Pathogenesis Of Chronic Rejection Research Articles

Tackling Chronic Kidney Transplant Rejection: Challenges and Promises.

Despite advances in post-transplant management, the long-term survival rate of kidney grafts and patients has not improved as approximately forty percent of transplants fails within ten years after transplantation. Both immunologic and non-immunologic factors contribute to late allograft loss. Chronic kidney transplant rejection (CKTR) is often clinically silent yet progressive allogeneic immune process that leads to cumulative graft injury, deterioration of graft function. Chronic active T cell mediated rejection (TCMR) and chronic active antibody-mediated rejection (ABMR) are classified as two principal subtypes of CKTR. While significant improvements have been made towards a better understanding of cellular and molecular mechanisms and diagnostic classifications of CKTR, lack of early detection, differential diagnosis and effective therapies continue to pose major challenges for long-term management. Recent development of high throughput cellular and molecular biotechnologies has allowed rapid development of new biomarkers associated with chronic renal injury, which not only provide insight into pathogenesis of chronic rejection but also allow for early detection. In parallel, several novel therapeutic strategies have emerged which may hold great promise for improvement of long-term graft and patient survival. With a brief overview of current understanding of pathogenesis, standard diagnosis and challenges in the context of CKTR, this mini-review aims to provide updates and insights into the latest development of promising novel biomarkers for diagnosis and novel therapeutic interventions to prevent and treat CKTR.

Role for Circulating Exosomes with Cardiac Self-Antigens (Myosin and Vimentin) in the Pathogenesis of Chronic Rejection in a Murine Heterotopic Model of Cardiac Transplantation

The aim of the study is to determine the of kinetics of circulating exosomes induced with cardiac self-antigens (SAgs) (Myosin, Vimentin) and their role in de novo development of antibodies (Abs) to SAgs leading to chronic rejection following heterotopic cardiac transplantation (HTx). Allogenic (BALB/c to C57BL/6) HTx was performed heterotopically in the abdominal cavity. Costimulatory blockade consisting of MR1 (250 μg i.p.) and CTLA4-Ig (200 μg i.p.) treatment (days 0 and 2, respectively) resulted in prolongation of HTx for 45-60 days. However, histopathological analysis demonstrated chronic rejection as evidenced by myocyte damage, cellular infiltration with mononuclear cells and fibrosis. Sera were collected on days 7, 15, 30, and 45 for kinetic analysis of exosome induction, Ab development, and characterization of exosomes for cardiac SAgs, transcription factors, class II MHC trans-activator (CIITA), nuclear factor κB (NF-κB) and 20S proteasome by western blot using specific Abs. BALB/c to C57BL/6 HTx rejected heart on day 7 to 8. Sera, at the time of rejection, demonstrated exosomes with SAgs, CIITA, NF-κB and 20S proteasome. HTx done following costimulatory blockade developed chronic rejection between 45 to 60 days. Kinetic studies demonstrated induction of circulating exosomes containing SAgs; Myosin (3.3 vs 1.09; p<0.05) and Vimentin (4 vs 1.35; p<0.01), CIITA (29.4 vs 1.55; p<0.01), NF-κB (2.3 vs 1.2; p<0.05) respectively on day 15 following transplantation. 20S proteasome levels were elevated on day 30 and 45 (5.4 & 9.0 vs 1.49; p<0.01). Development of Abs to Myosin also occurred on day 15 (772±557 vs 187±50; p<0.01) and persisted till day 45 (1289±409 vs 187±50) when chronic rejection of HTx noticed. Circulating exosomes containing SAgs, transcription factors, and development of Abs to SAgs preceded development of chronic rejection in a murine model of chronic rejection occurring after co-stimulation blockade in allogenic HTx, thus, supporting an important role for circulating exosomes induced following HTx in breaking the tolerance induced by co-stimulation blockade resulting in immune responses leading to chronic rejection.

