Nat. Neurosci. 21, 506–516 (2018)

Activation or dysfunction of the immune system is associated with neurodevelopmental disorders. In Nature Neuroscience, Yamashita and colleagues show that IgMhi B-1a cells are abundant in the brain of neonatal mice and promote the proliferation of oligodendrocyte precursor cells (OPCs). B-1a cells are recruited from neonatal blood in a manner dependent on the chemokine receptor CXCR5 and in response to the chemokine CXCL13 from the choroid plexus; their frequency peaks at day 1 after birth, and they are gone by day 10. Depletion of B-1a cells diminishes the number of oligodendrocytes in the developing brain. OPCs, but not mature oligodendrocytes, express the IgM receptor Fcα/μR, and IgM–Fcα/μR signaling regulates OPC proliferation in the neonatal brain.