Leukocyte influx into the central nervous system (CNS) and the associated cytotoxicity can have life-long debilitating effects because of the limited capacity of the CNS for regeneration. Leukocyte-endothelial adhesive interactions in brain inflammation in humans is not well understood, since the kinetics and cellular response involved cannot be directly studied; However valuable insights are being provided by animal studies. Direct experimentally induced inflammation in the cortex of rodents induces leukocyte recruitment that appears to be delayed compared to meninges and other non-CNS tissue. It has been proposed that endothelial cells, which play a pivotal role in the inflammatory response in other tissues, may be physiologically adapted in the cortex to modify immune responses such that effector mechanisms that invoke inflammation are suppressed. Although there maybe several mechanism involved, our working hypothesis is that the difference in leukocyte recruitment may be related in part to the differential pattern of expression of leukocyte adhesion molecules relative to endothelial cells in other tissues. An endothelial adhesion molecule implicated in the early recruitment of leukocytes is P-selectin which is stored in granules of platelet and endothelial cells. In support of four hypothesis, we have found a surprising absence of P-selectin constitutive expression in the cortex with selective expression in the leptomeninges. Cerebral cortical endothelial cells in culture had virtually no constitutive P-selectin but its expression in cells could be induced upon endothelial cell activation with inflammatory mediators. The recent generation and characterization of P-selectin deficient mice by the applicant, which appears to be severely compromised in leukocyte rolling and extravasation, establishes an important role for P-selectin in these critical steps of the inflammatory response. Our overall objective is to determine whether the pattern of P-selectin expression reflects in vivo function and pathophysiology. The primary goals are 1) To examine P-selectin expression in brain cerebral endothelium in vitro and 3) Determine the biological mechanisms and pathological relevance of P-selectin in the brain in vivo. The applicant has two powerful tools to carry out the proposed experiments: P-selectin deficient mice for the proposed murine models of CNS inflammation, and the ability to culture normal mouse brain microvascular endothelial cells as well as P-selectin-null endothelial cells for in vitro leukocyte adhesion studies.
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