Immune-related cells such as dendritic cells (DCs) and macrophages, as well as Toll-like receptors and cytokines such as interferon (IFN)- α, TNF-α, IFN-ɤ, IL-12, IL-22, IL-23, and IL-17, are closely associated with psoriasis pathogenesis. This evidence concerns the gene IL17A and psoriasis.