecan:
It is a hepran sulfate proteoglycan. Its C-terminal domain two sets of EGF-like repeats. Its angiogenic activity depends on LG3 subdomain, which was increased in patients with Banff grade II or III of AR. LG3 also behave as a neo Ag causing LG3-Ab. Abs especially when they were associated with DSA. There are two different mechanism of vascular injury for perlecan:
1-Direct injury 2-humoral immune responses.
Collagen:
Expression of matrix metalloproteases can modify collagen and release its fragments that causes auto Ab formation.
In kidney TXs, transplant glomerulopathy was associated with collagen IV and fibronectin auto-abs. Collagen V Abs in lung TXs is associated with BOS. TH17-mediated immunity to collagen V caused BOS in lung TXs and IL-17 A and IL-17F secretion by CD4+ TH17 are mediators that lead to the BOS.
Ab production in treatment:
Understanding mechanism of graft damage is important. IRI and chronic inflammation cause auto-abs presented to T or B cell by APC in the form of EV or TLT. IRI cause tissue damage, apoptosis and necrosis and releases DAMPs which can interact with TLR2 and TLR4 on myeloid cell, dendritic cells VECs and TECs. Allo-immune responses against TX occurs through the direct, indirect and semi-direct pathways. Indirect pathway can spread and this process is called epitope spreading and leads to chronic rejection.
EV:
Extracellular vesicles cause cell-to-cell communication and auto-immune and allo-immune responses. EVs contain mRNA, mi RNA, DNA and protein, lipid and CHOs that modulate immunity. They have three classes: exosomes, micro particle and apoptotic bodies containing auto-abs or activate T cells. T H17 cells are activated by TGF-β and IL-6 where Th17 cells are activated by IL-23 causing chronic inflammation.TH 17 can produce IL-17 which has an important role in rejection and autoimmune responses.
TLT:
It is similar to GC but in setting of chronic inflammation through lymphoid neo-genesis. It supports maturation of autoreactive B cells and is modulated by IL-17 secreted from TH17.
Conclusion: Ab formation against self-Ag is important in acute and chronic rejection. Treatment option for AMR caused by auto Abs is similar to AMR caused by DSAs. But more investigation is needed for more effective therapies. For example, IL-6 inhibitor (Tocilizumab) or IL-17 inhibitors are other treatment options.
Non HLA antibodies are involved in antibody mediated rejection leading to decreased graft survival . There are few Non- HLA antibodies and their features typically include positive FCXM in the absence of donor specific DSA on Luminex SAB .They are classified as allo- and auto- antibodies ;including
– AT1R- Angiotensin Type 1 Receptor
Present on endothelial cell surface and antibodies to AT1R are usually IgG1 & 3. and they are risk factor for malignant hypertension graft rejection.
-Preclan
Present on blood vessel wall and having antiangiogenic characters . Lamilin like globulin LG3 is highly antigenic and related to direct vascular injury.
– Collagen
Essentially important in Lung transplant
Mechanism of Non HLA Antibodies production involve Ischemic reperfusion injuries(IRI),allo immunity and Chronic inflammation
In summary, non HLA antibody production is multifactorial and result in AMR. Different approaches can be undertaken to manage AMR including IVIG , antibody and B cell depletion and protease inhibitors. More studies are required for better understanding of pathogenesis of rejection to make long term graft survival much better.
The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival. Although our knowledge of non-HLA antibodies is incomplete, recent studies provide compelling experimental and clinical findings demonstrating that antibodies directed against autoantigens contribute to the process of antibody-mediated acute and chronic rejection. Important areas for investigation remain understanding the mechanisms underlying the production of autoantibodies in the setting of organ transplantation. Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organ-derived autoantigens in the form of soluble antigens, extracellular vesicles or apoptotic bodies that are presented in context of the transplant recipient’s antigen presenting cells to stimulate autoantibody production. Th17 cells are essential in the orchestrating autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promoteallograft rejection. Identification of the immunologic phenotypes of transplant recipients at risk of non-HLA antibody-mediated rejection and the development of targeted therapies to treat these rejections are sorely needed to improve both transplant and patient survival.
Principal targets of the humoral immune response to the renal allograft are the
highly polymorphic HLA antigens, but studies have also implicated antibodies
directed against non-HLA antigens in the process of AMR.
Non-HLA antibodies are classified into two main categories:
Alloantibodies: directed against polymorphic antigens that differ between the
recipient and donor, autoantibodies: and antibodies that recognize self-antigens.
AECA:
Higher:
In failed transplants than in those with functioning grafts at 1 year post.
In HLA-sensitized renal transplant candidates than in non-sensitized candidates.
Despite generating autoantibodies following transplantation, the majority of patients
did not experience rejection or graft dysfunction. This finding suggests that the
pathogenicity of the autoantibodies is conditional upon other factors such as ligand
expression, ischemic injury and/or the state of inflammation within the
microenvironment of the allograft.
Angiotensin type 1 receptor (AT1R)
AT1R is a G protein receptor that is expressed at the endothelial cell surface, binds
to angiotensin II and regulates water–salt balance and blood pressure.
Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth
muscle migration and proliferation.
AT1R antibody correlated with an increased incidence of AMR and inferior graft
survival.
Significantly higher levels of AT1R antibodies were observed in recipients with
FSGS recurrence.
Clinical studies in heart transplantation:
Increased Pretransplant levels of AT1R antibodies are associated with heart
transplant ACR and AMR as well as early onset of microvasculopathy.
A study showed that elevated pretransplant AT1R antibody levels alone were not
associated with increased risk of rejection, but when both HLA-DSA and AT1R
antibodies were present, the risk of AMR and ACR increased significantly,
suggesting a synergism .
AT1R negative prior to LVAD implantation developed de novo AT1R after LVAD.
Mechanisms of injury:
AB identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a
subset of patients.
Biopsy shows increased tissue factor expression and thrombotic occlusions.
Perlecan:
Heparan sulfate proteoglycan — is a major component of the vessel wall.
The C-terminal domain of perlecan, endorepellin, is best known for its anti-
angiogenic properties68 and contains three laminin-like globular (LG) domains
separated by two sets of epidermal growth factor (EGF) – like repeats. Most of the
antiangiogenic activity of endorepellin resides in the LG3 subdomain.
Studies have shown increased serum LG3 levels in renal transplant recipients with
immune-mediated vascular injury and renal dysfunction.
Similar to AT1R antibodies, HLADSA and LG3 autoantibodies can synergize to elicit
endothelial cell and graft damage.
Mechanisms of injury:
Perlecan cause vascular injury and neointimal formation directly by promoting
migration of donor vascular smooth muscle and/or recipient-derived mesenchymal
cells, and/or elicit humoral immune responses that accelerate immune-mediated
vascular injury and remodelling.
Collagen:
Clinical studies in lung transplantation:
Graft injury is thought to induce the expression of matrix metalloproteases that
modify collagen and release collagen fragments that serve as a major target for
autoantibody production.
Clinical studies in renal and heart transplantation:
Autoantibodies to collagen IV and fibronectin has been reported in renal transplant
recipients diagnosed with transplant glomerulopathy.
In heart transplantation, development of HLA DSA in recipients diagnosed with
AMR correlated with the development of autoantibodies to collagen V.
Mechanisms of injury:
Type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant
vasculopathy in the absence of alloimmunity.
Autoantibody production in transplantation:
Autoantibody production in the transplant setting depends on multiple factors:
Graft damage mediated through IRI.
Alloimmunity.
Chronic inflammation.
Can cause intracellular proteins to be expressed on the surface of apoptotic cells,
raising the possibility that these cells act as an autoantigen reservoirs.
Autoantigens can be subsequently presented to autoreactive T cells and B cells
either by recipient or donor antigen presenting cells (APCs), in the context of
extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT).
Conclusion:
Patterns of clinical presentation and response to desensitization therapy of non-
HLA antibodies have not been clearly established.
Current treatment strategies for AMR due to autoantibodies are similar to that
reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG,
Proteosome inhibitor sand complement inhibitor.
However, it is not clear whether these regimens are effective either alone or in
combination.
The importance of non-HLA antibodies in transplantation:
The antibodies causing AMR can be either against HLA or non-HLA antibodies . Non-HLA antibodies are said to be a cause of AMR in patients with absence of donor specific HLA antibodies.
Some of these antibodies act against autoantigens like angiotensin type 1 receptor (AT1R), perlecan and collagen. Most of them show C4d negative AMR due to involvement of non-complement dependent pathways.
IRI, allo-immunity and chronic inflammation lead to increased expression of intracellular proteins on surface of apoptotic cells, acting as autoantigen presenting to autoreactive T and B cells by APCs in extracellular vesicles and tertiary lymphoid tissue (TLT). Indirect allo-recognition leads to intramolecular epitope spreading causing formation of allo-antibodies.. Th17 cells give rise to IL-17 which cause tertiary lymphoid tissue (TLT) formation and leukocyte recruitment, release of autoantigens and graft damage. Then B cell differentiation and plasma cell with antibody formation. This autoantibody graft injury can trigger DSA’s.
Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and impedes long-term renal transplant survival . The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR. The most convincing evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings .
Non-HLA antibodies are classified into two main categories: alloantibodies & autoantibodies. As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the nonHLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. Brasile et al. were the first to report a patient with pretransplant antiendothelial cell antibodies (AECA) . AECA has been reported to be higher in renal recipients with failed transplants than in those with functioning grafts at 1 year posttransplant. AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates. Interestingly, many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection. Although AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patient and in animal models , others have reported the absence of C4d staining in biopsy samples from patients with AECA. This discrepancy could result from the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. Even in the absence of complement deposition, however, AECA+ biopsy samples exhibit histologic findings consistent with AMR, including glomerulitis, transplant glomerulopathy, focal interstitial haemorrhage, focal capillary thrombosis, and margination of neutrophils, monocytes and macrophages in the peritubular capillaries.
●Angiotensin type 1 receptor (AT1R)
Clinical studies in renal transplantation—Angiotensin type 1 receptor (AT1R) is is expressed at the endothelial cell surface, binds to angiotensin II , its Hyperactivity causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation .. In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA . Even though the AT1R antibodies were IgG1 and IgG3, graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition ( suggesting that complement-independent mechanisms contributed to graft injury)
. Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy. These results indicate that agonistic antibodies targeting AT1R can mediate vascular injury. Subsequent studies confirmed these initial findings and showed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival .
AT1R autoantibody positivity was associated with a higher risk of acute rejection within the first 4 months after transplantation and a higher risk of graft failure beyond 3 years post-transplantation.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement
The presence of AT1R autoantibodies prior to renal transplantation is a risk factor for vascular rejection and malignant hypertension. Not all renal recipients with AT1R antibodies reject their grafts, however, indicating that additional co-factors or environmental conditions might be needed to promote rejection.
●Perlecan
Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties. and contains three laminin-like globular (LG) domains , Most of the antiangiogenic activity resides in the LG3 subdomain . Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction .
●Collagen
Clinical studies in renal and heart transplantation—Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Transplant glomerulopathy is characterized by duplication of the glomerular basement membrane and is associated with chronic renal allograft rejection.
Autoantibody production in transplantation
Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs .
Ischaemia reperfusion injury—Organ transplantation inevitably involves varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft. Although the immune system has a number of checkpoints to preserve tolerance to self-antigens, defects in these checkpoints coupled with the constant presence of autoantigen leads to chronic inflammation.
Interplay between alloimmunity and autoimmunity
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways. Once initiated, the indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading. This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs . Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process.
Conclusion
●The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival.
●Ischaemiareperfusion injury, surgical trauma and/or alloimmune responses can result in the release of organderived autoantigens in the form of soluble antigens, extracellular vesicles or apoptotic bodies that are presented in context of the transplant recipient’s antigen presenting cells to stimulate autoantibody production
●Th17 cells are essential in the orchestrating autoantibody production by supporting the proliferation and maturation of autoreactive B cells within ectopic tertiary lymphoid tissue. Conversely, autoantibody-mediated graft damage can trigger alloimmunity and the development of donor-specific HLA antibodies that can act in synergy to promoteallograft rejection
The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
immunity to nonHLA antigens also portends poorer long-term allograft outcome. Two large multicenter studies using independent registry data unexpectedly showed reduced long-term survival of renal transplants performed between HLA-haplotype-matched sibling donors, underscoring the importance of non-HLA immunity to the allograft in chronic rejection
Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies
Angiotensin type 1 receptor (AT1R)
Clinical studies in renal transplantation—Angiotensin type 1 receptor (AT1R) is a Gprotein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure
. Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation
Subsequent studies confirmed these initial findings and showed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival
only one of 6 AT1R+ recipients with AMR had C4d staining in their biopsy sample, again suggesting that complement-independent mechanisms contributed to graft injury.
patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone, suggesting a synergistic effect of these autoantibodies
overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype
Mechanisms of injury
—Although AT1R antibodies implicated in renal rejection were identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of patients, suggesting the involvement of complement-independent pathogenesis of these antibodies
Although angiotensin II binds to several sites in the extracellular loops and transmembrane helices of AT1R58, AT1R antibodies implicated in renal allograft rejection have been mapped to the AFJYESQ and ENTNIT epitopes present in the second extracellular loop (ECL2) of AT1R
Perlecan
Clinical studies in renal transplantation—Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)like repeats.
