Insulin treatment prevents diabetes mellitus but not thyroiditis in RT6-depleted diabetes resistant BB/Wor rats

100 Years of Insulin: Lifesaver, immune target, and potential remedy for prevention

In this review, we bring our personal experiences to showcase insulin from its breakthrough discovery as a life-saving drug 100 years ago to its uncovering as the autoantigen and potential cause of type 1 diabetes and eventually as an opportunity to prevent autoimmune diabetes. The work covers the birth of insulin to treat patients, which is now 100 years ago, the development of human insulin, insulin analogues, devices, and the way into automated insulin delivery, the realization that insulin is the primary autoimmune target of type 1 diabetes in children, novel approaches of immunotherapy using insulin for immune tolerance induction, the possible limitations of insulin immunotherapy, and an outlook how modern vaccines could remove the need for another 100 years of insulin therapy.

The Effect of DPT-1 Intravenous Insulin Infusion and Daily Subcutaneous Insulin on Endogenous Insulin Secretion and Postprandial Glucose Tolerance

OBJECTIVE

To investigate the effect of parenteral insulin therapy on endogenous insulin secretion in the Diabetes Prevention Trial-Type 1 (DPT-1).

RESEARCH DESIGN AND METHODS

In the parenteral insulin arm of DPT-1, subjects without diabetes at high risk of future type 1 diabetes randomized to active treatment received a yearly 4-day intravenous insulin infusion (IV-I) and daily subcutaneous insulin (SC-I). To examine the effects of these insulin therapies on endogenous insulin secretion, C-peptide and glucose levels were compared during oral glucose tolerance tests (OGTTs) performed on and off IV-I and SC-I. Forty-six paired OGTTs were performed in 30 subjects from DPT-1 to determine the effect of IV-I. Twenty paired OGTTs were performed in 15 subjects from DPT-1 to determine the effect of SC-I.

RESULTS

IV-I suppressed fasting and OGTT-stimulated C-peptide (62% and 40%, respectively), and it significantly lowered fasting glucose (67.4 ± 4.5 mg/dL during IV-I vs. 90.9 ± 1.8 mg/dL off insulin; P < 0.05). By contrast, post-OGTT glucose levels were significantly higher during IV-I: Glucose during IV-I versus off insulin at 120 min was 203.9 ± 15.1 vs. 151.6 ± 10.2 mg/dL, respectively (P < 0.05); 49% of OGTTs became transiently diabetic (>200 mg/dL at 120 min) when receiving IV-I. Fasting glucose was significantly lower when receiving SC-I versus when off insulin (85 ± 3 vs. 94 ± 2 mg/dL, respectively; P < 0.05), but SC-I did not significantly alter fasting or OGTT-stimulated C-peptide compared with being off insulin.

CONCLUSIONS

These data demonstrate that the IV-I used in the DPT-1 markedly suppressed endogenous insulin secretion, which was frequently associated with postprandial glucose intolerance. SC-I, however, did not.

The BB rat as a model of human type 1 diabetes

The BB rat is an important rodent model of human type 1 diabetes (T1D) and has been used to study mechanisms of diabetes pathogenesis as well as to investigate potential intervention therapies for clinical trials. The Diabetes-Prone BB (BBDP) rat spontaneously develops autoimmune T1D between 50 and 90 days of age. The Diabetes-Resistant BB (BBDR) rat has similar diabetes-susceptible genes as the BBDP, but does not become diabetic in viral antibody-free conditions. However, the BBDR rat can be induced to develop T1D in response to certain treatments such as regulatory T cell (T(reg)) depletion, toll-like receptor ligation, or virus infection. These diabetes-inducible rats develop hyperglycemia under well-controlled circumstances and within a short, predictable time frame (14-21 days), thus facilitating their utility for investigations of specific stages of diabetes development. Therefore, these rat strains are invaluable models for studying autoimmune diabetes and the role of environmental factors in its development, of particular importance due to the influx of studies associating virus infection and human T1D.

Insulin treatment in IA-2A-positive relatives of type 1 diabetic patients

AIMS

We examined whether parenteral regular insulin can prevent diabetes in IA-2 antibody-positive (IA-2A+) relatives of type 1 diabetic patients, using a trial protocol that differed substantially from that of the Diabetes Prevention Trial-1.

METHODS

Twenty-five IA-2A+ relatives received regular human insulin twice a day for 36 months, during which time they were followed (median [interquartile range; IQR]: 47 [19-66] months) for glucose tolerance, HbA(1c) and islet autoantibodies, together with 25 IA-2A+ relatives (observation/control group) who fulfilled the same inclusion criteria, but were observed for 52 [27-67] months (P=0.58).

