A multiplicity of protein antigens in subcellular fractions of rat insulinoma tissue are able to stimulate T cells obtained from non-obese diabetic mice

Enhanced tumorigenicity of insulinoma by X-irradiation of the gastric regions in Sprague-Dawley male rats

BACKGROUND AND AIMS

There has been no suitable animal model for human insulinoma because incidence of pancreatic tumours induced by whole-body irradiation or chemicals has been very low. The purpose of this study was to establish an experimental model with a high incidence of insulinoma. The induction of islet cell tumour by X-irradiation was investigated.

METHODS

Forty Sprague-Dawley male rats were used in this study. Twenty-eight rats were irradiated with two 10-Gy doses to the gastric region at a 3-day interval, and 12 rats not subjected to X-irradiation served as a control group. The rats were killed 16 months after the first irradiation. Expression of insulin mRNA and protein was examined by northern blot analysis and immunohistochemistry, respectively. Rat serum insulin and glucose levels were measured using enzyme-linked immunosorbent assay.

RESULTS

Tumour incidence was 89.3% (25/28) in X-ray group and 8.3% (1/12) in the control group (P < 0.05). Pancreatic tumours, which appeared in all 25 rats with tumours, showed the highest incidence of all neoplasms detected. Tumour cells showed strong immunoreactivity for insulin in 20 of 25 pancreatic tumours (80%). Expression of insulin mRNA was confirmed by northern blot analysis. Furthermore, rats with pancreatic tumours had lower serum glucose levels and higher insulin levels than the control rats.

CONCLUSION

X-irradiated SD rats may be considered a suitable model for insulinoma because of their high tumorigenicity.

Evidence for recognition of novel islet T cell antigens by granule-specific T cell lines from new onset type 1 diabetic patients

Type 1 diabetes is a T cell-mediated autoimmune disease where a number of islet beta-cell target autoantigens have been characterized on the basis of reactivity with autoantibodies. Nevertheless, there remains uncertainty of the nature of another group of autoantigens associated with the secretory granule fraction of islet beta-cells that appear to be targeted predominantly by autoreactive T cells. We have previously characterized CD4+, HLA-DR-restricted T cell lines from new onset type 1 diabetic patients that are specific for the secretory granule fraction of rat tumour insulinoma, RIN. The T cell line from the first patient, HS, proliferates in response to crude microsomal membranes prepared from a recently established, pure human islet beta-cell line NES2Y. In addition, the HS line also responds to secretory granule fractions prepared from a murine tumour insulinoma grown in RIP-Tag mice, showing the recognition of species-conserved antigen(s) in beta-cells. Using partially matched antigen-presenting cells, the HS T cells and another line derived from a second patient, MR, were shown to be restricted by disease-associated DRB1*0101 and DRB1*0404 alleles, respectively. Neither the HS or MR T cell lines proliferate in response to a large panel of candidate islet cell antigens, including insulin, proinsulin, glutamic acid decarboxylase, the protein tyrosine phosphatase IA-2/phogrin, imogen-38, ICA69 or hsp60. Our data provide compelling evidence of the presence of a group of antigens associated with the secretory granule fraction of islet beta-cells recognized by the T cell lines, whose definition may contribute to our knowledge of disease induction as well as to diagnosis.

Prevention of autoimmune diabetes by oral administration of syngeneic pancreatic extract to young NOD mice

Oral administration of relevant autoantigens is being considered as a realistic approach for the prevention of several autoimmune diseases. In this study we administered, orally, to young female NOD/Ak mice (diabetes incidence, 40%) and NOD/LtJ mice (diabetes incidence, 70%) whole pancreatic extract on days 19, 20, 21, 22, 23, 26, and 27 and studied its effects on the development of diabetes until day 250. The cumulative incidence of diabetes in both the colonies after pancreatic extract treatment was compared with the incidence after oral administration of syngeneic liver extract or in untreated mice. In the NOD/Ak mice, the incidence of diabetes in the pancreatic extract group was significantly lower (6%; n = 34, p = 0.004) and was delayed compared with 33% in the liver group (n = 34) and 44% in the untreated group (n = 18). Significant protection from diabetes and a delay in its onset also were observed in the NOD/LtJ mice treated with pancreatic extract (16%; n = 19, p = 0.002) compared with those liver extract treated (72%; n = 18) and in untreated mice (60%; n = 22). Pancreatic histology at day 90 from all the study groups showed that the protection from diabetes in the pancreatic-extract group was not associated with reduced insulitis. We speculate that the marked disease protection observed in this study with orally administered pancreatic extract may be associated with the presence of immunoregulatory cells with a predominant Th2 cytokine bias. Our studies may have implications for the prevention of insulin-dependent diabetes mellitus (IDDM) in humans.