Mechanisms of injury
First, they showed that passive transfer of anti-LG3 IgG in a murine model of vascular rejection significantly increased infiltration of T cells and natural killer cells, C4d deposition and obliterative vascular remodelling in recipients of ischaemic aortic allografts, but not in adjacent non-ischaemic native aortas70. Second, they showed that escalating serum LG3 levels in murine aortic allograft recipients significantly increased neointima formation
Collagen
Clinical studies in lung transplantation—
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IRI
. Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production
Clinical studies in renal and heart transplantation
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy
These patients displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection
Mechanisms of injury
The role of IL-17-dependent cell-mediated immunity to collagen V in the development of BOS was first demonstrated in a study of lung transplant recipients who were monitored over a period of 7 years following transplantation. Strong collagen V responses correlated with both the frequency and severity of BOS
Autoantibody production in transplantation
alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs
The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs), in the context of extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT)
Ischaemia reperfusion injury—
The tissue damage caused by IRI can lead to acute kidney injury and delayed graft Author Manuscript Author Manuscript Author Manuscript function, which can impair graft survival88. Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1
Interplay between alloimmunity and autoimmunity—
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways
indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading
Extracellular vesicles
Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses
Conclusions and future perspectives
Current treatment strategies for AMR due to autoantibodies are similar to that reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG proteosome inhibitors and complement inhibitors
However, it is not clear whether these regimens are effective either alone or in combination. This issue was highlighted in a case report of renal artery thrombosis, accelerated rejection and graft loss associated with AT1R antibody that was refractory to AT1R blockade, plasmapheresis, IVIG, corticosteroids and eculizumab
A need clearly exists for further investigation into the pathogenic mechanisms of autoantibodies and the identification of more effective therapies.
IMPORTANCE OF NON-HLA ABS:
This Review focus on the clinical significance of a selected group of well-characterized autoantibodies and discuss current theories concerning their pathogens and production in renal transplantation.
Introduction:
Antibody mediated rejection can contribute to acute and chronic allograft dysfunction and lead to progressive graft loss. still the effect of non-HLA antibodies on kidney transplant not completely understood, based on evidence from few studies and registry reports which shows that non-HLA antigens associated with increased risk of acute and chronic AMR and accelerated AMR in recipients of renal transplants from HLA-identical siblings. With unexpectedly reduced long-term survival of renal transplants (11,12).
Classification of non-HLA abs
1- Alloantibodies directed against polymorphic antigens
2-Autoantibodies against recognize self-antigens in the endothelial cells
endothelial injury can be triggered by ischemic reperfusion injury, post-surgical trauma and/or alloimmune responses.
AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patients and in animal models with negative C4D staining mimicking cellular rejection this can be explained by the fact that the endothelial-cell-reactive antibodies are enriched for non-complement-fixing subclasses IgG2 and IgG4(31), and still histologically its look like AMR.
The frequency of the AECA was found higher in kidney transplant recipient with previous history of failed graft or presensitization. And organs from deceased donors might have higher levels of non-HLA antibody compared to organs from LD.
Angiotensin type 1 receptor (AT1R):
G-protein coupled receptor that expressed in the endothelial cell surface combined to angiotensin 11 , It regulate the water -salt balance and BP control . increased activity of AR1R lead to hypertension and vasoconstriction with smooth muscle migration and proliferation. also associated with preeclampsia and malignant HTN Prevalence of AT1R vary from 17-59% this variation in prevalence may be explained by the different methods and different cutoff value used for its detection.
In renal transplant elevated levels of AT1R antibodies were first reported in recipients with severe steroid-resistant vascular rejection and malignant hypertension in the absence of HLA-DSA .
AT1R antibodies were IgG1 and IgG3, associated with complement independent endovascular injury and malignant HTN. correlated with an increased incidence of AMR and inferior graft survival. Studies shows combination of HLA-ABS with AT1R have synergistic effect and increase the risk of AMR and graft loss. Renal biopsy specimens from transplant recipients with AT1R-mediated rejection also had increased tissue factor expression and thrombotic occlusions.
Experimental studies address the role of AT1R expression in podocytes with the increase rate of FSGS recurrence post kidney transplant. Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement (52).
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy and also reduced the podocyte injury ().
AT1R might serve as a biomarker for risk of FSGS recurrence.
In heart transplant Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of micro vasculopathy (5). DenovoAT1R found in 60% of the patients with ACD insertion. Combination of AT1R, HLA DSAs increased the risk of both cellular and antibody rejection rate.
Perlecan :
a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties. Most of the antiangiogenic activity of endorepellin resides in the LG3, LG3 important regulator of vascular remodeling. Its mainly cuase vascular injury and neointimal formation by stimulating autoantibody production and/or by
promoting the migration of vascular smooth muscle cells and/or MSCs. Few case based studies confirm that renal transplant recipient with high LG3 level have more immune-mediated vascular injury, higher incidence of Banff grade II or III acute vascular rejection and renal dysfunction.LG3 level consider prognostic marker as its associated with higher Risk of acute vascular rejection and reduced 1 years graft survival.
collagen:
collagen autoantibodies effect is mainly assessed in lung transplantation.
Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients, triggers by IRI , ischemic immune injury
While in renal transplant recipients diagnosed with transplant glomerulopathy due to the development of autoantibodies to collagen IV and fibronectin. increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection.
In heart transplantation both the production of DSA to HLA and autoantibodies to collagen V was accompanied by increased frequencies of collagen V specific CD4+Th cells secreting IL-17 and higher risk of CAV.
Autoantibody production in transplantation:
many factors affect the production of autoantibodies Like IRI ischemic reperfusion injury All immunity with chronic inflammation. Understanding of the mechanisms that lead to autoantibody formation will help in identification of target therapeutic agents to prevent and control vascular remodeling and rejection
Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity(70).defect in the immune check points after IRI in the presence of autoantigens can lead to chronic inflammation and damage .,many autoantigens during IRI can be released , processed and presented to autoreactive T cells by recruited APC . Circulating B cells bind these autoantigens and become activated by autoreactive T cells, resulting in the secretion of autoantibodies. In addition, complement activation can potentiate autoantibody production.
TH17 cells have a greater capacity to provide cognate B cell help than do TH1 cell populations by higher clonal expansion, production. Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.1L17 important for in solid organ transplant rejection and generation of autoimmune responses.
Conclusions remarks:
————————————
Autoantibody production might occur via several mechanisms, including failure of efficient clearance of extracellular vesicles, particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and interplay between innate and adaptive immunity.
A lot of debates regarding the main clinical characteristics and response to desensitization protocols in non-HLA autoantibodies and they just follow the same available treatment protocols for AMR targeting Abs depletion, B cells depletion, IVIG, proteosome inhibitors, Complement inhibitors, 1L-6 Tocilizumab,
Still evidence lacking for the effectiveness of the current use of above treatment regimens alone we need further studies to address the main pathogenic mechanisms of autoantibodies and the use of more effective targeted therapies. Like 1L17 Pathways, miRNA regulation148–150 and exosomes.
Non HLA Anti body
recent studies provide compelling experimental and clinical findings demonstrating that antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival in post renal transplantion.
The evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings.
Many factors lead to auto antibodies formation such as
Ischaemia-reperfusion injury, surgical trauma and/or alloimmune responses , extracellular vesicles or apoptotic bodies .
Th17 cells are essential in the regulating autoantibody production by thier effect in proliferation and maturation of autoreactive B cells .
Non-HLA antibodies are classified into two main categories: alloantibodies directed against difference between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the non HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. Brasile et al. were the first to report a patient with pretransplant anti endothelial cell antibodies (AECA) that caused hyperacute rejection, Notably, these
recipients displayed negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injure
Sensitized patient have higher frequency in devoloping AECA.
kidney transplant recipients with pretransplant AECA had increased episodes of early acute rejection and higher creatinine levels than those without AECA.
deceased donors might exhibit higher levels of non-HLA antibody ,because patients AECA and received live kidney not associated with acute rejection or with inferior renal graft function. They were negative for the complement degradation product C4d and graded as cellular rejection.
Angiotensin type I receptor ( AT1R):
Is a G- protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II, and regulates the water-salt balance and BP.
In renal transplantation, elevated level were reported in patients with severe steroid resistance vascular rejection, and malignant hypertension in the absence of HLA-DSA. The main stay of treatment for these patients is by a combination of plasmapheresis, IVIG and losartan.resulted in improved allograft survival compered to patients recovering standard anti rejection therapy.
Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and
FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
Perclean
is a major component of the vessel wall ,known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains.
LG3 regulates vascular remodelling.
Mechanism of injury ,the current paradigm of perlecan-mediated graft injury considers two interdependent mechanisms as follows the perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
Collagen V is present on airway epithelial cells and it increases following immune-mediated injury and/or IRI
Mechanism of injury ; in renal transplant recipients :development of autoantibodies to collagen IV and fibronectin has been detected
In renal transplantation recipients diagnosed with transplant glomerulopathy.
-Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and long-term graft survival.
-The targets of the humoral immune response to the renal allograft are HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
– The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival.
-Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
– Pretransplant anti-endothelial cell antibodies (AECA) caused the hyperacute rejection.
-The frequency of AECA has been reported to be higher in renal recipients with failed transplants than in those with functioning grafts at 1-year post-transplant and in HLA-sensitized renal transplant candidates than in non-sensitized patients.
-Many of the renal rejections that were reported to be associated with AECA were negative for C4d and graded as cellular rejection.
-The endothelial-cell-reactive antibodies are enriched for non-complement-fixing subclasses IgG2 and IgG431.
-Despite generating AECA following transplantation, the majority of patients did not experience rejection or graft dysfunction.
-The pathogenicity of the autoantibodies depends on ligand expression, ischaemic injury, and/or the state of inflammation within the microenvironment of the allograft.
–Angiotensin type 1 receptor (AT1R):
-It is a G-protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water-salt balance and blood pressure.
– In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA .
-Graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition.
-Treatment of AT1R antibody-positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
– AT1R antibody correlated with an increased incidence of AMR and inferior graft survival.
-AT1R autoantibody positivity was associated with a higher risk of acute rejection within the first 4 months after transplantation and a 2.6-fold higher risk of graft failure beyond 3 years post-transplantation.
-Patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
– Studies suggest a role for AT1R in FSGS; overexpression of human AT1R in podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
-Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
-Significantly higher levels of AT1R antibodies were observed in recipients with FSGS recurrence.
– Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
-A study showed that with elevated pretransplant AT1R antibody levels and the presence of HLA-DSA, the risk of AMR and ACR increased significantly.
Mechanisms of injury:
-Although AT1R antibodies implicated in renal rejection were identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of patients.
-Renal biopsy specimens from transplant recipients with AT1R-mediated rejection also had increased tissue factor expression and thrombotic occlusions.
-These occlusions decreased following treatment with losartan and this effect was accompanied by improved renal function and graft outcome.
-Binding of autoantibody binding to AT1R contributes to rejection by mimicking the action of angiotensin II.
Perlecan:
-It is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic .
-Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction
-LG3 is a regulator of vascular remodelling.
-Pre-transplant and post-transplant levels of LG3 antibodies of the IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection.
-Patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival.
Mechanisms of injury:
-Perlecan-mediated graft injury by two differentmechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodeling.
Collagen
-The clinical significance of collagen autoantibodies has mainly been assessed in the setting of lung transplantation.
-Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production.
-Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome (BOS) in lung transplant recipients.
-Patients with idiopathic pulmonary fibrosis and cystic fibrosis reportedly have the highest prevalence of antibodies to collagen V and Kα-tubulin and are at increased risk of developing primary graft dysfunction, HLA-DSA, and BOS79.
-Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
-In heart transplantation, development of HLA DSA in recipients diagnosed with AMR correlated with the development of autoantibodies to collagen V.
Mechanisms of injury:
-The role of IL-17-dependent cell-mediated immunity to collagen V in the development of BOS was first demonstrated in a study of lung transplant recipients who were monitored over a period of 7 years following transplantation. Strong collagen V responses correlated with both the frequency and severity of BOS77.
-Type 17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity.
-Treatment with neutralizing IL-17 prevented BOS in orthotopic lung transplantation and chronic corneal allograft rejection in experimental mouse models.
-IL-17A and IL-17F secreted by CD4+ TH17 cells specific to lung self-antigens are critical mediators of autoimmunity leading to the pathogenesis of BOS.
Autoantibody production in transplantation
-Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated , alloimmunity and chronic inflammation.
-The autoantigens can be subsequently presented to autoreactive T cells and B cells either by the recipient or donor antigen-presenting cells (APCs).
-Ischaemia reperfusion injury (IRI)is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation, and leukocyte recruitment .
-The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival.
– Apoptosis and necrosis caused by IRI result in the release of damage-associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1.
-This process in turn causes downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
-Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
– IRI, natural antibodies, HLA-DSA and complement can damage the vascular endothelium leading to release of autoantigens from necrotic and apoptotic cells .
Interplay between alloimmunity and autoimmunity:
-Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways.
Extracellular vesicles :
-Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
-Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
– Based on their biogenesis, extracellular vesicles can be categorized into three classes — exosomes, microparticles and apoptotic bodies — all of which contain numerous autoantigens.
-Although high concentrations of exosomes can directly activate T cells, the activatory effect of this type of antigen presentation is much weaker than that of antigen presentation by professional APCs owing to the lack of co-stimulatory molecules .
-Exosomes efficiently activate T cells when they interact with dendritic cells.
TH17 cells and tertiary lymphoid tissue:
-TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases.
-It is activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.
About the question
Positive FCXM with negative Flowcymetry cPRA
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The importance of non-HLA antibodies in transplantation
The development of post-transplant antibodies against non-HLA autoantigens is associated with
rejection and decreased long-term graft survival.
