The effect of ciamexone on lymphocytic thyroiditis and insulin-dependent diabetes mellitus in the BB/Wor rat

Previous studies have suggested that ciamexone, a 2-cyan-aziridine derivative, is a selective immunomodulatory agent with potential therapeutic application in a variety of autoimmune diseases. In the present study, the effects of ciamexone on autoimmune lymphocytic thyroiditis and diabetes mellitus were studied in the BB rat. The data suggest that, in this animal model, ciamexone does not affect the frequency of autoimmune diabetes or lymphocytic thyroiditis nor does it affect the serum TSH or T4 concentrations.

Autoimmune destruction of islets transplanted into RT6-depleted diabetes-resistant BB/Wor rats

We report a novel animal model of islet transplantation that distinguishes recurrence of autoimmunity from allograft rejection. In this study, diabetes-resistant (DR) BB rats, less than 1% of which develop spontaneous diabetes, were made hyperglycemic by either a single injection of streptozocin (STZ) or in vivo immune elimination of a regulatory T-lymphocyte subset that expresses the RT6 alloantigen. DR islet grafts were then transplanted into both groups. DR transplants into STZ-induced diabetic DR rats produced long-term normoglycemia. In contrast, DR transplants into DR rats that had been treated with anti-RT6 monoclonal antibody were all destroyed within an average of 4 days. Allogeneic islets transplanted into both STZ-induced and RT6-depleted diabetic DR rats were rejected within a mean of 3 days. We conclude that failure of DR islet grafts in RT6-depleted diabetic DR BB rats represents recurrent autoimmunity.

The pathogenesis of autoimmune diabetes mellitus

There is increasing evidence that both DP and DR BB rats fail to clonally delete autoreactive T cells in the thymus that are important in the development of autoimmune IDDM. The DP BB rat also has a defect in its ability to generate a regulatory (RT6+) T-cell population that would prevent the onset of diabetes and, therefore, it becomes spontaneously diabetic. The DR rat develops autoreactive T cells, but does not express diabetes because of the concurrent development of a regulatory (RT6+) T-cell population. We suggest that in the BB rat, the initial immunological lesion is orchestrated by an APC in close proximity to pancreatic islet beta cells, and may be specifically directed to the beta cell itself. The release of cytokines in the vicinity of the beta cell destroys this highly susceptible target, causing the release of beta cell 'autoantigens'. These autoantigens, in turn, target autoreactive T cells to the beta cells, allowing a focal destructive process to spread throughout the pancreas. The ultimate destruction of the islets and the development of diabetes result from a cascading effect of this process, with the recruitment of other non-specific immune mediators. A similar process may also be initiated by APC within the thyroid of the rat, resulting in thyroiditis. The fact that the thyrocyte does not die is unexplained, but it could relate to the relative insensitivity of this cell type to various cytokines.

Prevention of diabetes in the BB rat by essential fatty acid deficiency. Relationship between physiological and biochemical changes

