Figure 1. Differentiation of helper T cell subsets.

Following activation by antigen-presenting cells such as dendritic cells (DCs), naive CD4⁺ T cells can be polarized into different effector T cell subsets — T helper 1 (T_H1), T_H2, T_H17 and regulatory T (T_Reg) cells — depending on the local cytokine environment. The differentiation of each of these effector T cell subsets is controlled by distinct sets of transcription factors. In the presence of interleukin-6 (IL-6) and transforming growth factor-β (TGFβ), naive T cells can differentiate into T_H17 cells, which are characterized by expression of the transcription factors retinoic acid receptor-related orphan receptor-γt (RORγt) and signal transducer and activator of transcription 3 (STAT3). Furthermore, IL-1 and IL-23 can promote and/or stabilize T_H17 cell differentiation and expansion. FOXP3, forkhead box P3; GATA3, GATA-binding protein 3; IFNγ, interferon-γ; TCR, T cell receptor.