4-1BB Receptor, a member of the TNF superfamily of receptors, is mainly expressed on the surface of a variety of T cells, but also found in B cells, monocytes, and various transformed cell lines. 4-1BB Receptor binds to 4-1BBL to provide a co-stimulatory signal for T lymphocytes. Signaling by 4-1BB Receptor has been implicated in the antigen-presentation process and generation of cytotoxic T cells. The human 4-1BB Receptor gene codes for a 255 amino acid type I transmembrane protein containing a 17 amino acid N-terminal signal sequence, a 169 amino acid extracellular domain, a 27 amino acid transmembrane domain and a 42 amino acid cytoplasmic domain. Recombinant human soluble 4-1BB Receptor is a 167 amino acid polypeptide (17.7 kDa), which contains the cysteine rich TNFR-like extracellular domain of 4-1BB Receptor.