Multiple low-dose streptozotocin-induced hyperglycemia and insulitis in C57BL mice: influence of inbred background, sex, and thymus.

Insulin-dependent diabetes induced in susceptible strains of mice by multiple, low-dose streptozotocin treatment has been proposed to entail a thymus-dependent, autoimmune destruction of beta cells. In this study, thymectomized and genetically athymic mice have been tested for susceptibility to streptozotocin. Thymectomy was performed on newborn (day 1) to 3-day-old C57BL/KsJ mice. At 8 wk of age, thymectomized and sham-operated mice of both sexes were tested for susceptibility to diabetes induction by multiple, low-dose streptozotocin treatment (35 mg/kg of body weight per day for 6 consecutive days). Thymectomy failed to block susceptibility of males to induction of severe hyperglycemia. Beta cell necrosis and inflammatory cell infiltrates (insulitis) were consistent histopathological features. In general, females-both thymus-intact and thymectomized-were less susceptible than males to streptozotocin-induced hyperglycemia, and females exhibited an equally severe insulitis by experimental day 14; thus, the detection of an underlying insulitis did not predict the development of a more severe hyperglycemia because most streptozotocin-treated females at experimental day 35 continued to show only a modest hyperglycemia (about 200 mg/dl) compared to males (>400 mg/dl). That streptozotocin-induced hyperglycemia could occur in the absence of an intact thymus was further demonstrated in genetically athymic C57BL/6J NIcrOu nu/nu males and thymus-intact +/? littermate controls. C57BL/6J mice were resistant to streptozotocin-induced insulitis. This study shows that the presence of insulitis does not necessarily presage onset of severe hyperglycemia (e.g., C57BL/KsJ females), and conversely, the presence of severe hyperglycemia after low-dose streptozotocin treatment is not necessarily diagnostic of an underlying insulitis (e.g., C57BL/6J +/? and nu/nu males). These data stress the need for caution in the interpretation of studies of streptozotocin-insulitis sensitivities of nude mice.