The differentiation of naive CD4⁺ T cells into Th1 and Th2 cells regulated by cytokines is defined as polarization. Th1 cells are induced by IL-12, depend on the transcription factor T-bet, secrete IFN-γ, and mediate cellular immunity. Th2 cells are induced by IL-4, rely on GATA3, and produce IL-4, IL-5 and IL-13 to mediate humoral immunity. The two subsets mutually inhibit each other to maintain immune homeostasis.