RESULTS

Twelve (48%) insulin-treated relatives and 15 (60%) relatives in the control group developed diabetes. There was no difference in diabetes-free survival between the two groups (P=0.97). Five-year progression (95% confidence interval) was 44% (25-69) in the insulin-treated group and 49% (29-70) in the observation group. At inclusion, progressors tended to have a higher pro-insulin/C-peptide ratio than non-progressors when measured 2 hours after a standardized glucose load (median [IQR]: 2.7% [1.8-4.3] vs. 1.6% [1.1-2.1]; P=0.01). No major hypoglycaemic episodes or significant increases in body mass index or diabetes autoantibodies were observed.

CONCLUSION

Prophylactic injections of regular human insulin were well tolerated, but failed to prevent type 1 diabetes onset in IA-2A+ relatives.

Iodine and tri-iodo-thyronine reduce the incidence of type 1 diabetes mellitus in the autoimmune prone BB rats

Thyroid hormones modulate the immune system and metabolism, influence insulin secretion, and cause decreased glucose tolerance. Thyroid hormones have been described to change the incidence of spontaneous autoimmune thyroiditis in Bio-Breeding/Worcester (BB) rats but it is unknown how these hormones affect the development of type 1 diabetes mellitus (T1DM). The aim was to investigate the influence of changes in thyroid function during postnatal development on the prevalence of T1DM in BB rats and the influence of T3 on the beta cell mass in non-diabetic Wistar rats. BB rats were treated with sodium iodine (NaI) or thyroid stimulating hormone (TSH) neonatally or with tri-iodo-thyronine (T3) during adolescence. At the age of 19 weeks the incidence of T1DM and the degree of insulitis were evaluated. The influence of T3 treatment on the beta cell mass was evaluated in Wistar rats by unbiased stereological methods. The incidence of T1DM in control BB rats was 68% at the age of 19 weeks. NaI and T3 reduced the incidence, whereas TSH had no effect. In Wistar rats T3 treatment increased the beta cell mass per bodyweight. The modulation of thyroid function during postnatal development may thus affect the precipitation of T1DM in genetically susceptible individuals.

Insulin intervention in slowly progressive insulin-dependent (type 1) diabetes mellitus

OBJECTIVE

We tested the hypothesis that insulin therapy rather than sulfonylurea (SU) treatment is preferable to reverse or preserve beta-cell function among patients with slowly progressive insulin-dependent (type 1) diabetes (SPIDDM) or latent autoimmune diabetes in adults.

METHODS

This multicenter, randomized, nonblinded clinical study screened 4089 non-insulin-dependent diabetic patients for glutamic acid decarboxylase autoantibodies (GADAb). Sixty GADAb-positive non-insulin-requiring diabetic patients with a 5-yr duration or shorter of diabetes were assigned to either the SU group (n = 30) or the insulin group (n = 30). Serum C-peptide responses to annual oral glucose tolerance tests were followed up for a mean of 57 months. The primary endpoint was an insulin-dependent state defined by the sum of serum C-peptide values during the oral glucose tolerance test (SigmaC-peptide) less than 4 ng/ml (1.32 nmol/liter).

RESULTS

The progression rate to an insulin-dependent state in the insulin group (three of 30, 10%) was lower than that in the SU group (13 of 30, 43%; P = 0.003, log-rank). Longitudinal analysis demonstrated that SigmaC-peptide values were better preserved in the insulin group than in the SU group. Multiple regression analysis demonstrated that insulin treatment, a preserved C-peptide response, and a low GADAb titer at entry were independent factors in preventing progression to an insulin-dependent state. Subgroup analysis suggested that insulin intervention was highly effective for SPIDDM patients with high GADAb titers [> or =10 U/ml (180 World Health Organization U/ml)] and preserved beta-cell function [SigmaC-peptide > or = 10 ng/ml (3.31 nmol/liter)] at entry. No severe hypoglycemic episodes occurred during the study.

CONCLUSIONS

Insulin intervention to preserve beta-cell function is effective and safe for patients with SPIDDM or latent autoimmune diabetes in adults.

Immunological responses to exogenous insulin

Regardless of purity and origin, therapeutic insulins continue to be immunogenic in humans. However, severe immunological complications occur rarely, and less severe events affect a small minority of patients. Insulin autoantibodies (IAAs) may be detectable in insulin-naive individuals who have a high likelihood of developing type 1 diabetes or in patients who have had viral disorders, have been treated with various drugs, or have autoimmune disorders or paraneoplastic syndromes. This suggests that under certain circumstances, immune tolerance to insulin can be overcome. Factors that can lead to more or less susceptibility to humoral responses to exogenous insulin include the recipient's immune response genes, age, the presence of sufficient circulating autologous insulin, and the site of insulin delivery. Little proof exists, however, that the development of insulin antibodies (IAs) to exogenous insulin therapy affects integrated glucose control, insulin dose requirements, and incidence of hypoglycemia, or contributes to beta-cell failure or to long-term complications of diabetes. Studies in which pregnant women with diabetes were monitored for glycemic control argue against a connection between IAs and fetal risk. Although studies have shown increased levels of immune complexes in patients with diabetic microangiopathic complications, these immune complexes often do not contain insulin or IAs, and insulin administration does not contribute to their formation. The majority of studies have shown no relationship between IAs and diabetic angiopathic complications, including nephropathy, retinopathy, and neuropathy. With the advent of novel insulin formulations and delivery systems, such as insulin pumps and inhaled insulin, examination of these issues is increasingly relevant.

