Ontogeny and function of microglia and nerve-associated macrophages.

Macrophages are essential immune cells that arise early during embryogenesis and persist as tissue-resident cells into adulthood. This chapter explores macrophage development, focusing on their roles in the nervous system. We describe their distinct origins from early hematopoietic waves and their differentiation into specialized populations such as microglia and border-associated macrophages (BAMs) in the central nervous system (CNS) as well as nerve-associated macrophages in the peripheral (PNS) and enteric nervous system (ENS). These macrophage populations are crucial for tissue development, maintenance, and repair mediating their effects through intricate cellular communication networks with neighboring cells. Furthermore, we discuss how disruptions in macrophage development - driven by factors such as maternal obesity, stress, or environmental pollutants - can have profound and lasting impacts on neurodevelopmental and neurodegenerative outcomes. Gaining a deeper understanding of these developmental processes offers valuable insights into nervous system integrity and reveals potential therapeutic avenues for mitigating disease-related consequences.