Immunology of the central nervous system

Immunology of the central nervous system (CNS) is a growing field of study. Until recently the brain was considered an 'immunologically privileged' site. It is increasingly apparent that the CNS has a significant but tightly regulated capability to mount an inflammatory and immune response. This article serves as an introduction to the special section at the start of this issue on neuroimmunology. We also focus on several immunological concepts that are particularly relevant in the context of neuroimmunology-cross-reactivity, the immunological synapse and the nature of the immune response to transplantation in the CNS. We conclude that the fundamental concepts are common to all branches of immunology. Better understanding of the basic mechanisms will blur the borders between the different areas of immunology.