TNF and rheumatoid arthritis: Cytokines, such as IL-1β, IL-6, IL-17, and TNF-α, promote RANKL expression in the RA synovium, leading to increased osteoclastogenesis; however, contrary to expectations, a recent study demonstrated that IL-26 inhibited osteoclastogenesis by downregulation of NF-κB activation and nuclear translocation of nuclear factor of activated T cells, cytoplasmic 1 (NFATc1) in RAW264.7 cells, a murine macrophage cell line [13].