ABSTRACT
A large body of evidence in the last two decades has established the concept that the blood-brain barrier (BBB) is an active participant in a wide spectrum of pathological processes having as a common theme the entry of circulating leukocytes into the brain, notably immune responses and tissue injury. The movement of leukocytes across the BBB requires direct communication with the endothelium, which depends upon the timely and coordinated expression of endothelial cell (EC) surface molecules that recognize corresponding receptors on leukocytes. Some of these surface proteins mediate leukocyte adhesion and extravasation, while others contribute to the specifi city of the immune response by providing costimulatory signals to antigen-specifi c T lymphocytes. In addition, it is becoming increasingly evident that adhesion molecules function as signaling receptors transmitting intracellular signals that enable EC to actively participate in leukocyte recruitment.
