CD137-Ligand, also known as 4-1BB-Ligand or TNFRSF9-Ligand, is the natural agonist of the CD137 receptor, and a member of the TNF superfamily. CD137-Ligand is expressed on antigen presenting cells, such as dendritic cells, B cells, and macrophages. The binding of CD137-Ligand to its receptor plays a central role in co-stimulation of T cells by antigen presenting cells, and it is required for development of memory T cells. CD137-Ligand is studied for its role in the activation of immune response against infections and cancer, and for its involvement in autoimmunity. CD137-Ligand exists as a membrane-bound and a soluble form resulting from proteolytic cleavage of the extracellular domain. Like other Ligands from the TNFSF family, active CD137-Ligand is expected to form a non-covalent homotrimer.
