Molecular bases of the immune response to neural antigens

Long-standing ideas about the immune response to neural antigens can now be revised. While the brain may be ‘immunologically privileged’, the privilege is not absolute; both immune and autoimmune responses can occur. While the blood-brain barrier contributes to this immunological isolation, other factors are also important. One is the normal absence of products of the major histocompatibility complex (MHC) from neural tissue. Without these cell surface proteins, neural cells are protected from T cell-mediated immune surveillance. MHC expression and modulation in neural tissue, and the implications for understanding and control of the immune response to neural antigens, are reviewed below.