This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
[{'content': 'Secondary allograft rejection is mediated by? \nSelect and explain. \nA. Memory cells, B. Antibodies, C. Immune complexes, D. None of the above', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Secondary rejection (accelerated rejection)\n\nAfter hyperacute rejection, transplantation of a second graft, which shares a significant number of\xa0antigenic determinants with the first one, results in a rapid (2-5 days) rejection. It is due to the presence of T lymphocytes\xa0sensitized during the first graft rejection memory cells). Accelerated rejection is mediated\xa0by immediate production of lymphokines, activation of monocytes and macrophages, and induction of\xa0cytotoxic lymphocytes.', 'role': 'assistant'}]