Interleukin-4 deficiency does not exacerbate disease in NOD mice

Cytokines in type 1 diabetes: mechanisms of action and immunotherapeutic targets

Cytokines play crucial roles in orchestrating complex multicellular interactions between pancreatic β cells and immune cells in the development of type 1 diabetes (T1D) and are thus potential immunotherapeutic targets for this disorder. Cytokines that can induce regulatory functions-for example, IL-10, TGF-β and IL-33-are thought to restore immune tolerance and prevent β-cell damage. By contrast, cytokines such as IL-6, IL-17, IL-21 and TNF, which promote the differentiation and function of diabetogenic immune cells, are thought to lead to T1D onset and progression. However, targeting these dysregulated cytokine networks does not always result in consistent effects because anti-inflammatory or proinflammatory functions of cytokines, responsible for β-cell destruction, are context dependent. In this review, we summarise the current knowledge on the involvement of well-known cytokines in both the initiation and destruction phases of T1D and discuss advances in recently discovered roles of cytokines. Additionally, we emphasise the complexity and implications of cytokine modulation therapy and discuss the ways in which this strategy has been translated into clinical trials.

Microbiota in T-cell homeostasis and inflammatory diseases

The etiology of disease pathogenesis can be largely explained by genetic variations and several types of environmental factors. In genetically disease-susceptible individuals, subsequent environmental triggers may induce disease development. The human body is colonized by complex commensal microbes that have co-evolved with the host immune system. With the adaptation to modern lifestyles, its composition has changed depending on host genetics, changes in diet, overuse of antibiotics against infection and elimination of natural enemies through the strengthening of sanitation. In particular, commensal microbiota is necessary in the development, induction and function of T cells to maintain host immune homeostasis. Alterations in the compositional diversity and abundance levels of microbiota, known as dysbiosis, can trigger several types of autoimmune and inflammatory diseases through the imbalance of T-cell subpopulations, such as Th1, Th2, Th17 and Treg cells. Recently, emerging evidence has identified that dysbiosis is involved in the progression of rheumatoid arthritis, type 1 and 2 diabetic mellitus, and asthma, together with dysregulated T-cell subpopulations. In this review, we will focus on understanding the complicated microbiota-T-cell axis between homeostatic and pathogenic conditions and elucidate important insights for the development of novel targets for disease therapy.

Cytokines and Pancreatic β-Cell Apoptosis

The discovery 30 years ago that inflammatory cytokines cause a concentration, activity, and time-dependent bimodal response in pancreatic β-cell function and viability has been a game-changer in the fields of research directed at understanding inflammatory regulation of β-cell function and survival and the causes of β-cell failure and destruction in diabetes. Having until then been confined to the use of pathophysiologically irrelevant β-cell toxic chemicals as a model of β-cell death, researchers could now mimic endocrine and paracrine effects of the cytokine response in vitro by titrating concentrations in the low to the high picomolar-femtomolar range and vary exposure time for up to 14-16h to reproduce the acute regulatory effects of systemic inflammation on β-cell secretory responses, with a shift to inhibition at high picomolar concentrations or more than 16h of exposure to illustrate adverse effects of local, chronic islet inflammation. Since then, numerous studies have clarified how these bimodal responses depend on discrete signaling pathways. Most interest has been devoted to the proapoptotic response dependent upon mainly nuclear factor κ B and mitogen-activated protein kinase activation, leading to gene expressional changes, endoplasmic reticulum stress, and triggering of mitochondrial dysfunction. Preclinical studies have shown preventive effects of cytokine antagonism in animal models of diabetes, and clinical trials demonstrating proof of concept are emerging. The full clinical potential of anticytokine therapies has yet to be shown by testing the incremental effects of appropriate dosing, timing, and combinations of treatments. Due to the considerable translational importance of enhancing the precision, specificity, and safety of antiinflammatory treatments of diabetes, we review here the cellular, preclinical, and clinical evidence of which of the death pathways recently proposed in the Nomenclature Committee on Cell Death 2012 Recommendations are activated by inflammatory cytokines in the pancreatic β-cell to guide the identification of antidiabetic targets. Although there are still scarce human data, the cellular and preclinical studies point to the caspase-dependent intrinsic apoptosis pathway as the prime effector of inflammatory β-cell apoptosis.

