Immunity to self and self-maintenance: a unified theory of brain pathologies.

Although there is a growing acceptance that immune cells could play a protective role under various injurious or pathological conditions of the central nervous system (CNS), the possibility that the immune system is constantly involved in day-to-day maintenance of CNS functional integrity has not been acknowledged. Here, we propose a unifying hypothesis, based on a recent collection of experimental results, suggesting that the loss of immunity to certain self-antigens or its insufficiency when encountering increased levels of risk factors is an important underlying factor in the onset or escalation of neurodegenerative processes, age-related dementia or mental dysfunction. We further suggest a model that explains how immunity to self exerts its roles in the special immune-privileged context of the CNS.