Microbial traversal of the blood-brain barrier is required for the development of central nervous system infection, but the underlying mechanisms remain incompletely understood. The blood-brain barrier is a structural and functional barrier that is formed by brain microvascular endothelial cells and protects the brain from any microorganisms circulating in the blood, but recent studies have shown that meningitis-causing pathogens are able to cross the blood-brain barrier as live organisms. We have developed the in vitro blood-brain barrier model by isolation and cultivation of human brain microvascular endothelial cells (HBMEC). Upon cultivation on collagen-coated Transwell inserts the HBMEC monolayers exhibit morphological and functional properties of tight junction formation and polar monolayer. Our Preliminary Studies revealed that meningitis-causing pathogens traverse the HBMEC monolayers without affecting the HBMEC integrity, as assessed by transendothelial electrical resistance and permeability, and microbial traversal of the HBMEC monolayers involves specific host signal transduction pathways. Our additional Preliminary Studies using pharmacological inhibition and gene deletion suggest for the first time that host 5-lipoxygenase is likely to be involved in microbial traversal of the blood-brain barrier. Leukotrienes are synthesized by 5-lipoxygenase and shown to have pathophysiological roles in respiratory diseases, allergic diseases and cardiovascular diseases, but their role in microbial traversal of the blood-brain barrier has not been explored. Our Preliminary Studies with the receptor antagonists revealed that cysteinyl leukotrienes are likely to be involved in microbial traversal of the blood-brain barrier. The overall aim of this application is to investigate and characterize the host signaling molecules involved in microbial traversal of the blood- brain barrier. The information derived from this application will demonstrate the novel contributions of 5- lipoxygenase and leukotrienes to microbial traversal of the blood-brain barrier.