Autoimmune Diabetes: An Overview of Experimental Models and Novel Therapeutics

Type 1 diabetes (T1D) results from a chronic and selective destruction of insulin-secreting β-cells within the islets of Langerhans of the pancreas by autoreactive CD4(+) and CD8(+) T lymphocytes. The use of animal models of T1D was instrumental for deciphering the steps of the autoimmune process leading to T1D. The non-obese diabetic (NOD) mouse and the bio-breeding (BB) rat spontaneously develop the disease similar to the human pathology in terms of the immune responses triggering autoimmune diabetes and of the genetic and environmental factors influencing disease susceptibility. The generation of genetically modified models allowed refining our understanding of the etiology and the pathogenesis of the disease. In the present review, we provide an overview of the experimental models generated and used to gain knowledge on the molecular and cellular mechanisms underlying the breakdown of self-tolerance in T1D and the progression of the autoimmune response. Immunotherapeutic interventions designed in these animal models and translated into the clinical arena in T1D patients will also be discussed.

CD4 T cell differentiation in type 1 diabetes

Susceptibility to type 1 diabetes is associated strongly with human leucocyte antigen (HLA) genes, implicating T cells in disease pathogenesis. In humans, CD8 T cells predominantly infiltrate the islets, yet their activation and propagation probably requires CD4 T cell help. CD4 T cells can select from several differentiation fates following activation, and this choice has profound consequences for their subsequent cytokine production and migratory potential. In turn, these features dictate which other immune cell types T cells interact with and influence, thereby determining downstream effector functions. Obtaining an accurate picture of the type of CD4 T cell differentiation associated with a particular immune-mediated disease therefore constitutes an important clue when planning intervention strategies. Early models of T cell differentiation focused on the dichotomy between T helper type 1 (Th1) and Th2 responses, with type 1 diabetes (T1D) being viewed mainly as a Th1-mediated pathology. However, several additional fate choices have emerged in recent years, including Th17 cells and follicular helper T cells. Here we revisit the issue of T cell differentiation in autoimmune diabetes, highlighting new evidence from both mouse models and patient samples. We assess the strengths and the weaknesses of the Th1 paradigm, review the data on interleukin (IL)-17 production in type 1 diabetes and discuss emerging evidence for the roles of IL-21 and follicular helper T cells in this disease setting. A better understanding of the phenotype of CD4 T cells in T1D will undoubtedly inform biomarker development, improve patient stratification and potentially reveal new targets for therapeutic intervention.

Th17 cells in immunity and autoimmunity

Th17 and IL-17 play important roles in the clearance of extracellular bacterial and fungal infections. However, strong evidence also implicates the Th17 lineage in several autoimmune disorders including multiple sclerosis, psoriasis, rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, and asthma. The Th17 subset has also been connected with type I diabetes, although whether it plays a role in the pathogenicity of or protection from the disease remains a controversial issue. In this review we have provided a comprehensive overview of Th17 pathogenicity and function, including novel evidence for a protective role of Th17 cells in conjunction with the microbiota gut flora in T1D onset and progression.

Breakdown in peripheral tolerance in type 1 diabetes in mice and humans

Type 1 Diabetes (T1D), also called juvenile diabetes because of its classically early onset, is considered an autoimmune disease targeting the insulin-producing β cells in the pancreatic islets of Langerhans. T1D reflects a loss of tolerance to tissue self-antigens caused by defects in both central tolerance, which aims at eliminating potentially autoreactive lymphocytes developing in the thymus, and peripheral tolerance, which normally controls autoreactive T cells that escaped the thymus. Like in other autoimmune diseases, the mechanisms leading to T1D are multifactorial and depend on a complex combination of genetic, epigenetic, molecular, and cellular elements that result in the breakdown of peripheral tolerance. In this article, we discuss the contribution of these factors in the development of the autoimmune response targeting pancreatic islets in T1D and the therapeutic strategies currently being explored to correct these defects.

