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: Answer- A. Memory cellsAfter hlperacute rejection, transplantation of a second gfaft, which shares a significant number of antigenic determinants with the first one, results in a rapid (2 - 5 days) rejection. It is due to presence of T-lymphocyte sensitized during the first graft rejection(memory cells).', 'role': 'assistant'}]