Essential fatty acid (EFA) deficiency exerts a striking protective effect in several animal models of autoimmune disease. We now report that EFA deprivation prevents diabetes in the BB rat, an animal model of human insulin-dependent diabetes mellitus. In diabetes-prone (DP)-BB rats, the incidences of spontaneous diabetes and insulitis (the pathological substrate of autoimmune diabetes) were greatly reduced by EFA deficiency. This beneficial effect of the deficiency state was also seen in diabetes-resistant (DR)-BB rats that, after treatment with antibody to eliminate RT6+ T cells, would otherwise have become diabetic. The susceptibility of EFA-deprived DP-BB rats to spontaneous diabetes was restored when they were given dietary supplements of linoleate at 70 d of age (during the usual period of susceptibility), but not when they were repleted beginning at 120 d (after the peak incidence of diabetes). EFA deficiency did lead to growth retardation, but calorically restricted control rats demonstrated that the protective effect of the deficiency state was not a function of decreased weight. To examine the relationship between the biochemical changes of EFA deficiency and its physiological effects in this system, we compared the fatty acid changes that occurred in EFA-deficient animals that did and did not develop diabetes. Nondiabetic animals had significantly lower levels of (n-6) fatty acids (i.e., linoleate and arachidonate) and higher levels of oleate, an (n-9) fatty acid, than did diabetic animals. Levels of 20:3(n-9), the fatty acid that uniquely characterizes EFA deficiency, were similar in both groups, however. Among diabetic EFA-deficient rats, the age at onset of diabetes was found to correlate inversely with the level of (n-6) fatty acids, the least depleted animals becoming diabetic earliest, whereas there was no correlation with levels of 20:3(n-9). Among animals repleted with linoleate beginning at 70 d, restoration of susceptibility to diabetes correlated with normalization of the level of arachidonate. In summary, EFA deprivation reduced the frequency of diabetes in both DP and RT6-depleted DR-BB rats. This protective effect was strongly associated with depletion of (n-6) fatty acids, particularly arachidonate, but not with accumulation of the abnormal 20:3(n-9). Conjecturally, arachidonate and/or a metabolite may play a key role in mediating inflammatory injury in this animal model of autoimmune diabetes.

Morphological and physiological characteristics of pancreas-specific venular permeability induced by Monastral blue B

Leaky blood vessels in the microcirculation can be detected in vivo by injecting an animal with colloidal pigments such as Monastral blue B (MbB) or carbon black. We have previously used the MbB labeling method in the spontaneously diabetic BB/W or rat and detected increased vascular permeability restricted to the venules of the pancreas. We now report the morphological and physiological characteristics of this phenomenon in additional rat strains. Susceptibility to pancreatic labeling with MbB among strains was found to be a highly variable, heritable characteristic, but in no strain did vessels label in any organ other than the pancreas. Pancreatic labeling by MbB was dose dependent, was observed in both inbred and outbred rats, and was not related to major histocompatibility complex haplotype. Enhanced permeability was induced by MbB within minutes of its administration as a result of the formation of gaps between endothelial cells; these gaps then closed within 15 min. Pretreatment with silica or carrageenan, agents known to affect macrophage function, completely blocked pancreatic MbB venular labeling, but the effect was reversible over a period of several days. We hypothesize that presence of MbB in the pancreatic circulation induces organ-specific venular leakage either by a direct effect on pancreatic endothelial cells or via the local release of a mediator.

Plasma from BB/Wor rats increases insulin secretion by perfused rat pancreas

Diabetes-prone (DP) BB rats develop spontaneous autoimmune diabetes mellitus in the context of multiple abnormalities of humoral and cellular immunity. Diabetes-resistant (DR) BB rats have phenotypically normal immune systems and rarely become spontaneously hyperglycemic, but can be rendered diabetic by in vivo immune elimination of T cells that express the RT6 surface alloantigen. To determine if humoral factors in these animals influence beta-cell function, we studied the effect of BB rat plasma on glucose-induced insulin secretion from the isolated perfused rat pancreas. We found that plasma dialyzed to remove molecules less than 14 kD from nondiabetic DR and DP BB rats significantly enhanced total insulin secretion [4806 +/- 711 ng (+/- SEM; n = 6) and 4968 +/- 1235 ng (n = 7), respectively] from perfused pancreata when compared with the effects of either plasma from Wistar-Furth rats (2585 +/- 336 ng; n = 9) or medium containing no plasma (1862 +/- 92 ng; n = 38). The presence of chemically induced diabetes was also associated with enhanced insulin secretion [3276 +/- 414 ng (n = 8) using alloxan and 3956 +/- 470 ng (n = 7) using streptozocin], but the greatest degree of enhancement was observed with plasma from spontaneously diabetic BB rats (6521 +/- 751 ng; n = 17). The enhancement of insulin secretion by BB rat plasma, both diabetic and nondiabetic (DR and DP), was characterized by preservation of first and second phase hormone release. Heat inactivation of acutely diabetic BB rat plasma did not affect its ability to stimulate insulin secretion. We conclude that the plasma of BB rats, both before and after the onset of autoimmune diabetes mellitus, contains a factor other than complement of greater than or equal to 14 kD that enhances insulin secretion in vitro from the isolated perfused pancreas.