A look to the future: prediction, prevention, and cure including islet transplantation and stem cell therapy

Type 1 diabetes mellitus (T1DM) is characterized by the almost complete absence of insulin secretion, which is secondary to an autoimmune destruction or dysfunction of the insulin-producing cells of the pancreatic islets of Langerhans. Because T1DM is an autoimmune disease with a long preclinical course, the predictive testing of individuals before the clinical onset of the disease has provided a real opportunity for the identification of risk markers and the design of therapeutic intervention. With such a high degree of predictability using a combination of immunologic markers, strategies to prevent T1DM may become possible. A number of novel therapeutic strategies are under investigation in newly diagnosed T1DM patients and might ultimately be applied to prevent T1DM.

Of mice and men: use of animal models to identify possible interventions for the prevention of autoimmune type 1 diabetes in humans

Animal model and clinical studies indicate that type 1 diabetes (T1D) results from T cell-mediated autoimmune destruction of insulin-producing pancreatic beta-cells. This review discusses the knowledge gained from animal models about the nature of the autoreactive T cells that cause T1D and the possible basis for their development. Based on this information, the possible positive and negative aspects of various antigen-specific and non-specific immunotherapies, which could potentially prevent the onset of T1D in at risk individuals, are discussed.

Rat models of type 1 diabetes: genetics, environment, and autoimmunity

For many years, the vast amount of data gathered from analysis of nonobese diabetic (NOD) and congenic NOD mice has eclipsed interest in the rat for the study of type 1 diabetes. The study of rat models has continued, however, and recently there has been a reanimation of interest for several reasons. First, genetic analysis of the rat has accelerated. Ian4L1, cblb, and Iddm4 are now known to play major roles in rat autoimmunity. Second, rats are amenable to study the interactions of genetics and environment that may be critical for disease expression in humans. Environmental perturbants that predictably enhance the expression of rat autoimmune diabetes include viral infection, toll-like receptor ligation, and depletion of regulatory T cell populations. Finally, data generated in the rat have correctly predicted the outcome of several human diabetes prevention trials, notably the failure of nicotinamide and low dose parenteral and oral insulin therapies.

Recessive tolerance to preproinsulin 2 reduces but does not abolish type 1 diabetes

Although autoimmune diseases can be initiated by immunization with a single antigen, it is not clear whether a single self antigen is essential for the initiation and, perhaps, the perpetuation of spontaneous autoimmunity. Some studies have suggested that insulin may represent an essential autoantigen in type 1 diabetes. Here we show that unlike tolerance to glutamic acid decarboxylase, tolerance to transgenically overexpressed preproinsulin 2 substantially reduced the onset and severity of type 1 diabetes in nonobese diabetic mice. However, some mice still developed type 1 diabetes, suggesting that insulin is a key, but not absolutely essential, autoantigen. The results are consistent with the idea that the human IDDM2 locus controls susceptibility to type 1 diabetes by regulating intrathymic preproinsulin expression.

Multicenter prevention trial of slowly progressive type 1 diabetes with small dose of insulin (the Tokyo study): preliminary report

In 1996, we designed a randomized multicenter study to assess the effects of small doses of insulin on beta cell failure in slowly progressive type 1 diabetes (the Tokyo Study). We report here the preliminary results of this study. Glutamic acid decarboxylase 65 antibody (GADA)-positive patients were randomly divided into 2 groups: one group received insulin (Ins group), the other a sulfonylurea (SU group). Fifty-four patients (24 Ins group, 30 SU group) were analyzed at the end of a 4-year period. All patients underwent a 75 g oral-glucose test (O-GTT) every 6-12 months. The insulin-dependent stage was defined based on an integrated value of serum C-peptide levels on O-GTT ( summation operator CPR; sum of CPR at 0, 30, 60, 90, and 120 min) below 4.0 ng/mL. The summation operator CPR in the SU group decreased progressively from 22.0 +/- 10.6 to 11.3 +/- 7.5 ng/mL over the 48-month period (p < 0.001 vs. baseline). The summation operator CPR in the Ins group was unchanged. Among the SU group, 30% of subjects (9/30) progressed to IDDM, while 8.3% of Ins group subjects (2/24) progressed to IDDM (p = 0.087). With regard to the subjects who had a preserved C-peptide response ( summation operator CPR >/= 10 ng/mL), the proportion of SU group subjects who progressed to IDDM was significantly higher than that of the Ins group (7/28, 25% vs. 0/21, 0%, p = 0.015). Among subjects with a high GADA titer (>/=0 U/mL), 9/14 (64.3%) of the SU group, but only 2/16 (12.5%) of the Ins group, developed IDDM (p = 0.0068). As to those with a high GADA titer and a preserved C-peptide response, SU group subjects progressed to IDDM (7/12, 58.3%) more frequently than Ins group subjects (0/14, 0%) (p = 0.0012). In summary, our results suggest that small doses of insulin effectively prevent beta cell failure in slowly progressive type 1 diabetes. We recommend avoiding SU treatment and instead administering insulin to NIDDM patients with high GADA titer.