Studies have also implicated antibodies directed against non-HLA antigens in the process of antibody mediated rejection. The most convincing evidence comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings
Non-HLA antibodies are classified into two main categories: alloantibodies directed against
polymorphic antigens that differ between the recipient and donor, and antibodies that
recognize self-antigens — autoantibodies
Antiendothelial cells antibodies (AECA) are non HLA antibodies that were found a cause of AMR.
Interestingly, many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection. Although AECA have been shown to activate complement resulting in C4d or C3d deposition in the graft in patients and in animal models others have reported the absence of C4d staining in biopsy samples from patients with AECA. This discrepancy could result from the fact that endothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4. Even in the absence of complement deposition, however, AECA+ biopsy samples exhibit histologic
findings consistent with AMR, including glomerulitis, transplant glomerulopathy, focal
interstitial haemorrhage, focal capillary thrombosis, and margination of neutrophils, monocytes and macrophages in the peritubular capillaries
In this article, a selected group of well-characterized autoantibodies are discussed and the current
theories concerning their pathogens and production in renal transplantation.
1-Angiotensin type 1 receptor (AT1R)
Although the AT1R antibodies were IgG1 and IgG3, graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition. Instead, the samples displayed increased expression of tissue factor, which was reduced following treatment with the angiotensin II receptor antagonist losartan. Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
These results indicate that agonistic antibodies targeting AT1R can mediate vascular injury.
Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause podocyte damage and foot process effacement consistent with a FSGS phenotype.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and
FSGS with severe podocyte effacement. Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
2- Perlecan
a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains separated by two sets of epidermal growth factor (EGF)- like repeats. Most of the antiangiogenic activity of endorepellin resides in the LG3
subdomain. Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
3-Collagen
Development of autoantibodies to collagen IV and fibronectin has been reported in
renal transplant recipients diagnosed with transplant glomerulopathy
Conclusion
Mounting evidence supports the importance of immunity to self-antigens in both acute and
chronic rejection of solid-organ transplants. Autoantibody production might occur via
several mechanisms, including failure of efficient clearance of extracellular vesicles,
particularly apoptotic bodies, cross-reactivity between self and foreign antigens, and
interplay between innate and adaptive immunity.
The patterns of clinical presentation and response to desensitization therapy of non-HLA
antibodies have not been clearly established.
Current treatment strategies for AMR due to autoantibodies are similar to that reported for HLA antibodies, including antibody depletion, B-cell depletion, IVIG proteosome inhibitors and complement inhibitors.
However, it is not clear whether these regimens are effective either alone or in combination. Accelerated rejection and graft loss associated with AT1R antibody that was refractory to
AT1R blockade, plasmapheresis, IVIG, corticosteroids and eculizumab . A need clearly
exists for further investigation into the pathogenic mechanisms of autoantibodies and the
identification of more effective therapies. A potential candidate is the IL-6 inhibitor
tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney
transplant recipients in a small pilot study. Therapeutic strategies targeting IL-17
pathways, miRNA regulation and exosomes might also become viable options to treat
autoantibody-mediated AMR and improve graft survival
The purpose of this paper is to shed light on the significance of non-HLA antibodies in renal transplantation.
In the initial study of AMR, it was shown that the production of post-transplant antibodies against non-HLA autoantigens is related to rejection and lower long-term graft survival. This was discovered in a sibling with matched HLA antigens and negative DSA who developed AMR.
Despite the fact that antibodies directed against non-HLA antigens have been involved in the process of AMR, the primary targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, which are the most common targets of AMR.
Generally speaking, non-HLA antibodies may be divided into two categories: alloantibodies, which are directed against polymorphic antigens that vary between the recipient’s and donor’s immune systems, and autoantibodies, which are antibodies that identify self-antigens.
In part, because the vasculature serves as an interface between the recipient immune system and the transplanted organ, a significant fraction of the non-HLA antibodies that have been found to drive renal rejection to identify autoantigens generated by the endothelial cells in the kidney. It has been shown that patients who have AECA prior to transplantation are more susceptible to hyperacute rejection, despite the fact that they have a negative lymphocyte cross-match and do not have DSA.
Despite the fact that C4 d is usually negative, the histology results are consistent with AMR.
Angiotensin type 1 receptor: This receptor is found in vascular endothelial cells and has been observed in certain individuals with severe steroid-resistant hypertension.
Two, perlecan, is a significant component of blood vessel walls.
3- Collagen type IV and fibronectin are two important proteins.
The processes that underlie the development and pathogenicity of non-HLA antibodies are currently poorly understood, and more research is needed. Examples of mechanisms include the ones listed below:
-Ischemia-reperfusion injury is the first kind of injury.
– a surgical complication
– An alloimmune response occurs.
– the significance of Th17 cells. Their involvement in the generation of autoantibodies by B cells in ectopic secondary lymphoid organs is critical.
– alloimmunity produced by autoantibodies graft injury and the development of DSA of different HLA types
Patients who are at risk of non-HLA antibody-mediated rejection will be identified, and tailored medications will be administered to such patients, resulting in improved graft survival.
The current therapy for AMR caused by autoantibodies is quite similar to the treatment for HLA-related AMR.
This article focus on importance of non HLA antibody in transplant.
Antibody mediated rejection (AMA) are responsible for both acute & chronic allograft rejection and decrease log term survival transplant.
Case series study who discovered by Brasile shows formation of pre transplant anti endothelial cell antibody (AECA) in patient develops hyperacute rejection in twice renal transplant despite negative lymphocytes cross match & negative DSA.
Many multicenter study discover increase level of AECA in sensitised patients develops acute kidney transplant rejection and noticed that it is not associated with complement activation (Cd40),
AECA is riched with non complement fixing sub class IgG2 & IgG4.
Histological feature of patients with AMR & high level of AECA includes glomerulitis / transplant glomerulopathy / focal interstitial haemorrhage/ focal capillary thrombosis/ migration of neutrophils and monocytes & macrophage in peri tubular capillaries.
Majority of patients who have generation of autoantibodies following transplant not develops rejection and graft dysfunction and this may related to many factors such as ligand expression and ischemic injury and inflammation within graft.
Angiotensin type 1 receptor (AT1R) : it’s G protein responsible for regulating water & salt balance and blood pressure.
In renal transplant shows who have high level of AT1R antibodies even in absence of DSA associated with malignant hypertension & severe steroid refractory vascular injury. it’s can treated by Losartan / Plasmapheresis and IV IG results in significant improvement of allograft.
AT1R also complement independent and associated with AMR especially if patients have DSA.
Recurrence of FSGS after kidney transplant accelerate allograft failure.
FSGS may be idiopathic or hereditary and manifested by proteinuria & affeciment & damage of podocytes. there’s relation between recurrence of FSCG and level of AT1R.
clinical study in heart transplant: presence of both AT1R & DSA associated with develops Acute cellular rejection (ACR) & AMR in comparison of high level AT1R alone. they reported increase level of AT1R in patients with left ventricle assist device but no evidence of rejection post transplant and it’s mechanism unknown. Presence of AT1R autoantibodies prior to transplant is a risk for vascular rejection and malignant hypertension but not all patients develop rejection and there’s another factors contribute to rejection which is ischemic reperfusion injury.
Perlecan : large heparan sulfate proteoglycan. it’s major component of blood vessel. it’s called antiangiogenic properties. it’s contain 3 laminin like globular domin separated by 2 set of epidermal growth factor. most of endorepellin resides LG3. Apoptolic endothelial cell liberate cathpsin L which cleave LG3. they show increase level of LG3 in rejected patients with Banff grade II & III. study found that pre- post transplant level of LG3 antibodies of IgG1, IgG2 isotype were significant higher in patients with acute vascular rejection. Also they show relation of LG3 & DSA together against graft.
Collagen : Release of collegen fragments can lead to autoantibodies production and accelerate graft injury in lung transplant.
Post transplant formation of collagen antibody associated with development of bronchitis obliterance syndrome in lung transplant recipients. it’s also high level of collagen in patients with idiopathic pulmonary fibrosis & cystic fibrosis and contributes to graft rejection.
Clinical study in renal & heart transplant: Formation of autoantibodies to collagen IV & fibrorectin associated with chronic allograft nephropathy and increase risk of transplant glomerulopathy, Those patients with chronic rejection shows increase level of collagen IV specific & fibronectin specific CD4 T cell that secret INF-gamma & IL-17 & reduction of IL-10.
Experimental study on rate which are immunized with collagen V induce up regulation IL17 & IL23, mRNA expression T cell and adaptive transfer of Th17 will induce BOS lesion in lung isograft.
they hardly discover drug targeting against Th17 may improve long term survival graft.
Intrabronchial administration of anti- MHC class 1 control IL-17 may reduce cellular infiltration and decrease fibrosis and reduce collagen V antibody level.
So IL-17 A, IL17F are secreted by CD4 Th17 cell are specific to lung specific antigen and have roles in autoimmunity in developing BOS in lung transplant.
Autoantibody production in treatment:
it’s important to understand mechanism of autoantibodies by production to identify new therapies to prevent and control transplant rejection.
Ischemic reperfusion injury (IRI):
it’s has many factors like surgical trauma and tissue damage can induce innate inflammatory response which lead to generation alloimmune and autoimmune on graft.
IRI is complex pathophysiology mechanism which lead to generation of reactive oxygen species/ complement activation / coagulation / endothelial activation and leukocyte recruitment.
Tissue damage due to IRI lead to acute kidney injury and delay graft function and improve graft survival.
IRI can lead to release of pro-inflammatory mediators which lead to activation of adaptive immune response that lead to exacerbate allograft damage.
Interplay between alloimmunity and autoimmunity: alloimmune response in transplant organ can related to direct/ indirect and semi direct allorecoganise pathway.
Extra cellular vesicles are responsible for communication between cells. it’s categories to exosome and micro particles and apotopic bodies; these contain many antigens and it’s role regulating autoantibodies.
Th17 cells & tertiary lymphoid tissue involved in many autoimmune disease and lead to produce IL17 which responsible to promote chronic tissue inflammation & anti immunity.
Conclusion;
Autoantibodies production may occur by several mechanisms.
Patterns of clinical presentation and response to desensitisation therapy of non HLA Ab still not clear.
Current treatment strategy of AMR due to antibodies are similar to HLA antibodies including antibodies depletion and B cell depletion and IV Ig / complement inhibitors and it’s still not clear if it’s effective alone or combination.
Well done
· Many non -HLA antibodies are formed against released Ag from the graft upon exposure to traumatic events like (ischemia-reperfusion injury and surgery itself), those antibodies were corelated to both active and chronic AMR and eventually worse graft outcome.
· The evidence of the role of non-HLA antibodies in rejection comes from rejection in HLA identically transplant couples.
· Non-HLA antibodies are either directed against:
o Polymorphic allogenic antigens in graft.
o Autoantibodies: directed against own Ag (as endothelial Ag- anti-endothelial cell antibodies) after their exposure to traumatic event.
· These anti-endothelial auto-antibodies characterized by:
§ Higher among sensitized than non-sensitized patients and correlated to the graft outcome.
§ Cause hyperacute AR that occurred on table and reoccurred in 2nd transplant.
§ Occur in cases that had negative cross match and no detected DSA before transplantation.
§ Pathology of acute rejection here not exclusive AMR, but commonly presented with TCMR and C4d negative.
· Not all cases with non-HLA antibodies develop AR as many coexisting factors like cold ischemia time, ischemic reperfusion injury and state of microvascular inflammation.
Examples of non-HLA antibodies with significant impact on graft outcome:
o Angiotensin II, type 1 receptor antibodies:
§ Characterized by severe steroid resistant vascular rejection, no detected DSA and malignant hypertension which was treated by combined plasma exchange, IvIg and losartan.
§ Persistent positive antibodies post transplant and denovo antibodies carry worse outcome than those with positive antibodies pretransplant and turned negative after transplant.
§ Combined presence of those antibodies and DSA carry worse outcome than DSA alone.
§ Patients with recurrent FSGS post transplant demonstrated higher levels of those antibodies, which can be related to their role in podocyte injury and foot processes effacement. Treatment with PEX and losartan improved their outcome.
§ The pathogenesis related to effect of AII receptor effect and the pathology shows marked vascular injury (endarteritis and intravascular inflammatory infiltrate).
§ In heart transplantation, only their coexistence with DSA (rather than isolated anti AII receptor type 1 antibodies) carry worse outcome and increased risk of AMR and TCMR.
o Anti LG 3 (laminin like globular, component of perlecan present in structure of blood vessel).
o Anti collagen V antibodies: associated with increased IL17
§ Especially in lung transplantation in cystic fibrosis with marked injury of bronchioles basement membrane and bronchiolitis obliterans syndrome.
§ Renal transplant: may be responsible for transplant glomerulopathy (GBM multilayering).
§ Heart: associated with increased DSA and coexistence carry worse prognosis of the graft.
Factors increase risk of autoantibodies:
o Release and processing of self antigens on apoptotic cells and its presentation by either donor or recipient APC to auto-reactive B and T cells.
o Ischemic reperfusion injury which release reactive oxygen species and other inflammatory mediators that lead to endothelial injury and leukocyte recruitment.
o Alloimmune-autoimmune interaction: Alloimmune recognition occurs either direct ( by donor APC), indirect (by recipient APC) and semidirect (by allo-peptides bound to donor Ag).
o Cell to cell communication through extracellular vesicle as apoptotic bodies. Failure of clearance of those extracellular vesicles lead to recognition by APC and B, T cells activation with immune mediated graft damage.