Circulating Exosomes with Lung Self-Antigens, Kα1Tubulin and Collagen V, and Immune Responses to Lung Self-Antigens Precedes Histological Evidence of Chronic Rejection Following Orthotopic Murine Lung Transplantation

Purpose Lung transplantation (LTx) is a treatment option for end-stage pulmonary diseases. Despite improvements in surgical techniques and post-transplant (Tx) immunosuppression, LTx continues to have one of the poorest long-term outcomes compared to other solid organ Tx, with five year survival of about 50%. Methods Using an orthotopic single LTx model of B6D2F1/J to DBA/2J strain combination, we demonstrate that >80% of transplanted animals developed histological signs of chronic rejection by day 30 of the transplanted lung but not native. We collected blood at days 7, 14, 28, and 30 and serum was tested by ELISA for development of antibodies to lung self-antigens (SAgs), Collagen V (Col-V) and K-alpha 1 Tubulin (Kα1T). Results Significantly elevated levels of antibodies to Col-V and Kα1T were demonstrable on day 14 when there was no histological evidence for chronic rejection of the transplanted lungs. Circulating exosomes were isolated from sera collected on days 7 and 14 which demonstrated increased levels of lung SAgs by western blots in the exosomes isolated from day 14 sera. These results clearly demonstrate that not only antibodies to lung SAgs are present in sera from day 14, but also circulating exosomes with Col-V and Ka1T are easily demonstrable in sera collected on day-14. Semi-quantitation of western blot by densitometry further demonstrated significantly increased levels of exosomes with lung SAgs starting from day 14 until sacrifice on day 30. Splenocytes isolated following sacrifice demonstrated specific reactivity to lung SAgs with significantly high frequency of IFN-γ (Col-V 109±2.5, Kα1T 101±5.5) and TNF-α (Col-V 39±1.5, Kα1T 53±5.5) secreting cells by ELISPOT. Conclusion Taken together our results demonstrate that circulating exosomes with lung SAgs and de novo development of antibodies to lung SAgs occurs prior to histological evidence of chronic rejection in this murine model of chronic rejection following orthotopic single LTx suggesting that circulating exosomes with lung SAgs can contribute in the pathogenesis of chronic rejection following LTx. Further, our data suggests that circulating exosomes with lung SAgs could be a potential biomarker for patients at risk for developing chronic rejection following human LTx.

Circulating Exosomes from Lung Transplant Recipients Diagnosed with Bronchiolitis Obliterans Syndrome Induces Immune Responses in C57BL/6 Mice Leading to Obliterative Airway Disease and miRNA 155 Plays an Essential Role in Immune Activation

Purpose MicroRNAs (miRNAs) are single-strand RNAs that are 18-25 nucleotides in length. Genes of miRNAs suppress newly synthesized proteins by causing miRNA degradation or inhibiting miRNA translation into proteins. MicroRNA-155 (miR155) has also been implicated as a positive regulator of inflammatory cytokine production especially IL17. miR155 is a pivotal regulator of the immune system and we determined the role of miR155 in immune activation of C57BL/6 and miR155 knock out (KO) mice leading to development of Abs and induction of exosomes with lung self-antigens (SAgs) following immunization with circulating exosomes isolated from human lung transplant recipients (LTxRs). Methods C57BL/6 and miR155 KO mice were immunized with exosomes isolated from stable and bronchiolitis obliterans syndrome (BOS) without Freund's adjuvant (20ug/injection, at 1,6,15 and 21 days). After last injection, mice were sacrificed, lungs were analyzed by H&E and trichrome staining. Blood samples collected at days 2,7,16 and 26, were analyzed for the development of Abs to K-alpha 1 Tubulin (KA1T), Collagen V (Col-V) and Col-I (control) by ELISA. Results Cellular immune responses to KA1T, Col-V, and Col-I were enumerated using ELISPOT. Circulating exosomes were isolated and analyzed for lung SAgs by western blot. Our results demonstrate development of Abs to lung SAgs with increased frequencies of IFN-γ and IL-17-producing cells with reduction of IL-10 producing cells (stable vs BOS) against lung-SAgs-following immunization of wild type C57BL/6 animals with BOS exosomes but not exosomes from stable LTxRs. Histological analysis of lungs demonstrated obliterative airway disease (OAD) following immunization with exosomes isolated from BOS but not stable. In contrast, immunization of miR155 KO mice did not result in Abs to lung SAgs, cellular immune response to lung SAgs, nor induction of circulating exosomes with lung SAgs (control vs stable and BOS). These animals also did not develop OAD lesions in the lungs. Conclusion We conclude that circulating exosomes plays a pivotal role in immune activation leading to chronic rejection and miR155 exerts an obligatory role in the pathogenesis of chronic rejection following human lung transplantation.