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.

Anti-GAD monoclonal antibody delays the onset of diabetes mellitus in NOD mice

Insulin Dependent Diabetes Mellitus (IDDM type I) is the result of autoimmune destruction of insulin producing pancreatic beta-cells by the cellular immune system, specifically, autoreactive T cells. Disease progression is evident by multiple autoantibodies responding to self-antigens in a cascade mechanism, wherein the first self-antigen induces the activation of the immune system, leading to the destruction of beta-cells and consequently, exposure of other antigens. Glutamic Acid Decarboxylase (GAD) is recognized in the literature as a primary autoantigen involved in the cascade. We questioned the immunological involvement of this autoantigen in the overall progression of the disease, specifically if antigen recognition by the cellular immune system (T cells) is necessary for organ specific autoimmunity and cellular toxicity. We tested this hypothesis by isolating, purifying and injecting monoclonal antibodies against GAD (anti-GAD Ab; 0.1 mg or 0.3 mg) into non-obese diabetic (NOD) mice on a weekly basis. We suggest that the anti-GAD Ab will bind to the GAD antigen, or perhaps bind to the epitope presented in association with APC-MHC and prevent T cell recognition, thereby delaying disease onset. Our results demonstrate a delay in the onset of diabetes and a decrease in the severity of insulitis in our test animals, when compared to controls. The mechanism of action of the anti-GAD Ab may be associated with a passive protection mechanism, as evidenced by the fact that splenocytes transferred from anti-GAD Ab treated mice did not prevent or delay diabetes in syngeneic irradiated NOD mice. The mechanism of diabetes prevention by administration of anti-GAD antibody could be associated with an interference in recognition of GAD by T cells, and continuing research will be perform to investigate this hypothesis.

Analysis of leukocytes recruited to the pancreas by diabetogenic T cell clones

To investigate host leukocytes recruited to the pancreas by diabetogenic T cells, we administered islet-specific CD4(+) T cell clones to 2-week-old nonobese diabetic (NOD) mice and examined the resulting pancreatic infiltrate by flow cytometry. Two different Vbeta4(+)CD4(+) T cell clones, BDC 2.5 and BDC 6.9, were found to recruit a heterogeneous T cell population as determined by staining with a panel of anti-TCR Vbeta monoclonal antibodies. The majority of the diabetes-initiating, Vbeta4(+) T cell clones migrated to the spleen whereas only 5-8% of the T cell population infiltrating the pancreas was Vbeta4(+). Anti-IL-2 receptor staining indicated that fewer than 10% of the total population of infiltrating lymphocytes within the pancreas were in a highly activated state. We have further found that normal splenic T cells from the NOD mouse proliferate poorly to IL-2 in vitro, yet secrete IFN-gamma in response to IL-2 stimulation. These results suggest that the recruited host T cells in our disease transfer system are not directly pathogenic but, rather, are responding to the small numbers of inflammatory T cell clones by providing cytokines that facilitate the disease process.

Development of an I-Ag7-expressing antigen-presenting cell line: intrinsic molecular defect in compact I-Ag7 dimer generation

Insulin-dependent diabetes mellitus (IDDM) results from chronic, T-cell dependent, autoimmune destruction of the insulin-producing beta-cells in the Langerhans' islets of the pancreas. Non-obese diabetic (NOD) mice spontaneously develop IDDM that resembles human type I diabetes. The susceptibility to diabetes in the NOD strain is a complex polygenic trait that determines a phenotype of immune alterations. The unique MHC class II molecule expressed by NOD mice (I-Ag7) plays a major role in the development of disease. Recently, it has been reported that I-Ag7 molecules generate a lower proportion of compact alphabeta heterodimers, compared to other haplotypes. However, it is not clear whether this reflects an intrinsic defect of this molecule to bind peptide stably or is the result of abnormal processing and/or peptide loading into the I-Ag7 molecule. Our aim was to develop and characterize a suitable antigen-presenting cell (APC) that expressed I-Ag7 in the context of a non-diabetes-prone antigen processing and presentation machinery. Here, we report the generation of a mouse DAP.3 fibroblast cell line (DAP.3Ag7) that constitutively expresses high levels of I-Ag7. Using DAP.3 cells transfected with I-Ag7 or I-Ak, we show that the expression of compact dimers in the same cell type is proportionally less for I-Ag7 molecules than for I-Ak molecules, implying an intrinsic defect of the I-Ag7 molecule as the cause for the low generation of compact dimers. However, DAP.3Ag7 cells are able to process and present antigen, as indicated by I-Ag7-dependent IL-2 production by a GAD67-specific NDO T-cell hybridoma after stimulation with GAD and live, but not fixed, DAP.3Ag7 cells. The IL-2 response to GAD when presented by DAP.3Ag7 was significantly higher than the response to GAD presented by NOD splenocytes. Based on these data, we conclude that the low generations of compact dimers is an intrinsic feature of I-Ag7 molecules and not affected by other genes in the NOD background. The DAP.3Ag7 cell line should be a valuable tool with which to dissect the role of the I-Ag7 molecule in antigen presentation and T-cell activation in NOD mice, which clearly contributes to the development of IDDM.