Treatment of non-HLA antibodies mediated vascular rejection;
o Yet, not clear.
o It may be resistant to current ttt for AMR including steroids, PEX, IvIg, rituximab, ecluzimab. A need clearly exists for further investigation into the pathogenic mechanisms of autoantibodies and the identification of more effective therapies.
o IL-6 inhibitor tocilizumab may be beneficial.
o New therapeutic options targeting IL-17 pathways, miRNA may be future target.
The importance of non-HLA antibodies in transplantation
The long-term graft survival gets affected by antibody mediated rejection (AMR). The antibodies causing AMR can be either against HLA or non-HLA antibodies which can be further divided into alloantibody against polymorphic antigens differing between the recipient and the donor or autoantibodies that recognize self-antigens. Non-HLA antibodies have been incriminated as cause of AMR in patients with absence of donor specific HLA antibodies (DSA). especially in deceased donor transplants.
A substantial number of these antibodies act against autoantigens like angiotensin type 1 receptor (AT1R), perlecan and collagen. Most of these show C4d negative AMR due to involvement of non-complement dependent pathways. AT1R antibodies act on AT1R (especially ECL2 loop) leading to phosphorylation of ERK kinase stimulating AP-1 and NFKB in endothelial cells and smooth muscle cells. This gets aggravated in presence of cofactors like ischemia (ischemia-reperfusion injury, IRI). Perlecan is found in vessel wall and its C terminal domain called endorepellin has anti-angiogenic properties due to its LG3 subdomain. Serum LG3 levels have been found to be high in acute vascular rejection and are associated with poor graft survival. Bioactive forms of perlecan can cause direct vascular injury as well as antibody mediated vascular injury and remodelling. Antibodies to Collagen IV and fibronectin in kidneys have been shown to be associated with rejection with specific CD4+ T cells secreting interferon gamma and IL-17 and decreased levels of IL-10.
IRI, alloimmunity and chronic inflammation lead to increased expression of intracellular proteins on surface of apoptotic cells, acting as autoantigen presenting to autoreactive T and B cells by APCs in extracellular vesicles and tertiary lymphoid tissue (TLT). Indirect allorecognition leads to intramolecular epitope spreading causing formation of alloantibodies. Extracellular vesicles including exosomes, microparticles and apoptotic bodies contain autoantigens which can activate T cells, although weakly due to absence of co-stimulation. Th17 cells give rise to IL-17 which cause tertiary lymphoid tissue (TLT) formation and leukocyte recruitment, release of autoantigens and graft damage. Il-21 released by them cause B cell differentiation and plasma cell with antibody formation. This autoantibody mediated graft injury can trigger DSA development and further graft deterioration.
Dear All
Non-HLA is expected when the crossmatch is positive (CDC/FCXM) in the absence of DSA.
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-Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection and impedes long-term renal transplant survival.
-Non-HLA antibodies are classified into two main categories: alloantibodies directed against
polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens autoantibodies.
-Brasile et al. were the first to report a patient with pretransplant antiendothelial cell antibodies (AECA) that caused hyperacute rejection of a maternal renal allograft.
-At the population level, the frequency of AECA has been reported to be higher in renal
recipients with failed transplants than in those with functioning grafts at 1 year posttransplant.
-The specificity of the autoantibodies developed during the immune response to the allograft
is diverse.
** Angiotensin type 1 receptor (AT1R):
-Clinical studies in renal transplantation Angiotensin type 1 receptor (AT1R) is a Gprotein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin
II and regulates water–salt balance and blood pressure37. Hyperactivity of AT1R causes
hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
-In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA.
-Subsequent studies confirmed these initial findings and showed that AT1R antibody
correlated with an increased incidence of AMR and inferior graft survival.
-Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation
causes accelerated allograft loss in approximately 30% of recipients.
-Studies in an experimental rat model suggest a role for AT1R in FSGS; overexpression of human AT1R in rat podocytes was sufficient to cause
podocyte damage and foot process effacement consistent with a FSGS phenotype.
-Depletion of AT1R antibodies by plasma
exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in
this patient.
*Clinical studies in heart transplantation Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
* Mechanisms of injury—Although AT1R antibodies implicated in renal rejection were
identified as IgG1 and IgG3 isotypes, C4d deposition was only detected in a subset of
patients, suggesting the involvement of complement-independent pathogenesis of these
antibodies.
-the presence of AT1R autoantibodies prior to renal transplantation is a
risk factor for vascular rejection and malignant hypertension.
** Perlecan:
*Clinical studies in renal transplantation—Perlecan a large heparan sulfate .proteoglycan is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties.
* Mechanisms of injury:
-The current paradigm of perlecan-mediated graft injury considers two different, but interdependent mechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
** Collagen:
*Clinical studies in lung transplantation:
-The clinical significance of collagen
autoantibodies has mainly been assessed in the setting of lung transplantation . Collagen V is present on airway epithelial cells and its
expression increases following immune-mediated injury and/or IRI.
*Mechanisms of injury:
-Administration of collagen-V-specific CD4+ T cells or antibodies to collagen V can induce BOS in experimental models of lung transplantation.
*Autoantibody production in transplantation:
-Autoantibody production in the transplant setting depends on multiple factors. Graft damage
mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs.
*Ischaemia reperfusion injury:
-Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in
the absence of alloimmunity. For example, adoptive transfer of collagen-V-reactive
lymphocytes to Wistar Kyoto rats induced grade 2 rejection in fresh isografts and collagen V
expression (detected using immunhistochemistry) in fresh and well-healed isografts, but not
in native lungs.
-In a murine chronic lung transplant model, C3a increased IL-17 production by collagen-Vreactive T cells, suggesting an important role of
complement in the development of autoantibody responses.
*Interplay between alloimmunity and autoimmunity:
-Alloimmune responses to the
transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition
pathways.
-Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process.The indirect alloresponse triggers autoimmunity after transplantation presumably via antigen mimicry between autoantigen peptides and donor MHC peptides.
-Once autoreactive T cells are generated, chronic stimulation of these cells can lead to epitope spreading, which has been reported to contribute to the generation of autoantibodies.
* Extracellular vesicles :
-Cell to cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and
alloimmune responses.
-Extracellular vesicles released by APCs also carry
surface MHC class I and II molecules plus bound peptides that can activate T cells.Although high concentrations of exosomes can directly activate T cells.
* TH17 cells and tertiary lymphoid tissue:
-TH17 cells are the major producers of IL-17
and have been implicated in many autoimmune diseases. TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and
autoimmunity.
-The development of TLT has been reported in chronic allograft rejection of kidney. lung and heart transplants .TLT is an ectopic accumulation of lymphoid cells, with characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis.
References:
1. Stegall MD, et al. Terminal complement inhibition decreases antibody-mediated rejection in sensitized renal transplant recipients. Am J Transplant. 2011; 11:2405–13. [PubMed: 21942930] .
2. Amico P, et al. Clinical relevance of pretransplant donor-specific HLA antibodies detected by singleantigen flow-beads. Transplantation. 2009; 87:1681–8. [PubMed: 19502960] .
3. Gloor JM, et al. Baseline donor-specific antibody levels and outcomes in positive crossmatch kidney transplantation. Am J Transplant. 2010; 10:582–9. [PubMed: 20121740] .
4. Everly MJ. Incidence and hazards of alloantibodies in renal transplantation. Clin Transpl. 2013:313–7. [PubMed: 25095523] .
5. Wiebe C, et al. Evolution and clinical pathologic correlations of de novo donor-specific HLA
antibody post kidney transplant. Am J Transplant. 2012; 12:1157–67. [PubMed: 22429309] .
6. Lefaucheur C, et al. Preexisting donor-specific HLA antibodies predict outcome in kidney
transplantation. J Am Soc Nephrol. 2010; 21:1398–406. [PubMed: 20634297] .
7. Gourishankar S, et al. Pathological and clinical characterization of the ‘troubled transplant’: data
from the DeKAF study. Am J Transplant. 2010; 10:324–30. [PubMed: 20055809] .
8. Grafft CA, et al. Antibody-mediated rejection following transplantation from an HLA-identical
sibling. Nephrol Dial Transplant. 2010; 25:307–10. [PubMed: 19846396] .
9. Kalil J, et al. Humoral rejection in two HLA identical living related donor kidney transplants.
Transplant Proc. 1989; 21:711–3. [PubMed: 2650236] .
10. Montoliu J, et al. Delayed hyperacute rejection in recipients of kidney transplants from HLA
identical sibling donors. Am J Med. 1979; 67:590–6. [PubMed: 386793] .
11. Terasaki PI. Deduction of the fraction of immunologic and non-immunologic failure in cadaver donor transplants. Clin Transpl.2003:449–52. [PubMed: 15387129].
This article resume studies about non-HLA autoantigens directed against autoantigens contributing to the process of antibody-mediated acute and chronic rejection. The most convincing evidence of this mechanism comes from reports of accelerated AMR in recipients of renal transplants from HLA-identical siblings.
Non-HLA antibodies are classified into two main categories:
1 – alloantibodies directed against polymorphic antigens that differ between the recipient and donor;
2 – antibodies that recognize self-antigens — autoantibodies;
ANTI – ENDOTHELIAL CELL ANTIBODIES
A substantial proportion of the non-HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells (AECA). This kind of recipients displayed negative lymphocyte crossmatches and tested negative for donor-specific HLA antibodies (DSAs), implicating AECA as the mediator of graft injury.
ANGIOTENSIN TYPE 1 RECEPTOR (AT1R)
Antibodies to angiotensin type 1 receptor (AT1R), are others kind of antibody no-HLA involved with antibody-mediated rejection (AMR) and inferior graft survival. A study showed that elevated pretransplant AT1R antibody levels alone were not associated with increased risk of rejection, but when both HLA-DSA and AT1R antibodies were present, the risk of AMR and ACR increased significantly, suggesting a synergism between AT1R and HLA antibodies in promoting rejection.
PERLECAN
Perlecan — a large heparan sulfate proteoglycan — is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG). Most of the antiangiogenic activity of endorepellin resides in the LG3 subdomain. Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
COLAGENN
Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
AUTOANTIBODY PRODUCTION IN TRANSPLANTATION
Autoantibody production in the transplant setting depends on multiple factors. Graft damage mediated through ischaemia reperfusion injury (IRI), alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen reservoirs. The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs), in the context of extracellular vesicles (EV) or in tertiary lymphoid tissue (TLT).
INTERPLAY BETWEEN ALLOIMMUNITY AND AUTOIMMUNITY
Alloimmune responses to the transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathways. Once initiated, the indirect alloimmune response can spread to additional determinants within the primary target antigen, this process is termed intramolecular epitope spreading This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs
Similarly, the indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process. The indirect alloresponse triggers autoimmunity after transplantation presumably via antigen mimicry between autoantigen peptides and donor MHC peptides108. Several studies have shown that autoreactive proinflammatory T cells specific for collagen V and cardiac myosin are detected after lung and heart transplantation, respectively. Clonal expansion of these T cells occurs only after an alloresponse, and once stimulated they can induce rejection of allogeneic transplants.
EXTRACELLULAR VESICLES
Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses. Depending on their cellular source, extracellular vesicles contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses.
TH17 CELLS AND TERTIARY LYMPHOID TISSUE
TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases. TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity. A large body of data demonstrates the importance of IL-17 in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection
Humoral immunity may find different pathways for antibody production, either primarily (autoantibodies) or by exposing donor antigens outside the HLA complex (alloantibodies), inducing antibody-mediated rejection. This response is quite heterogeneous and multifactorial, involving increased or decreased expressions, ischemic injury, and inflammatory state of the allograft.
Angiotensin type 1 receptor (AT1R)
– Triggers apparently vascular lesion refractory to the use of corticosteroids
– Malignant hypertension
– Major vascular rejection
– Usually does not use complement to trigger the lesion
– May trigger acute rejection in the first 4 months or late after 3 years of transplantation
– Appears to be related to recurrent focal and segmental glomerulosclerosis
– When associated with DSA/HLA, the prognosis worsens
– Treatment is based on a combination of plasmapheresis, intravenous immunoglobulin, and losartan
Perlecan
– Important component of vascular endothelium
– Predominant activity in the LG3 subdomain
– LG3 suggests being a regulator of vascular remodeling
– May lead to vascular lesions and synergize with HLA-DSA, similar to what occurs with AT1R antibodies
Collagen
– Expresses metalloproteases that modify collagen and lead to the production of autoantibodies
– In lung transplantation, it is common to trigger bronchiolitis obliterans syndrome
– In kidney transplantation, it is common to cause transplantation glomerulopathy
– Uses the Th17 axis and interleukins can lead to direct graft injury (IL17) or autoantibody production (IL23)
Autoantibody production in transplantation
– Ischaemia reperfusion injury
– Alloimmunity x Autoimmunity
– Extracellular vesicles
– Th17 cells and tertiary lymphoid tissues
All of these paths can occur autoantibody production might occur via several mechanisms, including extracellular vesicles, apoptotic bodies, cross-reactivity between self and foreign antigens, and the interplay between innate and adaptive immunity induced by the Th17 IL 12-17-23 path.
Conclusion
Depending on the interleukins involved and the antibodies produced, new strategies such as antibody depletion, B cell depletion, IVIG, proteasome inhibitors, and complement inhibitors may be used with better results in the treatment of classical immunosuppression.
