TNFSF11 and rheumatoid arthritis: However, although previous studies have reported that many proinflammatory cytokines, such as interleukin (IL)-18 [11], IL-6 [12], IL-22 [13], and IL-29 [14], may induce RANKL expression in fibroblast-like synoviocytes, the underlying mechanism regulating RANKL expression in RA synovial cells has not been elucidated.