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

The β-Cell in Type 1 Diabetes Pathogenesis: A Victim of Circumstances or an Instigator of Tragic Events?

Recent reports have revived interest in the active role that β-cells may play in type 1 diabetes pathogenesis at different stages of disease. In some studies, investigators suggested an initiating role and proposed that type 1 diabetes may be primarily a disease of β-cells and only secondarily a disease of autoimmunity. This scenario is possible and invites the search for environmental triggers damaging β-cells. Another major contribution of β-cells may be to amplify autoimmune vulnerability and to eventually drive it into an intrinsic, self-detrimental state that turns the T cell-mediated homicide into a β-cell suicide. On the other hand, protective mechanisms are also mounted by β-cells and may provide novel therapeutic targets to combine immunomodulatory and β-cell protective agents. This integrated view of autoimmunity as a disease of T-cell/β-cell cross talk will ultimately advance our understanding of type 1 diabetes pathogenesis and improve our chances of preventing or reversing disease progression.

Tet2 Controls the Responses of β cells to Inflammation in Autoimmune Diabetes

β cells may participate and contribute to their own demise during Type 1 diabetes (T1D). Here we report a role of their expression of Tet2 in regulating immune killing. Tet2 is induced in murine and human β cells with inflammation but its expression is reduced in surviving β cells. Tet2-KO mice that receive WT bone marrow transplants develop insulitis but not diabetes and islet infiltrates do not eliminate β cells even though immune cells from the mice can transfer diabetes to NOD/scid recipients. Tet2-KO recipients are protected from transfer of disease by diabetogenic immune cells.Tet2-KO β cells show reduced expression of IFNγ-induced inflammatory genes that are needed to activate diabetogenic T cells. Here we show that Tet2 regulates pathologic interactions between β cells and immune cells and controls damaging inflammatory pathways. Our data suggests that eliminating TET2 in β cells may reduce activating pathologic immune cells and killing of β cells.

Mechanisms of diabetic autoimmunity: I--the inductive interface between islets and the immune system at onset of inflammation

The mechanisms of autoimmune reactivity onset in type 1 diabetes (T1D) remain elusive despite extensive experimentation and discussion. We reconsider several key aspects of the early stages of autoimmunity at four levels: islets, pancreatic lymph nodes, thymic function and peripheral immune homeostasis. Antigen presentation is the islets and has the capacity to provoke immune sensitization, either in the process of physiological neonatal β cell apoptosis or as a consequence of cytolytic activity of self-reactive thymocytes that escaped negative regulation. Diabetogenic effectors are efficiently expanded in both the islets and the lymph nodes under conditions of empty lymphoid niches during a period of time coinciding with a synchronized wave of β cell apoptosis surrounding weaning. A major drive of effector cell activation and expansion is inherent peripheral lymphopenia characteristic of neonates, though it remains unclear when is autoimmunity triggered in subjects displaying hyperglycemia in late adolescence. Our analysis suggests that T1D evolves through coordinated activity of multiple physiological mechanisms of stimulation within specific characteristics of the neonate immune system.

Mechanisms of diabetic autoimmunity: II--Is diabetes a central or peripheral disorder of effector and regulatory cells?

Two competing hypotheses aiming to explain the onset of autoimmune reactions are discussed in the context of genetic and environmental predisposition to type 1 diabetes (T1D). The first hypothesis has evolved along characterization of the mechanisms of self-discrimination and attributes diabetic autoimmunity to escape of reactive T cells from central regulation in the thymus. The second considers frequent occurrence of autoimmune reactions within the immune homunculus, which are adequately suppressed by regulatory T cells originating from the thymus, and occasionally, insufficient suppression results in autoimmunity. Besides thymic dysfunction, deregulation of both effector and suppressor cells can in fact result from homeostatic aberrations at the peripheral level during initial stages of evolution of adaptive immunity. Pathogenic cells sensitized in the islets are efficiently expanded in the target tissue and pancreatic lymph nodes of lymphopenic neonates. In parallel, the same mechanisms of peripheral sensitization contribute to tolerization through education of naïve/effector T cells and expansion of regulatory T cells. Experimental evidence presented for each individual mechanism implies that T1D may result from a primary effector or suppressor immune abnormality. Disturbed self-tolerance leading to T1D may well result from peripheral deregulation of innate and adaptive immunity, with variable contribution of central thymic dysfunction.

Glia-neuron interactions in the mammalian retina

The mammalian retina provides an excellent opportunity to study glia-neuron interactions and the interactions of glia with blood vessels. Three main types of glial cells are found in the mammalian retina that serve to maintain retinal homeostasis: astrocytes, Müller cells and resident microglia. Müller cells, astrocytes and microglia not only provide structural support but they are also involved in metabolism, the phagocytosis of neuronal debris, the release of certain transmitters and trophic factors and K(+) uptake. Astrocytes are mostly located in the nerve fibre layer and they accompany the blood vessels in the inner nuclear layer. Indeed, like Müller cells, astrocytic processes cover the blood vessels forming the retinal blood barrier and they fulfil a significant role in ion homeostasis. Among other activities, microglia can be stimulated to fulfil a macrophage function, as well as to interact with other glial cells and neurons by secreting growth factors. This review summarizes the main functional relationships between retinal glial cells and neurons, presenting a general picture of the retina recently modified based on experimental observations. The preferential involvement of the distinct glia cells in terms of the activity in the retina is discussed, for example, while Müller cells may serve as progenitors of retinal neurons, astrocytes and microglia are responsible for synaptic pruning. Since different types of glia participate together in certain activities in the retina, it is imperative to explore the order of redundancy and to explore the heterogeneity among these cells. Recent studies revealed the association of glia cell heterogeneity with specific functions. Finally, the neuroprotective effects of glia on photoreceptors and ganglion cells under normal and adverse conditions will also be explored.

