Description: The 17B5 monoclonal antibody reacts with mouse CD137, also known as 4-1BB, a member of the TNFR superfamily. CD137 is expressed as monomers, dimers, and tetramers on the surface of activated T cells around day 4-6 after activation through the TCR complex. Interaction of CD137 with its ligand, 4-1BBL, is reported to deliver a costimulatory signal important in the T-APC interaction. Recent data suggests CD317 is expressed on Tregs and may play a role in their proliferation. The monoclonal antibody 17B5 has strong antagonistic effect in in vitro functional assays.