Swine tissue can express antigens similar to human A/B blood types. We evaluated whether the variation in human blood type influences the human xenoreactive antibody-mediated cytotoxicity and modifies the protective effect of human decay-accelerating factor (hDAF) exogene, a complement activation regulator, on swine endothelium. Methods. Pig aortic endothelial cells were harvested form normal and hDAF transgenic pigs. Cellular viability was evaluated with an MTT assay. Results. As compared with that of other human blood types, human serum from blood type O donors induced more prominent cytotoxicity on swine endothelial cells both from hDAF transgenic or normal pigs (P