Potential role of IL-17-producing iNKT cells in type 1 diabetes

We explored in this study the status and potential role of IL-17-producing iNKT cells (iNKT17) in type 1 diabetes (T1D) by analyzing these cells in patients with T1D, and in NOD mice, a mouse model for T1D. Our analysis in mice showed an increase of iNKT17 cells in NOD vs control C57BL/6 mice, partly due to a better survival of these cells in the periphery. We also found a higher frequency of these cells in autoimmune-targeted organs with the occurrence of diabetes, suggesting their implication in the disease development. In humans, though absent in fresh PMBCs, iNKT17 cells are detected in vitro with a higher frequency in T1D patients compared to control subjects in the presence of the proinflammatory cytokine IL-1β, known to contribute to diabetes occurrence. These IL-1β-stimulated iNKT cells from T1D patients keep their potential to produce IFN-γ, a cytokine that drives islet β-cell destruction, but not IL-4, with a reverse picture observed in healthy volunteers. On the whole, our results argue in favour of a potential role of IL-17-producing iNKT cells in T1D and suggest that inflammation in T1D patients could induce a Th1/Th17 cytokine secretion profile in iNKT cells promoting disease development.

Estrogen treatment predisposes to severe and persistent vaginal candidiasis in diabetic mice

Background

Increased levels of estrogen and diabetes mellitus separately predispose to vaginal candidiasis (VC). However, the compounding effect of estrogen on the severity and persistence of VC in diabetic females is not clear.

Methods

To address this issue, a diabetic mouse model with estrogen-maintained VC was developed and evaluated for vaginal fungal burden (VFB) and immune competence at different time points throughout the study period.

Results

Blood glucose levels in estrogen-treated diabetic mice were consistently lower than that in untreated counterparts. Estrogen-treated C. albicans-infected non-diabetic mice experienced persistent episodes of VC as compared with naïve controls (P < 0.01). However, severity and persistence of VC in estrogen-treated C. albicans-infected diabetic mice was significantly greater than that in non-diabetic counterparts (P < 0.05). Mortality rates among estrogen-treated C. albicans-infected diabetic mice were significantly higher (P < 0.05) than that in non-diabetic counterparts. Statistically significant (P < 0.05) and persistent suppression of the delayed hypersensitivity response (DTH) was evident in estrogen-treated C. albicans-infected diabetic and non-diabetic mice as compared with controls. Levels of expression of the inhibitory molecule CD152 on vaginal and splenic T cells isolated from estrogen-treated C. albicans infected mice was significantly higher than that in naive untreated controls (P < 0.01).

Conclusions

These findings suggest that estrogen treatment in diabetic females may protect against the progression of DM on the one hand and predispose to severe and persistent VC on the other. The later outcome could be related to the immunosuppressed status of the host.

T-lymphocyte recognition of beta cells in type 1 diabetes: clinical perspectives

Type 1 diabetes (T1D) is an autoimmune disease characterized by the activation of lymphocytes against pancreatic β cells. Landmarks in the history of T1D were the description of insulitis and of islet cell autoantibodies, and report an association between T1D and a limited number of HLA alleles. Another step was the study of T-lymphocytes, now known to be central to the disease process of T1D whether in mice or men. In humans, T-lymphocytes, and especially CD8⁺ T-cells, are predominant in insulitis. The characterization of antigenic fragments--peptides--recognized by T-cells paves the way towards new assays for predicting T1D and its prevention using antigen- or peptide-specific immunotherapy, while avoiding side effects that may counteract the limited efficacy of immunosuppression and immunomodulation in preserving β-cells from autoimmune destruction in recent-onset T1D patients. The current need for new preclinical models for testing strategies of antigen-specific immune tolerance is also highlighted.

Pancreatic islet autoimmunity

Type 1 diabetes (T1D) represents 10 to 15% of all forms of diabetes. Its incidence shows a consistent rise in all countries under survey. Evidence for autoimmunity in human T1D relies on the detection of insulitis, of islet cell antibodies, of activated β-cell-specific T lymphocytes and on the association of T1D with a restricted set of class II major histocompatibility complex (MHC) alleles. However, mechanisms that initiate the failure of immune tolerance to β-cell autoantigens remain elusive in common forms of T1D. T1D commonly develop as a multifactorial disease in which environmental factors concur with a highly multigenic background. The disease is driven by the activation of T-lymphocytes against pancreatic β-cells. Several years elapse between initial triggering of the autoimmune response to β cells, as evidenced by the appearance or islet cell autoantibodies, and the onset of clinical diabetes, defining a prediabetes stage. Active mechanisms hold back autoreactive effector T-cells in prediabetes, in particular a subset of CD4+ T-cells (T(reg)) and other regulatory T-cells, such as invariant NKT cells. There is evidence in experimental models that systemic or local infections can trigger autoimmune reactions to β-cells. However, epidemiological observations that have accumulated over years have failed to identify undisputable environmental factors that trigger T1D. Moreover, multiple environmental factors may intervene in the disease evolution and protective as weel as triggering environmental factors may be involved. Available models also indicate that local signals within the islets are required for full-blown diabetes to develop. Many autoantigens that are expressed by β-cells but also by the other endocrine islet cells and by neurons are recognized by lymphocytes along the development of T1D. The immune image of β-cells is that of native components of the β-cell membrane, as seen by B-lymphocytes, and of fragments of intracellular β-cell proteins in the form of peptides loaded onto class I MHC molecules on the β-cell surface and class I and class II molecules onto professional antigen presenting cells. Given the key role of T lymphocytes in T1D, the cartography of autoantigen-derived peptides that are presented to class I-restricted CD8(+) T-cells and class II-restricted CD4(+) T-cells is of outmost importance and is a necessary step in the development of diagnostic T-cell assays and of immunotherapy of T1D.

