IL17A and rheumatoid arthritis: IL-23 plays a key role in the development of pathogenic Th17 cells that produce the cytokine IL-17, which induces the production of several pro-inflammatory cytokines, such as TNF-α and IL-6, chemokines, and some other additional novel factors responsible for RA and other autoimmune diseases (Bettelli et al. 2008; Langrish et al. 2005).