Osteoclasts are the cells resulting in bone erosion in RA, and macrophage‐colony stimulating factor (M‐CSF) and receptor activator of nuclear factor κ‐B ligand (RANKL) are key ligands that promote osteoclast formation.[96] Osteoprotegerin (OPG), a competitive inhibitor of osteoblast‐derived RANK, inhibits osteoclast formation and reduces bone erosion. This evidence concerns the gene CSF1 and rheumatoid arthritis.