T cell populations in the pancreatic lymph node naturally and consistently expand and contract in NOD mice as disease progresses

Nonobese diabetic (NOD) mice develop spontaneous autoimmune Type 1 diabetes (T1D) that results from the destruction of insulin secreting β cells by diabetogenic T cells. The activation of autoreactive T cells occurs in the pancreatic lymph nodes (PLN) from where effector T cells migrate to the pancreas. This study was designed to explore whether T cell populations in the NOD PLN expand in a predictable and reproducible way during disease progression. Complementary determining region (CDR) 3 length spectratype analysis of 19 TCR Vβ families was used to identify the relative frequency of T populations in PLN of 4 and 10 week old NOD mice and mice at T1D onset. Significant and highly reproducible changes in specific T cell populations were detected in 14 of Vβ families tested at all stages of disease. However, of these, the CDR3 spectratype of only four Vβ families was significantly more perturbed at T1D onset than in 10 week old mice. Intriguingly, when diabetes was induced in 10 week old mice with cyclophosphamide (CYP) the same four Vβ families, Vβ5.1, Vβ9, Vβ10, and Vβ15, were again significantly more perturbed than in the untreated non-diabetic age matched mice. Taken together the data show that while T cell responses in PLN of NOD mice are heterogeneous, they are ordered and consistent throughout disease development. The finding that within this heterogeneous response four Vβ families are significantly more perturbed in diabetic mice, whether spontaneous or induced, strongly suggests their selection as part of the disease process.

T cell recognition of autoantigens in human type 1 diabetes: clinical perspectives

Type 1 diabetes (T1D) is an autoimmune disease driven by the activation of lymphocytes against pancreatic β-cells. Among β-cell autoantigens, preproinsulin has been ascribed a key role in the T1D process. The successive steps that control the activation of autoreactive lymphocytes have been extensively studied in animal models of T1D, but remains ill defined in man. In man, T lymphocytes, especially CD8⁺ T cells, are predominant within insulitis. Developing T-cell assays in diabetes autoimmunity is, thus, a major challenge. It is expected to help defining autoantigens and epitopes that drive the disease process, to pinpoint key functional features of epitope-specific T lymphocytes along the natural history of diabetes and to pave the way towards therapeutic strategies to induce immune tolerance to β-cells. New T-cell technologies will allow defining autoreactive T-cell differentiation programs and characterizing autoimmune responses in comparison with physiologically appropriate immune responses. This may prove instrumental in the discovery of immune correlates of efficacy in clinical trials.

Unexpected functional consequences of xenogeneic transgene expression in beta-cells of NOD mice

We describe unexpected alterations in the non-obese diabetic (NOD/Lt) mouse model of type 1 diabetes (T1D) following forced beta-cell expression of non-mammalian genes ligated to an insulin promoter sequence. These include the jellyfish green fluorescent protein (GFP), useful for beta-cell identification, and the bacteriophage P1 Cre recombinase, necessary for beta cell-specific ablation of a gene using a Cre-loxP system. Homozygous expression of GFP, driven by the mouse insulin 1 gene promoter (MIP-GFP) in a single transgenic line of NOD mice, produced T1D in postnatal mice that was not associated with insulitis, but rather beta cell-depleted islets. Hemizygous transgene expression suppressed spontaneous autoimmune T1D in females, and produced a male glucose intolerance syndrome associated with age-dependent declines in plasma insulin content. Among lines of transgenic NOD/Lt mice expressing Cre recombinase driven by the rat insulin 2 promoter (RIP-Cre), high, non-mosaic expression correlated with suppressed T1D development. These findings emphasize the need for careful characterization of genetically manipulated NOD mouse stocks to insure that model characteristics have not been compromised.

Microglial changes occur without neural cell death in diabetic retinopathy

Very early neuroglial changes have been observed to precede major vascular changes in the retina of diabetic patients and animal models. We investigated the sequence of these neuroglial changes further, in mice with alloxan-induced diabetes. Diabetes was induced by a single injection of Alloxan into C57/Bl6 mice, which subsequently received daily insulin injections. Diabetic and control animals were weighed and their blood glucose levels were determined weekly. Electroretinographic recordings and scanner laser ophthalmoscope (SLO) examinations were carried out 15 days, one month and three months after the onset of diabetes. Diabetes induction was confirmed by the presence of glucose in the urine, a tripling of blood glucose level, weight loss and an increase in glycated haemoglobin levels. Three months after diabetes onset, the electroretinogram b/a wave amplitude ratio was decreased at the highest light intensities and oscillatory potentials were delayed. The retinal fundus and vessels remained unchanged. No cell apoptosis was detected in vertical and horizontal sections of the retina by TUNEL or immunocytochemistry for the active caspase 3. No increase in GFAP-immunostaining indicative of a glial reaction was observed in Müller glial cells. By contrast, changes in the morphology of microglial cells were observed, with marked shortening of the dendrites. Thus, the microglial reaction occurs very early in progression to diabetic retinopathy, at about the same time as early electroretinographic modifications. The absence of apoptotic cells, contrasting with previous results in mice with streptozotocin-induced diabetes, is consistent with insulin neuroprotection.