The importance of non-HLA antibodies in transplantation
Acute and chronic antibody mediated rejection known to affects long term graft survival
HLA and Non- HLA antibodies have a role in pathogenesis of AMR
Non-HLA antibodies consists of:
· Alloantibodies -directed against polymorphic antigens that differ between the recipient and donor
· Autoantibodies: antibodies that recognize self-antigens
Antiendothelial cell antibody (AECA):
Directed against kidney are found more common in deceased donor transplants and in highly sensitized recipients
As endothelium is the most common tissue exposed to the circulating blood- directed against the endothelium cause hyperacute rejection in the renal transplant recipients
Usually negative for DSA and cross matches
Features of glomerulitis, capillary thrombosis, transplant glomerulopathy with or without c4d deposition are found
not activated by complement due to AECA being IgG2 or IgG4 antibodies in nature
Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation revealed:
Antibodies to AT1R are associated with severe resistant vascular rejection and malignant hypertension
The combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy
Its complement-independent mechanisms graft injury – HLA -DSA negative and no C4d in renal biopsy
Positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
Some studies revealed that AT1R has a role in recurrence of FSGS in post-transplant recipients as it found mostly in recurrence than first occurrence
Perlecan:
The C-terminal domain of Perlecan, endorepellin- known for its anti-angiogenic properties which resides in the LG3 subdomain
High LG3 level associated with poor graft outcome
HLA-DSA positive with high LG3 level were associated with vascular rejection and more graft failure comparison to HLA-DSA positive alone
Collagen:
autoantibodies to collagen IV and fibronectin have been reported in renal transplant recipients diagnosed with transplant glomerulopathy (TG)
displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection
Autoantibody production in transplant:
Depends on multiple factors including graft damage due to ischemia reperfusion injury, alloimmunity and chronic inflammation
Ischemia reperfusion injury (IRI):
Can induce innate inflammatory response resulting in alloimmune and autoimmune response to the graft – cause graft damage and delayed graft function
studies showed that it may induce autoimmune response in absence of alloimmunity
Interplay between autoimmunity and alloimmunity:
Indirect alloimmune response can trigger autoimmunity after transplant via antigen mimicry between autoantigen peptides and donor MHC peptides
Tissue damage due to alloresponse to donor HLA antigens may cause release of sequestrated autoantigens leading to triggering of autoimmune response at site of the graft
Extracellular vesicles:
Cell to cell communication via extracellular vesicles can elicit autoimmune and alloimmune response as they contain numerous autoantigens.
Th17 cells and tertiary lymphoid tissue (TLT):
Th17 cells secrete IL-17 that has a role in solid organ transplant rejection and in generation of autoimmune response
Development of TLT was reported in chronic allograft rejection, it is an ectopic accumulation of lymphoid cells similar to germinal centre in a secondary lymphoid organ which occur in chronic inflammation through lymphoid neogenesis
Conclusion:
Non HLA antibody production is multifactorial and leads to AMR. Multiple strategies can be adopted to treat AMR. These include IVIG , antibody and B cell depletion and protease inhibitors. More efforts are required to understand more the pathogenies to as to improve long term graft survival
This article throw light on importance of non HLA antibodies in renal transplantation.
The development of post-transplant antibodies against non-HLA autoantigens is associated with rejection and decreased long-term graft survival, this was shown first in sibling with matching HLA antigens and negative DSA who developed AMR.
The principal targets of the humoral immune response to the renal allograft are the highly polymorphic HLA antigens, but studies have also implicated antibodies directed against non-HLA antigens in the process of AMR.
Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
Anti-endothelial cell antibodies (AECA): As the vasculature is at the interface of the recipient immune system and the transplanted organ, a substantial proportion of the non- HLA antibodies reported to mediate renal rejection recognize autoantigens expressed by endothelial cells. It has been seen that patients having AECA prior to transplant are more prone to hyper acute rejection though having negative Lymphocyte cross match and absence of DSA.
The histological findings are consistent with AMR though C4 d is negative most of times.
Angiotensin type 1 receptor antibody (AT1R )– can cause steroid resistant vascular rejection, malignant hypertension and will be HLA-DSA negative.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.Depletion of AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury.
Perlecan a large heparan sulfate proteoglycan is a major component of the vessel wall.
The current paradigm of perlecan-mediated graft injury considers two different, but interdependent mechanisms whereby bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
Collagen
Late renal allograft failure owing to chronic allograft nephropathy is one of the major challenges to the long-term success of renal transplantation. Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
Autoantibody production in transplantation.
Autoantibody production in the transplant setting depends on multiple factors. The autoantigens can be subsequently presented to autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
Ischaemia reperfusion injury—Organ transplantation inevitably involves varying levels of surgical trauma, tissue damage and IRI, all of which can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft.
Interplay between alloimmunity and autoimmunity. This expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs.
Extracellular vesicles—Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
TH17 cells and tertiary lymphoid tissue.
A large body of data demonstrates the importance of IL-17 in solid organ transplant rejection and generation of autoimmune responses.
The importance of non-HLA antibodies in transplantation
This is a review article highlighting the different non-HLA antibodies, their mechanism and role in transplant rejection.
Rejection due to non- HLA antibodies was first described in sibling with matching HLA antigens and negative DSA who developed AMR.
Two types of non- HLA antibodies- Antibodies against polymorphic antigens and autoantibodies.
Anti-endothelial cell antibodies (AECA) cause hyperacute rejection, non- complement fixing and may be C4d negative. The biopsy features are similar to those found in AMR.
Mechanism of action- activating endothelial cells and dependent on presence of other factors like inflammation and ischaemic injury to be full pathogenic.
Angiotensin type 1 receptor antibody (AT1R )– can cause steroid resistant vascular rejection, malignant hypertension and will be HLA-DSA negative.
Treatment is largely plasmapheresis, IV ig and Losartan.
Development of denovo ATIR antibodies leads to graft loss.
Presence of pretransplant antibodies has variable outcomes.
Could also have a role in initiating FSGS recurrence.
Have synergistic activity in the presence of HLA- DSA.
Mechanism of action is through activating the angiotensin type 1 receptor and mimic the action of angiotensin II.
Hence causing hypertension and vascular damage like endarteritis and increasing tissue factor leading to thrombotic occlusions.
Not all patients with AT1R antibodies develop rejection other additional factors may be needed.
Prelecan- Has c terminal domain called endorepellin which contains LG3 domains.
LG3 antibodies may associated with chronic rejection.
Cause vascular injury and neointimal formation.
Have synergistic activity with HLA- DSA.
Collagen
Collagen V antibodies in lung transplant are associated with development of bronchiolitis obliterans syndrome.
Collagen type IV antibodies may be associated with development of transplant glomerulopathy.
Auto-antibody production
May be due to ischaemia reperfusion injury
TH17 cells which produce IL17 may have a role in autoimmune pathogenesis.
Week 1
Journal club
V.The importance of non-HLA antibodies in transplantation
Introduction
Anti–HLA DSAs are involved in the majority of patients with ABMR, however rejection can also occur in those who are negative for DSA.
Non-HLA auto-antibodies have been associated with rejection in kidney, heart, & lung transplant recipients.
The evidence comes from reports of accelerated AMR among recipients from HLA identical siblings.
Reduced long-term outcomes was also shown in transplant between HLA-haplotype-matched siblings.
Classification of non-HLA antibodies:
(i) Alloantibodies: -target polymorphic antigens that differ between the recipient
& donor
(ii) Autoantibodies: -recognize self antigens
Unlike HLAs, which are expressed on the cell surface of the allograft endothelium, auto-antigens are cryptic & become exposed after tissue damage due to ischemia-reperfusion or allograft injury.
Thus non-HLA antibodies that mediate rejection recognize auto-antigens that expressed by endothelial cells.
Auto-antibodies can, in turn, accelerate &/or enhance renal allograft damage.
Anti-endothelial cell antibodies (AECA):
Kidney transplant recipients with pre-transplant AECA had increased events of early acute rejection & higher creatinine levels than those without AECA.
Angiotensin type 1 receptor (AT1R):
-is a G-protein coupled receptor
-expressed at the endothelial cell surface
-binds to angiotensin II
-regulates water–salt balance & BP.
–AT1R antibodies associated with severe steroid-refractory vascular rejection &
malignant hypertension.
-AT1R antibody correlated with an increased incidence of AMR & inferior graft
survival
Perlecan (a large heparan sulfate proteoglycan):
– A major component of the vessel wall.
– It contains 3 laminin-like globular (LG) domains, the LG3 domain is the most
anti-angiogenic one.
– Increased serum LG3 levels seen in renal transplant recipients with
immune-mediated vascular injury & renal dysfunction.
Auto-antibodies to collagen IV & fibronectin:
– reported in renal transplant recipients diagnosed with transplant
glomerulopathy; implicating collagen IV in the pathogenesis of chronic
rejection.
Autoantibody production in transplantation:
Depends on multiple factors that lead to exposure of intracellular proteins:
– Graft damage mediated through IRI
– Alloimmunity
– Chronic inflammation
– Auto-antigens can then be presented to auto-reactive T cells & B cells either
by recipient or donor APCs.
Ischaemia reperfusion injury(IRI):
– SOT involves surgical trauma, tissue damage & IRI.
– All of the above can elicit innate inflammatory reactions leading to the
generation of alloimmune & autoimmune responses to the graft.
– Immune system has a number of checkpoints to keep tolerance to self-
antigens, but defects in these checkpoints coupled with the constant
presence of autoantigen leads to chronic inflammation.
– This process in turn causes downstream production of pro-inflammatory
cytokines( e.g. IL-1β, IL-6, & TNF), which activation adaptive immune
responses that can exacerbate allograft damage & exposure to autoantigens.
– Autoantigens released from the injured graft are processed & presented to
autoreactive T cells by APC recruited during IRI
– Circulating B cells bind these autoantigens & become activated by auto-
reactive T cells, resulting in the secretion of autoantibodies.
– In addition, complement activation can potentiate autoantibody production in
the transplant setting.
Interplay between alloimmunity & autoimmunity:
– Alloimmune responses to the transplanted organ occur through the direct,
indirect & semi-direct allorecognition pathways.
– The expansion of alloreactive T cells to donor-derived MHC antigen via the
indirect allorecognition pathway is associated with chronic rejection &
linked to the generation of DSAs.
– Cell-to-cell communication via extracellular vesicles is known to elicit
autoimmune & alloimmune responses.
– IL-17 plays important role in SOT rejection & generation of autoimmune
responses, particularly in lung allograft rejection.
Conclusions & future perspectives
– Autoantibody production to self-antigens is seen in both acute &
chronic rejection of SOTs
– Responsible mechanisms include:
-failure to clear apoptotic bodies
-cross-reactivity between self & foreign antigens
-interaction between innate & adaptive immunity.
The clinical presentation & response to desensitization therapy of non-
HLA antibodies have not been clearly established.
Treatment of AMR due to auto-antibodies doesn’t differ from that
used for HLA antibodies.
There is a need for further investigation to delineate pathogenic
mechanisms of autoantibodies & to identify more effective therapies.
Tocilizumab, an IL-6 inhibitor was promising in a small pilot study.
Targeting IL-17, miRNA & exosomes are some possible options to
treat autoantibody-mediated AMR & improve graft life.
Modern genomics & proteomics platforms provide new chances to
improve our understanding of the mechanism, pathogenesis &
therapeutic options of auto-antibodies.
The importance of non-HLA antibodies in transplantation.
Introduction
Antibody-mediated rejection AMR could be from antibodies against HLA and Non-HLA autoantigens. Our knowledge of non-HLA antibodies is limited but recent studies showed increased long-term graft failure of renal transplants between HLA-matched sibling donors which showed the importance of non-HLA antibodies especially in chronic allograft rejection.
Non-HLA antibodies are divided into two groups. First is Alloantibodies against polymorphic antigen that differ between the recipient and donor. Second is autoantibodies against various antigens in the body which may cause cytokine activation and tissue injury. One of the important Non-HLA autoantibodies is anti-endothelial cell antibodies (AECA) that was reported to cause hyperacute rejection of a maternal renal allograft which suggests a role for AECA in the pathogenesis of accelerated AMR.
AECA were found to be significantly higher in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates and correlated with AMR in heart transplantation. AECA can cause renal rejections through activation of the complement pathway resulting in C4d and C3d deposition. However, many rejections associated with AECA were negative for C4d deposition and was graded as cellular rejection which could be explained by the fact that AECA are enriched for the non-complement fixing subclasses IgG2 and IgG4 although the biopsy samples showed histologic features suggestive of AMR.
Auto-antibodies specificity developed during the immune response to allograft varies and depends on many conditions such as ligand expression, ischemic injury and inflammation of the allograft. The expression of autoantigens on the endothelium is diverse and depending on anatomic location, vessel type and inflammation. All of these factors contribute to the challenges in determining the clinical relevance of non-HLA autoantibodies.
Here, the summary of discussion of non-HLA clinical significant autoantibodies.
Angiotensin type 1 receptor (AT1R).
AT1R is a G-protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. Increased activity of this receptor leads to hypertension, vasoconstriction and vascular smooth muscle migration and proliferation. Initially Antibodies to AT1R (IgG1 and IgG3 isotypes) were found to be associated in pre-eclampsia with increased maternal and fetal morbidity and mortality. Now AT1R antibody is recognized to be associated with increased risk of AMR and graft failure as a result of vascular injury. AMR antibodies can induce vascular injury with complement independent mechanisms (without C4d deposition in a biopsy) in most cases. In fact biopsy samples showed increased expression of tissue factor which was reduced after treatment with angiotensin II receptor blockers (ARBS). These findings are consistent with the hypothesis that AT1R antibodies contribute to rejection by mimicking the action of angiotensin II. Using plasmapheresis, IVIG and losartan for these patients improved allograft survival in comparison to standard anti-rejection therapy.
