This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
[{'content': 'Ahur reaction is what type of hypersensitivity reaction \nSelect and explain. \nA. Localised immune complex, B. Ag-Ab reaction, C. Complement mediated, D. Ab mediated', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref Robbins 8/p205.,7/e p215, 9/e p207 Local Immune Complex Disease A model of local immune complex diseases is the Ahus reaction, in which an area of tissue necrosis appears as a result of acute immune complex vasculitis. The reaction is produced experimentally by injecting an antigen into the skin of a previously immunized animal (i.e., pre-formed antibodies against the antigen are already present in the circulation). Because of the initial antibody excess, immune complexes are formed as the antigen diffuses into the vas- cular wall; these are precipitated at the site of injection and trigger the same inflammatory reaction and histologic appearance as in systemic immune complex disease. Ahus lesions evolve over a few hours and reach a peak 4 to 10 hours after injection, when the injection site develops visible edema with severe hemorrhage, occasionally fol- lowed by ulceration.', 'role': 'assistant'}]