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 (SIRP), a membrane protein, induced CD11c+ microglia in the brain white matter. Mice lacking CD47, a physiological ligand of SIRP, and microglia-specific SIRP knockout mice exhibited the same phenotype, suggesting the interaction between microglial SIRP and CD47 on neighbouring cells suppressed the emergence of CD11c+ microglia. A lack of SIRP 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 SIRP. Thus, microglial SIRP suppresses the induction of CD11c+ microglia that have the potential to accelerate the repair of damaged white matter.