Figure 2. Cytokines IL-21, IL-6, TGFβ acting on the receptors of naive T-cells, activate via STAT 3 the transcription factors IRF-4 and RORγt, leading to the synthesis of IL-17 A and IL-17 F, IL-21, and the expression of the functional IL-23 receptor on the membrane. The synthesis of IL-17 and the transcription factor RORγt are considered the main markers of the Th17 subset. Adapted from Ghilardi and Ouyang, 2007⁽¹²⁾ .