Human serum induces apoptosis of xenogeneic cardiomyocytes in vivo and in vitro

Discordant xenotransplantation is complicated by delayed xenograft rejectio n (DXR). Previous studies have demonstrated that anti-apoptotic genes are p rotective against DXR. This study examines the hypothesis that apoptosis pl ays a role in human anti-xenograft responses. C57BL/6 mice and NOD SCID mic e were given a single intravenous injection of either a lethal dose (LD, su rvival < 30 min) or a sublethal dose (SLD) of human serum, and isolated pig and mouse rod-shaped cardiomyocytes were exposed to human serum in vitro. In situ detection of apoptotic cells in mouse hearts was assessed using a t erminal deoxynucleotidyl transferase-mediated dUTP nicked-end labeling assa y. Mice transfused with human serum had approximately a 10-fold increased p ercentage of apoptotic cells after SLD 18 h post-injection compared with an imals given saline, and a fourfold increase over LD. Administration of cobr a venom factor (CVF) decomplemented SLD 18 h did not significantly (P > 0.0 5) alter the percentage apoptosis. The addition of 20 mM Gal-alpha-1,3-Gal to SLD 18 h significantly (P < 0.05) reduced percentage apoptosis to levels comparable to saline treated control animals. In vitro using mouse and pig cardiomyocytes demonstrated parallel results as in vivo experiments. Human serum induces apoptosis of cardiomyocytes in immunocompetent and immu noincompetent mice in vivo, as well as mouse and pig cardiomyocytes in vitr o. Further, this apoptotic response can be inhibited by the addition of Gal -alpha-1,3-Gal without affecting the capacity of the serum to cause HAR. Th ese results demonstrate that a putative human serum factor induces a delaye d apoptotic injury of xenograft tissues, and supports the hypothesis that a poptosis may be an important mediator of DXR.