OX-2 membrane glycoprotein, also named CD200 (Cluster of Differentiation 200) is a human protein encoded by the CD200 gene. CD200 gene is in human located on chromosome 3 in proximity to genes encoding other B7 proteins CD80/CD86. In mice CD200 gene is on chromosome 16. The protein encoded by this gene is a type-1 membrane glycoprotein, which contains two IgSF immunoglobulin domains, transmembrane region and a 19 amino acid long cytoplasmatic domain. CD 200 belongs to the immunoglobulin superfamily, particularly belongs to the B7 receptor family.