Interleukin 17A,Interleukin 17A (IL-17A) is a proinflammatory cytokine produced by activated T cells. IL-17A-mediated downstream pathways induce the production of inflammatory molecules, chemokines, antimicrobial peptides, and remodeling proteins. It plays an important role in connecting T cell-mediated adaptive immunity and acute inflammatory response to destroy extracellular bacteria and fungi. It is the signature effector cytokine of Th17 cells, and in this role it primarily induces neutrophil activation and recruitment at infection and inflammatory sites. High levels of IL-17A are associated with rheumatoid arthritis, psoriasis, multiple sclerosis, and another inflammatory diseases, including lung injugy during severe COVID 19. This cytokine also contributes to germinal center formation by regulating the chemotactic response of B cells to CXCL12 and CXCL13, enhancing retention of B cells within the germinal centers, B cell somatic hypermutation rate and selection toward plasma cells. It is an effector cytokine for invariant NKT cells (iNKT), and it is involved in epithelial barrier formation upon injury.,Interleukin 17