What's Hot, What's New From the 2016 American Transplant Congress.

From June 11-15, 2016 the American Transplant Congress, the joint meeting of the American Society of Transplantation and the American Society of Transplant Surgeons, held its annual meeting in Boston, MA. The meeting, attended by 5200 registrants, included pre-meeting conferences, focused topic sessions, and hundreds of high-quality presentations from the transplant field. This meeting report highlights key findings from specific basic science, translational, and clinical research presentations deemed to have notable impact in thematic areas. In particular, there were a number of transformative studies indicating important advances in the understanding of alloimmunity, chronic rejection, tolerance, and organ-specific outcomes. Many of these results are discussed in the context of the published literature to showcase rapid advances in the transplant field.

Dysregulated MicroRNA Expression and Chronic Lung Allograft Rejection in Recipients With Antibodies to Donor HLA

The pathogenesis of chronic rejection, Bronchiolitis Obliterans Syndrome (BOS) following lung transplantation (LT) is poorly understood. We hypothesized that development of antibodies to HLA (DSA) is associated with dysregulation of microRNA (miRNA) that predisposes BOS. Towards this, miRNA profiling of mononuclear cells from 10 stable LT (DSA(-) BOS(-) ), 10 LT with DSA(+) BOS(-) (DSA group) and 10 LT with DSA(+) BOS(+) (BOS group) were performed. Prediction by mirPath indicated that differential miRNAs in DSA(+) BOS(-) compared to stable are significantly up-regulated (relative fold >2, p < 0.05) for TGF-β and B cell receptor signal pathways. A total of seventy-four miRNAs were up-regulated and six miRNAs were down regulated in LT with DSA(+) BOS(+) when compared to stable (relative fold >2, p < 0.05). There was also significant enrichment of cell cycle and gap junction pathways. An inverse correlation between expression of two key miRNAs and their target genes were observed: miR-369-5p and miR-548d were down regulated in DSA(+) LT while their gene targets in TGF-β signal pathways were up-regulated. In addition, miR-628-5p and miR-134 were down regulated and their target genes (B cell development) were up-regulated. Therefore, we conclude that alloimmunity induced changes in miRNAs affecting the TGF-β and B cell receptor signal pathways play important roles in BOS development.

Antibodies to Lung Self-Antigens (Ka1 Tubulin or Collagen V) Lead to Epitope Spreading, Loss of Tolerance and Rejection of CTLA4/MR1 Induced Tolerant Murine Lung Allograft

Purpose Immune responses against lung self-antigens (SAg) [Kα1tubulin (Kα1T) and Collagen V (ColV)] are critical in the pathogenesis of chronic rejection in human lung transplantation (LT). Our goal was to determine the mechanisms by which antibodies (Abs) to SAgs lead to rejection in co-stimulatory blockade induced tolerant murine LT. Methods and Materials LT was done from Balb/c to Bl/6 and tolerance was induced with MR1 (250μg) and CTLA4-Ig (200μg) on post-LT days 1 and 2. Abs to Kα1T or ColV or both (200μg/dose, i/p) or isotype control were given on days -10, -2, 0 & weekly following LT. Lungs were analyzed by H&E, trichrome and immunostains. Kα1T and ColV specific IFN-γ, IL-10, IL-4 and IL-17 cells were enumerated by ELISpot. Abs to allo-MHC was determined by FACS. Cytokine and growth factors in lung were done by RTPCR. Results Allo-LT with co-stimulatory blockade did not show evidence of rejection for >100 days. However, administration of Abs to Kα1T or ColV or both resulted in loss of tolerance and rejection (cellular infiltration, airway remodeling) by day 45-60. Isotype controls did not demonstrate rejection pathology. Abs to SAgs in tolerant mice led to Infiltration of CD4 and CD8 T cells, B-cells and neutrophils, increase in SAg specific T-cells secreting IFNγ (p=0.002), IL-4 (p=0.047) and IL-17 (p=0.001) and decrease in IL-10 (p=0.03). Abs to either SAgs resulted in immune responses to both the SAgs and donor specific Abs to allo-MHC (MFI>2000 against Balb/c - H2kd), demonstrating epitope spreading to other SAgs and linked allo-MHC. Upregulation of IL-6 (7.1 fold), IL-1β (17 fold), IFN-γ(4.8 fold), IL-17 (10.1 fold), VEGF (2.9 fold), TGF-β (3.8 fold) was also noted in the lung tissue. Conclusions Administration of Abs to lung Sags resulted in epitope spreading of immune responses not only to Sags but also to the linked allo-MHC leading to loss of tolerance induced by co-stimulatory blockade.

