<s>[INST] context: Hyperacute rejection is due to preformed antibodies. "Hyperacute rejection occurs when preformed antibodies react with donor antigens on the vascular endothelium of the graft. Subsequent complement activation triggers rapid intravascular thrombosis and graft necrosis."-Sabiston 20/e p618 TYPES OF GRAFT REJECTION Hyperacute Rejection Acute (cellular) Rejection Chronic Rejection Immediate (within minutes to hours) graft destruction due to ABO or pre-formed anti-HLA antibodiesQ. Characterised by intravascular thrombosisQ Kidney transplants are paicularly vulnerableQto hyperacute graft rejection Hea and liver transplants are relatively resistantQ. Occurs during the first 6 monthsQ Most commonly presents between 5-30Q days after transplantation T-cell dependent, characterized by mononuclear cell infiltrationQ Usually reversibleQ Occurs after the first 6 monthsQ MC cause of graft failureQ Non-immune factors may contribute to pathogenesis Characterized by myointimal proliferation in graft aeries leading to ischemia and fibrosisQ [/INST] question: Hyperacute rejection is due to:- | options: A: Preformed antibodies B: Cytotoxic T-lymphocyte medicated injury C: Circulating macrophage mediated injury D: Endothelitis caused by donor antibodies | answer: A </s>