Vitamin D has been applied in the treatment of moderately severe psoriasis because DCs treated with vitamin D have lower expression of MHC-II and costimulatory molecules CD80, CD86, and CD40L, which can reduce the production of IL-12 while secreting IL-10 and ultimately inhibit the proliferation of T cells and the secretion of IFN-γ and IL-17 (Hau et al., 2018). Here, IL17A is linked to psoriasis.