Receptor activator of nuclear factor kappa-B (RANK) ligand, also known as tumor necrosis factor ligand superfamily member 11 (TNFSF11), together with RANK, is a member of the TNF superfamily of ligands and receptors involved in activation of immune response and in bone regeneration. RANK-Ligand is expressed in several tissues and cell types, including fibroblasts, T cells, and osteoblasts, and functions by binding its cell surface signaling receptor RANK. RANK-Ligand is expressed by T helper cells and is involved in dendritic cell maturation. Binding of osteoprotegerin (OPG) by RANK-Ligand inhibits osteoclastogenesis and leads to accumulation of bone and cartilage. High expression of RANK-Ligand is observed during degenerative bone diseases and in tumors. Mouse RANK-Ligand shares with human 85% amino acid identity.