Presence of pretransplant AT1R auto-antibody is associated with high risk of acute rejection within the first four months as well as increased graft failure after 3 years post-transplantation. Strength of the AT1R antibody positivity level correlates with the time of rejection. AT1R auto-antibody can occur after transplantation -de novo- and can be associated with positive HLA-DSA and might have a synergistic effect. Studies showed that the level of AT1R antibody is significantly high in recipient patients with recurrent focal segmental glomerulosclerosis (FSGS) after transplantation. In heart transplantation, high levels of pre-transplant levels of AT1R antibody was associated with ACR, AMR and early onset of microvasculopathy especially when HLA-DSA was also positive which implies AT1R antibody synergistic effect. De novo AT1R antibody was noticed in patients with left ventricular assist device LVAD as a bridge to transplantation but didn’t affect the incidence of rejection or transplant survival.
AT1R antibodies were not involved in rejection for all renal transplant grafts which indicated the presence of other factors which may contribute and promote the rejection. Many studies supported that ischemic reperfusion injury (IRI) mediated damage of the endothelium increased AT1R expression which facilitated the interactions with AT1R antibodies.
Perlecan.
Perlecan is considered a major component of cell wall which is large heparan sulfate proteoglycan and has C terminal domain (endorepellin). Endorepellin has antiangiogenic properties which reside mostly in the laminin-like globular third subdomain (LG3). Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan. High levels of LG3 is associated with vascular rejection and neointima formation by stimulating autoantibody production or/and promoting the migration of the vascular smooth muscle cells and mesenchymal stem cells. As AT1R antibodies, LG3 antibodies have a synergistic effect with HLA-DSA to induce graft damage.
Collagen.
Collagen V is presented on the airway lining which increases following immune-mediated injury or IRI. Its clinical significance is related to autoantibodies formation in lung transplantation as these antibodies are associated with bronchitis obliterans syndrome (BOS). Patients with idiopathic pulmonary fibrosis and cystic fibrosis have the highest prevalence of antibodies to collagen V and Kα-tubulin and are at increased risk of developing primary graft dysfunction, HLA-DSA and BOS. Autoantibodies to collagen IV and fibronectin have been reported in patients with transplant glomerulopathy which is characterized by duplication of glomerular basement membrane leading to chronic renal allograft rejection.
Autoantibody production in transplantation
Many factors can lead to autoantibody production in the transplant settings which leads to graft damage. This graft damage occurred because IRI, alloimmunity and chronic inflammation causes cells to present antigens on their surface as autoantigens. These autoantigens will be presented to T and B cells by different ways and forms but will eventually lead to formation of autoantibodies.
Ischemic reperfusion injury (IRI)
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. IRI can cause tissue damage which can lead to AKI and delayed graft function and can impair graft survival. Apoptosis and necrosis caused by IRI eventually decreases with production of proinflammatory cytokines and promotes activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity
There are three ways for alloimmune response to occur in transplanted tissue which are direct, indirect and semi-direct allorecognition pathways. Intermolecular epitope spreading is when indirect alloimmune response can spread to additional determinants within the primary target antigen which is associated with chronic rejection and linked to formation of DSAs. The indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process. Intermolecular epitope spreading has been described for indirect pathway responses to donor alloantigen.
Extracellular vesicles
extracellular vesicles is a way for cell-to-cell communication that can elicits autoimmune and alloimmune responses as they contain mRNAs, miRNAs, DNA, proteins, lipids and carbohydrates, and can positively or negatively modulate immune responses. There are categorized into three classes based on their biogenesis: exosomes, microparticles and apoptotic bodies. Extracellular vesicles released by APCs also carry surface MHC class I and II molecules plus bound peptides that can activate T cells.
TH17 cells and tertiary lymphoid tissue
TH17 cells are the major producers of IL-17 and have been implicated in many autoimmune diseases. They are activated by IL-23 to promote chronic tissue inflammation and autoimmunity. IL-17 is important in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection. IL-17 plays an important role in the formation of Tertiary Lymphoid Tissue (TLT). TLT is an ectopic accumulation of lymphoid cells, with characteristics similar to that of a germinal center within a secondary lymphoid organ that arise in the setting of chronic inflammation through a process called lymphoid neogenesis. Under pro-inflammatory conditions, TLT is constantly fed neo-antigens released by tissue injury and trapped by defective lymphatic drainage leading to the production of pathogenic autoantibodies
Conclusion
Immunity to self-antigens plays an important role in both acute and chronic rejection of solid organ transplantation. Autoantibodies can be produced in many ways. Further studying is needed to establish a better knowledge of clinical presentation patterns and response to the desensitization therapy for non-HLA antibodies which can improve graft survival. Necrosis caused by IRI eventually decreases with production of proinflammatory cytokines and promotes activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
*Antibody-mediated rejection (AMR) contributes to both acute and chronic allograft rejection dueto the implicated antibodies directed against HLA antigens and non-HLA antigens .
* Non-HLA antibodies are two types -Alloantibodies directed against HLA that are not identical.
-Antibodies that recognize self-antigens (autoantibodies).
* Non HLA antibodies mediate renal rejection by recognize autoantigens expressed by endothelial cells in vasculatur tissue, so presence of pretransplant antiendothelial cell antibodies (AECA) can cause hyperacute rejection.
* Organs from deceased donors might exhibit higher levels of non-HLA antibody ligands than hose from living donors. *Many of the rejections associated with AECA were negative for the complement degradation product C4d and graded as cellular rejection, although AECA have been shown to activate complement
resulting in C4d or C3d deposition in the graft ,this discrepancy could result from the fact that endothelial-cell-reactive
antibodies are enriched for non complement-fixing subclasses IgG2 and IgG4.
* clinical significance of a selected group of well-characterized autoantibodies :-
* Angiotensin type 1 receptor (AT1R)
—AT1R is a Gprotein coupled receptor expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. *Hyperactivity of AT1R causes
hypertension, vasoconstriction and vascular smooth muscle migration and proliferation
* Antibodies to AT1R( IgG1 , IgG3) were reported in recipients with severe steroid refractory vascular rejection and malignant hypertension in the absence of HLA DSA, biopsy did not show evidence of complement deposition.
* Treatment of AT1R antibody positive patients with (plasmapheresis, IVIG and losartan )improved allograft survival compared to patients receiving standard anti-rejection therapy indicate that it mediated vascular injury.
* AT1R autoantibodies might impact long-term graft survival.
* patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
* Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation causes accelerated allograft loss due to podocyte damage resulting in proteinuria and loss of graft function.
*Causes of FSGS can be hereditary or idiopathic, autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.
* using plasma exchange and losartan therapy improving AMR and reduced podocyte injury.
*Clinical studies in heart transplantation Increased pretransplant levels of AT1R antibodies are associated with heart transplant ACR and AMR as well as early onset of microvasculopathy.
* Elevated AT1R antibody levels were also reported in patients witha left ventricular assist device LVDA , were AT1R negative prior to LVAD implantation developed de novo AT1R antibodies after the procedure.
.
*Perlecan
Is a large heparan sulfate proteoglycan (major component of the vessel wall).
The C-terminal domain of perlecan, endorepellin is best known for its anti-angiogenic properties and contains three laminin-like globular (LG) Most of the antiangiogenic activity of endorepellin resides in the LG3
subdomain.
* Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal dysfunction, and also associated with increasedd neointima formation.
* The IgG1 and IgG3 isotypes were significantly higher in renal transplant recipients with acute vascular rejection than in those without evidence of rejection.
* patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival.
* Collagen
Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IRI.
* Graft injury is thought to induce the expression of matrix metalloproteases that modify collagen and release collagen fragments that serve as a major target for autoantibody production.
* Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrome in lung transplantation.
* Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
*Ischaemia reperfusion injury can elicit innate inflammatory responses contributing to the generation of alloimmune and autoimmune responses to the graft.
* Alloimmune responses to the
transplanted organ or tissue occur through the direct, indirect and semi-direct allorecognition pathway
* The indirect alloimmune response can spread to determinants within the antigen, this proces intramolecular epitope spreading, this expansion of alloreactive T cells to donor-derived MHC antigen via the indirect allorecognition pathway is associated with chronic rejection and linked to the generation of DSAs.
*The indirect recognition pathway can also promote the development of autoimmune T and B cells that contribute to the rejection process and triggers autoimmunity after transplantation via antigen mimicry between autoantigen peptides and donor MHC peptides.
*TH17 cells are the major producers of IL-17 have been implicated in many autoimmune diseases and it play an important role in solid organ transplant rejection and generation of autoimmune responses, particularly in lung allograft rejection.
The importance of non-HLA antibodies in transplantation.
Acute and chronic antibody mediated rejection (AMR) affects long term graft survival.
HLA and Non- HLA antibodies have a role in pathogenesis of antibody mediated rejection.
Non-HLA antibodies are classified to :
1-Alloantibodies directed against polymorphic antigens that differ between the recipient and donor.
2-Autoantibodies : antibodies that recognize self-antigens.
Angiotensin type 1 receptor (AT1R):
Clinical studies in renal transplantation reveled the following:
Antibodies to AT1R are associated with severe resistant vascular rejection and malignant hypertension and combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival compared to patients receiving standard anti-rejection therapy.
Most of the patients are HLA -DSA negative and no C4d in renal biopsy as its complement-independent mechanisms graft injury.
Patients who were positive for both AT1R antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
Some studies reveled that AT1R has a role in recurrence of FSGS in post-transplant recipients.
Perlecan:
The C-terminal domain of Perlecan, endorepellin, is best known for its anti-angiogenic properties which resides in the LG3 subdomain, high LG3 level associated with poor graft outcome.
Again patient with HLA-DSA positive with high LG3 level were associated with vascular rejection and more graft failure comparison to HLA-DSA positive alone.
Collagen:
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
These patients displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells that secreted IFN-γ and IL-17, as well as a reduction in IL-10 levels, implicating collagen IV in the pathogenesis of chronic rejection.
Causes of Autoantibody production in transplantation:
1- Ischemia reperfusion injury: induced damage to vascular endothelial and tubular epithelial cells triggers the release of damage associated molecular patterns (DAMPs), which interact with recognition receptors on APC and led to production of proinflammatory cytokines, which promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
2- Interplay between alloimmunity and autoimmunity:
Alloimmune responses to the transplanted organ occur through the direct, indirect and semi-direct all recognition pathways.
Indirect recognition pathway can promote the development of autoimmune T and B cells that contribute to the rejection process.
3- Extracellular vesicles: released by APCs also carry surface MHC class I and II molecules that can activate T cells.
4-TH17 cells and tertiary lymphoid tissue: which produce IL-
17 that has major role in solid organ transplant rejection and generation of autoimmune responses.
Conclusions:
Desensitization therapy has no role in Non-HLA DSA yet.
AMR due to autoantibodies is similar to HLA antibodies
Which are antibody depletion, B-cell depletion, IVIG , proteasome inhibitors, and complement inhibitors which used alone or combination.
IL-6 inhibitor tocilizumab, which reduced the production of HLA-DSAs in desensitization-resistant kidney transplant recipients in a small pilot study.
Therapeutic strategies targeting IL-17 pathways, miRNA regulation and exosomes might also become viable options to treat autoantibody-mediated AMR and improve graft survival.
Dear All
How do you know that the crossmatch is positive due to non-HLA antibodies?
There is a reward (Kidney Transplantation 2021 – picture is below) for the correct answer (one sentence is required).
I think typical picture of non-HLA antibodies is to found FCXM positive for T and B cells
with no DSA(repeated many times) and auto cross match is negative.
Hello Professor Ahmed.
I think a positive crossmatch due to non HLA antibodies occur:
1. When here is no history of sensitization to anti HLA antibodies ( pregnancy, previous transplant and post transfusion) .
3. When is no history of desensitization protocols such as rituximab, antithymocyte globulin, or intravenous immunoglobulins
3. The recipient serum is tested negative for DSA on many occasions.
4. Negative autocrossmatch.
5. Crossmatch after serum treatment with heating or DDT( for IgM class antibodies) is negative.
Thanks
Non-HLA Antibody (IgG) can be detected in patient sera by ELISA testing.
Presence of non HLA revealed by positive CDC cross match with negative luminex HLA antibodies which is more sensitive in detecting DSA.
Endothelial Cell Crossmatch
Crossmatch would be positive due to non-HLA antibodies in case of:
1- Negative Lymphocyte cross match.
2- Confirmation of absence DSA on recipient serum and absence history of sensitization to HLA-antibodies.
3- No history of desensitization prior to organ transplantation using therapeutic antibody such as rituximab.
In case of positive CDC and flow crossmatch in the absence of SAB (single antigen bead) non-HLA comes to mind..
by detection of different types of non-HLA antibodies such as MICA (MICA-Ab) or MICB, or angiotensin II type 1 receptor (AT1R-Ab), endothelin-1 type A receptor (ETAR-Ab), perlecan, agrin or vimentin, and other non-HLA antibodies performing crossmatches with primary aortic endothelial cells (EC-XM).
You missed the answer Dr Doaa
positive B cell / T cell crossmatch with negative DSA testing, no history of desensitization, and negative auto-crossmatching is mostly due to the presence of Non-HLA antibodies.
