Bacterial Infections of the Central Nervous System: A Critical Role for Resident Glial Cells in the Initiation and Progression of Inflammation

While bacterial infections of the central nervous system (CNS) constitute a group of serious and often life threatening diseases, the pathophysiology of these diseases remains poorly understood. Resident glia have traditionally been considered to be victim cells during bacterial infections, but it has become increasingly apparent that resident cells of the CNS have the potential to contribute to the initiation and/or progression of inflammatory host responses following bacterial invasion of the brain. Microglia and astrocytes have the ability to perceive bacterial pathogens and assume many of the functions of systemic immune cells following challenge. These responses include the production of large quantities of cytokines and chemokines that can precipitate recruitment of leukocytes into the CNS, and the expression of cell surface molecules that can initiate antigen-specific activation of these immune cells. In this article, we describe the most common clinical manifestations of bacterial infections in the brain and discuss the methods utilized by bacterial pathogens to breach the blood-brain-barrier. Furthermore, we outline the inflammatory responses associated with such infections, and discuss the potential role of resident glial cells in the pathogenesis of bacterially induced CNS disorders.