OX40 is a type 1 transmembrane glycoprotein, reported nearly 30 years ago as a cell surface antigen expressed on activated T cells. Since its discovery, it has been validated as a bone fide costimulatory molecule for T cells and member of the TNF receptor family. Tumor necrosis factor receptor superfamily, member 4 (TNFRSF4), also known as CD134 and OX40 receptor, is a fellow of the TNFR-superfamily of receptors. It is a protein which in humans is encoded by the TNFRSF4 gene which contains 9 exons. It also has been demonstrated to have a key role in the survival and homeostasis of effector and memory T cells in transplantation and autoimmunity. OX40 is not constitutively expressed on resting naive T cells, unlike CD28. As a secondary co-stimulatory immune checkpoint molecule, it expresses after 24 to 72 hours following activation; its ligand, OX40L, is also not expressed on resting antigen presenting cells and resting naive T cells, but is following their activation. Expression of OX40 is dependent on full activation of the T cell and the expression of CD28; without CD28, expression of OX40 is delayed and of fourfold lower levels.

OX40 Signaling Pathway References