Role of beta-cells in type 1 diabetes pathogenesis

Whether autoimmunity results primarily from a defect of the immune system, target organ dysfunction, or both remains an open issue in most human autoimmune diseases. The highly multigenic background on which diabetes develops in the NOD mouse and in the human suggests that numerous gene variants associate in contributing to activation of autoimmunity to beta-cells. Both immune genes and islet-related genes are involved. The presence of beta-cells is required for initiation of diabetes autoimmunity to proceed. Available experiments in the NOD mouse and epidemiological evidence in the human point to proinsulin as a key autoantigen in diabetes. The functional importance of insulin, the high number of autoantigens characterized at different stages of diabetes, and their clustering within beta-cell subparticles point to the islet as a starting point in the initiation phase of the disease. Genes that direct the autoimmune reaction toward the beta-cell target, autoantigens that are recognized by autoreactive B- and T-cells along the autoimmune process, the importance of beta-cells in the activation of autoreactive lymphocytes, and the expression level of key beta-cell molecules along diabetes development are successively considered in this review.

Regulatory T cells in the control of autoimmune diabetes: the case of the NOD mouse

Over the last few years, there has been a revival of the concept of suppressor/regulatory T cells being central players in the control of various immune responses, including autoimmune responses and immune response to transplants, tumors, and infectious agents. It appears that regulatory T cells are diverse in their phenotypes, antigen specificity, and modes of action. Here we summarize studies from various groups, including our own, demonstrating that specialized subsets of regulatory T cells are pivotal in the control of autoimmune diabetes as well shown by the compelling evidence accumulated using the non-obese diabetic (NOD) mouse model. We also provide a discussion of the evidence showing that some biological products (such as CD3-specific monoclonal antibodies) are representatives of a new category of immunotherapeutic agents endowed with unique capacities to promote immunological tolerance (an antigen-specific unresponsiveness in the absence of long-term generalized immunosuppression) through their ability to induce immunoregulatory T cells.

Recognition of a subregion of human proinsulin by class I-restricted T cells in type 1 diabetic patients

Proinsulin is a key autoantigen in type 1 diabetes. Evidence in the mouse has underscored the importance of the insulin B chain region in autoimmunity to pancreatic beta cells. In man, a majority of proteasome cleavage sites are predicted by proteasome cleavage algorithms within this region. To study CD8+ T cell responses to the insulin B chain and adjacent C peptide, we selected 8- to 11-mer peptides according to proteasome cleavage patterns obtained by digestion of two peptides covering proinsulin residues 28 to 64. We studied their binding to purified HLA class I molecules and their recognition by T cells from diabetic patients. Peripheral blood mononuclear cells from 17 of 19 recent-onset and 12 of 13 long-standing type 1 diabetic patients produced IFN-gamma in response to proinsulin peptides as shown by using an ELISPOT assay. In most patients, the response was against several class I-restricted peptides. Nine peptides were recognized within the proinsulin region covering residues 34 to 61. Four yielded a high frequency of recognition in HLA-A1 and -B8 patients. Three peptides located in the proinsulin region 41-51 were shown to bind several HLA molecules and to be recognized in a high percentage of diabetic patients.

Gene expression profiling in type 1 diabetes prone NOD mice immunized with a disease protective autoantigenic peptide

Immunization with autoantigenic peptides skews T cell responses in type 1 diabetes (T1D), yet the gene-expression signature characterizing this change is unclear. We used cDNA microarray technology to identify genes differentially regulated in splenocytes of T1D prone NOD mice after immunization with a disease protective glutamic acid decarboxylase 65 (GAD(65) P14) peptide. We identified 96 genes involved in cytokine secretion, humoral immune response, T cell activation, signal transduction, cell proliferation, complement activation and inflammatory responses. Up-regulation of seven chemokine and cytokine genes confirmed our previous findings of increased interferon-gamma (IFN-gamma) secretion, which may lead to a protective response in T1D. Hierarchical clustering was used to organize treated and control groups on the basis of their overall similarity in gene-expression patterns, suggesting association or co-regulation. Semi-quantitative RT-PCR was used to confirm the expression of selected genes in spleen and pancreatic draining lymph nodes. These findings can be used to compare other immunization strategies affecting the expression of these genes and explore their mechanisms of action. This microarray-based study, thus, unravels the molecular mechanism of beta-cell associated autoantigenic peptide immunization in T1D prone NOD mice, paving the way for identification of diagnostic markers and drug targets for modulating immune responses in T1D.

Autoimmune diabetes onset results from qualitative rather than quantitative age-dependent changes in pathogenic T-cells

Diabetogenic T-cells can be detected in pre-diabetic nonobese diabetic (NOD) mice after transfer in NOD-SCID recipients. Here we demonstrate that 6-week-old pre-diabetic NOD mice, >2 months before disease onset, already harbor pathogenic T-cells in equal numbers to overtly diabetic animals. The delay in diabetes appearance is explained by the presence of regulatory CD4+ CD25+ T-cells that control diabetogenic effectors and that are, in our hands, transforming growth factor (TGF)-beta-dependent. Our present results suggest, however, that diabetes onset is only partly explained by a decline in this regulatory T-cell activity. Another major factor appears to be the progressive resistance of diabetogenic cells to TGF-beta-dependent mediated inhibition. We propose that progression to overt disease correlates with the pathogenic T-cell's escape from TGF-beta-dependent T-cell-mediated regulation.

