Figure 1
Current understanding of T-helper cell differentiation. Naive CD4+ T cells, after activation by signaling through the T-cell receptor and co-stimulatory molecules such as CD28 and cytotoxic T lymphocyte-associated protein 4 (CTLA-4), can differentiate into three lineages of effector T helper(Th) cells, namely Th1, Th2, or Th17 cells. Th cell subsets produce different cytokines and have distinct immunoregulatory functions. Th2 cells produce interleukin (IL)-4, IL-5, and IL-10 and promote immunity against parasites such as helminths. Th1 cells produce interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α) and provide immunity against intracellular pathogens. Th17 cells produce the cytokines IL-17/IL-17F, IL-22, IL-21, and TNF-α and primarily promote immunity against extracellular pathogens.
