Influence of viral infection on anti-erythrocyte autoantibody response after immunization of mice with rat red blood cells

Implications of infectious agents on results of animal experiments

Report of the Working Group on Hygiene of the Gesellschaft für Versuchstierkunde–Society for Laboratory Animal Science (GV-SOLAS)

GV-SOLAS Working Group on Hygiene: Werner Nicklas (Chairman), Felix R. Homberger, Brunhilde Illgen-Wilcke, Karin Jacobi, Volker Kraft, Ivo Kunstyr, Michael Mähler, Herbert Meyer & Gabi Pohlmeyer-Esch

Enhancement of autoantibody pathogenicity by viral infections in mouse models of anemia and thrombocytopenia

Viral infections are involved in the pathogenesis of blood autoimmune diseases such as hemolytic anemia and thrombocytopenia. Although antigenic mimicry has been proposed as a major mechanism by which viruses could trigger the development of such diseases, it is not easy to understand how widely different viruses might induce these blood autoimmune diseases by this sole mechanism. In mice infected with lactate dehydrogenase-elevating virus (LDV), or mouse hepatitis virus, and treated with anti-erythrocyte or anti-platelet monoclonal autoantibodies at a dose insufficient to induce clinical disease by themselves, the infection sharply enhances the pathogenicity of autoantibodies, leading to severe anemia or thrombocytopenia. This effect is observed only with antibodies that induce disease through phagocytosis. Moreover, the phagocytic activity of macrophages from infected mice is increased and the enhancing effect of infection on autoantibody-mediated pathogenicity is strongly suppressed by treatment of mice with clodronate-containing liposomes. Finally, the disease induced by LDV after administration of autoantibodies is largely suppressed in animals deficient for gamma-interferon receptor. Together, these observations suggest that viruses may trigger autoantibody-mediated anemia or thrombocytopenia by activating macrophages through gamma-interferon production, a mechanism that may account for the pathogenic similarities of multiple infectious agents.

Protective role of infections and vaccinations on autoimmune diseases

Infectious agents may induce autoimmune disease through several mechanisms, notably antigen mimicry and inflammation of the target organ; conversely, infections may protect from autoimmune diseases. This paradoxical effect has been demonstrated for a number of bacteria, viruses and parasites on a variety of spontaneous or experimentally induced animal models of autoimmune diseases (e.g. experimental allergic encephalomyelitis, lupus mice, non-obese diabetic mice). The mechanisms of the protection are still ill-defined, and probably vary according to models. Stimulation of immunoregulatory CD4 T cells has been shown to play a central role in several major models. The role of superantigens is also important, like that of Toll-like receptors. Antigen competition is another major mechanism, itself open to several interpretations. Epidemiological data support a protective role of infections on human allergic and autoimmune diseases. These diseases are much more common in countries with high socio-economic development (typically Northern countries in Europe). The reason for this cannot be fully explained by genetic differences because migrating populations develop these diseases with the same incidence of the adoptive country rather than that of the country of origin. It is interesting that the frequency of these diseases has been increasing in developed countries over the last 20 years but not in undeveloped ones.

Exacerbation of autoantibody-mediated hemolytic anemia by viral infection

Strong enhancement of the pathogenicity of an antierythrocyte monoclonal antibody was observed after infection of mice with lactate dehydrogenase-elevating virus. While injection of the antierythrocyte antibody alone induced only moderate anemia, concomitant infection with this virus, which is harmless in most normal mice, led to a dramatic drop in the hematocrit and to death of infected animals. In vitro and in vivo analyses showed a dramatic increase in the ability of macrophages from infected mice to phagocytose antibody-coated erythrocytes. These results indicate that viruses can trigger the onset of autoimmune disease by enhancing the pathogenicity of autoantibodies. They may explain how unrelated viruses could be implicated in the etiology of autoantibody-mediated autoimmune diseases.

Regulation of immune complexes during infection of mice with lactate dehydrogenase-elevating virus: studies with interferon-gamma gene knockout and tolerant mice

