Diabetes in the Bio-Breeding/Worcester rat. Induction and acceleration by spleen cell-conditioned media

The role of the intestinal microbiota in type 1 diabetes

The digestive tract hosts trillions of bacteria that interact with the immune system and can influence the balance between pro-inflammatory and regulatory immune responses. Recent studies suggest that alterations in the composition of the intestinal microbiota may be linked with the development of type 1 diabetes (T1D). Data from the biobreeding diabetes prone (BBDP) and the LEW1.WR1 models of T1D support the hypothesis that intestinal bacteria may be involved in early disease mechanisms. The data indicate that cross-talk between the gut microbiota and the innate immune system may be involved in islet destruction. Whether a causal link between intestinal microbiota and T1D exists, the identity of the bacteria and the mechanism whereby they promote the disease remain to be examined. A better understanding of the interplay between microbes and innate immune pathways in early disease stages holds promise for the design of immune interventions and disease prevention in genetically susceptible individuals.

Interleukins increase surface ganglioside expression of pancreatic islet cells in vitro

This experiment was conducted in order to investigate whether expression of gangliosides on islet cell surface in vitro is influenced by cytokines, especially interleukin 1. Islets from adult Lewis rats were incubated with different concentrations of recombinant-derived human cytokines. Following dispase treatment, the single cells were labeled with monoclonal antiganglioside antibodies A2B5 or R2D6, and conjugate. Both are directed against beta cells; A2B5 is recognized to bind specifically to pancreatic islet cells, while R2D6 is shown to bind no other pancreatic cells than beta cells. Surface labeling was evaluated in blind trials using a fluorescence microscope and a fluorescence-activated cell sorter (FACS). A2B5 staining demonstrated a significantly higher number of labeled cells after incubation with interleukin 1 alpha (14.9% +/- 2.8; p less than 0.005), interleukin 1 beta (23.2% +/- 4.2; p less than 0.0005) or TNF alpha (16.1% +/- 4.0; p = 0.005) compared to endotoxin controls (4.1% +/- 1.1). Interleukin 1 beta (9.5% +/- 1.5; p less than 0.005) showed a significantly increased number of R2D6-stained cells (control: 2.3% +/- 1.3). A similar but not significant effect was seen with interleukin 1 alpha and TNF alpha. Interleukin 6 had no effect on the antigen expression. The intensity of labeling was elevated among interleukin 1 beta-incubated cells compared to control samples. Thus, treatment of islets with different cytokines, especially interleukin 1 beta, increases surface antigen expression. We suggest that this mechanism of action in vitro may be of importance for the putative diabetogenic effect of interleukin 1.

Complement-dependent antibody-mediated cytotoxicity in the spontaneously diabetic BB/OK rat: association with beta cell volume density

The present study examined in the spontaneously diabetic BB/OK rat whether a relationship exists between the appearance of complement-dependent antibody-mediated cytotoxicity (C'AMC) in serum and the relative beta cell volume density determined in pancreatic biopsies. C'AMC was estimated by 51Cr release from prelabeled major histocompatibility complex-compatible neonatal rat islet cells after exposure to rat serum and rabbit complement. Fifty-one percent (72/141) of sera from BB/OK rats with newly diagnosed diabetes were positive for C'AMC. At onset of hyperglycemia, insulin-immunoreactive beta cells were only detectable in pancreas biopsies of 25% (10/40) of the BB/OK rats who displayed mild hyperglycemia (plasma glucose 8.3-13.0 mmol/l) and low serum C'AMC. A twofold increase (p less than 0.01) of C'AMC and loss of the remaining beta cells was evident in untreated animals upon their reexamination within 1 week after diagnosis of hyperglycemia. Initiation of insulin therapy prevented neither the increase in C'AMC activity nor the decrease in the beta cell volume density. In contrast, three out of four mildly hyperglycemic BB/OK rats treated with cyclosporin A maintained both their initial C'AMC levels and relative beta cell volume density not only throughout the treatment period (4 weeks) but also for at least 4 weeks thereafter. In one additional animal receiving cyclosporin A no protection of the remaining beta cells could be achieved and C'AMC levels were markedly increased. It is concluded that the appearance of increased C'AMC in serum may reflect autoimmune reactions against the islet beta cells of spontaneously diabetic BB/OK rats. The increase of C'AMC seen in untreated as well as insulin-treated BB/OK rats, which were even devoid of beta cells, suggests that C'AMC activity appears secondary to the loss of beta cells. These results do not support the hypothesis of a direct beta cell destruction via intrainsular complement activation.

