ABSTRACT
The blood-brain barrier (BBB) is a composite structure formed by the fusion of several different cell types and the extracellular matrix (ECM). The major constituents of the BBB are endothelial cells, which undergo barrier specialization as a result of their interaction with the foot processes of astrocytes (glia limitans). The perivascular space is a tightly regulated microenvironment and harbors three cell types: perivascular macrophages (PVM), pericytes, and smooth muscle cells. This chapter deals with PVM, which are distinct from their myeloid counterparts found within the brain parenchyma (microglia) and outside the brain parenchyma (monocytes). Due to their strategic location at the BBB, PVM have important cellular functions including recognition, phagocytosis, degradation, and transport of pathogens, antigen presentation to T lymphocytes, and production of immune regulatory mediators. Furthermore, some aspects of the phenotype of PVM suggest that they contribute to the maintenance of the BBB.
