Hypothesis: bipolar disorder is an Epstein-Barr virus-driven chronic autoimmune disease - implications for immunotherapy.

Bipolar disorder (BD) is a chronic disease characterised by episodes of major depression and episodes of mania or hypomania, with a worldwide prevalence of 2.4%. The cause of BD is unknown. Here, I propose the hypothesis that BD is a chronic autoimmune disease caused by Epstein-Barr virus (EBV) infection of autoreactive B cells. It is postulated that EBV-infected autoreactive B cells accumulate in the brain where they provide costimulatory survival signals to autoreactive T cells and differentiate into plasma cells producing pathogenic autoantibodies targeting brain components such as the N-methyl-D-aspartate receptor. It is also proposed that the accumulation of EBV-infected autoreactive B cells in the brain is a consequence of a genetically determined defect in the ability of CD8+ T cells to control EBV infection. The theory is supported by studies indicating that autoimmunity, EBV infection and CD8+ T-cell deficiency all have roles in the pathogenesis of BD. According to the hypothesis, BD should be able to be treated by EBV-specific T-cell therapy and to be prevented by vaccination against EBV in early childhood. Exposure to sunlight or appropriate artificial light should also be beneficial in BD by augmenting CD8+ T-cell control of EBV infection.