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': 'An important step in activation of naive CD4 +T cells and initiation of cell-mediated immune response is played by Interleukin- \nSelect and explain. \nA. 2, B. 1, C. 3, D. 4', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Activation\xa0of CD4\xa0+T cells:\n\nNaive CD4\xa0+T cells cells recognize peptides\xa0displayed by dendritic\xa0cells and secrete IL-2, which functions\xa0as an\xa0autocrine growth factor to stimulate proliferation of the antigen-responsive T cells.\nThe subsequent differentiation of antigen-stimulated\xa0T cells to TH1 or TH17 cells is driven by the cytokines\xa0produced by APCs at the time of T-cell activation.\nIn some situations, the APCs (dendritic\xa0cells and macrophages) produce 1L-12, which induces\xa0the differentiation\xa0of CD4\xa0+T\xa0cells to the TH1 subset. IFN-γ produced by these effector cells promotes further\xa0TH1 development, thus amplifying the reaction.\nIf the APCs produce inflammatory cytokines such as IL-1, IL-6, and a close relative\xa0of IL-12 called IL-23,\xa0these stimulate differentiation\xa0of T cells to the TH17 subset.', 'role': 'assistant'}]