Cytokine sensitivity of Langerhans' islets of diabetes-prone BB/OK rats under hypoglycemic conditions

Islets of Langerhans isolated from diabetes-prone BB/OK rats were exposed to interleukin-1beta (IL-1beta) or to a combination of tumor necrosis factor-alpha (TNF-alpha) plus interferon-gamma (IFN-gamma) under hypoglycemia at glucose concentrations of 2.2 and 3.2 mmol/l or in the presence of stimulatory conditions at 6.0 and 11 mmol/l glucose. For estimating cytokine effects the islets were functionally assayed by measurement of glucose stimulated insulin secretion. Pancreatic islets exposed for 24 h to IL-1beta at a glucose concentration of 6.0 mmol/l exhibited a reduced insulin secretion following a 48h recovery period compared to islets which were cytokine treated at 2.2 or 3.2mmol/l glucose, respectively. Islets pre-exposed for 24h to TNF-alpha plus IFN-gamma at 2.2, 3.2 or 6.0 mmol/l glucose displayed no alterations of insulin secretion following a 48 h regeneration. A temporary (3 h) influence of IL-1beta under hyperglycemic conditions at 11 mmol/l glucose caused a reduction of the subsequent insulin secretion of Langerhans' islets prior incubated for 24 h at 6.0 mmol/l glucose without cytokines, but not of islets precultured at 2.2 mmol/l glucose. In contrast, a 3 h treatment with TNF-alpha plus IFN-gamma at 11 mmol/l glucose did not affect insulin secretion of islets prior held at 6.0 mmol/l glucose, whereas a transient exposure for 6h to IL-1beta as well as TNF-alpha plus IFN-gamma under similar conditions diminished insulin secretion of islets preincubated at 2.2 or 6.0 mmol/l glucose. In conclusion, hypoglycemia reduces the sensitivity of BB/OK rat islets to IL-1beta, whereas a slight elevation of glucose concentration to 6.0 mmol/l increases again their vulnerability. TNF-alpha plus IFN-gamma at concentrations capable to decrease insulin secretion of islets during hyperglycemia do not affect the insulin output in a range between 2.2 and 6.0 mmol/l glucose. During glucose stimulation at 11 mmol/l islets' insulin secretory machinery is protected from IL-1beta as well as TNF-alpha plus IFN-gamma for 3 h by a preceding 24 h hypoglycemia, but its vulnerability is restored within additional 3 h.

Effects of insulin in relatives of patients with type 1 diabetes mellitus

BACKGROUND

It is unknown whether insulin therapy can delay or prevent diabetes in nondiabetic relatives of patients with diabetes.

METHODS

In a randomized, controlled, nonblinded clinical trial, we screened 84,228 first-degree and second-degree relatives of patients with diabetes for islet-cell antibodies; 3152 tested positive; 2103 of the 3152 underwent genetic, immunologic, and metabolic staging to quantify their risk; 372 of the 2103 had a projected five-year risk of more than 50 percent; 339 of the 372 (median age, 11.2 years) were randomly assigned to undergo either close observation or an intervention that consisted of low-dose subcutaneous ultralente insulin, administered twice daily for a total dose of 0.25 unit per kilogram of body weight per day, plus annual four-day continuous intravenous infusions of insulin. Oral glucose-tolerance tests were performed every six months. Median follow-up was 3.7 years. The primary end point was a diagnosis of diabetes.

RESULTS

Diabetes was diagnosed in 69 subjects in the intervention group and 70 subjects in the observation group. The annualized rate of progression to diabetes was 15.1 percent in the intervention group and 14.6 percent in the observation group. The cumulative incidence of diabetes was similar in the two groups (relative risk in the intervention group as compared with the observation group, 0.96). Most subjects in whom diabetes developed were asymptomatic. Progression to diabetes occurred at a faster rate among subjects with abnormal base-line glucose tolerance (22 percent per year) than among those with normal base-line glucose tolerance (10 percent per year, P<0.001). There were no episodes of severe hypoglycemia. The incidence of chemical hypoglycemia, assessed without ascertainment bias, was similar in the two groups.

CONCLUSIONS

In persons at high risk for diabetes, insulin at the dosage used in this study does not delay or prevent type 1 diabetes.

