Fig2. Diagram of Th17 cell differentiation: differentiation of Th17 cells in mice needs to be initiated by TGF-β and IL-6, expanded by IL-21, and stabilized by IL-23. IL-23 can promote the secretion of IL-17 to generate an inflammatory response, and plays an important role in the stabilization of Th17 cells. In human cells, the combination of TGF-β and IL-21 is sufficient to induce naive T cells to differentiate into Th17 cells.