Humoral rejection and endothelial cell activation, 2001

Anti-huCD20 antibody therapy for antibody-mediated rejection of renal allografts in a mouse model

We have reported that B6.CCR5(-/-) mice reject renal allografts with high serum donor-specific antibody (DSA) titers and marked C4d deposition in grafts, features consistent with antibody-mediated rejection (AMR). B6.huCD20/CCR5(-/-) mice, where human CD20 expression is restricted to B cells, rejected A/J renal allografts by day 26 posttransplant with DSA first detected in serum on day 5 posttransplant and increased thereafter. Recipient treatment with anti-huCD20 mAb prior to the transplant and weekly up to 7 weeks posttransplant promoted long-term allograft survival (>100 days) with low DSA titers. To investigate the effect of B cell depletion at the time serum DSA was first detected, recipients were treated with anti-huCD20 mAb on days 5, 8, and 12 posttransplant. This regimen significantly reduced DSA titers and graft inflammation on day 15 posttransplant and prolonged allograft survival >60 days. However, DSA returned to the titers observed in control treated recipients by day 30 posttransplant and histological analyses on day 60 posttransplant indicated severe interstitial fibrosis. These results indicate that anti-huCD20 mAb had the greatest effect as a prophylactic treatment and that the distinct kinetics of DSA responses accounts for acute renal allograft failure versus the development of fibrosis.

Endothelial injury in renal antibody-mediated allograft rejection: a schematic view based on pathogenesis

Circulating donor-specific antibodies (DSA) cause profound changes in endothelial cells (EC) of the allograft microvasculature. EC injury ranges from rapid cellular necrosis to adaptive changes allowing for EC survival, but with modifications of morphology and function resulting in obliteration of the microvasculature.Lytic EC injury: Lethal exposure to DSA/complement predominates in early-acute antibody-mediated rejection (AMR) and presents with EC swelling, cell necrosis, denudation of the underlying matrix and platelet aggregation, thrombotic microangiopathy, and neutrophilic infiltration.Sublytic EC injury: Sublethal exposure to DSA with EC activation predominates in late-chronic AMR. Sublytic injury presents with (a) EC shape and proliferative-reparative alterations: ongoing cycles of cellular injury and repair manifested with EC swelling/loss of fenestrations and expression of growth and mitogenic factors, leading to proliferative changes and matrix remodeling (transplant glomerulopathy and capillaropathy); (b) EC procoagulant changes: EC activation and disruption of the endothelium integrity is associated with production of procoagulant factors, platelet aggregation, and facilitation of thrombotic events manifested with acute and chronic thrombotic microangiopathy; and (c) EC proinflammatory changes: increased EC expression of adhesion molecules including monocyte chemotactic protein-1 and complement and platelet-derived mediators attract inflammatory cells, predominantly macrophages manifested as glomerulitis and capillaritis.Throughout the course of AMR, lytic and sublytic EC injury coexist, providing the basis for the overwhelming morphologic and clinical heterogeneity of AMR. This can be satisfactorily explained by correlating the ultrastructural EC changes and pathophysiology.The vast array of EC responses provides great opportunities for intervention but also represents a colossal challenge for the development of universally successful therapies.

Antibodies to MHC class II molecules induce autoimmunity: critical role for macrophages in the immunopathogenesis of obliterative airway disease

Previous studies have shown that intrabronchial administration of antibodies (Abs) to MHC class I resulted in development of obliterative airway disease (OAD), a correlate of chronic human lung allograft rejection. Since development of Abs specific to mismatched donor HLA class II have also been associated with chronic human lung allograft rejection, we analyzed the role of Abs to MHC class II in inducing OAD. Administration of MHC class II Abs (M5/114) to C57BL/6 mice induced the classical features of OAD even though MHC class II expression is absent de novo on murine lung epithelial and endothelial cells. The induction of OAD was accompanied by enhanced cellular and humoral immune responses to self-antigens (Collagen V and K- α1Tubulin). Further, lung-infiltrating macrophages demonstrated a switch in their phenotype predominance from MΦ1 (F4/80⁺CD11c⁺) to MΦ2 (F4/80⁺CD206⁺) following administration of Abs and prior to development of OAD. Passive administration of macrophages harvested from animals with OAD but not from naïve animals induced OAD lesions. We conclude that MHC class II Abs induces a phenotype switch of lung infiltrating macrophages from MΦ1 (F4/80⁺CD11c⁺) to MΦ2 (F4/80⁺CD206⁺) resulting in the breakdown of self-tolerance along with an increase in autoimmune Th17 response leading to OAD.

Antibody-mediated rejection of single class I MHC-disparate cardiac allografts

Murine CCR5(-/-) recipients produce high titers of antibody to complete MHC-mismatched heart and renal allografts. To study mechanisms of class I MHC antibody-mediated allograft injury, we tested the rejection of heart allografts transgenically expressing a single class I MHC disparity in wild-type C57BL/6 (H-2(b)) and B6.CCR5(-/-) recipients. Donor-specific antibody titers in CCR5(-/-) recipients were 30-fold higher than in wild-type recipients. B6.K(d) allografts survived longer than 60 days in wild-type recipients whereas CCR5(-/-) recipients rejected all allografts within 14 days. Rejection was accompanied by infiltration of CD8 T cells, neutrophils and macrophages, and C4d deposition in the graft capillaries. B6.K(d) allografts were rejected by CD8(-/-)/CCR5(-/-), but not μMT(-/-)/CCR5(-/-), recipients indicating the need for antibody but not CD8 T cells. Grafts recovered at day 10 from CCR5(-/-) and CD8(-/-)/CCR5(-/-) recipients and from RAG-1(-/-) allograft recipients injected with anti-K(d) antibodies expressed high levels of perforin, myeloperoxidase and CCL5 mRNA. These studies indicate that the continual production of antidonor class I MHC antibody can mediate allograft rejection, that donor-reactive CD8 T cells synergize with the antibody to contribute to rejection, and that expression of three biomarkers during rejection can occur in the absence of this CD8 T cell activity.

Mechanisms and Role of HLA and non-HLA Alloantibodies

The role of alloantibodies against HLA and non-HLA targets is becoming increasingly recognized as critical in the pathogenesis of acute and chronic renal allograft outcomes. This review discusses the antigenic targets, the mechanisms of T and B cell activation that result in the production of antibody, the complement cascade, methods of antibody detection, and the evidence that alloantibody-mediated mechanisms are active in acute and chronic rejection.

Antibody-mediated organ-allograft rejection

Recent studies show that alloantibodies mediate a substantial proportion of graft-rejection episodes, contributing to both early and late graft loss. Rejection that is caused by antibody is mediated by different mechanisms from rejection that is caused by T cells, thereby requiring other approaches to treatment and prevention. Antibody induces rejection acutely through the fixation of complement, resulting in tissue injury and coagulation. In addition, complement activation recruits macrophages and neutrophils, causing additional endothelial injury. Antibody and complement also induce gene expression by endothelial cells, which is thought to remodel arteries and basement membranes, leading to fixed and irreversible anatomical lesions that permanently compromise graft function.