This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunity, Subject name: Pathology
[{'content': 'Hyperacute rejection occurs within:? \nSelect and explain. \nA. 12 hours, B. 2 weeks, C. 1 month, D. 3 months', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. (a) 12 hours(Ref: Robbins 9th ed p 233)Hyperacute rejection occurs when preformed antidonor antibodies are present in the circulation of the recipient. 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.', 'role': 'assistant'}]