Unique role of CD4+CD62L+ regulatory T cells in the control of autoimmune diabetes in T cell receptor transgenic mice

Converging experimental evidence indicates that CD4(+) regulatory T cells control progression of autoimmune insulitis in nonobese diabetic (NOD) mice. Here, we studied the nature of these regulatory T cells and their mode of action in diabetes-prone NOD Rag(-/-) or severe combined immunodeficient (SCID) mice harboring a transgenic T cell receptor derived from the diabetogenic T cell clone BDC2.5. We first show that diabetes onset is prevented in such mice by infusion of polyclonal CD4(+) T cells expressing L-selectin (CD62L) but not prevented or only marginally prevented by CD4(+)CD25(+) T cells. Similarly, we found with a cotransfer model that CD4(+)CD62L(+) T cells but not CD4(+)CD25(+) T cells inhibited diabetes transfer into NOD SCID recipients by transgenic NOD BDC2.5 SCID cells. Unexpectedly, cotransfer of transgenic NOD BDC2.5 SCID cells and spleen cells from WT diabetic NOD mice did not induce diabetes, whereas each individual population did so. Data are presented arguing for the role of CD4(+)CD62L(+) T cells present within the polyclonal diabetogenic population in mediating this apparently paradoxical effect. Collectively, these data confirm the central role of CD4(+)CD62L(+) regulatory T cells in controlling disease onset in a well defined transgenic model of autoimmune diabetes and suggest the intervention of homeostatic mechanisms as part of their mode of action.

Prévention du diabète de type 1. Où en sommes-nous? Que dire et proposer aux familles?

Prevention of type 1 diabetes in high risk individuals presents with both positive and negative aspects. On one hand, the availability of reliable and convenient screening tools (antibodies) allows us to quantify the risk of diabetes in the short term. Large randomised studies have provided indisputable answers regarding the efficiency of selection of at risk patients. Unfortunately, both DPT-1 study (using insulin) and ENDIT trial (with nicotinamide) ruined the hopes raised from solid experimental data. These studies have also demonstrated the huge costs in terms of number of subjects, time for follow-up, and financial burden, requiring an international collaboration. Finally, only a small number of such studies can be conducted simultaneously. Progress and obstacles paving this research area must be explained to diabetic patients and their family. Current mitigated results should not drive us to give up screening campaigns. Rather, these results should prompt diabetes centers and families to participate in the selection of high risk individuals in order to explore new therapeutic options within future prevention trials.

Beta cell MHC class I is a late requirement for diabetes

Type 1 diabetes occurs as a result of an autoimmune attack on the insulin-producing beta cells. Although CD8 T cells have been implicated both early and late in this process, the requirement for direct interaction between these cells and MHC class I on the beta cells has not been demonstrated. By using nonobese diabetic mice lacking beta cell class I expression, we show that both initiation and progression of insulitis proceeds unperturbed. However, without beta cell class I expression, the vast majority of these mice do not develop hyperglycemia. These findings demonstrate that a direct interaction between CD8 T cells and beta cells is not required for initiation or early disease progression. The requirement for class I on beta cells is a relatively late checkpoint in the development of diabetes.

Acceleration of type 1 diabetes mellitus in proinsulin 2-deficient NOD mice

Accumulating evidence favors a role for proinsulin as a key autoantigen in diabetes. In the mouse, two proinsulin isoforms coexist. Most studies point to proinsulin 2 as the major isoform recognized by T cells in the NOD mouse. We studied mice in which a null proinsulin 2 mutation was transferred from proinsulin 2-deficient 129 mice onto the NOD background along with 16 genetic markers (including I-A(g7) MHC molecule) associated with diabetes. Intercross mice from the fourth backcross generation showed that proinsulin 2(-/-) mice develop accelerated insulitis and diabetes. The high prevalence of anti-insulin autoantibodies in proinsulin 2(-/-) mice indicates that diabetes acceleration relates to altered recognition of proinsulin. The prevalence of anti-glutamic acid decarboxylase autoantibodies and of sialitis is not increased in proinsulin 2(-/-) mice. We give evidence that proinsulin 2 expression leads to silencing of T cells specific for an epitope shared by proinsulin 1 and proinsulin 2. In the human, alleles located in the VNTR region flanking the insulin gene control beta cell response to glucose and proinsulin expression in the thymus and are key determinants of diabetes susceptibility. Proinsulin 2(-/-) NOD mice provide a model to study the role of thymic expression of insulin in susceptibility to diabetes.

Optimization of monomethoxy-polyethylene glycol grafting on the pancreatic islet capsules

As a new approach to islet transplantation, biocompatible monomethoxy-poly(ethylene glycol) (mPEG) was chemically grafted onto the pancreatic islet capsule. The aim of this study was to determine the optimal conditions for completely covering the islet by the mPEG while maintaining a high viability of islets according to the reaction time and the repeating number of the reaction. By grafting the fluorescein-PEG instead of mPEG, we determined the optimal mPEG grafting time as 1 h, during which time the procedure did not reduce islet viability. Insulin secretion from islets where the mPEG was grafted on for 3 times was similar to that of control islets. Moreover, the mPEG-grafted islets rapidly responded to the changes in the glucose concentration in the same pattern as did control islets. These results showed that mPEG grafting did not damage the function of islets. In conclusion, when the mPEG grafting was performed for 1 h and repeated twice with 1-day culture between each mPEG-grafting step, the mPEG completely covered the islet capsules without any damage to the viability and function of the islets. The main advantage of mPEG grafting on the islet capsule is that it can protect the islet against the host's immune system without increasing the islet size so that it can be administered into the portal vein by the catheter.

Proinsulin 2 knockout NOD mice: a model for genetic variation of insulin gene expression in type 1 diabetes

Insulin is a major disease determinant in type 1 diabetes, type 2 diabetes, and related disorders. The role of variations in the expression of the insulin gene has been proposed in genetic susceptibility to the three pathological conditions in humans. In contrast to humans, rodents express two proinsulin isoforms. One isoform, proinsulin 1, is expressed exclusively in islets. The second, proinsulin 2, is expressed in islets and in other tissues, especially the thymus. We took advantage of the expression of these two isoforms to introduce a null proinsulin 2 allele in NOD mice and to evaluate the consequence of a variation of proinsulin 2 gene expression on the development of type 1 diabetes on the NOD genetic background. Heterozygote NOD mutant mice carrying a null proinsulin 2 mutation showed an increased incidence of type 1 diabetes at successive backcross generations. Plasma glucose and insulin levels were identical in prediabetic mutant and in wild-type mice at 4 weeks of age. Variation in insulin gene expression is hypothesized to interfere with diabetes development at both the islet and the thymus level.

