In 1999, we have already reported that IL-17 levels in synovial fluids are significantly higher in RA patients than in osteoarthritis patients and that IL-17 induces murine osteoclastogenesis by inducing the expression of RANKL via a mechanism involving the synthesis of prostaglandin E2 in osteoblasts in vitro [25]. Here, TNFSF11 is linked to rheumatoid arthritis.