CD8+ T-Cell Deficiency, Epstein-Barr Virus Infection, Vitamin D Deficiency, and Steps to Autoimmunity: A Unifying Hypothesis

Figure 1

Proposed role of EBV infection in the development of chronic autoimmune diseases. During primary infection EBV infects autoreactive naïve B cells in the tonsil, driving them to enter germinal centres where they proliferate and differentiate into latently infected autoreactive memory B cells (path 1) which then exit from the tonsil and circulate in the blood (path 2). The number of EBV-infected B cells is normally controlled by EBV-specific cytotoxic CD8+ T cells, which kill proliferating and lytically infected B cells, but not if there is a defect in this defence mechanism. Surviving EBV-infected autoreactive memory B cells enter the target organ where they take up residence and produce oligoclonal IgG and pathogenic autoantibodies which attack components of the target organ (path 3). Autoreactive T cells that have been activated in peripheral lymphoid organs by cross-reacting foreign antigens circulate in the blood and enter the target organ where they are reactivated by EBV-infected autoreactive B cells presenting target organ peptides (Tp) bound to major histocompatibility complex (MHC) molecules (path 4). These EBV-infected B cells provide costimulatory survival signals (B7) to the CD28 receptor on the autoreactive T cells and thereby inhibit the activation-induced T-cell apoptosis which normally occurs when autoreactive T cells enter the target organ and interact with nonprofessional antigen-presenting cells (APCs) which do not express B7 costimulatory molecules [168, 169] (Path 6). After the autoreactive T cells have been reactivated by EBV-infected autoreactive B cells, they produce cytokines such as interleukin-2 (IL2), interferon-γ (IFNγ) and tumour necrosis factor-β (TNFβ) and orchestrate an autoimmune attack on the target organ (Path 5). BCR, B cell receptor; TCR, T cell receptor.