Imogen 38: a novel 38-kD islet mitochondrial autoantigen recognized by T cells from a newly diagnosed type 1 diabetic patient

Cell-mediated autoimmune attack directed against islet proteins of approximately 38 kD in size has been associated with type 1 diabetes. A novel murine cDNA encoding an antigen of this size was cloned using a screening procedure based on the proliferative response of a human diabetic T cell clone (1C6) to a recombinant antigen epitope library. Membrane preparations from COS 7 cells transfected with the full-length 1,267-bp cDNA elicited a proliferative response from the reporter T cells comparable to that of the defined peptide epitope and native insulinoma antigen. In vitro translation and transfection experiments suggested that the protein is initially synthesized as a 44-kD protein and then processed to the native 38-kD form through the proteolytic removal of a 54-aa NH2-terminal mitochondrial targeting sequence. Differential centrifugation, Percoll density gradient centrifugation, and immunofluorescence studies confirmed localization of the antigen to mitochondria. Northern blot, Western blot, and 1C6 T cell proliferation assays showed that, although imogen 38 was more highly expressed in beta cell than alpha cell lines, it was also present in other tissues. It is concluded that imogen 38 may be a target for bystander autoimmune attack in diabetes rather than a primary autoantigen.

T-cell recognition of beta-cell autoantigens in insulin-dependent diabetes mellitus

Autoimmune T cells reactive to beta-cell autoantigens are generally believed to play an essential role in the immune-mediated selective pancreatic islet beta-cell destruction process leading to insulin-dependent diabetes mellitus (IDDM). Many of the supportive data have been obtained from animal models of this disease, but often these data remain to be validated in human IDDM, including the nature of the responsible autoreactive T cells and their targets on the beta cells. In the last few years, however, considerable progress has been made, and several candidate autoantigens have been identified. Diabetogenic T-cell clones have been isolated and characterized in animal models, but for the majority of these clones, the target autoantigen is unknown. In humans, the first islet autoantigens recognized by autoreactive T cells have been defined. This opens the way to designing immunointerventive strategies selective for these T cells and their candidate target antigens, in an attempt to prevent the onset of IDDM. In this review, we described the significance of T lymphocytes for the pathogenic process leading to type 1 diabetes and our studies showing (auto)immune responses by beta-cell-reactive T lymphocytes of newly diagnosed patients.

HLA-DR-restricted T cell lines from newly diagnosed type 1 diabetic patients specific for insulinoma and normal islet beta cell proteins: lack of reactivity to glutamic acid decarboxylase

T cells reacting with pancreatic islet beta cell proteins play a pivotal role in the pathogenesis of type 1 diabetes in experimental animal models and man, although the islet cell autoantigens against which these T cells are directed remain to be characterized. We have previously shown the presence of disease-related antigens residing in the transplantable RIN insulinoma membranes which are recognized by T cells from diabetic NOD mice. We now report on the establishment of CD4+, T cell lines reacting with insulinoma membranes from six newly diagnosed type 1 diabetic patients. Detailed examination of T cell lines from two patients revealed that both the lines continued to react with normal islet cell proteins and, interestingly, were also stimulated by antigens present in brain microsomes. The two T cell lines showed reactivity with different molecular weight proteins of the insulinoma membranes and both the lines were histocompatibility-linked antigen (HLA)-DR restricted. Although the insulinoma membrane preparation is known to contain glutamic acid decarboxylase (GAD), none of the six T cell lines proliferates in response to purified GAD. These T cell lines will be valuable in characterizing novel islet beta cell antigens which are likely to be implicated in type 1 diabetes.

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.

