<s>[INST] context: Hyperacute rejection Takes place from few minutes to few hours Takes place because of presence of preformed antibodies Eg: multiparous female, blood recipients (WBC/platelets) are associated with Sensitization of immune system We have high degree of expression of HLA or MHC antigens on the surface of WBC/platelets, which are responsible for the formation of preformed antibodies Hyperacute transplant rejection is an example of Type II hypersensitivity reaction Cross matching reduces the risk of development of hyperacute transplant rejection significantly Hyper acute rejection: This form of rejection occurs within minutes or hours after transplantation. A hyperacutely rejecting kidney rapidly becomes cyanotic, mottled, and flaccid, and may excrete a mere few drops of bloody urine. Immunoglobulin and complement are deposited in the vessel wall, causing endothelial injury and fibrin-platelet thrombi. Neutrophils rapidly accumulate within aerioles, glomeruli, and peritubular capillaries. As these changes become diffuse and intense, the glomeruli undergo thrombotic occlusion of the capillaries, and fibrinoid necrosis occurs in aerial walls. The kidney coex then undergoes outright necrosis (infarction), and such nonfunctioning kidneys have to be removed. Hyperacute rejection, Hyperacute rejection of a kidney allograft showing platelet and fibrin thrombi, early neutrophil infiltration, and severe ischemic injury in a [/INST] question: Hyperacute rejection occurs within:- | options: A: 12 hours B: 2 weeks C: 1 month D: 3 month | answer: A </s>