Studies on autoimmunity for initiation of beta-cell destruction. VI. Macrophages essential for development of beta-cell-specific cytotoxic effectors and insulitis in NOD mice

NOD mice were treated with silica (which is selectively toxic to macrophages) from 4 or 20.5 wk of age. Syngeneic neonatal pancreases were transplanted into the renal subcapsular space of the NOD mice at 21 wk of age. Silica treatment was continued until 24 wk of age, and then the mice were killed for examination of islet morphology. Neither the islets in transplanted pancreases nor the host pancreatic islets from the early long-term silica-treated animals revealed insulitis. In contrast, most of the islets in transplanted pancreases from the late short-term silica-treated animals showed severe insulitis and beta-cell necrosis, as did the host islets. A further experiment was performed to compare the effect of late short-term silica treatment with that of anti-L3T4-antibody treatment of the same time and duration. In contrast to the late short-term silica-treated animals, the transplanted pancreases in the anti-L3T4-antibody-treated animals revealed intact islets, although most of the host islets showed insulitis. The control group, which received no treatment but did receive neonatal pancreases, revealed severe insulitis and beta-cell necrosis of both transplanted and host islets. These results suggest that early macrophage depletion can abolish the development of beta-cell-specific immunologic effectors but that late macrophage depletion, after the development of insulitis, does not affect the destruction of beta-cells by preexisting effectors other than macrophages. We conclude that macrophages are essential for the development of beta-cell-specific cytotoxic effectors in the initial phase of insulitis in NOD mice.

Viruses as a triggering factor of type 1 diabetes and genetic markers related to the susceptibility to the virus-associated diabetes

Type 1 diabetes results from the destruction of insulin-producing pancreatic beta cells. Genetic and environmental factors are implicated in the beta cell destruction. As environmental factors affecting the induction of type 1 diabetes, diabetogenic viruses, chemicals, toxins, and diet are likely candidates as either primary injurious agents of beta cells or triggering agents for the induction of autoimmunity. Regarding viruses as a triggering factor of type 1 diabetes, there are at least two different pathogenic mechanisms in virus-induced diabetes: cytolytic infection of beta cells, leading to their destruction, and triggering of autoimmunity, leading to the autoimmune-mediated destruction of beta cells. Since there is no correlation between the induction of antibodies to Coxsackie B viruses and the presence of islet cell autoantibodies in patients with type 1 diabetes, the induction of diabetes by Coxsackie B viruses may be due to cytolytic infection of beta cells rather than an autoimmune response. In contrast, rubella virus and cytomegalovirus (CMV) do appear to be somehow associated with autoimmune type 1 diabetes since there is a strong correlation between the presence of islet cell autoantibodies and persistent infections. Regarding genetic factors, there are distinct markers related to the susceptibility to Coxsackie B4 virus-associated type 1 diabetes and CMV-associated type 1 diabetes. Four specific DNA restriction endonuclease fragments (BamHI-DQ-beta 6.6, TaqI-DR-beta 4.3, TaqI-DR-beta 2.5 and TaqI-DR-beta 1.5 kb) are related to the susceptibility to Coxsackie B4 virus-associated type 1 diabetes while six specific DNA restriction endonuclease fragments (BamHI-DQ-alpha 12.5, -beta 3.7 and -beta 3.2 kb, TaqI-DQ-alpha 7.2, -beta 7.2 and -beta 5.4 kb) are related to the susceptibility to CMV-associated type 1 diabetes.