Tolerance to islet antigens and prevention from diabetes induced by limited apoptosis of pancreatic beta cells

Crosspresentation of self-antigens by antigen-presenting cells is critical for the induction of peripheral tolerance. As apoptosis facilitates the entry of antigens into the crosspresentation pathway, we sought to prevent the development of autoimmune diabetes by inducing pancreatic beta cell apoptosis before disease onset. Accordingly, young nonobese diabetic (NOD) mice injected with a single low dose of streptozotocin (SZ), a drug cytotoxic for beta cells, exhibited impaired T cell responses to islet antigens and were protected from spontaneous diabetes. Furthermore, beta cell apoptosis was necessary for protection since SZ did not protect RIP-CrmA transgenic NOD mice in which beta cells expressed the caspase inhibitor CrmA. Our results support a model in which apoptosis of pancreatic beta cells induces the development of regulatory cells leading to the tolerization of self-reactive T cells and protection from diabetes.

ICA69(null) nonobese diabetic mice develop diabetes, but resist disease acceleration by cyclophosphamide

ICA69 (islet cell Ag 69 kDa) is a diabetes-associated autoantigen with high expression levels in beta cells and brain. Its function is unknown, but knockout of its Caenorhabditis elegans homologue, ric-19, compromised neurotransmission. We disrupted the murine gene, ica-1, in 129-strain mice. These animals aged normally, but speed-congenic ICA69(null) nonobese diabetic (NOD) mice developed mid-life lethality, reminiscent of NOD-specific, late lethal seizures in glutamic acid decarboxylase 65-deficient mice. In contrast to wild-type and heterozygous animals, ICA69(null) NOD congenics fail to generate, even after immunization, cross-reactive T cells that recognize the dominant Tep69 epitope in ICA69, and its environmental mimicry Ag, the ABBOS epitope in BSA. This antigenic mimicry is thus driven by the endogenous self Ag, and not initiated by the environmental mimic. Insulitis, spontaneous, and adoptively transferred diabetes develop normally in ICA69(null) NOD congenics. Like glutamic acid decarboxylase 65, ICA69 is not an obligate autoantigen in diabetes. Unexpectedly, ICA69(null) NOD mice were resistant to cyclophosphamide (CY)-accelerated diabetes. Transplantation experiments with hemopoietic and islet tissue linked CY resistance to ICA69 deficiency in islets. CY-accelerated diabetes involves not only ablation of lymphoid cells, but ICA69-dependent drug toxicity in beta cells that boosts autoreactivity in the regenerating lymphoid system.

Islet glutamic acid decarboxylase modified by reactive oxygen species is recognized by antibodies from patients with type 1 diabetes mellitus

The generation of an autoimmune response against islet beta-cells is central to the pathogenesis of type 1 diabetes mellitus, and this response is driven by the stimulation of autoreactive lymphocytes by components of the beta-cells themselves. Reactive oxygen species (ROS) have been implicated in the beta-cell destruction which leads to type 1 diabetes and may modify beta-cell components so as to enhance their immunogenicity. We investigated the effects of oxidation reactions catalysed by copper or iron on the major beta-cell autoantigen glutamic acid decarboxylase (GAD). Lysates of purified rat islets were exposed to copper or iron sulphate with or without hydrogen peroxide or ascorbic acid. Immunostaining showed that these treatments generated high molecular weight covalently linked aggregates containing GAD. These are not formed by intermolecular disulphide bonds between cysteine residues since they cannot be resolved into monomeric form when electrophoresed under extreme reducing conditions. There was no modification of insulin or pro-insulin by ROS. The same oxidative changes to GAD could be induced in viable islet cells treated with copper sulphate and hydrogen peroxide, and thus the modifications are not an artefact of the catalysed oxidation of cell-free lysates. Sera from patients with type 1 diabetes and stiffman syndrome containing GAD antibodies reacted predominantly with the highest molecular weight modified protein band of GAD: normal human sera did not precipitate GAD. Thus, oxidatively modified aggregates of GAD react with serum antibodies of type 1 diabetes patients and some SMS patients: this is consistent with oxidative modifications of autoantigens being relevant to the pathogenesis of type 1 diabetes.

Tolerance to islet autoantigens in type 1 diabetes

Tolerance to beta cell autoantigens represents a fragile equilibrium. Autoreactive T cells specific to these autoantigens are present in most normal individuals but are kept under control by a number of peripheral tolerance mechanisms, among which CD4(+) CD25(+) CD62L(+) T cell-mediated regulation probably plays a central role. The equilibrium may be disrupted by inappropriate activation of autoantigen-specific T cells, notably following to local inflammation that enhances the expression of the various molecules contributing to antigen recognition by T cells. Even when T cell activation finally overrides regulation, stimulation of regulatory cells by CD3 antibodies may reset the control of autoimmunity. Other procedures may also lead to disease prevention. These procedures are essentially focused on Th2 cytokines, whether used systemically or produced by Th2 cells after specific stimulation by autoantigens. Protection can also be obtained by NK T cell stimulation. Administration of beta cell antigens or CD3 antibodies is now being tested in clinical trials in prediabetics and/or recently diagnosed diabetes.

