CD200 is highly expressed by neurons, and to a lesser extent by oligodendrocytes, whereas CD47 is expressed by neurons, oligodendrocytes and astrocytes.20 Binding of CD200 and CD47 to their receptors CD200R and SIRPα, respectively, on microglia, results in maintaining microglia in a ramified, antiphagocytic state.21-24 Interestingly, in major depressive disorder, increased expression of CD200 and CD47 is thought to regulate an immune-suppressed microglial phenotype.25 The gene discussed is CD200; the disease is major depressive disorder.