A positive FCXM (with a negative autocrossmatch) in absence of DSA points towards non-HLA antibodies as the reason for the positive crossmatch
I think if u have a positive CDC cross match in a given clinical scenario with positive auto cross match and absence of DSA on SAB
Positive T cell with negative B cell crossmatch with negative DSA usually indicates non-HLA antibody.
Detection of donor-specific anti-endothelial cell antibodies in a flow cytometric crossmatch by using donor endothelial precursor cells (EPCs) as target cells has been to improve the sensitivity in detecting non-HLA antibody.
This technique is able to detect a non-HLA specific antibody population not detected by lymphocyte crossmatches
Test for anti-AT1R IgG Abs & 33 other non-HLA Abs(LABScreen Auto-Ab group 1 &2kits)
The answer is not clear Dr Mohamed
IgG4 high levels associated to negative DSA exams.
Not clear Filipe
-Flowcytometry crossmatch positive for T and B cells.
– Negative DSA.
– Negative Autocrossmatch.
– No history of desensitisation prior to transplantation.
positive FCXM with negative DSA in lumenix SAB
How do you know that the crossmatch is positive due to non-HLA antibodies?
As mentioned by my colleagues, I will suspect Non-HLA antibodies in the case of positive CDC and FCXM in the absence of detectable DSA by Luminex SAB (Negative virtual crossmatch)
Antibody mediated rejection is an important cause of acute and chronic graft loss. The occurrence of antibody mediated rejection even in identical twins with good HLA match pointd to the occurence of Non-HLA antibodies causing graft rejection.
They are classified into 2 categories: Alloantibodies against different HLA polymorphic antigens between donor and recipient. Autoantibodies directed against various antigens in the body which may cause cytokine activation and tissue injury.
Thanks
Non-HLA antibodies can contribute in AMR and are associated with poor graft survival.
They are alloantibodies against polymorphic antigens which are different between donor and recipient or autoantibodies that recognize self antigens.
Several autoantibodies are generated after transplant, the pathogenicity is conditioned upon ligand expression, ischemic injury and/or state of inflammation in the graft.
Anti-endothelia cell antibodies (AECA):
proportion of non-HLA antibodies that recognizes autoantigens expressed by endothelial cells in vasculature at interface between transplanted organ and immune system.
More common in patients with failed transplant and HLA-sensitized recipients.
include non complement fixing subclasses IgG2 and IgG4, graft biopsy show histologic findings of AMR without complement deposition
several reports showed that pretransplant AECA caused hyperacute rejection and/or accelerated AMR in transplant recipients with negative crossmatch and no DSA.
Angiotensin type1 receptor (AT1R) antibodies:
A receptor expressed on endothelial surface, regulates water and salt balance.
AT1R antibodies were first reported in recipients with steroid resistant vascular rejection, malignant hypertension and negative HLA-DSA, treatment with IVIG, plasmaphereses and losartan significantly improved graft survival compared to standard anti rejection treatment.
Studies showed that AT1R antibodies correlated with increased incidence of AMR and suggested complement independent mechanisms.
AT1R antibodies and HLA-DSA have synergistic effect and are associated with lower graft survival.
They may have a role in FSGS recurrence post transplant, a study showed that recipient with FSGS recurrence had significantly higher levels of AT1R antibodies.
Perlecan:
A major component of vessel wall, endorepellin is the C-terminal domain of perlecan which has anti-angiogenic activity mainly in the LG3 subdomains.
Studies showed that serum LG3 antibodies were higher in recipients with acute vascular rejection than in those without rejection, also recipients with Banff grade II or III acute vascular rejection had significantly higher levels of serum LG3 antibodies than those with tubulointerstitial rejection.
High pre transplant LG3 antibodies were associated with higher risk of vascular rejection.
HLA-DSA and LG3 autoantibodies had synergistic effect in graft failure.
Collagen:
Autoantibodies to collagen IV and fibronectin were detected in recipients with transplant glomerulopathy that is associated with chronic allograft rejection.
Autoantibody production in transplant:
Depends on multiple factors including graft damage due to ischemia reperfusion injury, alloimmunity and chronic inflammation.
Ischemia reperfusion injury:
Can induce innate inflammatory response resulting in alloimmune and autoimmune response to the graft which can cause graft damage and delayed graft function.
studies showed that it may induce autoimmune response in absence of alloimmunity.
Interplay between autoimmunity and alloimmunity:
Indirect alloimmune response can trigger autoimmunity after transplant via antigen mimcry between autoantigen peptides and donor MHC peptides.
Tissue damage due to alloresponse to donor HLA antigens may cause release of sequestrated autoantigens leading to triggering of autoimmune response at site of the graft.
Extracellular vesicles:
Cell to cell communication via extracellular vesicles can elicit autoimmune and alloimmune response as they contain numerous autoantigens.
Th17 cells and tertiary lymphoid tissue (TLT):
Th17 cells secrete IL-17 that has a role in solid organ transplant rejection and in generation of autoimmune response.
Development of TLT was reported in chronic allograft rejection, it is an ectopic accumulation of lymphoid cells similar to germinal center in a secondary lymphoid organ which occur in chronic inflammation through lymphoid neogenesis.
Conclusion:
Immunity to self antigen may contribute in acute and chronic rejection of transplanted organ.
Effect of desensitization on non-HLA antibodies is not clearly established.
Current strategies for treatment of AMR due to autoantibodies are similar to those used in treatment of AMR due to HLA antibodies and include antibody depletion, B cell depletion, IVIG, proteosome inhibitors and complement inhibitor.
The efficiency of these regimens is not clear.
Thanks
*The importance of non HLA antibodies in renal transplantation:
A cute and chronic allograft rejection post kiney transplantation can be caused by antibody mediated rejection (AMR).These antibodies are mainly HLA antibodies. But, non-HLA antibodies was reported in recipients from identical siblings.
* Non-HLA antibodies are classified into two main categories:
1.Alloantibodies: directed against
polymorphic antigens.
2.Autoantibodies that recognize self-
antigenss.
* Non-HLA include anti endothelial cell antibodies ( AECA) which were reported by Brasile et al., these antibodies are enriched for noncomplement- fixing subclasses IgG2 and IgG4.
■Examples of Non HLA antibodies:
1- Angiotensin type I receptor ( AT1R):
Is a G- protein coupled receptor that is expressed at the endothelial cell surface, binds to angiotensin II, and regulates the water-salt balance and BP.
In renal transplantation, elevated level were reported in patients with severe steroid resistance vascular rejection, and malignant hypertension in the absence of HLA-DSA. The main stay of treatment for these patients is by a combination of plasmapheresis, IVIG and losartan.
– AT1R autoantibodies might
impact long-term graft survival because they are associated with a higher risk of
acute rejection within the first 4 months after transplantation and a 2.6-fold higher risk of graft failure beyond 3 years post-transplantation,
Patients who were positive for both AT1R
antibody and HLA-DSA had lower graft survival than those with HLA-DSA alone.
– Recurrence of focal segmental glomerulosclerosis (FSGS) after kidney transplantation causes accelerated allograft loss in approximately 30% of recipients.
Causes of FSGS and studies in an experimental rat model suggest a role
for AT1R in FSGS
– Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement. Treatment of these pts depends on Depletion of AT1R antibodies by plasma
exchange + losartan.
▪︎Mechanisms of injury:
– AT1R antibodies of IgG1 and IgG3 isotypes were identified in patients with transplant rejection. But, C4d deposition was only detected in a subset of
patients, suggesting the involvement of complement-independent pathogenesis of these antibodies.
-Renal biopsy specimens from transplant recipients with AT1R-mediated rejection
had increased tissue factor expression and thrombotic occlusions.
– Additional co-factors or environmental conditions might be needed to promote rejection by AT1R antibodies. For example, Ischemia.
2- Perlecan:
– Is a major component of the vessel wall composed of a large heparan sulfate
proteoglycan . It’s C-terminal domain
(endorepellin) has anti-angiogenic properties.
– Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain
from the C-terminal fragment of perlecan. – – Studies have shown increased serum LG3 levels in renal transplant recipients with immune-mediated vascular injury and renal
dysfunction.
– Vascular rejection and elevated LG3 levels were associated with heightened neointima formation.
– LG3 behaves as a neoantigen capable of
driving the production of LG3 antibodies that can enhance the process of chronic rejection.
– Higher pretransplant levels of LG3 antibodies predicted recipients at risk of
vascular rejection.
– Patients with pretransplant DSA and strong post-transplant LG3 antibodies had significantly reduced 1-year graft survival
– HLA-DSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
▪︎Mechanisms of injury:
– The bioactive forms of perlecan cause vascular injury and neointimal formation directly by promoting migration of
donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
3- Collagen:
– Autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy. These patients
displayed increased collagen IV-specific and fibronectin-specific CD4+ T cells implicating collagen IV in the pathogenesis of chronic rejection
■Autoantibody production in transplantation:
– Graft damage mediated through Ischemic reperfusion injury, alloimmunity and chronic inflammation can cause intracellular
proteins to be expressed on the surface of apoptotic cells, raising the possibility that these cells act as a autoantigen which can be subsequently presented to
autoreactive T cells and B cells either by recipient or donor antigen presenting cells (APCs).
▪︎Ischaemia reperfusion injury:
– An innate inflammatory responses with generation of alloimmune and autoimmune responses to the graft can be elicited in organ transplantation due to surgical trauma, tissue damage and IRI.
– Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs) including self-nucleic acids, histones, and high mobility group protein B1.
– Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
– IRI can damage the vascular endothelium
leading to release of autoantigens from necrotic and apoptotic cells.
– Autoantigens such as vimentin, perlecan, and collagen V released from the injured allograft are processed and presented to autoreactive T cells by APC recruited during IRI.
– Circulating B cells bind these autoantigens and become activated by autoreactive T cells, resulting in the secretion of autoantibodies. In addition, complement activation can potentiate autoantibody
production in the transplant setting.
Thanks
This article highlights the importance of Non HLA antibodies which are involved in antibody mediated rejection ultimately leading to decreased graft survival . There a quite a few Non HLA antbodies and typical features include positive FCXM in the absence of donor specific antibodies on Luminex SAB..Mainly classified as allo and auto antibodies
These include:
1- AT1R- Angiotensin Type 1 Receptor
Present on endothelial cell surface and antibodies to AT1R are usually IgG1 and 3. and are risk factor for graft rejection and malignant hypertension
2-Preclan
Present on blood vessel wall with antiangiogenic properties. Lamilin like globulin LG3 is highly antigenic and associated with direct vascular insult
3- Collagen
Mainly important in Lung transplant
Mechanism of Non HLA Antibodies production.
Ischemic Reperfusion injuries
Alloimmunity
Chronic inflammation
In conclusion the Non HLA antibody production is multifactorial and leads to AMR. Mutiple strategies can be adopted to treat AMR.these include IVIG , antibody and B cell depletion and protease inhibitors. More efforts are required to understand more the pathogenis to as to imrove long term graft survival
Thanks
Please summarise this article.
1- Angiotensin type 1 receptor : expressed in vascular endothelial cells and reported in some patients with severe steroid resistant AMR.
2- Perlecan : amajor component of blood vessel walls.
3- Collagen type IV and Fibronectin
1- ischemia-reperfusion injury.
2- surgical trauma.
3- allo-immune reaction.
4- the role of Th17 cells. they are essential in auto-antibody production by B-cells within ectopic tertiary lymphoid tissues.
5- auto-antibody graft damage-induced alloimmunity and development of DSA of HLA types.
Thanks
non HLA antibodies were observed to play a role in ABMR,this was aboserved to some extent in kidney transplanted patient from HLA Identical twin.
non HLA antibodies are classifed into main categories ,
1-ALLOANTIBODIES
which is dirceted aganist polymorphic antigens that is different between recipent and donor .
2-AUTOANIBODIES
which is recognized as self antigens.
WHAT IS (AECA)?
WHAT IS ANGIOTENSINOGEN TYPE 1 RECEPTOR(AT1R)ANTIBODIES?
WHAT IS PERLECAN?
WHAT IS ANTI COLLAGEN ANTIBODIES?
CAUSES OF AUTANTIBODIES PRODUCTION
surgical trauma and tissue dadmge during transplant procees induces innate immunity .
studies had showen that (IRI) is ssufecient to induce an autoimmune responce in absence of alloimmunity.
threee basic mechanisms of alloimmune responses e.g direct, indirect, and semi-direct.
cell to cell commuication through extracellular vesicles can elicit autoimmune and allloimmiune respons.
Thanks
Introduction ;
Angiotensin type1 receptor(AT1R) ;
Perlecan ; A very big heparin sulfate and the main component of the vessel wall. The C-terminal is made up of 3 laminin-like globular domains( LG3) which is highly anti-antiogenic 68.
Collagen ;
Auto-antibodies ; Factors involved are ;
This leads to expression of proteins on the surface of the apoptotic cells= auto-antigens 86. This is then presented to auto-reaction T and B cells by recipient or donor APC in the setting of extracellular vesicles or in tertiary lymphoid tissue.
Tissue damage by IRI can lead to AKI, DGF which has impact on graft survival 88. Apoptosis & necrosis induced by IRI leads to release of DAMP e.g self-nucleic acids, histones, and high mobility group protein B1. DMAPs reacts with pattern recognition receptors e.g TLR2 & TLR4 express on myeloid cells,dendritic cells, vascular endothelial cells, and tubular epithelial cells 88-92. Ligation of TLRs leads to recuritment of MYD88 and the production of NF-kB. This results in productions of pro-infammatory cytokines IL-1B,IL-6 and TNF which prime adaptive immnue responses and causes allograft damages and exposure to auto-antigens.
