An immune inhibitory ligand/receptor pair that maintains immune quiescence in the CNS is CD200/CD200R. CD200 (OX2) is a highly expressed membrane glycoprotein with a broad tissue distribution. In the CNS, CD200 is expressed predominantly by neurons, down-modulating the activation state of perivascular macrophages and microglia through CD200R. Mice express multiple CD200R isoforms that exhibit tissue-restricted expression and heterogeneity of function. Recent studies have reported the expression of CD200R1 on microglia, macrophages, dendritic cells and a subpopulation of T cells. Ligation with its ligand, CD200, negatively regulates immune responses through multiple mechanisms including the activation of CD200R on MDSCs promoting tumorigenesis.
Moertel CL, Xia J, LaRue R, et al. CD200 in CNS tumor-induced immunosuppression: the role for CD200 pathway blockade in targeted immunotherapy. Journal for Immunotherapy of Cancer. 2014;2:46.