Endogenous oocyte antigens are required for rapid induction and progression of autoimmune ovarian disease following day-3 thymectomy

Female (C57BL/6xA/J)F(1) mice undergoing thymectomy on day 3 after birth (d3tx) developed autoimmune ovarian disease (AOD) and autoimmune disease of the lacrimal gland. As both were prevented by normal adult CD25(+) T cells, regulatory T cell depletion is responsible for d3tx diseases. AOD began as oophoritis at 3 wk. By 4 wk, AOD progressed to ovarian atrophy with autoantibody response against multiple oocyte Ag of early ontogeny. The requirement for immunogenic endogenous ovarian Ag was investigated in d3tx female mice, d3tx male mice, and d3tx neonatally ovariectomized (OX) females. At 8 wk, all mice had comparable lacrimalitis but only those with endogenous ovaries developed AOD in ovarian grafts. The duration of Ag exposure required to initiate AOD was evaluated in d3tx mice OX at 2, 3, or 4 wk and engrafted with an ovary at 4, 5, or 6 wk, respectively. The mice OX at 2 wk did not have oophoritis whereas approximately 80% of mice OX at 3 or 4 wk had maximal AOD, thus Ag stimulus for 2.5 wk following d3tx is sufficient. AOD progression requires additional endogenous Ag stimulation from the ovarian graft. In mice OX at 3 wk, ovaries engrafted at 5 wk had more severe oophoritis than ovaries engrafted at 6 or 12 wk; moreover, only mice engrafted at 5 wk developed ovarian atrophy and oocyte autoantibodies. Similar results were obtained in mice OX at 4 wk. Thus endogenous tissue Ag are critical in autoimmune disease induction and progression that occur spontaneously upon regulatory T cell depletion.

Type I diabetes and multiple sclerosis patients target islet plus central nervous system autoantigens; nonimmunized nonobese diabetic mice can develop autoimmune encephalitis

Type I diabetes and multiple sclerosis (MS) are distinct autoimmune diseases where T cells target either islet or CNS self-proteins. Unexpectedly, we found that autoreactive T cells in diabetic patients, relatives with high diabetes risk, nonobese diabetic (NOD) mice, and MS patients routinely target classical islet as well as CNS autoantigens. The pathogenic potential of CNS autoreactivity was testable in NOD mice. Pertussis holotoxin, without additional Ags or adjuvants, allowed development of an NOD mouse-specific, autoimmune encephalitis with variable primary-progressive, monophasic, and relapsing-remitting courses. T cells from diabetic donors transferred CNS disease to pertussis toxin-pretreated NOD.scid mice, with accumulation of CD3/IFN-gamma transcripts in the brain. Diabetes and MS appear more closely related than previously perceived. NOD mouse-specific, autoimmune encephalitis provides a new MS model to identify factors that determine alternative disease outcomes in hosts with similar autoreactive T cell repertoires.

The antiviral 2',5'-oligoadenylate synthetase is persistently activated in type 1 diabetes

Type 1 diabetes results from autoimmune destruction of the pancreatic beta-cells. Although viruses have been implicated as etiologic factors, specific pathogenic mechanisms have not been identified. Recently, increased attention has focused on the role of the innate antiviral defense system in directing adaptive immune responses. In this context, the pathogenesis of type 1 diabetes may involve an aberrant response to endogenous or exogenous viruses or their products. The family of 2',5' oligoadenylate synthetases (2', 5' AS) are IFN-alpha-inducible, RNA-dependent effector molecules in the antiviral defense system. We show that lymphocytic 2',5' AS activity is significantly increased in type 1 diabetes, both in recent-onset and in long-standing type 1 diabetes, and in diabetic twins from monozygotic twin pairs. The activity of 2',5' AS was not elevated in patients with type 2 diabetes or multiple sclerosis thus excluding hyperglycemia or autoimmunity per se as inducing upregulation of enzyme activity. In recent-onset diabetic patients, lymphocyte levels of protein kinase p68 and MxA, two other IFN-alpha-inducible antiviral proteins, were similar to control levels. These data suggest that the increased 2',5' AS activity may reflect an aberrant response to viruses or RNA molecules originating from exogenous or endogenous sources.

Islet mass plays a critical role in initiation, but not progression, of the diabetogenic process in NOD mice

Pancreatectomy (90%) at a preinsulitis age (7 weeks) protects NOD mice from diabetes while pancreatectomy at a mid-insulitis age (13 weeks) has no such protective effect. The present study examined the effects of islet transplantation in pancreatectomized diabetes-free NOD mice. Transplantation of syngeneic NOD islets as well as allogeneic C3H/He and C57BL/6 islets 3 weeks after pancreatectomy-induced spontaneous diabetes whereas transplantation of xenogeneic Sprague-Dawley rat islets or allogeneic C3H/He skin failed to induce diabetes, demonstrating that the diabetogenic antigen(s) of NOD islets is also expressed by islets of diabetes-resistant mouse strains but not by xenogeneic rat islets. Removal of NOD islet grafts by nephrectomy 7-14 days after transplantation had no effect on the subsequent chronic development of diabetes, while graft removal 3 days after transplantation completely abolished the diabetogenic effect of islet transplantation. Thus, activation of the diabetogenic response by islet isografting takes less than 7 days and the continuous presence of a large islet mass is not required for progression to diabetes. While islet transplantation at 10 and 15 weeks of age caused diabetes, delayed islet transplantation at 23 and 35 weeks of age failed to induce diabetes in pancreatectomized diabetes-free NOD mice, suggesting that initiation of the diabetogenic autoimmune process must take place within a certain window of time. The pancreatectomy/islet transplantation model is excellent for studying the immunological events surrounding activation and progression of the diabetogenic autoimmune process and for identifying the diabetogenic islet antigen(s).

