Insulin-dependent diabetes mellitus induced by subdiabetogenic doses of streptozotocin: obligatory role of cell-mediated autoimmune processes

Low-dose streptozotocin-induced autoimmune diabetes is under the genetic control of the major histocompatibility complex in mice

In mice, an experimental autoimmune diabetes can be induced by multiple injections with low doses of streptozotocin. Since different mouse strains show a varying susceptibility towards this treatment, we have examined whether the experimental autoimmune diabetes is under the genetic control of the major histocompatibility complex (H-2 complex). Mice of five congenic resistant strains, differing in their genome only at the H-2 region, were identically treated on five consecutive days with 40 mg streptozotocin/kg body weight. Genes at the H-2 complex were found to determine the susceptibility towards the diabetogenic effect of streptozotocin: mice of H-2 haplotype k (B10.BR) developed persistent and strong hyperglycaemia (blood glucose approximately 17 mmol/l), mice of strain B10.A (H-2a), C57BL/10 (H-2b) and B10.D2 (H-2d) reacted with moderate hyperglycaemia (between 11.5 and 15.5 mmol/l), whereas mice of strain B10.S (H-2s) were resistant to the diabetogenic effect of low-dose streptozotocin except for a small and transient rise of blood glucose levels. It is concluded that genes within the major histocompatibility complex affect the diabetogenic response to multiple low-dose streptozotocin treatment.

Glycaemic control and suppressor cell activity in patients with insulin-dependent diabetes mellitus

Suppressor cell activity (SCA) in patients with insulin-dependent diabetes mellitus (IDDM), has been found depressed at diagnosis and normal in the remission period. To investigate whether poor metabolic control as seen at diagnosis influences SCA, two groups of patients in poor glycaemic control were examined. Group 1 consisted of nine patients with IDDM of 27±4 months, with a mean glucosuria of 84±19 (s.e.m.) g/24 hr. Group 2 comprised eight patients with newly diagnosed IDDM, examined for the first time 4±1 days after diagnosis, when having a mean glucosuria of 43±14 g/24 hr. After 1 week of hospitalization with strict glycaemic control resulting in a massive reduction of the glucosuria (group 1 now showing 0±0 g/24 hr, group 2, 16±5 g/24 hr), the patients were re-examined. SCA was investigated for the third time after approximately 4 weeks (group 1) and after 5 months (group 2), when the patients were outpatients (glucosuria: group 1, 61±20 g/24 hr; group 2, 17±6 g/24 hr). The suppressive effect of lymphocytes was investigated after incubation with concanavalin A followed by inactivation. Suppression was measured as the ability of the lymphocytes to inhibit ³H-thymidine incorporation in concanavalin A-stimulated normal donor lymphocytes. There were no significant differences in SCA between the first (group 1,25±7; group 2, 22±11) and the second (group 1, 22±8; group 2, 15±5) examination. At the third examination, group 1 patients displayed 35±5, and group 2 patients, now being in the remission period, 44±4. Only the third value of group 2 patients was significantly higher than the second value (P<0·01). SCA of healthy controls were 35±3. It is concluded that short-term effects on SCA of improvement of the glycaemic control are unlikely, at least in patients without severe ketoacidosis. On the other hand, late effects on SCA of good metabolic control, after weeks or months, could not be excluded.

Suppressor cell activity and beta-cell function in insulin-dependent diabetics

Immunological mechanisms may play a role in the pathogenesis of insulin-dependent diabetes mellitus (IDDM), and suppressor cell activity (SCA) has been found depressed at diagnosis. The aim of the present study was to elucidate whether patients with preserved beta-cell function display a different SCA than other patients. Sixteen patients without and 12 patients with beta-cell function after averagely 9 years' duration of IDDM were examined. The suppressive effect of lymphocytes was investigated after incubation with concanavalin A followed by inactivation. Suppression was measured as the ability of the lymphocytes to inhibit 3H-thymidine incorporation in concanavalin A stimulated normal donor lymphocytes. The main findings were: (1) No significant differences in SCA between patients with and without beta-cell function, and one of these patient groups had SCA significantly different from normal controls. (2) A correlation between SCA and administered dose of insulin among patients without beta-cell function. It is concluded that the actual SCA several years after diagnosis is not connected with the beta-cell function in patients with IDDM.

The low dose streptozotocin murine model of type 1 (insulin-dependent) diabetes mellitus: studies in vivo and in vitro of the modulating effect of sex hormones

The influence of sex on pancreatic islet B cell susceptibility to streptozotocin was studied in mice given multiple low doses of streptozotocin. Male C3 D2 F1 mice developed a steadily increasing blood glucose level after a lag period of about 3 weeks, in contrast to females who were resistant. Spleen cells from streptozotocin treated female animals produced hyperglycaemia in total body irradiated syngeneic female recipients, but only if the recipients were treated with testosterone. Testosterone treatment of donors did not affect blood glucose levels of recipients. Streptozotocin cytotoxicity in vitro determined by a 51Cr-release assay revealed an increased sensitivity to streptozotocin in dispersed islet cells from adult male animals as compared with cells from adult female mice. The incubation of islet cells from animals of either sex with testosterone, or oestradiol plus progesterone, did not enhance the susceptibility to streptozotocin. Islet cells from sexually immature male or female mice were less susceptible to streptozotocin. The results demonstrate that sex determines susceptibility to streptozotocin in vivo and in vitro.

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.