CD200 is also known as OX-2 membrane glycoprotein (OX-2), is a type-1 membrane glycoprotein, which contains two immunoglobulin domains (1 Ig-like C2-type (immunoglobulin-like) domain and Ig-like V-type (immunoglobulin-like) domain), and thus belongs to the immunoglobulin superfamily. CD200 / OX-2 is widely expressed in multiple cell types. CD200 interacts with a structurally related receptor (CD200R) expressed mainly on myeloid cells and is involved in regulation of macrophage and mast cell function. OX-2 / CD200 and CD200R associate via their respective N-terminal Ig-like domains. CD200 also plays an important role in prevention of graft rejection, autoimmune diseases and spontaneous abortion.