Initiation of autoimmune diabetes by developmentally regulated presentation of islet cell antigens in the pancreatic lymph nodes

Little is known about the events triggering lymphocyte invasion of the pancreatic islets in prelude to autoimmune diabetes. For example, where islet-reactive T cells first encounter antigen has not been identified. We addressed this issue using BDC2.5 T cell receptor transgenic mice, which express a receptor recognizing a natural islet beta cell antigen. In BDC2.5 animals, activated T cells were found only in the islets and the lymph nodes draining them, and there was a close temporal correlation between lymph node T cell activation and islet infiltration. When naive BDC2.5 T cells were transferred into nontransgenic recipients, proliferating cells were observed only in pancreatic lymph nodes, and this occurred significantly before insulitis was detectable. Surprisingly, proliferation was not seen in 10-day-old recipients. This age-dependent dichotomy was reproduced in a second transfer system based on an unrelated antigen artificially expressed on beta cells. We conclude that beta cell antigens are transported specifically to pancreatic lymph nodes, where they trigger reactive T cells to invade the islets. Systemic or extrapancreatic T cell priming, indicative of activation via molecular mimicry or superantigens, was not seen. Compromised presentation of beta cell antigens in the pancreatic lymph nodes of juvenile animals may be the root of a first "checkpoint" in diabetes progression.

Are there unique autoantigens triggering autoimmune diseases?

Using three reference disease models--insulin-dependent diabetes mellitus (IDDM) as a prototype of T-cell mediated organ-specific autoimmune disease, myasthenia gravis (MG) as a prototype of autoantibody-mediated organ-specific autoimmune disease and systemic lupus erythematosus (SLE) as a prototype of non-organ-specific autoimmune disease--we have reached several conclusions: 1) All three diseases are associated with the presence of multiple autoantibodies and/or autoreactive T cells that recognize a large number of antigenic molecules. The apparent predominant role of certain antibodies in some diseases could relate to their functional properties such as acetylcholine receptor (AChR) blockade for anti-AChR autoantibodies in MG or anti-dsDNA in SLE. 2) Major target antigens are clustered in the target cell affected by organ-specific autoimmune diseases: beta cells in IDDM, striated-muscle cells in MG, or apoptotic cells in the case of SLE. 3) Antibodies and T cells recognize multiple epitopes in these molecules. 4) The most evident explanation for the observed clustering and diversity is autoantigen spreading. Spreading probably involves T cells secreting proinflammatory cytokines but also possibly antibodies as in the case of nucleosome autoantibodies in SLE. 5) The counterpart of antigen spreading is bystander suppression in which regulatory cytokines deviate the immune response towards a protective response. 6) The mechanisms underlying the initiation of the autoimmune response and antigen spreading are still undetermined. They could imply a direct abnormality of the target cell in the case of organ-specific autoimmune diseases (e.g. infection with a virus showing a selective tropism for the target cell in organ-specific autoimmune diseases, or loss of physiological regulation of major histocompatibility complex molecule expression) or could be consequence of a ubiquitous cell abnormality such as increased apoptosis in SLE. The respective roles of genetic and environmental factors in these triggering events remain to be determined.

Autoimmune diabetes: the role of T cells, MHC molecules and autoantigens

Type 1 diabetes (IDDM) is a T cell mediated autoimmune disease which in part is determined genetically by its association with major histocompatibility complex (MHC) class II alleles. The major role of MHC molecules is the regulation of immune responses through the presentation of peptide epitopes of processed protein antigens to the immune system. Recently it has been demonstrated that MHC molecules associated with autoimmune diseases preferentially present peptides of other endogenous MHC proteins, that often mimic autoantigen-derived peptides. Hence, these MHC-derived peptides might represent potential targets for autoreactive T cells. It has consistently been shown that humoral autoimmunity to insulin predominantly occurs in early childhood. The cellular immune response to insulin is relatively low in the peripheral blood of patients with IDDM. Studies in NOD mice however have shown, that lymphocytes isolated from pancreatic islet infiltrates display a high reactivity to insulin and in particular to an insulin peptide B 9-23. Furthermore we have evidence that cellular autoimmunity to insulin is higher in young pre-diabetic individuals, whereas cellular reactivity to other autoantigens is equally distributed in younger and older subjects. This implicates that insulin, in human childhood IDDM and animal autoimmune diabetes, acts as an important early antigen which may target the autoimmune response to pancreatic beta cells. Moreover, we observed that in the vast majority of newly diagnosed diabetic patients or individuals at risk for IDDM, T cell reactivity to various autoantigens occurs simultaneously. In contrast, cellular reactivity to a single autoantigen is found with equal frequency in (pre)-type 1 diabetic individuals as well as in control subjects. Therefore the autoimmune response in the inductive phase of IDDM may be targeted to pancreatic islets by the cellular and humoral reactivity to one beta-cell specific autoantigen, but spreading to a set of different antigens may be a prerequisite for progression to destructive insulitis and clinical disease. Due to mimic epitopes shared by autoantigen(s), autologous MHC molecules and environmental antigens autoimmunity may spread, intramolecularly and intermolecularly and amplify upon repeated reexposure to mimic epitopes of environmental triggers.

Temporal discontinuities in progression of NOD autoimmune diabetes

Consideration of the pathophysiology of insulin-dependent diabetes mellitus in the nonobese diabetic (NOD) mouse can be viewed from a temporal perspective. We argue that there are discontinuous phases and each phase may reflect a phenotype educed by a particular set of genetic and epigenetic events. Therefore, temporal dissection may be a useful platform for causal dissection and we have set out this article as follows: 1. Introduction. 2. "Pre-time." a. Genetics. b. Parental effects. 3. Development of insulitis. a. Development of autoimmunity vs waning of or failure to establish tolerance. b. Importance of beta cell mass. c. Homing. 4. Onset of beta cell destruction. 5. Further Discussion.