Critical Role for IL-17A/F in the Immunopathogenesis of Obliterative Airway Disease Induced by Anti-MHC I Antibodies

The IL-17 axis is implicated in pathogenesis of chronic rejection after human lung transplantation. Using a murine model of obliterative airway disease (OAD), we recently demonstrated that Abs to MHC class I antigens can induce immune responses to self-antigens that contributes to immunopathogenesis of chronic rejection. Using a murine model of OAD, we determined the role of IL-17 family members in induction of autoimmunity leading to OAD after ligation of MHC class I. Anti-MHC class I or control antibodies (Abs) were administered intrabronchially to wild-type (WT) and IL-17a knock out (IL-17A-/-) C57BL/6. By day 30, anti-MHC I administered endobronchially in IL-17A-/- mice demonstrated significant reduction in cellular infiltration, a 36.8% reduction in CD4 T cells, 62.7% in CD11b macrophages, 37.5% in degree of fibrosis, 1.94 fold and 2.17 fold decrease in anti-KAT and anti-Col-V, respectively, when compared with wild-type mice. Analysis of lung infiltrating cells in anti-MHC I WT revealed increase in IL-17A (KAT:92+21,Col-V:103+19spm) and IL-17F (KAT:5.03%,Col-V:2.75%) secreting CD4+ T cells. However, administration of anti-MHC I in IL-17A-/- demonstrated increase only in IL-17F for KAT (13.70%) and Col-V (7.08%). Anti-IL-17(A-F) mAb administration after anti-MHC I abrogated OAD in both WT and IL-17A-/-. Our findings indicate that 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 OAD.

Longitudinal analysis of the lung microbiome in lung transplantation.

Lung transplant recipients experience poor long-term survival, largely due to chronic rejection. The pathogenesis of chronic rejection is incompletely understood, but bacterial colonization of the lung is associated with chronic rejection, while antibiotic use slows its progression. The lung harbors a bacterial community, termed the microbiome, which is present both in health and disease. We hypothesize that the lung microbiome will change following transplantation, and these changes may correspond to the development of rejection. Twelve bronchoalveolar lavage fluid (BALF) samples were obtained from four patients at three time points after transplantation, and two BALF samples were obtained from healthy, nontransplant controls. The microbiome of each sample was determined by pyrosequencing the 16S rRNA gene hypervariable 3 region. The data were analyzed using mothur, Ribosomal Database Project Classifier, Fast UniFrac, and Metastats. Transplanted lungs contained more bacterial sequences and demonstrated more microbial diversity than did control lungs. Bacteria in the phyla Proteobacteria (class Betaproteobacteria) predominated in the transplant samples. In contrast, the microbiome of the healthy lung consisted of the phyla Proteobacteria (class Gammaproteobacteria) and Firmicutes. The microbiome of the transplanted lung is vastly different from that of healthy lungs, mainly due to the presence of the family Burkholderiaceae in transplant samples.

Chronic rejection: a significant role for Th17-mediated autoimmune responses to self-antigens

Despite progress in the field of organ transplantation for improvement in graft survival and function, long-term graft function is still limited by the development of chronic allograft rejection. Various immune-mediated and nonimmune-mediated processes have been postulated in the pathogenesis of chronic rejection. In this review, the authors discuss the important role of alloimmune responses to donor-specific antigens and autoimmune responses to tissue restricted self-antigens in the immunopathogenesis of chronic rejection following solid organ transplantation. In particular, the authors discuss the role of induction of Th17-type autoimmune responses and the crosstalk between autoimmune and alloimmune responses. These self-perpetuate each other leading to activation of profibrotic and proinflammatory cascades that ultimately result in the development of chronic rejection.

