Pancreatic islet cell monolayer cultures: Immunoperoxidase staining and autoradiography

Factors affecting the infection of the D variant of encephalomyocarditis virus in the B cells of C57BL/6J mice

The D variant of encephalomyocarditis virus is capable of infecting most inbred strains of mice. However, only certain strains are susceptible to the diabetogenic effect of this virus. In order to understand why some inbred strains do not become diabetic, the pathogenesis of infection was studied in diabetes-resistant C57BL/6J mice. It was the purpose of the investigation to ascertain whether specific host defense factors might play a crucial role in the mechanism of resistance. To determine whether perturbations of the immune response would alter the resistance of these animals, mice were treated with a high dose (1.15 mmol/kg body weight) of the T- and B-cell toxin cyclophosphamide prior to infection with the D variant. This treatment did not induce overt diabetes or glucose intolerance in the mice tested 7 days after infection. Based on this finding, it appeared likely that resistance to the D variant is conveyed by some factor other than cell-mediated immunity. A likely candidate to control this viral infection is the interferon system. To investigate this possibility, C57BL/6J mice were infected with the D variant and the concentrations of serum interferon titred at various intervals thereafter. In contrast to previous reports with diabetes susceptible mice, C57BL/6J mice were found to generate a substantial interferon response against this variant, with peak levels found in the serum at 24 h following infection. Additional studies were performed in which mice were treated with antibody to mouse interferon alpha/beta at the time of infection and again 3 days after infection with the D variant.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered pathogenesis in encephalomyocarditis virus (D variant)-infected diabetes-susceptible and resistant strains of mice

The D variant of encephalomyocarditis virus (EMCV-D) induces a diabetes mellitus-like disease in male SJL/J mice. Other inbred strains, while resistant to the diabetogenic effect, exhibit strikingly different responses to this virus. In these studies, infection of diabetes resistant C3H mice with the D variant produces massive acute pancreatitis with little apparent direct islet cell involvement. This exocrine tropism is not altered when C3H mice with an inherent macrophage defect are infected, and appears to be a gender-specific phenomenon, with female C3H mice resistant to this exocrine involvement. Long-term infection of both male and female C3H mice does not change their response to the virus. Castration of male C3H mice, using a protocol that has been reported to block the diabetogenic effect of this virus, does not alter the development of this acinar lesion. The B variant of EMCV does not induce acinar destruction, nor is it diabetogenic. However, preinfection with the B variant 3 days prior to infection with the D variant does protect against the development of the exocrine lesion. Coinfection with equal doses of the two variants also protects against this lesion, as does coinfection with a lower dose of B variant. Therefore, the host response that is generated against the B variant appears to be responsible for this protection from D variant exocrine destruction. Due to the short time frame, it is unlikely that this protection is the result of an antibody response. Rather, this data is more consistent with an interferon response generated against the B variant that would inhibit replication of the D variant.

Effects of the rodenticide Vacor on cultured rat pancreatic beta cells

Human ingestion of the rodenticide Vacor has been implicated in the onset of diabetes mellitus. We report here studies of the effects of Vacor on cultured rat pancreatic beta cells and fibroblasts to determine if this agent preferentially intoxicates insulin-producing beta cells. Cytotoxicity in beta cells was monitored both by phase contrast microscopy and the release of insulin into the culture medium. Changes in cellular protein were correlated with morphologic observations to determine fibroblast viability. Beta cells were 10-fold more sensitive to the toxic effects of Vacor than were fibroblasts. Vacor toxicity was reduced by treatment with nicotinamide but was unchanged by 3-O-methyl glucose. Both of these agents reduced the toxic effects of the known beta cell poison streptozotocin. The present studies indicate that Vacor possesses a toxic affinity for pancreatic beta cells and that its mechanism of toxicity may be similar but not identical to that of streptozotocin.