Effects of irradiation on diabetes in the BB/Wor rat

Lymphoid irradiation is known to prevent spontaneous autoimmune diabetes in susceptible BB rats. The present studies investigated further the effects of radiation in diabetes prone (DP) and resistant (DR) BB/Wor rats, and histocompatible Yoshida (YOS) rats. Single doses of total body gamma irradiation (125-600 rads) induced diabetes within 22-44 days in 20 of 102 (20%) 30 day old DR rats, less than 1% of which develop the disease. Radiation was also associated with (1) a reduction in the ratio of W3/25+ to OX8+ peripheral blood lymphocytes within 2 weeks, and (2) a decreased percentage of lymph node cells expressing the RT6.1 surface alloantigen 3-4 weeks after treatment. Similar doses of irradiation did not alter the frequency or age at onset of diabetes in DP rats, and did not induce diabetes in YOS rats. When a single dose of 250 or 500 rads of gamma irradiation was followed by injection of mitogen activated spleen cells from acutely diabetic rats to adoptively transfer diabetes, 16 of 19 (84%) DR and 8 of 14 (57%) YOS rats became diabetic. Long term exposure to ultraviolet irradiation (UVB) did not alter the frequency or age at onset of diabetes in either DP or DR rats. We conclude that there may exist a population of regulatory cells relatively sensitive to gamma irradiation that play a role in determining the susceptibility of rats to autoimmune diabetes mellitus.

Immunological aspects of diabetes mellitus: prospects for pharmacological modification

It is now well known that insulin-dependent diabetes is a chronic progressive autoimmune disease. The prolonged prediabetic phase of progressive beta-cell dysfunction is associated with immunological abnormalities. A prediabetic period is suggested by the appearance of islet cell antibodies, anti-insulin antibodies, and anti-insulin receptor antibodies. The existence of activated T lymphocytes and abnormal T cell subsets are also other markers. There is still no concensus about the use of the immunosuppression superimposed upon conventional insulin therapy in early diagnosed IDDM and the follow-up of the relatives of IDDM patients who share the genetic predisposition and serological markers for the risk of future onset of IDDM. Treatment in the prodromal period cannot be justified because a link between the disease and early markers such as ICA has not been established with certainty (Diabetes Research Program NIH, 1983). Many immunopharmacological manipulations were reported to be effective in animal models. However, most of them are not readily applied to human subjects. Moreover, IDDM patients are now believed to be heterogeneous, with a complex genetic background. HLA-DR, and more recently DQ, are closely related to the genetic predisposition to IDDM but those genes are not themselves diabetogenic. The contribution of autoimmunity does not appear to be uniform, and in some cases, the contribution of virus is considered more important. There is a lack of a marker for the future onset of IDDM. ICA and ICSA were found after mumps infection, but the existence of those autoantibodies and even the co-existence of HLA-DR3 do not always indicate the future trend to insulin dependency. More precise markers will be disclosed through the biochemical analysis of the target antigens on pancreatic beta-cell for islet antibodies and effector T cells. Much safer and more effective immunopharmacological treatment will be developed through animal experimentation using rat and mouse models. The recent development and interest in this field will further facilitate the attainment of the goal for the complete prevention of IDDM.

Major histocompatibility complex gene product expression on pancreatic beta cells in acutely diabetic BB rats

Type I diabetes mellitus was induced in young, diabetes-prone BB rats by the passive transfer of concanavalin A-activated T lymphocytes from the spleens of acutely diabetic BB rats. The pancreas of the recipients was examined 1-2 days after the onset of glycosuria by immunocytochemistry by means of monoclonal antibodies for determining whether 1) Class I and/or II major histocompatibility gene complex (MHC) products were expressed on beta cells and 2) the mononuclear cell infiltrates were represented by T cells. Marked expression of Class I MHC gene products was evident on beta cells. In contrast, Class II MHC gene products were not identified on normal-appearing beta cells. Dendritic cells dispersed throughout the acinar and interstitial pancreas were markedly increased in number. The mononuclear cell infiltrate contained few cells (1-15%) recognized by a pan-T cell marker. Although it is possible that this passive transfer model might differ considerably from the spontaneously occurring diabetic state in the rat, this study suggests that 1) Class I, rather than Class II, MHC gene expression may be pivotal to beta-cell injury in diabetic rats, and 2) non-T cells may constitute an effector cell population central to beta-cell necrosis in Type I diabetes mellitus.

Irradiated lymphocytes do not adoptively transfer diabetes or prevent spontaneous disease in the BB/W rat

Diabetes in the BB/W rat is autoimmune in origin, and lymphocytes from acutely diabetic animals activated by concanavalin A (con A) induce the disease in adoptive recipients. We report that irradiation of these cells prevents adoptive transfer of diabetes. Through 60 days of age, diabetes occurred in none of 47 BB/W rats given irradiated con A cells, but in 21 of 36 (58%) given nonirradiated cells. Between 60 and 130 days of age, however, spontaneous diabetes occurred in 18 of 34 untreated control rats (53%) and 16 of 32 rats (50%) given two injections of irradiated con A activated spleen cells. We conclude that irradiation prevents adoptive transfer of BB/W rat diabetes and that irradiated con A activated lymphocytes from acutely diabetic rats do not protect against spontaneous disease in susceptible recipients.