Microglia and immune signaling as architects of the brain

The focus of studies on immune signaling in the CNS is often placed on the effects of inflammation and overactive immune mechanisms in the context of neurodevelopmental and neurodegenerative pathology. However, many immune regulatory pathways are also essential for healthy neuronal development and proper circuit refinement. Appropriate levels of cytokines and chemokines along with many other immune signaling and phagocytic pathways are required for normal neurodevelopment. The complement pathway and other "eat me" signals often studied in the context of inflammation and neurodevelopmental disorders, likewise play a crucial role in this process. Immune receptors and membrane-associated molecules regulate growth, differentiation and the refinement process to help establish a functional network. This review will focus on the roles that immune signaling mechanisms play in neurodevelopment of healthy animals.