Final answer:
IL-12 stimulates the differentiation of naive T-helper cells into TH1 subpopulation, which is known for secreting cytokines that are essential for the cell-mediated immune response, such as IFN-γ, important for macrophage activation and the inflammatory response.
Step-by-step explanation:
Interleukin-12 (IL-12) stimulates the differentiation of "naive" T-helper cells into the TH1 subpopulation, which secretes various cytokines. TH1 cells are crucial for the cell-mediated immune response, particularly in stimulating macrophages and enhancing the activities of other immune cells such as cytotoxic T cells and natural killer cells. Depending on the cytokines encountered, a naive helper T cell can also differentiate into the TH2 or memory helper T cell subtypes, but in the presence of IL-12, the differentiation is generally towards TH1 cells.
The TH1 cytokines include interferon-gamma (IFN-γ), which activates macrophages and encourages the inflammation process, as well as helping in the development of more TH1 cells and cytotoxic T cells. In contrast, TH2 cells primarily produce cytokines like IL-4 and IL-5, which drive the differentiation of B cells into plasma cells for antibody production.