IL17A and psoriasis: In a study of patients with psoriasis, it is found that IL-21 up-regulates RORγt expression and down-regulates the expression of Foxp3, increases secretion of IL-17A and IL-22, and finally induces T-helper 17 (Th17) and Tregs imbalance and promotes inflammation in psoriasis (Shi et al., 2019).