Immunobiology of the blood-brain barrier.

The brain microvessel endothelial cells (BMVEC) that form the blood-brain barrier are uniquely positioned to influence immune responses within the central nervous system. As the biological interface separating the blood from the brain extracellular fluid, BMVEC regulate the entry of leukocytes into the brain. In addition, through the release of various soluble factors that affect immune responses, BMVEC may modulate immune responses in the brain. This review addresses the interplay between the immune system and the blood-brain barrier as it relates to the regulation of CNS defense and immunity.