TNFSF11 and arthritic joint disease: It is accepted that RANKL, RANK, and osteoprotegerin are essential for controlling the oesteoclast development and functions in bone remodeling, and inhibition of RANKL activity by osteoprotegerin injection results in significantly reduced bone loss in arthritis (Kong et al., 1999) and osteoporosis (Mizuno et al., 1998).