<prompt> Hyperacute rejection is due to:Preformed antibodiesCytotoxic T-lymphocyte medicated injuryCirculating macrophage mediated injuryEndothelitis caused by donor antibodies  <response>: Ans. a. Preformed antibodies Ref: Robbins 9e p233, 8ep228; Schwartz 9e p274-275; Bailey 25e p1408-1412Hyperacute rejection is due to preformed antibodies.Hyperacute rejection:Immediate within minutes to hours graft destruction due to ABO or pre-formed anti-HLA antibodiesQ.Characterised by intravascular thrombosisQKidney transplants are particularly vulnerableQ to hyperacute graft rejection.Types of Graft RejectionHyperacute RejectionAcute cellular RejectionChronic Rejection Immediate within minutes to hours graft destruction due to ABO or pre-formed anti- HLA antibodiesQ. Characterised by intravascular thrombosisQ Kidney transplants are particularly vulnerableQ to hyperacute graft rejection Heart 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 arteries leading to ischemia and fibrosisQ Pathological Features of Rejection ReactionsAcute cellular rejectionAcute humoral rejectionChronic rejection Interstitial mononuclear cell infiltration with edema Mild interstitial hemorrhage Focal tubular necrosis Endothelitis Necrotizing vasculitis with endothelial cell necrosisQ Neutrophilic infiltration Deposition of immunoglobulinsQ, complement and fibrin Renal cortical necrosisQ and atrophy Dense obliterative intimal fibrosis Interstitial fibrosis Glomerular loss with tubular atrophy Shrinkage of renal parenchyma 