Immunology in the clinic review series; focus on type 1 diabetes and viruses: role of antibodies enhancing the infection with Coxsackievirus-B in the pathogenesis of type 1 diabetes

Abstract

Type 1 diabetes results from an interaction between genetic and environmental factors. Coxsackieviruses B (CV-B) are major environmental candidates, as suggested by epidemiological and experimental studies. The mechanisms leading to the disease involve interactions between the virus, host target tissue (pancreas) and the immune system. The infection of target cells with viruses can be prevented by antibodies. Conversely, the infection can be enhanced by antibodies. The antibody-dependent enhancement (ADE) of infection has been described with various viruses, especially Picornaviruses. In mice infected with CV-B3 this phenomenon resulted in an extended inflammatory reaction and myocarditis. In the human system non-neutralizing antibodies can increase the infection of monocytes with CV-B4 and stimulate the production of interferon (IFN)-α by these cells in vitro. CV-B4/immunoglobulin (Ig)G immune complexes interacted with a specific viral receptor [Coxsackievirus and adenovirus receptor (CAR)] and with IgG Fc fraction receptors (FcγRII and FcγRIII) at the surface of monocytes. The virus-antibody complexes are internalized (CAR) and receptors for the Fc of IgG (FcγRII and FcγRIII). Such antibodies have been detected in patients with type 1 diabetes and they could be responsible for the presence of enteroviral RNA and IFN-α in peripheral blood mononuclear cells (PBMC) of these individuals. The target of enhancing antibodies has been identified as the VP4 protein, which allowed the detection of these antibodies by enzyme-linked immunosorbent assay (ELISA). It cannot be excluded that antibodies enhancing the infection with CV-B may play a role in the pathogenesis of type 1 diabetes, induced or aggravated by these viruses. They can cause a viral escape from the immune response and may participate in the spreading of viruses to β cells. Whether enhancing antibodies raised against VP4 can play a role in iterative homologous and/or heterologous CV-B infections and in the persistence of viruses within the host deserves further study.

Fig. 1

Antibodies enhance the infection with Coxsackievirus-B4 (CV-B4). Antibodies (IgG) bind CV-B4 and the complex interacts with the Coxsackievirus and adenovirus receptor (CAR) and with immunoglobulin (Ig)G Fc fraction receptors (FcγRII and FcγRIII) at the surface of monocytes. The virus–antibody complexes are internalized within the cell and viral RNA is uncoated. Entry of viral RNA stimulates the synthesis of interferon (IFN)-α. Viral RNA and proteins are produced, assembled and viral particles are released. The target of enhancing antibodies is a region of VP4.

Fig. 2

Antibody-dependent enhancement of Coxsackievirus-B (CV-B4) infection and pathogenesis of type 1 diabetes (T1D). Antibodies can enhance the infection of monocytes with CV-B in vitro. Enhancing antibodies and CV-B have been detected in patients with T1D. The presence of CV-B and interferon (IFN)-α in peripheral blood mononuclear cells (PBMC) of patients with T1D can be a result of the antibody-dependent enhancement (ADE) of CV-B infection (a). ADE can play a role in homologous or heterologous repeated infections with CV-B and iterative production of IFN-α that may be associated with the development of autoimmunity (b). Antibodies enhancing the infection of monocytes with CV-B can participate in the spreading of viruses to β cells and can be responsible for a higher viral load which can increase the damage to β cells (c). The infection of β cells with CV-B results in inflammation and innate immune response which is influenced by host genes, followed by a specific immune response with anti-viral cytotoxic T lymphocytes (CTL) that disrupt and clear virus-infected cells contributing to β cell antigen release (d). Innate and adaptive immune response to CV-B can result in the activation of autoreactive CTL directed towards β cells (e). The ADE of CV-B infection can result in the persistence of CV-B in pancreas and/or other organs and, conversely, the persistence of viruses can participate in maintaining the production of enhancing antibodies (f).