Prevention of diabetes in BB/Wor rat by single transfusion of spleen cells. Parameters that affect degree of protection

Previous studies have shown that multiple transfusions of spleen cells from histocompatible nondiabetic donors prevent autoimmune diabetes mellitus in diabetes-prone (DP) BioBreeding/Worcester (BB/Wor) rats. In this study, a single transfusion of greater than or equal to 50 x 10(6) cells from either diabetes-resistant (DR) BB/Wor or Wistar-Furth (WF) rats substantially reduced the incidence of diabetes when given to DP rats 27 or 46 days old but not 61 days old. Transfusion and protection were associated with the appearance of RT6+ donor lymph node cells in recipient rats. In vivo depletion of RT6+ T-lymphocytes in 150-day-old protected animals did not produce diabetes. DR BB/Wor and WF spleen cells were equally efficacious when given either intraperitoneally or intravenously. Mitogen-activated spleen cells were relatively less effective than untreated cells. We conclude that BB rat diabetes can be prevented by one transfusion of spleen cells from histocompatible DR and WF donors, and that the protective effect is dependent on recipient age and cell dose. The effect may be mediated by a population of RT6+ T-lymphocytes that, during a critical developmental period, regulate the expression of autoimmunity in these animals.

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.

Approaches to prevention and treatment of IDDM in animal models

Animal models of insulin-dependent diabetes mellitus (IDDM) provide a uniquely valuable tool for understanding the pathogenesis of this disease. To the extent that they represent the human disease, they permit innovative approaches to its study. Four animal models--the BB rat, the nonobese diabetic mouse, the streptozocin-induced diabetic mouse, and the encephalomyocarditis virus-infected mouse--are reviewed. The salient characteristics of each model and the various techniques and immunotherapeutic agents used in conjunction with them to study prevention and reversal of IDDM are described, particularly the modulatory techniques directed at the cellular cytotoxic system, the regulatory immune system, and the beta-cell.

Role of host immune system in BB/Wor rat. Predisposition to diabetes resides in bone marrow

The role of the immune system in the development of autoimmune diabetes mellitus in the BB/Wor rat was studied with bone marrow transplantation methodology. In the first experiment, diabetes-prone (DP) and diabetes-resistant (DR) BB/Wor rats were irradiated and reconstituted with bone marrow to create both reciprocal (DP donor----DR host; DR donor----DP host) and syngeneic (DR----DR; DP----DP) histocompatible chimeras. Both susceptibility and resistance to subsequent spontaneous diabetes in these chimeras were found to be a function of the type of donor bone marrow transplanted and not the genetic background of the host. In a second experiment, rats from three strains that share the RT1u major histocompatibility complex haplotype of the BB/Wor and rats from three non-RT1u strains were lethally irradiated and reconstituted with DP BB/Wor bone marrow. To rapidly induce diabetes and/or insulitis, they were then injected with mitogen-activated spleen cells from acutely diabetic DP BB/Wor donors, with standard passive-transfer methods. Diabetes and pancreatic insulitis were observed in RT1u recipients, whereas non-RT1u rats developed insulitis but not diabetes. The data suggest that predisposition to spontaneous diabetes in BB rats resides in bone marrow cells.

Speculations on etiology of diabetes mellitus. Tumbler hypothesis

Although clinically useful, the conventional partition of diabetes mellitus into two major classes, insulin dependent and non-insulin dependent, has become obsolete from an etiological standpoint. Contemporary research, particularly that with advanced cellular and molecular methodologies, suggests that the expression of diabetes depends on a wide range of factors. We suggest that the etiology of diabetes has become analogous to the cylinder of a lock containing many tumblers. Each tumbler, e.g., environment, genetics, or cellular interactions, must be aligned before the key can be turned and an understanding of the etiologic process claimed.

