IL17A and rheumatoid arthritis: During the pathogenesis of RA, Th17 cells produce various pro-inflammatory cytokines such as IL-17A and Granulocyte–macrophage Colony Stimulating Factor (GM-CSF), whereas T helper 1/2 cell (Th1/Th2) cells secret Interferon-γ (IFN-γ) and Interleukin-6 (IL-6), thereby promote synovitis [46].