Exosomes are weaker than APC in activating T cells but it has great efficiency to active T cells if they interact with dendritic cells 117-120
TH17 secrets IL-17 which plays role in autoimmune diseases 124-125.
TH17 activated by TGF-B & IL-6 leads to protective response against foreign antigens
TH17 activated by IL-23 leads chronic tissue inflammation & autoimmunity specially in lung allograft rejection 76-77-78-81-112
TLT represent ectopic aggregates of lymphoid tissue which is identical to that of a germinal center present in the secondary lypmoid organ. It is develop in situations of chronic inflammation by the process of lymphoid neo-genesis. Studies reported TLT in Chronic allograft rejection of the kidney 128-131 and lung 132.
Conclusion & future perspectives ;
Thanks
Ben
Reference should be between brackets
Thnxs, prof, will do that
ABMR has 2 forms: acute and chronic form, both forms affect the long-term outcome of the graft. The principal target of the immune system is the HLA antigens, but reports of ABMR in HLA-identical siblings highlight the presence and the importance of Non-HLA antibodies.
In general, Non-HLA antibodies are classified into:
Below are some types of Non-HLA antibodies:
Angiotensin type I receptor ( AT1R):
Mechanism of injury:
The 2 implicated isotypes are: IgG1 & IgG3, C4d deposition is noted in some subsets, so it is a complement independent process. There will be a process that is similar to the act of angiotensin II, so phosphorylation of ERK Kinase and activation of the transcription factors AP-1 & NF-kB in the endothelial and smooth muscle cells. clinical data are consistent with the hypothesis that binding of autoantibodies to AT1R contributes to rejection. So it is not only the AT1R that causes the rejection but a co-factor is needed which may be an autoantibody or environmental factor.
Perlecan:
Mechanism of injury:
Two interdependent mechanisms are implicated as the bioactive form of perlecan cause vascular injury and neointimal formation by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury.
Collagen:
Autoantibody production in transplantation:
Many events that happened during the process of transplantation such as ischemia-reperfusion, surgical trauma, and alloimmunity lead to the formation of autoantibodies in the form of soluble antigens, extracellular vesicles, or apoptotic bodies. these are presented to the APC and induce an immune response.
Th17 cells are essential for autoantibody production by supporting the proliferation and maturation of autoreactive B cells within the tertiary lymphoid tissues.
Thanks
Allograft antigens have been classically studied as the target of antibodies in the course of antibody mediated and acute cellular rejection. Classically antibodies against HLA classes I and II expressed on the allograft have been the target of immunosuppression. Also pretransplant screening tests aim to identify the presence of anti-HLA antibodies.
However a lot of reports demonstrated the development of hyperacute and acute antibody mediated rejection in matched receipient/donor with negative cross match and negative DSA.
Studies showed that antibodies directed against non-HLA antigens are implicated in the process of AMR.Non-HLA antibodies are classified into two main categories: alloantibodies directed against polymorphic antigens that differ between the recipient and donor, and antibodies that recognize self-antigens — autoantibodies.
Several studies reported non-HLA antibodies to mediate renal rejection by attacking self antigens expressed by endothelial cells.
Anti-endothelial cells antibodies have been reported to be higher in recipients with failed transplants than in those with functioning grafts at 1 year posttransplant.
AECA were also found at a significantly higher frequency in pretransplant sera from HLA-sensitized renal transplant candidates than in non-sensitized candidates and have been reported to correlate with AMR in heart transplantation.
The expression of antigens on the endothelium depends widely upon the type of injury, anatomical location, vessel type and inflammatory milieu.
Angiotensin type 1 receptor (AT1R) is another target of autoantibodies. Angiotensin type 1 receptor is expressed at the endothelial cell surface, binds to angiotensin II and regulates water–salt balance and blood pressure. Hyperactivity of AT1R causes hypertension, vasoconstriction and vascular smooth muscle migration and proliferation.
Elevated levels of AT1R antibodies were first reported in recipients with severe vascular rejection and malignant hypertension in the absence of HLA-DSA.
The IgG subtypes of AT1R antibodies involved in acute allograft rejection were IgG1 and IgG3, and graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition, although IgG1 and IgG 3 are complement fixing.
In patients with elevated AT1R 1 antibodies and biopsy proven antibody mediated rejection, treatment with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan significantly improved allograft survival. Subsequent studies confirmed that AT1R antibody correlated with an increased incidence of AMR and inferior graft survival.
AT1R antibodies have shown to be also implicated in the recurrence of focal segmental glomerulosclerosis after kidney transplantation. Studies in an experimental rat model suggest a role for AT1R in FSGS.Treatment aiming to deplete AT1R antibodies by plasma exchange combined with losartan therapy ameliorated AMR and reduced podocyte injury in this patient.
High levels of AT1R antibodies in the pretransplant period are associated with increased risk of heart transplant ACR and AMR as well as early onset of microvasculopathy. Elevated AT1R antibody levels were also reported in patients with a left ventricular assist device as a bridge to transplantation.
Another type of antibidides that have been evaluated , is Perlecan which is a major component of the vessel wall. The C-terminal domain of perlecan, endorepellin, is best known for its anti-angiogenic properties and contains three laminin-like globular (LG). High levels of serum LG3 levels were detected in recipients diagnosed with Banff grade II or III acute vascular rejection. High pretransplant levels of LG3 antibodies predict high risk of vascular rejection.
Collagen was evaluated for immunogenicity in patients with lung transplantation.. Collagen V is present on airway epithelial cells and its expression increases following immune-mediated injury and/or IR. Post-transplant development of collagen V antibody is associated with the development of bronchiolitis obliterans syndrom in lung transplant recipients
Autoantibody production in transplantation
Organ transplantation involves varying levels of surgical trauma, tissue hypoxia ,ischemia, damage and IRI, all of which can initiate and potentiate the inflammatory responses resulting in the generation of alloimmune and autoimmune responses to the graft.
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment. The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival. Several studies have demonstrated that IRI is sufficient to induce an autoimmune response in the absence of alloimmunity.
Thanks
Non-HLA antibodies are either alloantibodies directed against polymorphic antigens, and antibodies that recognize autoantibodies.
Brasile et al. notice pretransplant antiendothelial cell antibodies (AECA) that lead to hyperacute rejection of a maternal renal allograft.
Multiple studies demonstrated multiple successive hyperacute renal rejections and/or accelerated AMR due to pretransplant AECA meanwhile those recipients had negative lymphocyte crossmatches and tested negative for donor specific HLA antibodies (DSAs).
AECA were detected in failed renal transplants and in highly sensitised candidates, it was suggested that organs from deceased donors might exhibit higher levels of non-HLA antibody ligands than those from living donors.
Antiendothelial-cell-reactive antibodies are enriched for noncomplement-fixing subclasses IgG2 and IgG4.
Concerning AT1R ,it’s hyperactivity causes hypertension, vasoconstriction and vascular smooth muscle migration .
AT1R antibodies were detected in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA.
AT1R antibody correlated with an increased incidence of AMR and inferior graft survival
AT1R autoantibody positivity was accompanied with a higher risk of acute rejection within the first 4 months after transplantation and higher risk of graft failure 3 years post-transplantation.
overexpression of human AT1R in rat podocytes was consistent with a FSGS phenotype.
In heart transplantation the Increased pretransplant levels of AT1R antibodies are associated with heart transplant AMR specialy if associated with HLA DSA
Development of AT1R antibodies post LVAD did not impact incidence of rejection or transplant survival.
Mechanism of injury through binding of autoantibody to AT1R contributes to rejection by mimicking the action of angiotensin II.
additional co-factors or environmental conditions to AT1R antibody might be needed to promote rejection.
Perclean
is a major component of the vessel wall ,known for its anti-angiogenic properties and contains three laminin-like globular (LG) domains.
LG3 regulates vascular remodelling.
Mechanism of injury ,the current paradigm of perlecan-mediated graft injury considers two interdependent mechanisms as follows the perlecan cause vascular injury and neointimal formation directly by promoting migration of donor vascular smooth muscle and/or recipient-derived mesenchymal cells, and/or elicit humoral immune responses that accelerate immune-mediated vascular injury and remodelling.
Collagen V is present on airway epithelial cells and it increases following immune-mediated injury and/or IRI7
Mechanism of injury ; in renal transplant recipients diagnosed with transplant glomerulopathy autoantibodies to collagen IV and fibronectin has been detected
In lung transplantation Strong collagen V responses reflects severity of Bronchiolitis obliterans syndrome.
17 T helper (TH17)-mediated immunity to collagen V can induce transplant vasculopathy in the absence of alloimmunity
Autoantibody production in transplantation depends on multiple factors. Graft damage mediated through IRI, alloimmunity and chronic inflammation can cause intracellular proteins to be expressed on the surface of apoptotic cells, acting as as a autoantigen reservoirs
Interplay between alloimmunity and autoimmunity Alloimmune responses to the transplanted organ occur by direct, indirect and semi-direct allorecognition pathways
-Cell-to-cell communication through extracellular vesicles is increasingly recognized as a mechanism that elicits autoimmune and alloimmune responses.
-TH17 cells are the major producers of IL-17 involved in many autoimmune diseases.
Thanks
Non-HLA antigens are antigens expressed on the surface of graft tissue and sometimes on circulating lymphocytes, those which are expressed on the surface of lymphocytes can cause unexplained positive cross match
Several non-HLA antibodies were discovered , the most reported are Angiotensin II Type 1 Receptor (AT1R-Ab), anti endothelial cell antibodies (AECA), Anti-Perlecan (LG3) Abs and anti-collagen
Non HLA antibodies are either autoantibodies directed to self-antigens or alloantibodies directed to donor non HLA polymorphic antigens.
Risk factors for development of pathogenic non-HLA antibodies includes
Evidence of the significance of non-HLA Abs
Antiendothelial cell antibodies ( AECA)
Anti-Angiotensin II Type 1 Receptor (AT1R) Abs
Anti-Perlecan (LG3) Abs
Anti-Collagen Abs
Thank you All
I’m still waiting for all colleagues to complete their logging
The importance of non-HLA antibodies in transplantation
Non-HLA antibodies are classified into two main categories:
alloantibodies directed against polymorphic antigens that differ between the recipient and donor
antibodies that recognize self-antigens — autoantibodies
many of the renal rejections that were reported to be associated with AECA were negative for the complement degradation product C4d.
Angiotensin type 1 receptor (AT1R)
In renal transplantation, elevated levels of AT1R antibodies were first reported in recipients with severe steroid-refractory vascular rejection and malignant hypertension in the absence of HLA-DSA .
AT1R antibodies were IgG1 and IgG3,graft biopsy samples from anti-AT1R positive patients with vascular rejection did not show evidence of complement deposition.
Treatment of AT1R antibody positive patients with a combination of plasmapheresis, intravenous immunoglobulin (IVIG), and losartan resulted in significantly improved allograft survival.
Autoantibodies to AT1R were reported in a transplant recipient diagnosed with AMR and FSGS with severe podocyte effacement.
Mechanisms of injury
action of angiotensin II and triggered phosphorylation of ERK kinase and activation of the transcription factors AP-1 and NF-κB in endothelial and smooth muscle cells-increased tissue factor expression and thrombotic occlusions.
Perlecan
a large heparan sulfate proteoglycan — is a major component of the vessel wall.
Apoptotic endothelial cells liberate cathepsin-L, which cleaves the LG3 domain from the C-terminal fragment of perlecan.
increased serum LG3 levels are seen in renal transplant recipients with immune-mediated vascular injury and renal dysfunction.
similar to AT1R antibodies, HLA- DSA and LG3 autoantibodies can synergize to elicit endothelial cell and graft damage.
Mechanisms of injury
significantly increased infiltration of T cells and natural killer cells, C4d
deposition and obliterative vascular remodelling.
significantly increased neointima formation.
Collagen
Development of autoantibodies to collagen IV and fibronectin has been reported in renal transplant recipients diagnosed with transplant glomerulopathy.
Autoantibody production in transplantation
Ischaemia reperfusion injury
IRI is a complex pathophysiological process that involves the generation of reactive oxygen species, complement activation, coagulation, endothelial activation and leukocyte recruitment . The tissue damage caused by IRI can lead to acute kidney injury and delayed graft function, which can impair graft survival.
Apoptosis and necrosis caused by IRI results in the release of damage associated molecular patterns (DAMPs)- interact with pattern recognition receptors including Toll-like receptor (TLR) 2 and TLR4 expressed on myeloid cells,dendritic cells, vascular endothelial cells, and tubular epithelial cells- downstream production of proinflammatory cytokines, including IL-1β, IL-6, and TNF- promote the activation of adaptive immune responses that can exacerbate allograft damage and exposure to autoantigens.
Interplay between alloimmunity and autoimmunity
tissue damage caused by the alloresponse to donor HLA antigens can cause the release of sequestered autoantigens resulting in the presentation of cryptic self-determinants and thereby triggering an autoimmune process at the site of the graft.
Extracellular vesicles
High concentrations of exosomes can directly activate T cells, the activatory effect of this type of antigen presentation is much weaker than that of antigen presentation by professional APCs owing to the lack of co-stimulatory molecules . Exosomes efficiently activate T cells when they interact with dendritic cell.
TH17 cells and tertiary lymphoid tissue
TH17 cells activated by TGF-β and IL-6 are potent inducers of leukocyte recruitment and mediate protective responses to foreign pathogens, whereas Th17 cells activated by IL-23 promote chronic tissue inflammation and autoimmunity.