IL31 and rheumatoid arthritis: Further to the above, although the biological effect of IL-31 is currently unclear and its participation in some inflammatory processes is controversial, it has been shown to stimulate the secretion of proinflammatory cytokines, such as IL-6, and different chemokines and MMP, mainly in skin disorders [7,8], suggesting that this cytokine has a proinflammatory function and could therefore play a role in RA pathogenesis.