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
Secondary allograft rejection is mediated by? 
Select and explain. 
A. Memory cells, B. Antibodies, C. Immune complexes, D. None of the above
A: Memory cells
Answer: A: Memory cells 
Explanation: Secondary rejection (accelerated rejection)

After hyperacute rejection, transplantation of a second graft, which shares a significant number of antigenic determinants with the first one, results in a rapid (2-5 days) rejection. It is due to the presence of T lymphocytes sensitized during the first graft rejection memory cells). Accelerated rejection is mediated by immediate production of lymphokines, activation of monocytes and macrophages, and induction of cytotoxic lymphocytes.