4-1BB Receptor, also named TNFRSF9 is a member of the TNF superfamily of receptors. It 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.