Reviews on mysterious vascular endothelial cells in renal allografts

Endothelial cells (ECs) are involved in allograft rejection and are prime targets, but also key players. HLA antigens are the most prominent targets of alloantibodies in transplantation. Alloantibodies against other antigens such as ABO blood group antigens and non-HLA antigens could also be demonstrated. Alloantibodies undoubtedly cause allograft rejection. Activation of ECs by anti-EC antibodies and direct antibody- or complement mediated EC damage may be suggested. However, the mechanisms underlying acute antibody-mediated rejection (AAMR) and chronic rejection (CR) remain unclear. In this review, the relationship between vascular endothelium and rejection is discussed mainly from our reports, and the mechanism and pathogenesis of CR are discussed.

A shift in the collagen V antigenic epitope leads to T helper phenotype switch and immune response to self-antigen leading to chronic lung allograft rejection

Immune responses to human leucocyte antigen (HLA) and self-antigen collagen V (Col-V) have been proposed in the pathogenesis of chronic rejection (bronchiolitis obliterans syndrome, BOS) following human lung transplantation (LTx). In this study, we defined the role for the shift in immunodominant epitopes of Col-V in inducing T helper phenotype switch leading to immunity to Col-V and BOS. Sera and lavage from BOS(+) LTx recipients with antibodies to Col-V were analysed. Two years prior to BOS, patients developed antibodies to both Col-V,α1(V) and α2(V) chains. However, at clinical diagnosis of BOS, antibodies became restricted to α1(V). Further, lung biopsy from BOS(+) patients bound to antibodies to α1(V), indicating that these epitopes are exposed. Fourteen Col-V peptides [pep1-14, pep1-4 specific to α1(V), pep5-8 to α1,2(V) and pep9-14 to α2(V)] which bind to HLA-DR4 and -DR7, demonstrated that prior to BOS, pep 6, 7, 9, 11 and 14 were immunodominant and induced interleukin (IL)-10. However, at BOS, the response switched to pep1, 4 and 5 and induced interferon (IFN)-γ and IL-17 responses, but not IL-10. The T helper (Th) phenotype switch is accompanied by decreased frequency of regulatory T cells (T(regs) ) in the lavage. LTx recipients with antibodies to α1(V) also demonstrated increased matrix metalloproteinase (MMP) activation with decreased MMP inhibitor, tissue inhibitor of metalloproteinase (TIMP), suggesting that MMP activation may play a role in the exposure of new Col-V antigenic epitopes. We conclude that a shift in immunodominance of self-antigenic determinants of Col-V results in induction of IFN-γ and IL-17 with loss of tolerance leading to autoimmunity to Col-V, which leads to chronic lung allograft rejection.

Pathophysiologic Significance of B-Cell Clusters in Chronically Rejected Grafts

The role of antibodies in the pathogenesis of chronic rejection is increasingly acknowledged. In contrast, whether B-cell clusters, which have been recently identified in chronically rejected allografts, actively participate in the process or are only an epiphenomenon remain a matter of debate. Integrating recently published data, we put forward explanations that reconcile the conflicting conclusions of experimental and biopsy-based studies. Finally, we propose a unified model in which B-cell clusters as part of intragraft tertiary lymphoid tissue can play deleterious or regulatory roles and therefore actively modulate the kinetics of chronic rejection.

345 Ligation of Human Airway Epithelial Cells Antibodies Specific to K- α1-Tubulin Leads to Activation of HIF-1α Dependent Induction of Fibrinogenic Growth Factors: Role in the Pathogenesis of Chronic Rejection Following Human Lung Transplantation

345 Ligation of Human Airway Epithelial Cells Antibodies Specific to K- α1-Tubulin Leads to Activation of HIF-1α Dependent Induction of Fibrinogenic Growth Factors: Role in the Pathogenesis of Chronic Rejection Following Human Lung Transplantation

82 Antibody Directed Therapy for DSA Results in Diminished Autoimmune Response and Favorable Long Term Outcome Following Human Lung Transplantation