Insulin intervention to preserve beta cells in slowly progressive insulin-dependent (type 1) diabetes mellitus

Slowly progressive insulin-dependent (type 1) diabetes mellitus (SPIDDM) is characterized by (1) late age of onset, with initial features of NIDDM and subsequent progression to insulin-dependent stage; (2) high predictive value of autoantibodies against glutamic acid decarboxylase (GADAb) and islet cell antibodies (ICA) for progression of beta cell failure; (3) less predominant T cell response, which may attack and eventually destroy beta-cells in affected pancreas. These findings may suggest a rationale for intervention to prevent slowly progressive beta cell dysfunction in this type of diabetes. We identified three independent risk factors for progression of beta cell failure in SPIDDM: (1) sulfonylurea treatment; (2) ICA-positive periods; and (3) initial body weight. We hypothesized that removal of the risk factors for further progression of beta cell dysfunction will have beneficial effects on intervention strategy in treating SPIDDM. In our pilot study, we used a small dose of insulin instead of sulfonylurea in the early stage of treatment of patients with SPIDDM. Insulin-treated SPIDDM patients had a sustained C peptide response (CPR), while most of sulfonylurea-treated patients progressed to an insulin-dependent state. We organized a randomized multicenter clinical trial to study early treatment to prevent the progression of beta cell dysfunction in SPIDDM (the Tokyo Study). It was demonstrated that early intervention with insulin therapy is an effective treatment modality in the early stage of SPIDDM patients who had preserved beta cell function at entry (integrated value of serum C peptide values at 0, 30, 60, 90, and 120 minutes; Sigma CPR >or= 10 ng/mL) and high GADAb (>10 U/mL). Preventive insulin treatment was ineffective in the patients who had diminished insulin reserve at entry (Sigma CPR < 10 ng/mL). Insulin intervention to preserve beta cell dysfunction in SPIDDM is effective and safe in patients with preserved beta cell function and high GADAb titers at the initiation of insulin.

Beta cell rest and recovery--does it bring patients with latent autoimmune diabetes in adults to euglycemia?

Diabetes mellitus in humans is a heterogeneous disorder classified clinically into two main types. The diagnosis of type 1 versus type 2 diabetes is made phenotypically using criteria such as age at onset, abruptness of hyperglycemic symptoms, presence of ketosis, degree of obesity and the perceived need for insulin replacement. The pathogeneses of type 1 and type 2 diabetes are believed to be different. Type 1 diabetes is an autoimmune disease mediated by cellular effector mechanisms; whereas classic type 2 diabetes is not autoimmune but results from insulin resistance and a nonautoimmune insulin secretory defect. Most type 1 diabetes patients are diagnosed in childhood or young adulthood before the age of 35 years. However, there is clearly a subgroup of patients clinically diagnosed with type 2 diabetes who are greater than 35 years of age and have evidence of autoimmunity. The disease of these autoantibody-positive type 2 diabetics is often termed latent autoimmune diabetes in adults (LADA), slowly progressive type 1 diabetes, latent type 1 diabetes, and type 1.5 diabetes. This group of patients comprises approximately 10-15% of Caucasian type 2 diabetes patients. Type 1.5 diabetes patients tend to present with islet cell autoantibodies, islet-reactive T cells, higher HbA(1c) levels, lower C peptide, and a propensity toward insulin dependency compared to autoantibody-negative classic type 2 diabetes subjects.

Insulin-specific tolerance in diabetes

At present it is possible to predict the development of type 1A diabetes (immune-mediated diabetes) in man and prevent the disorder in animals. Studies of immunity to insulin play a prominent role in both disease prediction and disease prevention. For both man and the NOD mouse, insulin autoantibodies usually precede the development of diabetes and can be utilized to assist in disease prediction. T cells clones recognizing insulin, both CD4 and CD8, can transfer disease to young mice or immunodeficient animals. Specific insulin peptides reacting with these clones have been identified, their crystal structure when bound to a human "diabetogenic" MHC allele has been determined, and specific peptides can be used either to induce or to prevent disease. Clinical trials of both insulin and an altered peptide ligand of insulin to prevent islet beta-cell destruction are underway. Insulin is one of a number of islet autoantigens, but it is likely that immune responses to insulin will be central to both pathogenesis and immunologic protection.

Pathophysiology of immune-mediated (type 1) diabetes mellitus: potential for immunotherapy

Type 1 diabetes mellitus is a chronic T cell-mediated disease resulting from autoimmune destruction of pancreatic beta-cells. This process leads to progressive and irreversible failure of insulin secretion. Development of the disease involves both genetic and environmental factors. Genetic predisposition is mainly connected with the human leucocyte antigen (HLA) region, which encodes structures responsible for antigen presentation. A comprehensive molecular understanding of the pathogenesis of the disease is essential for the design of rational and well tolerated means of prevention. This paper describes recent experimental and clinical findings and elucidates the current possibilities for immunotherapy of type 1 diabetes. The nature of breakdown of self-tolerance and the mechanisms involved in its recovery are discussed.