Effect of interleukin-2 on diabetes in the BB/Wor rat

Young diabetes prone BB/Wor rats were treated for 4-7 weeks with low dose (1,000 units/week) or high dose (75,000 units/week) recombinant human interleukin-2 (IL-2) and observed through 150 days of age for the development of spontaneous diabetes mellitus. Comparing treated rats with controls, it was found that IL-2 did not affect the cumulative incidence of diabetes, the age at onset of the disease, or peripheral lymphocyte subset numbers. High dose IL-2 administered to diabetes resistant BB/Wor rats also failed to induce the disease.

Depletion of RT6.1+ T lymphocytes induces diabetes in resistant biobreeding/Worcester (BB/W) rats

To investigate the role of RT6+ T cells in the pathogenesis of diabetes in BB/W rats, we treated animals from the diabetes-resistant (DR) subline with anti-RT6.1 lymphocytotoxic mAb. This depleted greater than 95% of peripheral RT6+ T cells but did not substantially reduce levels of circulating T cells or the in vitro response of spleen cells to mitogen. Treatment of 30-d-old DR BB/W rats in this way: induced insulitis and diabetes, rendered nondiabetic RT6-depleted DR rats susceptible to the adoptive transfer of diabetes by spleen cells from acutely diabetic BB/W rats, and yielded DR spleen cell populations capable of the adoptive transfer of diabetes to diabetes-prone (DP) or DR recipients. Treatment of DR rats beginning at 60 d of age failed to produce these effects. These results suggest that both susceptibility and resistance to diabetes in the BB/W rat are in part regulated by the RT6+ T cell subset and provide evidence for the importance of regulatory T lymphocytes in the pathogenesis of autoimmunity and diabetes in BB/W rats.

A pancreatic venular defect in the BB/Wor rat

BB rats develop spontaneous autoimmune diabetes mellitus characterized morphologically by insulitis, an inflammatory lymphocytic infiltration of the islets of Langerhans. To investigate the role of the vascular endothelium of the pancreas in this destructive process, the authors injected diabetes-prone (DP) and diabetes-resistant (DR) BB/Wor rats as well as other nondiabetic strains of rats with Monastral blue B, a colloidal pigment that identifies leaky microvasculature. They found evidence of a venular defect limited to the pancreas that is specific to the BB rat. Light- and electron-microscopic evidence suggests that this defect is due to a population of trapped (marginating) intravascular monocytes, which may be activated by the colloidal pigment and release vasoactive mediators.

Transfusions enriched for W3/25+ helper/inducer T lymphocytes prevent spontaneous diabetes in the BB/W rat

Transfusions of spleen cells are known to prevent spontaneous autoimmune diabetes in susceptible BB/W rats, while T cell-depleted transfusions are ineffective. To characterize further the protective cell(s), we transfused young diabetes prone rats with splenocytes from diabetes resistant BB/W rats that were treated in vitro to enrich them in either OX8+ (suppressor/cytotoxic) T cells or W3/25+ (helper/inducer) T cells. Diabetes subsequently occurred in 19 of 29 (66%) recipients of OX8-enriched, W3/25-depleted cells and 20 of 37 (54%) controls, but in only 7 of 30 (23%) recipients of W3/25-enriched, OX8-depleted cells (p less than 0.005). Transfusion of spleen cells from diabetes resistant donor rats pretreated in vivo to deplete OX8+ cells also prevented diabetes in susceptible BB/W recipients. We conclude that transfusions of W3/25+ helper/inducer splenic T lymphocytes obtained from diabetes resistant animals prevent spontaneous diabetes in the BB/W rat.

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.

