4-1BB Receptor (CD137) is a member of the TNF receptor superfamily expressed on activated CD4 and CD8 T cells as well as on activated natural killer cells. The binding of 4-1BB Receptor to its TNF family ligand, 4-1BB ligand (4-1BBL) delivers a co-stimulatory signal to resting T cells leading to high level IL2 production independently of CD28 signaling. Recombinant Human 4-1BB Receptor represents the soluble, cysteine-rich TNFR-like extracellular domain of 4-1BB Receptor.