In chronic inflammatory bone diseases such as rheumatoid arthritis, proinflammatory cytokines TNF-α, IL-1β, and IL-6, as well as RANKL, have been shown to be important in disease progression and bone loss (Nair et al., 1996; Merkel et al., 1999; Kotake et al., 2001; Haynes, 2004; Wei et al., 2005). Here, TNFSF11 is linked to rheumatoid arthritis.