OX40 ligand, soluble

OX40L, a member of the TNF superfamily of structurally related proteins, exists primarily as a type II membrane bound, non-covalently linked homotrimeric protein. It is expressed on antigen presenting cells (APCs), such as dendritic cells and activated B-cells, and also on various other cells such as vascular endothelial cells, mast cells, and natural killer cells. OX40L signals specifically through the OX40 receptor, which is expressed predominantly on CD4+T cells but also on certain activated CD8+T cells. OX40/OX40L functions as a costimulatory signal, which is required for a productive interaction between antigen presenting cells and their target T-cells. It enhances cell proliferation and survival, and increases expression of RANTES, IL-2, IL-3, and IFNγ. OX40/OX40L signaling plays an important role in immuno-regulatory communication, enabling the immune system to distinguish between “friend vs. foe” during activation; a mechanism typically termed immuno-tolerance. Recombinant OX40L is a glycosylated 133 amino acid protein corresponding to the extracellular TNF homologous domain of the full length transmembrane protein. It migrates with an apparent molecular mass of 15.5 – 25.0 kDa on SDS-PAGE.