Diabetes enhancement and increased islet antigen expression following neonatal injections of glucose and arginine in non-obese diabetic mice

Modulation of beta-cell antigens at birth may affect the course of type I diabetes. Since the functional state of beta cells modulates antigen expression, we investigated whether neonatal injections of glucose and arginine (G-A) influence diabetes in non-obese diabetic (NOD) mice. Two groups of 90 mice (45 female, 45 male) were injected for the first 6 days of life with G-A or saline. To determine whether these injections influenced beta cell functional maturation, isolated islets were characterized according to insulin response to glucose or arginine. Modulation of antigens for islet-cell autoantibodies (ICA antigens) was analyzed by indirect immunofluorescence using ICA-positive human sera. Variations of pancreatic glutamic acid decarboxylase 67-kD (GAD 67) mRNA were evaluated by polymerase chain reaction (PCR), hybridization with a 32P-labeled probe, and densitometry of the autoradiographic bands. Female NOD mice treated with G-A displayed diabetes earlier and with a higher incidence (P < .01) than control mice, whereas the diabetes incidence was not statistically modified in G-A-treated male NOD mice. Insulitis was more severe (P < .03) in 2-month-old G-A-treated female NOD mice than in control mice, but was not statistically modified in male NOD mice. In both sexes, ICA antigens and GAD 67 mRNA were higher in G-A-treated mice than in control mice (P < .01). Islets isolated after neonatal G-A injections exhibited improved insulin sensitivity to both stimuli (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal injections of cyclosporin enhance autoimmune diabetes in non-obese diabetic mice

Since the modulation of the immune system at birth may influence the course of insulin-dependent (type 1) diabetes, we investigated whether neonatal injections of cyclosporin (CsA) to newborn non-obese diabetic (NOD) mice influence diabetes during later life. Two groups of 90 mice (45 female, 45 male) were injected intraperitoneally for the first 6 days of life with CsA (10 mg/kg per day) or with vehicle. In female NOD mice, the onset of diabetes was earlier and cumulative incidence was higher after neonatal treatment with CsA (P < 0.01). The incidence of diabetes was also dramatically enhanced in male NOD mice (P < 0.01), which normally display a very low disease incidence. Concomitantly, the severity of lymphocytic infiltration of the pancreatic islets was higher in female NOD mice neonatally treated by CsA (P < 0.02), and to a lesser extent in males, than in control mice. After administration of CsA to newborn NOD mice, there was a reduction (P < 0.01) of both CD4+CD8- and CD4-CD8+ thymocytes, whereas the number of double positive CD4+CD8+ thymocytes was increased. Concomitantly, Thy1-2+ cells in spleen were decreased (P < 0.01), and spleen cells expressing either CD3 molecule or alpha beta TCR complex were diminished (P < 0.01). Both CD4+ and CD8+ spleen T cells were depleted. By contrast, the low percentage of gamma delta TCR-expressing splenocytes was not modified. Numbers of MHC class 1+ or MHC class 2+ spleen cells were also depressed (P < 0.01). After neonatal injections of CsA, spleen cells showed a reduced response to concanavalin A (Con A) (P < 0.01). On the contrary, stimulation indices of splenocytes incubated with xenogeneic insulin-producing cell extracts were enhanced (P < 0.03). Proliferation indices of splenocytes to self class 2 antigens, generating suppressor cell activity, during syngeneic mixed lymphocyte reaction (SMLR) were significantly reduced (P < 0.01). Irradiated NOD mice were used as recipients for spleen cells from CsA-neonatally treated NOD mice. They displayed enhanced insulitis 2 weeks after transfer, and diabetes was successfully produced by 1 month after transfer in 50% of the recipients. By contrast, NOD mice which received control syngeneic spleen cells remained normoglycaemic, with only moderate islet infiltration which would be expected of NOD mice of this age. Thus, neonatal injections of CsA markedly enhance diabetes in both female and male NOD mice.(ABSTRACT TRUNCATED AT 400 WORDS)

GAD65 is recognized by T-cells, but not by antibodies from NOD-mice

Since the 64kDa-protein glutamic acid decarboxylase (GAD) is one of the major autoantigens in T-cell mediated Type 1 diabetes, its relevance as a T-cell antigen needs to be clarified. After isolation of splenic T-cells from non-obese diabetic (NOD) mice, a useful model for human Type 1 diabetes, we found that these T-cells proliferate spontaneously when incubated with human GAD65, but only marginally after incubation with GAD67, both recombinated in the baculovirus system. No effect was observed with non-diabetic NOD mice or with T-cells from H-2 identical NON-NOD-H-2g7 control mice. It has been published previously that NOD mice develop autoantibodies against a 64kDa protein detected with mouse beta cells. In immunoprecipitation experiments with sera from the same NOD mice and 35S-methionine-labelled GAD, no autoantibody binding could be detected. We conclude firstly that GAD65 is an important T-cell antigen which is relevant early in the development of Type 1 diabetes and secondly that there is an antigenic epitope in the human GAD65 molecule recognized by NOD T-cells, but not by NOD autoantibodies precipitating conformational epitopes. Our results therefore provide further evidence that GAD65 is a T-cell antigen in NOD mice, being possibly also involved in very early processes leading to the development of human Type 1 diabetes.