Receptor activator of NF-κB (RANK) ligand (RANKL) is type II transmembrane protein with an extracellular domain at the carboxy-terminus of TNF cytokine superfamily. RANKL is a 19.8 kDa protein containing 317 residues and high express in T cells and T cell rich organs, such as thymus and lymph nodes. RANKL-RANK (RANKL receptor) plays an important role in bone metabolism, dysregulation, and immune system.