– Cell surface glycoprotein CD200 Receptor 1 (CD200R1) is the receptor for the CD200 (OX-2) membrane glycoprotein. CD200R1 contains one C2- type Ig-like domain and one V-type Ig-like domain within its extracellular domain and a PTB-signaling motif in cytoplasmic domain. CD200R1 and CD200 associate via their respective N-terminal Ig-like domains. CD200R1 is restricted primarily to mast cells, basophils, macrophages, and dendritic cells. It propagates inhibitory signals despite its lacking a cytoplasmic ITIM (immunoreceptor tyrosinebased inhibitory motif). The receptor-substrate interaction may function as a myeloid downregulatory signal.