CD134 is a type I integral membrane protein also known as OX-40, ACT35, and tumor necrosis factor receptor superfamily member 4 (TNFRSF4). This receptor is expressed on activated CD4+ and CD8+ T cells and B cells. The OX-40 receptor binds to the OX-40 ligand (CD252) to provide a costimulatory signal that is independent of CD28. Blockade of OX40-OX40 ligand interactions has been shown to ameliorate experimental EAE and inflammatory bowel disease, which implies that these interactions are important in the pathogenesis of some autoimmune diseases.