title: Complement activation by anti-endothelial cell antibodies in MHC-mismatched and MHC-matched heart allograft rejection: anti-MHC-, but not anti non-MHC alloantibodies are effective in complement activation.
abstract: Classical complement activation is a major effector mechanism in the development of vascular lesions contributing to allograft rejection. We investigated complement activation by alloantibodies reactive with graft endothelial cell (EC) alloantigens in settings of MHC-mismatched and MHC-matched (non-MHC-mismatched) rat heart transplantation (Tx). Allosera and heart allografts were collected at the day of rejection (day 7-8 and day 28-35 in MHC-mismatched and non-MHC-mismatched Tx respectively) or earlier. Allosera reactivity was studied in vitro using rat-heart-endothelial-cell (RHEC) lines expressing the appropriate donor MHC and non-MHC alloantigen profile. Immunohistochemical analysis of rejected heart allografts showed deposition of alloantibodies in both MHC-mismatched and MHC-matched heart allografts, but expression of C3 was only seen in the vasculature of MHC-mismatched grafts. FACS analysis showed that anti MHC as well as anti non-MHC allosera were reactive with donor EC cell surface antigens. Both sera had similar IgG subclass profiles of anti-endothelial cell antibodies. Complement activation by anti MHC and anti non-MHC alloantibodies on EC was measured by FACS analysis of C3 and C5b-9 (MAC) expression. Distinct expression of C3 was noticed for EC incubated with anti-MHC allosera, but hardly for EC incubated with anti non-MHC allosera. C5b-9 was low but showed no difference between the two allosera. However, complement-mediated cytotoxicity experiments showed that functional (lytic) MAC was induced with anti MHC allosera but hardly with anti non-MHC allosera. Our data show that in settings of MHC-matched heart transplantation alloantibodies against endothelial non-MHC alloantigens are generated, but, in contrast to alloantibodies to MHC alloantigens, these alloantibodies have only poor complement-activating and lytic potentials. Whether anti non-MHC allolantibodies effect other biological processes relevant for heart allograft vasculopathy, including development of graft arteriosclerosis, needs further elucidation.
authors.affiliation: Department of Internal Medicine, CARIM, University of Maastricht, The Netherlands.
authors.forename: A M
authors.initials: AM
authors.lastname: Diujvestijn
authors.forename: J G
authors.initials: JG
authors.lastname: Derhaag
authors.forename: P J
authors.initials: PJ
authors.lastname: van Breda Vriesman
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003167:Complement Activation; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D006084:Graft Rejection / Q000276:immunology* / Q000473:pathology; D016027:Heart Transplantation / Q000276:immunology* / Q000473:pathology; D006650:Histocompatibility Testing; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D007518:Isoantibodies / Q000097:blood*; D008285:Major Histocompatibility Complex; D008297:Male; D051381:Rats; D011914:Rats, Inbred BN; D011917:Rats, Inbred Lew; D011994:Recombinant Proteins / Q000494:pharmacology; D014184:Transplantation, Homologous; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D007518:Isoantibodies; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D007371:Interferon-gamma