Purpose Current evidence demonstrates an important role for cross talk between alloimmunity and autoimmunity in the pathogenesis of chronic rejection following human lung transplantation (LTx) manifested as bronchiolitis obliterans syndrome (BOS). We recently demonstrated that preemptive antibody directed therapy (IVIG and Rituximab) in patients who develop de novo anti-HLA antibodies (DSA) resulted in removal of DSA and greater freedom from BOS. The goal of this study is to determine the impact of antibody directed therapy on autoimmunity and its influence in reducing the incidence of BOS. Methods and Materials Adult lung transplant recipients (n=116) were analyzed. BOS was diagnosed by ISHLT guidelines. DSA were measured by LABScreen Single antigen beads by Luminex every 3 months, antibodies (Abs) to self-antigens K-α1-tubulin (Kα1T) and Collagen V (Col-V) by ELISA and cytokines by Luminex kit. Results Among 116 LTx, 65 developed DSA within 3 months of LTx and were treated with IVIG and/or rituximab. Among the DSA cleared BOS- patients (n=28), there was a significant drop in Abs to Col-V (from 23/28 to 12/28) and Kα1T (from 25/28 to 14/28, p Conclusions Our results demonstrate that antibody directed therapy results in decreased circulating levels of pro inflammatory cytokines and development of auto-Abs and increased freedom from BOS.

Renal allograft pathology with C4d immunostaining in patients with graft dysfunction

Renal allograft biopsy is the gold standard for diagnosis of rejection. Incorporation of C4d as a marker for humoral rejection is a major addition for Banff Schema, 2005. We evaluated the pattern of C4d staining in indicated renal allograft biopsies from January 2005 to December 2009. Of the 67 biopsies analyzed, 21 were C4d-positive. They were 11 cases of acute rejection, seven chronic rejection and one biopsy each of acute tubular necrosis, BK virus nephropathy and normal biopsy. Morphologic features like peritubular capillary dilatation, tubulitis and interstitial inflammation were seen more frequently in C4d-positive biopsies and this was statistically significant. C4d positivity was noted in 50% of the chronic rejection cases indicating a humoral component in the pathogenesis of chronic rejection. There was no significant difference in the serum creatinine levels of C4d-positive and -negative patients, either at the time of biopsy or during the follow-up. This study supports the role of C4d immunostaining in confirming histologically diagnosed acute and chronic humoral rejections and in detecting histologically unsuspected cases.

Synergistic effect of antibodies to human leukocyte antigens and defensins in pathogenesis of bronchiolitis obliterans syndrome after human lung transplantation

This study aims to determine the role of antibodies to donor-mismatched human leukocyte antigen (HLA) developed during the post-transplant period in inducing defensins and their synergistic role in the pathogenesis of chronic rejection, bronchiolitis obliterans syndrome (BOS), after human lung transplantation (LTx). Bronchoalveolar lavage (BAL) and serum from 21 BOS+ LTx patients were assayed for β-defensins human neutrophil peptides (HNP) 1-3 (enzyme-linked immunosorbent assay [ELISA]) and anti-HLA antibodies (Luminex, Luminex Corp, Austin, TX). Human airway epithelial cells (AEC) were treated with anti-HLA antibodies, HNP-1/2, or both, and the levels of β-defensin were measured by ELISA. Using a mouse model of obliterative airway disease induced by anti-major histocompatibility (MHC) class-I antibodies, we quantitatively and qualitatively determined neutrophil infiltration by myeloperoxidase (MPO) staining and activity by MPO assay, and defensin levels in the BAL. In human LTx patients, higher defensin levels correlated with presence of circulating anti-HLA antibodies (p < 0.05). AEC treated with anti-HLA antibodies or HNP-1/2, produced β-defensin with synergistic effects in combination (612 ± 06 vs 520 ± 23 pg/ml anti-HLA antibody, or 590 ± 10 pg/ml for HNP treatment; p < 0.05). Neutrophil numbers (6-fold) and activity (5.5-fold) were higher in the lungs of mice treated with anti-MHC antibodies vs control. A 2-fold increase in α-defensin and β-defensin levels was also present in BAL on Day 5 after anti-MHC administrations. Anti-HLA antibodies developed during the post-transplant period and α-defensins stimulated β-defensin production by epithelial cells, leading to increased cellular infiltration and inflammation. Chronic stimulation of epithelium by antibodies to MHC and resulting increased levels of defensins induce growth factor production and epithelial proliferation contributing to the development of chronic rejection after LTx.

