Pro-inflammatory cytokines, such as TNF, IL-6, and IL-1, which are abundant in the synovial membrane and synovial fluid of patients with RA, promote RANKL expression by synovial fibroblasts, and TNF and M-CSF induce osteoclast production (Takayanagi, 2007; Okamoto et al., 2017; Shim et al., 2018). Here, TNF is linked to rheumatoid arthritis.