Tumor Necrosis Factor Receptor Superfamily, Member 4 (TNFRSF4)

CD134 is a member of the TNFR-superfamily of receptors which is not constitutively expressed on resting naive T cells, unlike CD28. OX40 is a secondary costimulatory molecule, expressed after 24 to 72 hours following activation; its ligand, OX40L, is also not expressed on resting antigen presenting cells, but is following their activation. Expression of OX40 is dependent on full activation of the T cell; without CD28, expression of OX40 is delayed and of fourfold lower levels.
OX40 has no effect on the proliferative abilities of CD4 cells for the first three days, however after this time proliferation begins to slow and cells die at a greater rate, due to an inability to maintain a high level of PKB activity and expression of Bcl-2, Bcl-XL and survivin.