Mice persistently infected with lactate dehydrogenase-elevating virus (LDV) develop circulating IgG-containing hydrophobic immune complexes, with a molecular mass of 150 to 300 kd, which bind to the surfaces of high-capacity enzyme-linked immunosorbent assay (ELISA) plates. LDV infection also stimulates polyclonal B-cell activation and autoimmunity. For this study, interferon-gamma gene knockout (GKO) mice were utilized to study circulating immune complexes and other parameters of LDV infection. The kinetics of LDV viremia, formation of plasma IgG anti-LDV antibodies, and LDV replication in the spleen and liver were essentially normal in GKO mice. Polyclonal activation of B cells, as reflected by increased total plasma IgG concentration during LDV infection, was found to be intact in GKO mice, although at a lower magnitude than in control mice. The plasma concentration of IgG-containing hydrophobic immune complexes was reduced about 75% in LDV-infected GKO mice relative to normal LDV-infected controls. Allogeneic tissue responses were also found to be reduced in LDV-infected GKO mice relative to those in normal LDV-infected controls. These results dissociate specific anti-LDV immunity from formation of hydrophobic immune complexes, show that the IgG anti-LDV response as well as LDV replication in the spleen and liver are insensitive to physiological levels of interferon (IFN)-gamma, and suggest that IgG-containing immune complexes stimulated by LDV infection are a marker for autoimmunity.

Association of viral load in plasma samples of HIV-infected hemophilia patients with autoantibodies and gp120-containing immune complexes on CD4+ lymphocytes

OBJECTIVE

We investigated whether the induction of antilymphocyte autoantibodies and immune complexes is associated with the activity of HIV replication.

METHODS

Viral HIV-1 RNA was measured in the plasma samples of 84 HIV+ hemophilia patients and correlated with the IgM, IgG, IgM/IgG and IgM/IgG/gp120 load of circulating CD4+ lymphocytes, CD4+ and CD8+ cell counts, plasma neopterin levels and in vitro T-cell responses to mitogens and pooled allogeneic stimulator cells.

RESULTS

Compared to patients with no immune complexes, on circulating CD4+ lymphocytes, viral load was increased in patients with IgM, IgM/IgG or IgM/IgG/gp120 complexes. Sequential analysis of HIV+ patients showed that peaks of retroviral activity were associated with the subsequent formation of CD4+ lymphocyte-reactive IgM and IgG autoantibodies and gp120-containing immune complexes.

CONCLUSION

The induction of autoantibodies and immune complexes attached to CD4+ lymphocytes is associated with periods of increased viral activity in HIV-infected patients.

IgG subclasses of canine anti-erythrocyte, antinuclear and anti-thyroglobulin autoantibodies

A panel of monoclonal antibodies (mAbs) reactive with the four canine IgG subclasses (IgG1, IgG2, IgG3 and IgG4) was used to investigate the activity of IgG subclasses in autoimmune responses to erythrocytes, nuclear antigens and thyroglobulin in dogs with autoimmune disease. mAbs specific for canine IgG1 and IgG4 were able to agglutinate normal dog erythrocytes coated with purified canine IgG containing each of the four subclasses. IgG1 autoantibodies were demonstrated on the surface of erythrocytes from seven dogs with Coombs'-positive autoimmune haemolytic anaemia and IgG4 autoantibodies were also present in two of these cases. Serum antinuclear antibody was shown in nine dogs to be predominantly of IgG1, IgG3 and IgG4 subclasses with only one of the dogs also producing an IgG2 antinuclear antibody. The IgG subclass profile of antinuclear antibodies differed between dogs with polyarthritis and dogs with other systemic disease. In six dogs with hypothyroidism, thyroglobulin autoantibodies of subclasses, IgG1, IgG2 and IgG4 predominated, but one dog also produced significant levels of IgG3 thyroglobulin autoantibodies. The mAbs are widely applicable to the study of the pathogenesis of canine autoimmune disease.

Quantitation of erythrocyte-bound IgG subclass autoantibodies in murine autoimmune haemolytic anaemia

A quantitative and sensitive cellular enzyme-linked immunosorbent assay was developed for determining the number of molecules of IgG of each subclass bound to the surface of murine red blood cells (RBC). To develop standard titration curves, RBC from normal mice were treated with tannic acid and coated with a known concentration of purified myeloma of each IgG subclass. The quantity of each subclass bound to the surface of erythrocytes was determined by calculating the protein concentration of the bound IgG, which was then converted into number of molecules of IgG/RBC. The assay was used to quantify the number of autoantibodies of all four IgG subclass bound to the erythrocytes of mice injected with rat RBC. Twenty one days after the first immunisation, a mean number of 84,000 molecules of IgG1/RBC were detected, which increased to 114,500 molecules/RBC on day 28. On days 56 and 96 the mean concentration of IgG1 remained high, however by day 110 the mean level of IgG1 had decreased slighty to 69,500 molecules/RBC. By contrast, the mean concentration of IgG2a autoantibodies was considerably lower throughout the experiment, starting at 40,200 molecules/RBC on day 21 and dropping to 2,500 molecules/RBC by day 110. The mean quantities of IgG2b and IgG3 autoantibodies were similar to each other, and intermediate between the levels of IgG1 and IgG2a autoantibodies.