IL17A and psoriasis: In psoriasis, the activation of immune cells (dendritic cells, T helper 1 (Th1) cells, and T helper 17 (Th17) cells, keratinocytes (KCs), macrophages, and neutrophils) and overproduction of key inflammatory cytokines (interferon (IFN)-α, IFN-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-17, IL-22, IL-12/IL-23, chemokines and antimicrobial peptides) are responsible for the chronic inflammation and epidermal hyperproliferation and impaired differentiation (14).