<prompt> An important step in activation of naive CD4 T cells and initiation of cell-mediated immune response is played by Interleukin-2134  <response>: Activation of CD4 T cells:Naive CD4 T cells cells recognize peptides displayed by dendritic cells and secrete IL-2, which functions as an autocrine growth factor to stimulate proliferation of the antigen-responsive T cells.The subsequent differentiation of antigen-stimulated T cells to TH1 or TH17 cells is driven by the cytokines produced by APCs at the time of T-cell activation.In some situations, the APCs dendritic cells and macrophages produce 1L-12, which induces the differentiation of CD4 T cells to the TH1 subset. IFN-γ produced by these effector cells promotes further TH1 development, thus amplifying the reaction.If the APCs produce inflammatory cytokines such as IL-1, IL-6, and a close relative of IL-12 called IL-23, these stimulate differentiation of T cells to the TH17 subset. 