Life without microglia

Microglia are involved in many aspects of postnatal brain development and neuronal plasticity. This article questions some of the assumptions inherent in current experimental models used to analyze microglial ontogeny and function which likely underestimate the contributions of blood monocytes to brain homeostasis. It summarizes evidence from animal models of congenital microglial deficiency that postnatal neuronal development and synaptic refinement do not require the presence of microglia. Instead, the absence of microglia is associated with accelerated progression in disease models and age-dependent neuropathology in humans, implying that the major essential function of microglia is to protect against neuronal injury.