Translating data from animal models into methods for preventing human autoimmune diabetes mellitus: caveat emptor and primum non nocere

Type 1 diabetes in humans is a serious autoimmune disorder of children that is still poorly understood, unpreventable, and irreversible. Study of its animal models, notably the NOD mouse and BB rat, has generated a wealth of information concerning genetics and immunopathogenesis, but that information has still not altered the way in which we treat children with diabetes. In this review we attempt to identify the most promising avenues of continuing research in these models and the most important issues that must be faced by the designers of human therapies based on the animal dataset.

BB rat thymocytes cultured in the presence of islets lose their ability to transfer autoimmune diabetes

Thymocytes from adult BB rats can adoptively transfer autoimmune diabetes to athymic recipients. It is also known that the development of BB rat T-cells is recapitulated in adult thymus organ cultures (ATOCs). Based on these observations, we tested the hypothesis that cells capable of the adoptive transfer of diabetes would be present in long-term ATOCs but could be rendered nondiabetogenic by co-culture with appropriate antigens. We observed that cells recovered from adult diabetes-resistant BB (BBDR) rat thymi cultured for up to 14 days can adoptively transfer disease to athymic WAG-rnu/rnu rats treated with polyinosinic: polycytidylic acid and a monoclonal antibody to preclude development of ART2a+ regulatory T-cells. Co-culture of adult BBDR thymi in the presence of BBDR thyrocytes had no effect on the ability of recovered cells to induce diabetes in 70-80% of adoptive recipients. In contrast, co-culture in the presence of islets prevented transfer of diabetes, on average, in >90% of recipients. Fresh islets, frozen islets, and islets pretreated with streptozotocin to deplete insulin were equally effective in preventing diabetes, but none prevented insulitis in nondiabetic recipients. Co-culture in the presence of islets was not associated with detectable alterations in phenotype or in the secretion of gamma-interferon or interleukin-4, either in cultures or in cells recovered from adoptive recipients. We conclude that islet antigens involved in the initiation of autoimmune diabetes in BB rats may be absent or deficient in BB rat thymi. Exposure of ATOCs to exogenous islets may lead to deletion or anergy of diabetogenic T-cells or to the positive selection of regulatory T-cells.

Levels of Art2+ cells but not soluble Art2 protein correlate with expression of autoimmune diabetes in the BB rat

ART2a and ART2b are isoenzymes expressed on the surface of mature T cells and intraepithelial lymphocytes (IELs) in the rat. They exhibit both adenosine diphosphoribosyltransferase and nicotine adenine dinucleotide (NAD) glycohydrolase activities, and both can generate a transmembrane signal that modulates T cell activation. The presence or absence of ART2+ T cells modulates the expression of autoimmune diabetes in the BB rat. ART2 also circulates in a soluble form whose function is unknown. We tested the hypothesis that circulating ART2 protein regulates the expression of autoimmunity. We compared the kinetics, regulation, and source of soluble ART2 in normal rats and in rats with autoimmune diabetes. Basal levels of soluble ART2 varied greatly among strains of rats and were lowest in the diabetes-prone BB (BBDP/Wor) rat. In diabetes-resistant BB (BBDR/Wor) rats, administration of anti-ART2a antibody, which is known to induce diabetes, resulted in transient clearing of soluble ART2a that was followed rapidly by a rebound increase. Repeated treatment of BBDR/Wor rats with anti-ART2a antibody resulted in sustained supraphysiologic levels of soluble ART2a. Although the number of peripheral ART2a+ T cells is known to correlate with the expression of diabetes in BBDR/Wor rats, the level of soluble ART2a protein did not. The source of the soluble ART2 protein in the rat appeared to be the gut. The results suggest that ART2+ T cells and soluble ART2 protein may subserve different immunomodulatory functions.

GAD65 and insulin B chain peptide (9-23) are not primary autoantigens in the type 1 diabetes syndrome of the BB rat

To investigate whether GAD65 whole molecule, GAD65 p35 or insulin B chain peptide (amino acids 9-23) play an essential role in the pathogenesis of type 1 diabetes in the BioBreeding (BB) rat, we gave serial injections of GAD65, p35 or insulin B chain (9-23) to six groups of BB/Worcester rats. The individual antigens were administered either intrathymically on day 2 and intraperitoneally in MF 59-0 adjuvant 5 times during the first 5 weeks, or by intranasal instillation once neonatally and 5 days/week for the following 6 weeks. Control groups were injected with vehicle only. Age of onset of diabetes and degree of insulitis were not different between controls and antigen-treated rats. Rats that received GAD65 intrathymically and intraperitoneally developed high GAD65-antibody titers without altering diabetes development. In GAD65-treated animals, serum antibodies recognized epitopes at 3 sites on GAD65 in diabetic animals but only at 1 site in non-diabetic animals. GAD65-injected animals also showed a significant reduction of IFN-gamma mRNA expression in the thymus. This study provides evidence against the hypothesis that GAD65 and insulin B chain peptide (9-23) are primary diabetogenic autoantigens in BB rats because immunizations with these antigens and GAD65-induced immune deviation did not alter the development of diabetes.

