The Blood-Brain Barrier in Immune Mediated Diseases of the Central Nervous System

Abstract

The blood-brain barrier (BBB) is essential for the maintenance and regulation of the neural microenvironment. The term BBB describes a complex cellular system of, astrocytes, perivascular macrophages, a basal lamina and endothelial cells that controls the exchange of molecules between the brain parenchima and the rest of the body. Astrocytes, which encircle the cerebral endothelial cells (CEC) with their extended foot processes, have a role in the induction and maintenance of BBB properties (Rubin and Staddon, 1999). The close contact between cells and astrocyte-derived factors probably mediate these effects. Furthermore, factors found in the extracellular matrix shared by astrocytes and endothelial cells seem to be involved in the maintenance of barrier properties (Engelhardt, 1997). The CEC are characterised by an extremely low rate of transcytotic transport via vesicles, and a restrictive paracellular diffusion barrier realized by the tight junctions coupling the CEC. These tight junctions, functionally connected to cytoskeletal proteins, are effective in restricting entry of proteins and cells from the blood into the brain and cerebrospinal fluid. The BBB-tight junctions are morphologically similar to epithelial tight junctions, but differ in being highly sensitive to changes in the endothelial environment (De Vries et al., 1997).