4-1BB/TNFRSF9/CD137: Proteins and Enzymes

4-1BB, also known as CD137 and TNFRSF9, is a transmembrane TNF receptor superfamily member that is expressed as on various populations of activated T cell including CD4+, CD8+, memory CD8+, NKT, and regulatory T cells as well as on myeloid and mast cell progenitors, dendritic cells, mast cells, and bacterially infected osteoblasts. 4-1BB binding by 4-1BB Ligand costimulates T cell proliferation, activation, and/or survival and can enhance the activation-induced cell death of repetitively stimulated T cells. 4-1BB can associate with OX40 on activated T cells, forming a complex that responds to either ligand and inhibits Treg and CD8+ T cell proliferation. Reverse signaling through 4-1BB Ligand inhibits the development of dendritic cells, B cells, and osteoclasts but supports mature dendritic cell survival and costimulates the proliferation and activation of mast cells.