Scientists probe immune system's role in brain function and neurological disease.

EMERGING EVIDENCE SUGGESTS that proteins associated with the immune system may play additional roles in normal brain development and in the healthy adult brain. Studies also suggest that perturbations of these roles may underlie some neurological diseases. Contrary to dogma that the bloodbrain barrier protects the brain from the immune system by acting as a barricade to its components, scientists have found that certain key immune system proteins are, in fact, expressed and active in healthy brains. For instance, a growing body of evidence highlighted at the annual meeting of the Society for Neuroscience in November suggests that proteins of the major histocompatibility complex class 1 (MHC 1), a large family of immune system proteins that mediate the identification and rejection of transplanted organs, help maintain appropriate connections in the developing and adult brain. And a study published in December suggests that the classic complement cascade, the immune system component charged with tagging foreign entities for destruction by phagocytes, plays a crucial role in pruning synapses in the developing brains of mice. These findings not only offer new avenues for understanding the development and molecular machinery of the central nervous system, they also may ult imate ly help scient is ts unravel the hitherto elusive etiologies of some developmental and neurodegenerative diseases. OVERLOOKED The role of various immune system components in the healthy developing and adult central nervous system has long escaped notice in part because scientists believed these molecules were not present, explained Lisa M. Boulanger, PhD, of the University of California-San Diego in an interview.