Effect of proinflammatory cytokines on blood-brain barrier integrity

The blood-brain barrier (BBB) consists of a unique system of brain microvascular endothelial cells, capillary basement membranes, and terminal branches ("end-feet") of astrocytes. The BBB's primary function is to protect the central nervous system from potentially harmful or toxic substances in the bloodstream by selectively controlling the entry of cells and molecules, including nutrients and immune system components. During neuroinflammation, the BBB loses its integrity, resulting in increased permeability, mostly due to the activity of inflammatory cytokines. However, the pathomechanism of structural and functional changes in the BBB caused by individual cytokines is poorly understood. This review summarizes the current state of knowledge on this topic, which is important from both the pathophysiological and clinical-therapeutic point of view. The structure and function of each of the components of the BBB are discussed with particular attention to phenotypic differences between brain microvascular endothelial cells and the vascular endothelium at other locations of the circulatory system. The protein composition of the inter-endothelial tight junctions in the context of regulating BBB permeability is presented, as is the role of the pericyte-BMEC interaction in the exchange of metabolites, ions, and nucleic acids. Finally, the documented actions of proinflammatory cytokines within the BBB are summarized.