Chapter 8 - Microglia and border-associated macrophages in the central nervous system

Abstract

The central nervous system (CNS) is a very complex organ in the body, responsible for orchestrating many essential physiological functions. This complexity is associated with well-regulated homeostatic mechanisms, and subtle dysfunctions could lead to severe disease or death. For many years, the CNS was considered an immune-privileged organ, lacking lymphatic vessels and infiltrating leukocytes under physiological conditions. This has been extensively revised, especially after the re-discovery of CNS lymphatics and the description of an abundance of meningeal immune cells. In fact, it is now accepted that CNS macrophages can be found both in the brain parenchyma, as microglial cells, and also at the blood-brain and cerebrospinal-brain interfaces, as perivascular macrophages (pvMΦ), choroid plexus macrophages (cpMΦ), and in the subdural space within the meninges (mMΦ), referred as border-associated macrophages (BAMs) [4]. The phenotype and function of these cells have now been deeply investigated, evidencing a remarkable role in supporting CNS homeostasis and assisting against tissue damage, invading pathogens, and circulating compounds [5]. In this chapter, we will discuss the heterogeneity of macrophages in the CNS, their phenotypes, functions, and role during CNS-related disorders.