CD200 receptor is a 60-100 kD type I transmembrane glycoprotein, also known as OX-2R or CD200R. It is a member of the immunoglobulin superfamily that is primarily expressed on macrophages/monocytes, granulocytes, mast cells, subsets of T (memory T) and B (memory B and plasmablasts) cells. The interaction of CD200R with its ligand, CD200, plays roles in down-regulation of myeloid cells activity and inhibition of dendritic cell-induced Th1 cytokine production, as well as in modulating microglial activation.