TNFSF11, also known as RANKL （Receptor Activator of Nuclear Factor Kappa-B Ligand）, is a cytokine belonging to the tumor necrosis factor （TNF） superfamily. It plays a crucial role in regulating bone metabolism and immune responses. TNFSF11 is primarily expressed by osteoblasts and activated T cells and functions as a key mediator of osteoclast differentiation and activation. By binding to its receptor RANK （Receptor Activator of Nuclear Factor Kappa-B） on osteoclast precursor cells, TNFSF11 stimulates osteoclastogenesis and bone resorption. Additionally, TNFSF11 is involved in the regulation of immune responses, lymph node development, and mammary gland development.