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 This evidence concerns the gene CD47 and major depressive disorder.