Summary: cd200/cd200R are highly conserved type i paired membrane glycoproteins that belong to the ig superfamily containing a two immunoglobulin -like domain (v, c). cd200 is broadly distributed in a variety of cell types, whereas CD200R is primarily expressed in myeloid and lymphoid cells. They fulfill multiple functions in regulating inflammation. the interaction between cd200/cd200R results in activation of the intracellular inhibitory pathway with Rasgap recruitment and thus contributes to effector cell inhibition. It was confirmed that the CD200R activation stimulates the differentiation of t cells to the treg subset, upregulates indoleamine 2,3 -dioxygenase activity, modulates cytokine environment from a Th1 to a Th2 pattern, and facilitates an antiinflammatory IL -10 and TGF -β synthesis. CD200/CD200R are required for maintaining self -tolerance. Many studies have demonstrated the importance of cd200 in controlling autoimmunity, inflammation, the development and spread of cancer, hypersensitivity, and spontaneous fetal loss.