4-1BB, also known as TNFRSF9 or CD137, is a receptor of the tumor necrosis factor superfamily. The human 4-1BB gene encodes a type I transmembrane protein consisting of 255 amino acids, including 17 amino acid N-terminal signaling peptide, 169 amino acid extracellular region, 27 amino acid transmembrane region, and 42 amino acid extracellular region. Recombinant Human soluble 4-1BB is a 167-amino acid polypeptide (17.7kDa), including cystine TNFR-like 4-1BB extracellular domain. 4-1BB is mainly expressed on the surface of various T cells, and is also expressed in B cells, monocytes and a variety of transformed cell lines. This protein contributes to clonal proliferation, survival and T cell development. It can also induce the proliferation of peripheral monocytes, enhance T cell apoptosis induced by TCR/CD3 activation, and regulate CD28 co-stimulation to promote Th1 cell response. The expression of this protein is induced by lymphocyte activation. TRAF adaptor binds to this protein and transduces the signal that activates NF-κB. It is also involved in the development of inflammation in high-fat foodborne metabolic syndrome.