4 - 1BB (CD137) is a 30 kD type I glycoprotein and again a typical transmembrane receptor in the TNFR superfamily, containing 4 full cysteine rich domains, and a relatively
short cytoplasmic tail, and also signals as a trimer when bound to 4 - 1BBL, its known ligand in the TNF family.
OX40 (CD134) is a 50 kD type I transmembrane glycoprotein in the TNFR superfamily, containing 3 full cysteine rich domains, and a relatively
short cytoplasmic tail, and although a monomer it signals as a trimer when bound to OX40L, its known ligand in the TNF family.