CD137/4-1BB (Tumor necrosis factor receptor superfamily member 9, T-cell antigen 4-1BB homolog, T-cell antigen ILA)

CD137 (ILA/4–1BB) is a member of the tumor necrosis factor receptor family, expressed on activated T lymphocytes. The expression of CD137 is strictly activation-dependent in primary cells. The soluble isoforms of CD137, sCD137, are generated by differential splicing and can be detected at enhanced concentrations in sera of patients suffering from various diseases.