New Concepts in the Immunopathogenesis of CNS Infections

Permission to reprint a book review printed in this section may be obtained only from the reviewer. The notion that the brain is an " im-munoprivileged site " has been a major impediment to understanding the true importance of the immune system in the pathogenesis of CNS infections. In medical school, we learned about the blood-brain barrier, which limits the entry of inflammatory cells and molecules into the CNS, about the low levels of expression of major histocompatibility antigens on CNS cells, and about the absence of resident lymphocytes within the brain parenchyma. Yet few of us learned about the complex nature of immune responses that do occur in response to CNS infections. Not only do lymphocytes from the circulation enter the brain, but the resident cells of the brain upregulate the expression of the major histocompatibility complex and release numerous immune mediators. Although the primary purpose of this orchestrated immune reaction may be to fend off foreign invaders, an untoward consequence may be the injury of neurons and other brain cells. Infections of the brain are widespread, especially in the setting of HIV infection, and they often have devastating, if not life-threatening, consequences. Understanding the complex interplay between specific CNS infectious agents and the immune response is critical if we are to unravel the pathogenesis of CNS infections and develop new strategies to control them. The book under review is an important step in this direction. It is a " state-of-the-art " description of our present knowledge about general features of the immune response in the CNS and about specific features relating to host defense against individual CNS pathogens. In the first part of the book, basic principles of neuroimmunology are reviewed, and there are chapters that focus on the entry of cells into the CNS, the immu-nomodulatory roles of astrocytes and mi-croglia, and the role of cytokines and che-mokines in the host's CNS defense. In the second section of the book, major clinical and experimental CNS infectious syndromes are discussed, including the following: bacterial meningitis, tu-berculous meningitis, neurologic Lyme disease, CNS toxoplasmosis, cryptococcal meningitis, herpes simplex encephalitis, progressive multifocal leukoencephalo-pathy, prion diseases, alphavirus enceph-alomyelitis, and infection with simian immunodeficiency virus, Borna disease virus, or Theiler's virus. In the final two chapters of the book, neurologic diseases of noninfectious etiology are discussed, including multiple sclerosis and neuro-degenerative diseases. This book arose from a meeting in Oc-tober 1999 that brought …