TNFSF11 and periodontitis: In periodontitis, lipopolysaccharide (LPS) produced by periodontal pathogens, and inflammatory cytokines produced by host immune cells act on the periodontal ligament cells and osteoblasts to induce the receptor activator of nuclear factor κB (NF-κB) ligand (RANKL) to differentiate into osteoclasts (4, 6).