This MAb recognizes a protein of 43kDa, identified as OX40, which is also known as CD134.OX40 is a type I integral membrane glycoprotein and member of the tumor necrosis factor/nerve growth factor receptor (TNFR/NGFR) family. It is expressed on activated T lymphocytes, hematopoietic precursor cells and fibroblasts. It functions as a T cell co-stimulatory receptor when bound by OX40 Ligand / TNFSF4 that is expressed by antigen presenting cells. OX40 thereby plays roles in T-cell activation as well as the regulation of differentiation, proliferation or apoptosis of normal and malignant lymphoid cells.OX40 is upregulated at the sites of inflammation, especially in case of multiple sclerosis and psoriatic lesions.