Biology of TH17 Lymphocytes, their Cytokines and Role in Disease

T lymphocytes that are involved in cellular mediated immunity include two types known as TCD8+ (Cytotoxic T lymphocytes) and TCD4+ (helper T lymphocytes). TCD4+ has four main subtypes, including TH1, TH2, TH17, and Treg Lymphocytes.TH17 lymphocytes play a role in defense against microbes that TH1 and TH2 lymphocytes have not the ability to respond to them. The most important cytokines, which are involved in induction of this subtype are the tumor growth factor &beta(TGF &beta) and interleukin 6(IL-6), and IL-17 is the most important cytokine, which is released by TH17 cells. IL-17 is the member of the cytokine family, which includs IL-17A-F and among them IL-17A and IL-17F are responsible for biological functions in this cytokine family that have most hemology together rather than other members. Also, TH17 cells produce and release other cytokine such as IL-21, IL-22 and IL-23, which may have the role in functional mechanisms of TH17 lymphocytes. Because of the TH17 lymphocytes roles in the defense against microbes and inflammatory reactions, it seems that TH17 lymphocytes may has a role in inflammatory disorders. The relationship between TH17 lymphocytes and diseases such as Asthma, Psoriasis, Systemic lupus erythematosus (SLE), Rheumatoid Arthritis(RA) and inflammatory bowel disease was shown. In this article, we review the TH17 lymphocytes, their released cytokines and their roles in different autoimmunre and inflammatory diseases.