The anatomical and cellular basis of immune surveillance in the central nervous system

In this Review, the authors describe how immune responses are initiated and propagated against antigens found in the central nervous system (CNS). They explain how the unique anatomy of the CNS affects immune surveillance of its tissues, and discuss the implications for autoimmune responses in the CNS. The central nervous system (CNS) comprises the brain, spinal cord, optic nerves and retina, and contains post-mitotic, delicate cells. As the rigid coverings of the CNS render swelling dangerous and destructive, inflammatory reactions must be carefully controlled in CNS tissues. Nevertheless, effector immune responses that protect the host during CNS infection still occur in the CNS. Here, we describe the anatomical and cellular basis of immune surveillance in the CNS, and explain how this shapes the unique immunology of these tissues. The Review focuses principally on insights gained from the study of autoimmune responses in the CNS and to a lesser extent on models of infectious disease. Furthermore, we propose a new model to explain how antigen-specific T cell responses occur in the CNS.