Human insulin B chain but not A chain decreases the rate of diabetes in BB rats

The autoimmune response seen in insulin-dependent diabetes mellitus (IDDM) includes a humoral immune response against human insulin. Early insulin treatment has been used to prevent IDDM in the rodent models of IDDM, and a prevention trial is underway in humans. The metabolic effects of insulin may not be involved in this prevention since, in NOD mice, the use of metabolically inert human insulin B chain was effective. We wished to ascertain whether immunization of diabetes-prone BB/W rats with insulin B chain, A chain, or both could alter the incidence of diabetes. Immunizations began by 30 days of age and the rats were followed until 120 days of age. Only immunization with insulin B chain plus adjuvant was effective in reducing the rate of diabetes. All immunization frequencies were effective, but a significantly lower rate of diabetes was achieved with injections every week. All of the doses tested resulted in significantly lower rates of diabetes. These data confirm in the BB rat model that immunization with insulin B chain in the presence of adjuvant can reduce diabetes incidence. The absence of any metabolic effect of B chain and the requirement for adjuvant suggest that this effect is mediated via modulation of the autoimmune response.

Mononuclear cytotoxicity and proliferation towards glucose stimulated rodent pancreatic islet cells

Diabetes is due to an autoimmune cellular immunologic destruction of the pancreatic beta cells. By the use of a chromium release assay and a proliferation assay we have investigated the possible role of beta cell activity for this destruction. Results show that in vitro glucose stimulated pancreatic islet cells are subjects to a slight but significantly higher cellular immunologic destruction by mononuclear spleen cells than unstimulated islet cells. The functional dependency of the islet cell destruction must be a product of both a mononuclear cell dysfunction and a specific islet cell pattern. This is due to the fact that all combinations of mononuclear cells and islet cells from diabetes prone BB rats and non-diabetes prone WF rats tested against each other, results in functional dependent cytotoxicity, except for the assay in which both effector cells and target cells are of WF rat origin. Additional observations indicate, that the diabetes prone BB rat mononuclear cells need previous in vivo activation as only cells from diabetic individuals, and not normoglycemic ones, display the reaction in question. Functional dependent cytotoxicity is validated in an other IDDM animal model--the NOD mouse. NOD mononuclear cells towards the murine MIN-6 beta cell line results in increased cellular cytotoxicity when the latter is glucose stimulated. Also the proliferative response of BB rat mononuclear cells to whole islets tend to show function dependency.

Isohormonal therapy of endocrine autoimmunity

For most autoimmune disorders, the site (if any) of chronic immunization required for perpetuation of autoimmunity is unknown. However, one possible site is the target organ itself. If this were the case, feedback regulation of target cell activity might influence autoimmunity. Here, Nanette Schloot and George Eisenbarth review several recent studies suggesting that therapies that inhibit hormonal secretion of target endocrine organs, and/or modulate immunity by therapy with the isohormone, are associated with disease suppression.

Time course of hypothalamic growth hormone-releasing hormone and somatostatin content in streptozocin diabetic rats: evidence for early changes in hypothalamic regulation

Growth hormone secretion is markedly suppressed early in streptozocin induced diabetes mellitus of the rat. Our studies were designed to delineate early changes in hypothalamic regulation by growth hormone-releasing hormone (GHRH) and somatostatin (SS) with the aim of determining the best time period for hypothalamic secretion studies. Although hypothalamic GHRH content (ng/hypothalamus) and SS concentration (ng/mg wet weight) were unchanged at 17 to 20 days in previous studies, we anticipated changes earlier in the time course from transient imbalances in release and synthesis. We examined hypothalamic GHRH content and SS concentration in control, diabetic, and insulin treated diabetic rats (n = 5-13; streptozocin 100 mg/kg i.p.) at 0, 2, 4, 7, 10 and 21 days. In diabetic rats GHRH content was greater at day 2 (142 +/- 9% of control-same day, P < 0.05) and day 4 (139 +/- 17%, P < 0.05), but was less at day 10 (67 +/- 4%, P < 0.01). GHRH content of insulin treated diabetic rats was elevated at day 2 (158 +/- 10%, P < 0.05), but subsequently was unchanged from control. In diabetic rats SS concentration was decreased at day 4 (78 +/- 5%, P < 0.01) and at day 21 (91 +/- 3%, P < 0.05). Our results show earliest changes compared to control in GHRH content at 2 days and in SS concentration at 4 days. These findings support early changes in hypothalamic secretion, define a time period of 1 to 10 days for further studies of release and gene expression, and suggest complex relationships of gene expression, peptide synthesis, and peptide release.

