Figure 1.

Both interleukin-6 and interleukin-21 can cooperate with transforming growth factor-β to promote Th17 differentiation from CD4⁺ Th-cells while interleukin-23 is important for Th17 cell expansion and activation. Interferon-γ and interleukin-27 have regulatory roles through the suppression of Th17 differentiation. Note that the sole presence of transforming growth factor-β induces Treg cell production from CD4⁺ Th-cells