Which cytokines promote Th1 differentiation and cell-mediated immunity?

• A. IL-12 and IFN-γ
• B. IL-4 and IL-5
• C. IL-10 and TGF-β
• D. IL-2 and IL-7

Answer: (A)

Th1 differentiation and cell-mediated immunity are driven by signals that bias CD4+ T cells toward a Th1 fate and activate macrophages. IL-12, produced by activated dendritic cells and macrophages, directs naive CD4+ T cells to become Th1 cells via STAT4 signaling, leading to IFN-γ production. IFN-γ then enhances macrophage killing of intracellular pathogens, upregulates MHC II, and supports cytotoxic T cell responses, reinforcing the Th1 pathway. In contrast, cytokines like IL-4 promote Th2 responses, while IL-10 and TGF-β dampen Th1 activity; IL-2 and IL-7 mainly support T cell growth and survival but are not the primary drivers of Th1 differentiation.