Th1Th2

Th1Th2 refers to the two major CD4+ T helper cell lineages, Th1 and Th2, and the balance between them. Th1 cells promote cell-mediated immunity to intracellular pathogens through cytokines like IFN-γ and IL-2; their differentiation is driven by IL-12 produced by dendritic cells and IFN-γ, with T-bet as the master transcription factor. Th2 cells support humoral immunity and defense against extracellular parasites, primarily via IL-4, IL-5, and IL-13; GATA-3 governs their differentiation. Each subset activates distinct effector pathways: Th1 activates macrophages; Th2 supports B cell activation and antibody production, including IgE class switching.

The Th1/Th2 paradigm also describes cross-regulation: cytokines from one lineage inhibit the development or function of the other. For example, IFN-γ and IL-12 favor Th1 differentiation, while IL-4 promotes Th2 differentiation. The net balance influences disease outcomes: Th1-biased responses are associated with certain autoimmune and inflammatory diseases, whereas Th2-biased responses are linked to allergies and helminth defenses. However, the paradigm is simplified; many other T helper lineages (such as Th17, Tfh, Treg) contribute to immunity, and plasticity allows switching between phenotypes.

In research and clinical contexts, Th1/Th2 polarization remains a foundational concept for understanding adaptive immunity, vaccine design, and immunopathology, though modern views emphasize a network of T helper subsets and context-dependent responses rather than a strict binary.