Although PsA patients were known to have higher IL-13 levels in their synovial fluids (but not sera) compared to patients with RA and osteoarthritis, [89] the role of IL13 polymorphisms on that finding and in the pathogenesis of PsA and autoimmune diseases remains to be elucidated since IL-13 is generally considered as an inhibitory regulator of Th1- and Th17-mediated inflammation [90]. This evidence concerns the gene IL13 and rheumatoid arthritis.