Figure 2. JAK-STAT and T helper cell differentiation of naïve T cells. Naïve T cells differentiate into several T helper cell subsets, Th1, Th2, of Th17. IL-12 is required for the differentiation into Th1 cells that secrete IFN-γ, TNF-α, and IL-2 to generate a response to intracellular pathogens. IL-4 is required for the differentiation into Th2 cells that secrete IL-4, IL-5, and IL-10 to generate defenses against Helminth infections. IL6, IL-21, and IL-23 are required for the differentiation into Th17 cells that secrete IL-17 and IL-22 to promote defense against extracellular pathogens.