Effects of antibody reactivity to major histocompatibility complex (MHC) and non-MHC alloantigens on graft endothelial cells in heart allograft rejection

Background. To gain insight in the pathogenesis of vascular lesions in hear t allograft rejection, we investigated effects of allosera reactive with ma jor histocompatibility complex (MHC) or non-MHC alloantigens on graft endot helial cells (EC) in a rat transplantation model. Methods. Anti-MHC and anti-non-MHC allosera were obtained from Brown Norway (RT.1(n)) recipients of a Lewis (RT.1(1)) or congenic LEW.1N (RT.1(n)) hea rt allograft respectively. Reactivity with endothelial alloantigens was stu died in vitro using a series of three rat heart endothelial cell (RHEC) lin es of Lewis origin. Phenotypic studies of MHC and non-MHC alloantigen expre ssion, and adhesion molecule induction on EC were performed by immunostaini ng and fluorescence-activated cell sorting analysis, Complement-mediated cy totoxicity of allosera was studied using a Cr-51 re lease assay, Results. Both anti-MHC allosera and anti-non-MHC allosera showed reactivity with all three RHEC lines. EC stimulation with tumor necrosis factor-alpha and interferon-gamma resulted in increased reactivity of anti-MHC but not of anti-non-MHC allosera, Anti-MHC allosera showed complement-mediated cyto toxicity for EC, which was strongly increased when cytokine-stimulated EC w ere used, With anti-non-MHC allosera, only minor cytotoxicity was measured, irrespective of the activation of EC, Anti-MHC and anti-non-MHC allosera f rom the day of rejection (days 7-8 and days 29-35, respectively) had simila r subclass profiles of allospecific IgG, except for allospecific IgM, which was only detected in anti-MWC allosera, Complement-mediated cytotoxicity o f anti-MHC allosera from the day of rejection was effected mainly by IgM al loantibodies, whereas, in allosera taken 4 days after rejection, a predomin ance of cytotoxic alloantibodies of the IgG class was observed. No indicati ons were found that either alloantibody reactivity alone or in combination with complement activation led to EC activation processes relevant to inter cellular adhesion molecule-1 or vascular cell adhesion molecule-1 induction . Conclusions. Our data show that, in heart allograft rejection, MHC but also non-MHC alloantigens on EC are target structures in the alloantibody respo nse. Alloantibodies reactive with endothelial MHC, but not those reactive w ith non-MHC alloantigens, may significantly contribute to vasculopathy by c omplement-mediated cytotoxicity, Although no evidence was found that alloan tibodies reactive with graft EC induce adhesion molecule expression, they m ay trigger other EC mechanisms relevant to graft vasculopathy.