Pancreatic islet beta cells drive T cell-immune responses in the nonobese diabetic mouse model

The role of autoantigens and that of target organs in which tissue lesions develop remains elusive in most spontaneous models of autoimmune diseases. Whether the presence of target autoantigens is required for the recruitment of autoreactive lymphocytes is unknown in most cases. To evaluate the importance of islet cells in the development of autoimmunity in the nonobese diabetic (NOD) mouse, we generated beta cell-deprived mice by injecting a high dose of alloxan, a toxic agent specific for beta cells. In contrast with spleen cells from 6-mo-old naive NOD mice which transfer diabetes in irradiated 8-mo-old male recipients, spleen cells from age-matched NOD mice which received a single injection of alloxan at 3 wk of age did not transfer diabetes. With the exception of the ability to transfer diabetes, beta cell-deprived NOD mice showed maintained immune competence. Furthermore, sialitis developed with the expected intensity and prevalence in beta cell-deprived mice. Already committed "diabetogenic" spleen cells collected from spontaneously diabetic mice also showed a reduced capacity to transfer diabetes after their removal from the diabetic mice and transient "parking" in beta cell-deprived mice. Taken together, our data bring evidence that involvement of autoreactive T cells detected by the capacity to transfer diabetes requires the presence of target beta cells.

Self and non-self antigen in diabetic autoimmunity: molecules and mechanisms

In this article, we have summarized current facts, models and views of the autoimmunity that leads to destruction of insulin-producing beta-cells and consequent Type 1 (insulin-dependent) diabetes mellitus. The presence of strong susceptibility and resistance gene loci distinguishes this condition from other autoimmune disorders, but environmental disease factors must conspire to produce disease. The mapping of most of the genetic risk (or disease resistance) to specific alleles in the major histocompatibility locus (MHC class II) has direct functional implications for our understanding of autoimmunity in diabetes and directly implies that presentation of a likely narrow set of peptides is critical to the development of diabetic autoimmunity. While many core scientific questions remain to be answered, current insight into the disease process is beginning to have direct clinical impact with concerted efforts towards disease prevention or intervention by immunological means. In this process, identification of the critical antigenic epitopes recognized by diabetes-associated T cells has achieved highest priority.

IDDM: an islet or an immune disease?

Insulin-dependent diabetes develops as a consequence of the selective destruction of insulin-producing cells by an autoimmune reaction. However, the precise series of events which trigger anti-islet autoreactive T cells is still being investigated. Major issues will need to be raised before a comprehensive view of the anti-islet autoimmune reaction can be delineated. These include defining the primary site of activation of autoreactive lymphocytes and exploring hypotheses to explain the chronicity of the diabetes process. These issues all relate with the more general dilemma of the actual role of the islets of Langerhans in breaking self tolerance to beta-cell antigens. By studying non-obese diabetic mice deprived of beta cells following a single injection of a high dose of alloxan at 3 weeks of age, we recently obtained evidence that the activation of autoreactive T cells requires the presence of target islet cells in order to develop.

T-cell autoimmunity in type 1 diabetes mellitus

Insulin dependent diabetes mellitus is a T-cell mediated autoimmune disease. Several beta-cell antigens, mostly non-tissue-specific, have been implicated in the disease process. The antigens and the autoimmune T cells exist in healthy individuals, as do many of the genes required for the development of diabetes. The question, then, is why and how exposure to undefined environmental agents activates an existing autoimmune potential and directs it to damage the beta cells.

Tolbutamide reduces the incidence of diabetes mellitus, but not insulitis, in the non-obese-diabetic mouse

The functional state of beta cells may influence the rate of their destruction in Type 1 (insulin-dependent) diabetes mellitus. We examined the effect of diazoxide, which inhibits insulin secretion, or tolbutamide, which stimulates insulin secretion, upon the incidence of diabetes in the non-obese-diabetic (NOD) mouse. Female mice were treated from 3-30 weeks of age with diet containing diazoxide 250 mg.kg-1 or tolbutamide 125 mg.kg-1. The cumulative incidence of diabetes at 35 weeks was similar in the diazoxide (16 of 24) and control (18 of 24) groups, but reduced in the tolbutamide group (10 of 23, p < 0.04 vs control group). In a second experiment, treatment was started from 9 weeks of age, by which time insulitis is already present. The cumulative incidence of diabetes at 35 weeks was 16 of 24 in controls, 15 of 24 on diazoxide and 11 of 24 on tolbutamide (p = NS vs control). A third experiment compared the effect of treatment from 3 weeks with control diet or diet containing tolbutamide 125 mg.kg-1 or 500 mg.kg-1. Diabetes was reduced by tolbutamide treatment, with a cumulative incidence of 25 of 31 in controls, 18 of 30 on tolbutamide 125 mg.kg-1 (p < 0.04) and 14 of 32 on 500 mg.kg-1 (p < 0.002), although the difference between the two treatment groups failed to reach statistical significance. A fourth experiment showed that treatment from 3-12 weeks with diazoxide 1000 mg.kg-1 increased the extent of insulitis compared with controls and animals treated with tolbutamide 500 mg.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)