Recently discovered, Th17 are a subpopulation of T-helper cells that produce mainly interleukin 17; they are considered evolutionarily distinct from Th1 and Th2 and play a key role in inflammatory processes and tissue damage in chronic conditions such as psoriasis, autoimmune uveitis, juvenile diabetes, rheumatoid arthritis, Crohn's disease, and multiple sclerosis [39, 40]. Here, IL17A is linked to psoriasis.