Microglial SIRPα regulates the emergence of CD11c+ microglia and demyelination damage in white matter

A characteristic subset of microglia expressing CD11c appears in response to brain damage. However, the functional role of CD11c + microglia, as well as the mechanism of its induction, are poorly understood. Here we report that the genetic ablation of signal regulatory protein α (SIRPα), a membrane protein, induced CD11c + microglia in the brain white matter. Mice lacking CD47, a physiological ligand of SIRPα, and microglia-specific SIRPα knockout mice exhibited the same phenotype, suggesting the interaction between microglial SIRPα and CD47 on neighbouring cells suppressed the emergence of CD11c + microglia. A lack of SIRPα did not cause detectable damage in the white matter, but resulted in the increased expression of genes characteristic of the repair phase after demyelination. In addition, cuprizone-induced demyelination was alleviated by the microglia-specific ablation of SIRPα. Thus, microglial SIRPα suppresses the induction of CD11c + microglia that have the potential to accelerate the repair of damaged white matter.