A reevaluation of the role of IgM Non-HLA antibodies in cardiac transplantation.

BACKGROUND: Preexisting IgG antibodies to donor human leukocyte antigens (HLA) are a risk factor for rapid allograft rejection. However, non-HLA antibodies, of the IgM class, also called autoreactive antibodies, are not believed to affect graft survival. The aim of this study was to determine the incidence and clinical relevance of pretransplant lymphocytotoxic non-HLA IgM antibodies on long-term cardiac allograft survival. METHODS: A retrospective study of 616 adult recipients of cardiac allografts, transplanted at this center between 1991 and 2003, has been performed. Antibodies in pretransplant sera were initially defined using complement-dependent cytotoxicity assays, and subsequently analyzed for HLA specificities using solid phase assays. RESULTS: HLA antibodies were present in 69 of 616 heart recipients (58 IgG, 11 IgM); in 22 of these, the antibodies were donor-specific. Non-HLA IgM antibodies were detected in 59 of 616 recipients who did not have HLA-specific antibodies; these patients had a 1, 2, 5, and 10 year survival of 55.9%, 54.2%, 49.9%, and 43.3% compared with 75.8%, 73.7%, 66.6%, and 52.8% for those without antibodies (P=0.0085 log-rank test). Multivariate analysis demonstrated pretransplant non-HLA IgM antibodies to be an independent risk factor for mortality (P=0.0001). Myocardial histology of postmortem heart and cardiac biopsies suggested an association with ischemic damage and "primary" allograft failure. CONCLUSIONS: We propose the hypothesis that the presence of cytotoxic IgM antibodies to non-HLAs before heart transplantation maybe a risk factor for early allograft failure.

Expression of endothelial intercellular adhesion molecule-1 is determined by genotype: effects on efficiency of leukocyte adhesion to human endothelial cells.

Two biallelic polymorphisms, previously described in the human intercellular adhesion molecule (ICAM)-1 gene at codon 241 (glycine [G] to arginine [R] substitution) and codon 469 (glutamic acid [E] to lysine [K] substitution) have been associated with a number of diseases including myocardial infarction, transplant rejection, and diabetes. However, the functional significance of these polymorphisms has not been determined. ICAM-1 cell surface expression and ICAM-1-mediated leukocyte adhesion were investigated using Cos7 transfected with ICAM-1 polymorphic variants or human umbilical vein endothelial cells (HUVEC) of different ICAM-1 genotypes. There was significantly higher expression of surface ICAM-1 on Cos7 transfected with a plasmid encoding the GE (G241/E469) ICAM-1 variant or untreated HUVEC of GEGE (G241/E469 homozygous genotype). ICAM-1-mediated adhesion of peripheral blood mononuclear cells (PBMC) to GE-Cos7 cells or TNF-treated GEGE HUVEC was significantly increased. However, there was no significant difference in adhesion of PBMC to recombinant ICAM-1 of each polymorphic variant plated onto plastic wells. We conclude that the GE genotype of ICAM-1 is associated with greater cell surface expression of ICAM-1, which in turn leads to greater adhesion of leukocytes. This may explain the previously described associations of ICAM-1 polymorphisms with chronic inflammatory disease.

Anti-intercellular adhesion molecule-1 antibodies in sera of heart transplant recipients: a role in endothelial cell activation.

BACKGROUND: Antiendothelial antibodies to non-human leukocyte antigens are made by a subset of heart transplant recipients, but the specificity of such antibodies is undefined. Intercellular adhesion molecule (ICAM)-1 is an abundantly expressed adhesion molecule with polymorphic residues, expressed on the surface of endothelial cells. The hypothesis that ICAM-1 acts as a minor histocompatibility antigen and that anti-ICAM-1 antibodies, directed against polymorphic residues, could be one component of the antiendothelial antibodies found after heart transplantation has been tested. METHODS: Chinese hamster ovary cells were transfected with full-length polymorphic variants of human ICAM-1. The binding of antibodies (immunoglobulin [Ig] G or IgM) to these cells was measured using sera from 50 heart transplant recipients (pretransplant and 1 and 2 years posttransplant) and sera from 20 normal volunteers by flow cytometry. The recipients and donors were genotyped for ICAM-1 polymorphisms. RESULTS: Sixty-eight percent (n=34) of patients made IgM antibodies that bound to ICAM-1. However, it seems unlikely that ICAM-1 is a minor transplantation antigen, because there were no differences in antibody production from recipients matched or mismatched for ICAM-1 alleles. The antibodies bound to mouse endothelial cells that were engineered to overexpress human ICAM-1, and induced a robust activation of the Erk-2 mitogen-activated protein kinase pathway. CONCLUSIONS: Anti-ICAM-1 antibodies are produced after cardiac transplantation, but not to polymorphic residues. Such antibodies may contribute to the endothelial activation by binding to the endothelium, causing activation of proinflammatory signaling pathways.

A role for indirect allorecognition in lung transplant recipients with obliterative bronchiolitis.

Obliterative bronchiolitis (OB) occurs in 50% of patients 2 years after lung transplantation. Although a correlation between OB and indirect recognition of donor peptides has been reported, the relative roles of direct vs. indirect recognition have not been investigated. Limiting dilution analysis was used to determine the frequencies of recipient T-helper cells recognizing donor and third-party alloantigens in 19 patients (8 OB positive, 11 OB negative). The assays were designed to distinguish between indirect and direct presentation. In three patients the direct and indirect assay were performed on the same blood sample. Six out of seven patients with OB were hyperresponsive in the indirect pathway to donor antigens compared to third-party, the corresponding figure for OB negative patients being 2/7. In contrast, 5/7 patients were hyporesponsive in the direct pathway; hyporesponsiveness in the direct pathway did not correlate with freedom from OB. The patients in whom the assays were performed from the same blood sample confirmed that donor specific hyperresponsiveness in the indirect route can coexist with donor-specific hyporesponsiveness in the direct route. In conclusion, lung allograft recipients, like recipients of other organ allografts, become hyporesponsive in the direct route but sensitization via the indirect pathway is associated with chronic rejection.