IL15 and rheumatoid arthritis: However, it has been shown that the profile of synovial fluid (SF) cytokines in very early RA is different from that in established RA, and has a Th2 and Th17 bias (i.e., displays elevated concentration of interleukin (IL)-2, IL-4, IL-13, IL-17, IL-15, basic fibroblast growth factor, and epidermal growth factor compared to established RA) [8].