Neuronal/lymphoid membrane glycoprotein MRC OX-2 is a member of the immunoglobulin superfamily with a light-chain-like structure.

The MRC OX-2 antigen is a membrane glycoprotein of about 45,000 Mr present on rat neurons, thymocytes, B cells, follicular dendritic cells, endothelium and smooth muscle. Sequence of cDNA clones indicates it is a member of the Ig superfamily containing 248 amino acids organized like an Ig light chain with a V-like domain and a C-like domain followed by a transmembrane and cytoplasmic sections. There is a sequence with homologies with J-regions but analysis of the gene for human OX-2 shows that this is part of the V-domain exon and there is not a separate J-region exon as in the T cell receptor or Ig chains. The relationship of OX-2 to the other Ig-related neuronal/thymocyte antigen Thy-1 and the evolution of the Ig superfamily are discussed.