The OX-86 monoclonal antibody specifically binds to the OX-40 antigen (CD134), also known as OX-40L receptor. CD134 is a 50-kDa type-I membrane glycoprotein that belongs to the NGFR/TNFR superfamily. Mouse CD134 is expressed on activated CD4+ and CD8+ T lymphocytes and has been shown to be the sole receptor for the OX-40 Ligand (OX-40L). In the brains of mice with actively induced experimental allergic encephalomyelitis, the expression of CD134 on CD4+ T lymphocytes correlates with disease progression. The OX-40/OX-40L system supplies a costimulatory signal for T-cell proliferation and B-cell proliferation and differentiation. In addition, OX-40 antigen provides a costimulatory signal that induces T cells to proliferate in a CD28-independent manner. In the intact animal, CD134 does not appear to be essential for many T-cell responses, but it seems to play a major role in the pathogenesis of some autoimmune diseases. The OX-86 mAb stains both CD4+ and CD8+ activated T cells, and this expression pattern has been confirmed using OX-40L-Ig fusion protein. CD134 was also detected, using OX-86 mAb, on B cells after stimulation with anti-IgM plus anti-CD40 mAb HM40-3 (Cat. no. 553721). OX-86 mAb does not block binding of OX-40L to OX-40, and it stimulates T-cell proliferation mildly.