CD200 antigen, also known as OX-2, is a type I transmembrane protein belonging to the Ig superfamily. It has a 202 amino acid extracellular domain and a short (19 aa) cytoplasmic tail. At least two alternate splice isoforms exist that differ in their cytoplasmic domains. CD200 is widely expressed in multiple cell types. It interacts with CD200 R1, another Ig superfamily inhibitory receptor primarily expressed on leukocytes of the myeloid lineage, to inhibit myeloid functions.
CD200 R1, also known as OX-2 receptor, is a transmembrane glycoprotein and member of the immunoglobulin superfamily. It is expressed primarily in cells of the myeloid lineage, while its ligand, CD200, is widely distributed. CD200 R1 is though to propagate inhibitory signals and disruption of the CD200/CD200 R1 receptor-ligand pair leads to a predisposition to autoimmune phenotypes.