The necrotic and apoptotic injury of cardiac xenotransplants caused by human seru

Xenotransplants are injured by preformed immune components found in the serum of the recipient. Human serum mediates the necrosis of a xenotransplant by the activation of the complement cascade by preformed xenoantibody. This form of immunological rejection is called hyperacute rejection (HAR), which has been attributed to cause endothelial cell necrosis. In the absence of HAR there is the onset of delayed xenograft rejection (DXR). The pathological mechanism of DXR remains controversial, however apoptosis has been implicated as a possible mechanism of injury. These studies investigate the role of human serum in mediating both necrotic and apoptotic injury to xenotransplants and the participation of these processes in HAR and DXR.;Monoclonal antibodies directed against human xenogeneic IgM antibodies (anti-XeIgM) significantly reduced xenogeneic IgM (XeIgM) binding to cultured porcine endothelial cells (PAEC) as much as 83.2 +/- 2.1%, as measured by enzyme linked immunosorbant assay. There was no significant reduction in IgG binding by any antiXeIgM. The reduction of XeIgM also reduced complement mediated cell cytotoxicity of PAEC in vitro, and prevented HAR in vivo. The pathological analysis of heart biopsies from mice that received human serum treated with anti-XeIgM revealed no signs of necrosis and no classical signs of HAR.;Heart biopsies from mice transfused with human serum were examined for the presence of apoptosis in situ by terminal dUTP nicked end labeling (TUNEL). Mice in whom HAR was prevented had approximately a ten fold increase in the percentage of apoptotic cells (% apoptosis) 18 hours post injection compared to animals given saline, and a four fold increase over animals that experienced HAR. Administration of cobra venom factor (CVF) decomplemented human serum did not significantly (p > 0.05) alter the % apoptosis demonstrating that the classical mediators of HAR, namely antibodies and complement, do not participate in xenograft apoptosis. The addition of 20 mM Gal alpha 1,3 Gal to human serum significantly (p < 0.05) reduced % apoptosis to levels observed in saline treated control animals. Human serum induces apoptosis of isolated pig and mouse rod shaped cardiomyocytes, but not cultured human cardiomyocytes in vitro. Supplementation of culture media with recombinant human TNF-alpha did not induce apoptosis of xenogeneic cardiomyocytes at concentrations found in normal human serum. These results demonstrate that human serum initiates both a necrosis and an apoptosis via two separate pathways to injure the cardiac xenograft.