Spleen cell transfusion in the Bio-Breeding/Worcester rat. Prevention of diabetes, major histocompatibility complex restriction, and long-term persistence of transfused cells

We report that transfusions of RT1u Wistar-Furth (WF) spleen cells prevented spontaneous diabetes in the RT1u BB/W rat while RT1b Buffalo rat spleen cells did not. In addition, donor origin WF T lymphocytes were detected in nondiabetic-susceptible BB/W recipients 5 mo after transfusion. Survival of donor-origin lymphocytes may provide the cellular mechanism by which major histocompatibility complex-compatible WF spleen cell transfusions prevent BB rat diabetes.

Absence of the RT-6 T cell subset in diabetes-prone BB/W rats

Diabetes-prone Bio-breeding/Worcester (DP) rats exhibit a severe T cell lymphopenia and autoimmune pancreatic insulitis. The present results indicate that the T cell lymphopenia is due in large part, if not entirely, to the absence of the RT-6+ peripheral T cell subset, which includes members of both the helper/inducer (W3/25) and suppressor/cytotoxic (OX 8) antigenic phenotypes. Delineation of the causal mechanism(s) for the selective absence of RT-6+ T cells in DP rats may provide important insights into the cellular basis of the insulin-dependent diabetes mellitus syndrome in these animals.

Absence of the RT-6 T cell subset in diabetes-prone BB/W rats

Diabetes-prone Bio-breeding/Worcester (DP) rats exhibit a severe T cell lymphopenia and autoimmune pancreatic insulitis. The present results indicate that the T cell lymphopenia is due in large part, if not entirely, to the absence of the RT-6+ peripheral T cell subset, which includes members of both the helper/inducer (W3/25) and suppressor/cytotoxic (OX 8) antigenic phenotypes. Delineation of the causal mechanism(s) for the selective absence of RT-6+ T cells in DP rats may provide important insights into the cellular basis of the insulin-dependent diabetes mellitus syndrome in these animals.

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

Injections of media conditioned by concanavalin A-activated spleen cells from acutely diabetic rats accelerated the appearance of diabetes in young Bio-Breeding/Worcester (BB/W) rats. Activity was also found in media conditioned by spleen cells from nondiabetic, W-line Wistar Furth and Buffalo rats. Unconditioned media containing mitogen had no activity. Conditioned media also induced diabetes in resistant W-line BB/W rats but not in Wistar Furth rats. A soluble factor may activate a BB lymphocyte population that promotes diabetes.

Immunology of insulin-dependent diabetes mellitus

We have attempted to illustrate the major trends in research in human IDDM and in the animal models of this disease. We have stressed the utility and importance of the animal models. Their contribution to understanding the human disease is great but the limitations inherent in their use should also be evident. Extrapolation from rodent to human is always treacherous. Nonetheless, the animals still offer great promise in unraveling the pathogenesis of diabetes. The excellent results obtained in BB rats have already led to the use of cyclosporin in human trials. It is clear that we have learned a great deal from diabetic animals and that they have a good deal yet to teach us. Hopefully, an enhanced understanding of the pathogenesis of human insulin-dependent diabetes will follow and lead to preventive and curative therapies that are both safe and effective.

Adoptive transfer of autoimmune diabetes mellitus in biobreeding/Worcester (BB/W) inbred and hybrid rats

Adoptive transfer of diabetes was accomplished by the injection of Con A-activated acutely diabetic BB/W rat spleen cells into immunosuppressed diabetes-resistant BB/W control rats and F1 hybrid offspring produced by BB/W X Lewis, BN, Yashida, and NEDH matings. Immune suppression methods that facilitated adoptive transfer of diabetes included neonatal thymectomy, cyclophosphamide, and splenectomy plus rabbit anti-rat lymphocyte serum injections. The successful transfer of BB/W diabetes to otherwise normal (BB/W X inbred)F1 rats and to diabetes-resistant BB/W animals suggests that antigenically normal pancreatic beta cells were destroyed by the injected effector cells. Diabetes-resistant BB/W control rats also evidenced diabetes after the injection of cyclophosphamide alone. The requirement for immunosuppression suggests that an intact immune system protects against adoptive transfer and diabetes in diabetes-resistant BB/W rats.