Alloimmunity and autoimmunity in chronic rejection

Recent studies demonstrate an increasing role for alloimmune responses in the disruption of self-tolerance leading to immune responses to self-antigens that play a role in the immunopathogenesis of chronic rejection following solid organ transplantation. This review summarizes recent studies and implications for the alloimmune-response-induced de-novo development of autoimmune responses following solid organ transplantations. Immediately following organ transplantation, several factors lead to enduring an inflammatory milieu. Studies from our laboratory and others have demonstrated that development of antihuman leukocyte antigen antibodies precedes the development of chronic rejection. Using an in-vivo murine model, we have demonstrated that administration of anti-major histocompatibility complex (MHC) class I directly into the native lungs leads to chronic rejection pathology. Further, the in-vitro ligation of epithelial cell surface MHC class I molecules by specific anti-MHC can lead to cell activation and production of fibrinogenic growth factors. On the basis of these findings, we hypothesized that alloimmune responses can lead to autoimmunity, thus playing an important role in chronic rejection. Characterization of both the temporal occurrence and functional significance of antibodies to self-antigens may provide insight into the pathogenesis of chronic rejection and these antibodies can serve as clinically useful biomarkers.

Lipid raft facilitated ligation of K-α1-tubulin by specific antibodies on epithelial cells: Role in pathogenesis of chronic rejection following human lung transplantation

Long term function of human lung allografts is hindered by development of chronic rejection manifested as Bronchiolitis Obliterans Syndrome (BOS). We have previously identified the development of antibodies (Abs) following lung transplantation to K-α1-tubulin (KAT), an epithelial surface gap junction cytoskeletal protein, in patients who develop BOS. However, the biochemical and molecular basis of the interactions and signaling cascades mediated by KAT Abs are yet to be defined. In this report, we investigated the biophysical basis of the epithelial cell membrane surface interaction between KAT and its specific Abs. Towards this, we analyzed the role of the lipid raft-domains in the membrane interactions which lead to cell signaling and ultimately increased growth factor expression. Normal human bronchial epithelial (NHBE) cells, upon specific ligation with Abs to KAT obtained either from the serum of BOS(+) patients or monoclonal KAT Abs, resulted in upregulation of growth factors VEGF, PDGF, and bFGF (6.4±1.1-, 3.2±0.9-, and 3.4±1.1-fold increase, respectively) all of which are important in the pathogenesis of BOS. To define the role for lipid raft in augmenting surface interactions, we analyzed the changes in the growth factor expression pattern upon depletion and enrichment with lipid raft following the ligation of the epithelial cell membranes with Abs specific for KAT. NHBE cells cultured in the presence of β-methyl cyclodextran (βMCD) had significantly reduced growth factor expression (1.3±0.3, vs βMCD untreated being 6.4±1.1-fold increase) upon stimulation with KAT Abs. Depletion of cholesterol on NHBE cells upon treatment with βMCD also resulted in decreased partitioning of caveolin in the membrane fraction indicating a decrease in raft-domains. In conclusion, our results demonstrate an important role for lipid raft-mediated ligation of Abs to KAT on the epithelial cell membrane, which results in the upregulation of growth factor cascades involved in the pathogenesis of BOS following human lung transplantation.

Antihuman leukocyte antigen antibody-induced autoimmunity: role in chronic rejection

We provide evidence for the role of de-novo development of immune responses to self-antigens in the posttransplant period and its possible induction by alloimmunity in the pathogenesis of chronic rejection following lung, heart and kidney transplantation. The present review details recent findings for the two distinct yet interdependent immune processes in the immunopathogenesis of chronic rejection. The contribution of both humoral and cell-mediated alloimmune responses against mismatched donor histocompatibility antigens (HLA) in the pathogenesis of chronic rejection is well established. Recent studies have focused on development of immune responses to self-antigens during the posttransplant period and its correlation with chronic rejection. These self-antigens include myosin and vimentin in cardiac, K-alpha-1-tubulin and collagen-V in lung and angiotensin II type 1 receptor, collagen-IV and VI in kidney transplants. During the posttransplant period, the development of immune responses to self-antigens is facilitated by induction of a distinct subset of autoreactive T-helper cells referred to as Th17 cells. Following organ transplantation, tissue injury and remodeling inflicted by antibodies (Abs) to HLA antigens is conducive to develop autoimmunity. Abs to HLA and self-antigens are detectable in the serum of transplant recipients who develop chronic rejection. Anti-HLA Abs are often present transiently but precede the development of Abs to self-antigens.