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.A causal connection between viral infection and the development of clinical pathology has long been suspected for a number of autoimmune diseases mediated by autoantibodies (reviewed in reference 36). Interestingly, in most cases, several different viruses have been proposed as etiologic agents of the same disease. Experimental data have suggested that viruses trigger an autoimmune humoral response by distinct mechanisms, including polyclonal B-lymphocyte activation, antigenic mimicry, modification of self-antigen, production of anti-idiotypic antibodies, or enhancement of major histocompatibility complex molecule expression on potential antigen-presenting cells (4,9,11,15,20,25,31,37). However, although it has been conclusively shown in several models that autoantibody secretion was triggered by infection, the actual pathogenicity of these antibodies has not always been demonstrated. Similarly, other stimuli, like immunization of mice with rat red blood cells, may lead to autoantibody production without development of the corresponding disease, in this case, hemolytic anemia (8,24,34). Therefore, it may be that mere autoantibody secretion is not sufficient to trigger an autoimmune disease and that the immune environment of the host plays an important role in the pathogenicity of such autoantibodies.Viruses have also been shown to variably affect macrophage functions, including cytokine production and the ability to present antigens (6, 16). Since it is known that some autoantibody-mediated diseases involve phagocytosis by macrophages, we postulated that modulation of this cellular function may explain the induction of such clinical diseases observed in the course of viral infections. To test this hypothesis, we used an experimental model of anemia induced by administration of antierythrocyte monoclonal antibodies (29). Our results indicate that a viral infection with lactate dehydrogenase-elevating virus (LDV) may trigger a dramatic hemolytic disease by enhancing the pathogenicity of autoantibodies. If confirmed with other models, this observation may indicate how different viruses can trigger similar clinical autoimmune diseases and open the way to novel therapeutic approaches. MATERIALS AND METHODSMice. Female BALB/c mice w...

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.

T-lymphocyte subsets were studied in two patient groups: (1) 50 patients with homozygous sickle cell anaemia (SCA) (mean age 12 (range 3-32) years old) in good health at the time of the study who showed no infectious complication. (2) 50 patients (mean age 13 (range 4-29) years old) with normal haemoglobin rate. The global response revealed a significant increase in levels of CD3+ (P=0.04) and CD8+ (P=0.04) cells when compared with the control group, there was no significant difference in levels of CD4+ cells (P=0.05) between the two groups. However, there was a relationship between T-cell subpopulation levels and spleen status. The average values of T-cell subsets (CD4+ and CD8+) in patients with SCA-induced splenic defects (asplenic, splenomegaly or splenectomized patients) were significantly reduced when compared to SCA patients with normal spleens and the control groups. These data show that T-cell activity was reduced in patients with splenic defects. A correlation between splenic status and a perturbed host defence system in patients with SCA suggests that monitoring T-cell subsets might have prognostic value in the course of sickle cell disease.

Viruses are associated with the development of autoantibody-mediated blood autoimmune diseases. A two-step mechanism could explain virus involvement in the development of experimental hemolytic anemia. Immunization of normal mice with rat erythrocytes results in an autoantibody production that could be enhanced by viral infection, without erythrocyte destruction. Inoculation of the same virus when autoantibodies are at high levels triggers clinical anemia. This results from macrophage activation by gamma-interferon, leading to exacerbated erythrophagocytosis. Thus the development of anemia during the course of viral infection may require two independent stimuli, in which the first triggers autoantibody production and the second enhances the pathogenicity of these autoantibodies.