Communicating systems in the body: how microbiota and microglia cooperate

Microglia are tissue macrophages of the central nervous system (CNS). Their key tasks are immune surveillance as well as responding to infections or other pathological states such as neurological diseases or injury. In recent years it has been discovered that microglia are additionally crucial for the maintenance of brain homeostasis during development and adulthood by adjusting the neuronal network and phagocytosing neuronal debris. Microglia persist in the CNS throughout the life of the organism and self-renew without engraftment of bone-marrow-derived cells. Until recently it remained unknown what controls their maturation and activation under homeostatic conditions. In this review we discuss new aspects of the interaction between host microbiota and brain function with special focus on the brain-resident innate immune cells, the microglia.