Mouse secreted CD137, also known as Tumor Necrosis Factor Receptor Superfamily member 9, TNFRSF9, and ILA, GenBank Accession No. NM_011612, a.a. 24-187 fused at the C-terminus to the Fc portion of human IgG1, expressed in a HEK293 cell expression system. MW = 44 kDa (monomer). This protein runs at a higher MW by SDS-PAGE due to glycosylation.