Long-term remission of diabetes in NOD mice is induced by nondepleting anti-CD4 and anti-CD8 antibodies

Residual β-cells found at the time of clinical onset of type 1 diabetes are sufficient to control hyperglycemia if rescued from ongoing autoimmune destruction. The challenge, however, is to develop an immunotherapy that not only selectively suppresses the diabetogenic response and efficiently reverses diabetes, but also establishes long-term β-cell-specific tolerance to maintain remission. In the current study, we show that a short course of nondepleting antibodies (Abs) specific for the CD4 and CD8 coreceptors rapidly reversed clinical disease in recent-onset diabetic NOD mice. Once established, remission was maintained indefinitely and immunity to foreign antigens unimpaired. Induction of remission involved selective T-cell purging of the pancreas and draining pancreatic lymph nodes and upregulation of transforming growth factor (TGF)-β1 by pancreas-resident antigen-presenting cells. Neutralization of TGF-β blocked the induction of remission. In contrast, maintenance of remission was associated with tissue-specific immunoregulatory T cells. These findings demonstrate that the use of nondepleting Ab specific for CD4 and CD8 is a robust approach to establish long-term β-cell-specific T-cell tolerance at the onset of clinical diabetes.

An N-terminal mutation of the Foxp3 transcription factor alleviates arthritis but exacerbates diabetes

Maintenance of lymphoid homeostasis in a number of immunological and inflammatory contexts is served by a variety of regulatory T (Treg) cell subtypes and depends on interaction of the transcription factor FoxP3 with specific transcriptional cofactors. We report that a commonly used insertional mutant of FoxP3 (GFP-Foxp3) modified its molecular interactions, blocking HIF-1α but increasing IRF4 interactions. The transcriptional profile of these Treg cells was subtly altered, with an overrepresentation of IRF4-dependent transcripts. In keeping with IRF4-dependent function of Treg cells to preferentially suppress T cell help to B cells and Th2 and Th17 cell-type differentiation, GFP-FoxP3 mice showed a divergent susceptibility to autoimmune disease: protection against antibody-mediated arthritis in the K/BxN model, but greater susceptibility to diabetes on the NOD background. Thus, specific subfunctions of Treg cells and the immune diseases they regulate can be influenced by FoxP3's molecular interactions, which result in divergent immunoregulation.

Helminth protection against autoimmune diabetes in nonobese diabetic mice is independent of a type 2 immune shift and requires TGF-β

Leading hypotheses to explain helminth-mediated protection against autoimmunity postulate that type 2 or regulatory immune responses induced by helminth infections in the host limit pathogenic Th1-driven autoimmune responses. We tested these hypotheses by investigating whether infection with the filarial nematode Litomosoides sigmodontis prevents diabetes onset in IL-4-deficient NOD mice and whether depletion or absence of regulatory T cells, IL-10, or TGF-β alters helminth-mediated protection. In contrast to IL-4-competent NOD mice, IL-4-deficient NOD mice failed to develop a type 2 shift in either cytokine or Ab production during L. sigmodontis infection. Despite the absence of a type 2 immune shift, infection of IL-4-deficient NOD mice with L. sigmodontis prevented diabetes onset in all mice studied. Infections in immunocompetent and IL-4-deficient NOD mice were accompanied by increases in CD4(+)CD25(+)Foxp3(+) regulatory T cell frequencies and numbers, respectively, and helminth infection increased the proliferation of CD4(+)Foxp3(+) cells. However, depletion of CD25(+) cells in NOD mice or Foxp3(+) T cells from splenocytes transferred into NOD.scid mice did not decrease helminth-mediated protection against diabetes onset. Continuous depletion of the anti-inflammatory cytokine TGF-β, but not blockade of IL-10 signaling, prevented the beneficial effect of helminth infection on diabetes. Changes in Th17 responses did not seem to play an important role in helminth-mediated protection against autoimmunity, because helminth infection was not associated with a decreased Th17 immune response. This study demonstrates that L. sigmodontis-mediated protection against diabetes in NOD mice is not dependent on the induction of a type 2 immune shift but does require TGF-β.

Islet lymphocyte subsets in male and female NOD mice are qualitatively similar but quantitatively distinct

Islet-infiltrating lymphocytes of individual male and female non-obese diabetic (NOD) mice were examined with the purpose of determining the differences that lead to a predominance of diabetes in female versus males NOD mice. When normalized for the amount of islet lymphocytes recovered, the infiltrating lymphocytes of female NOD mice were indistinguishable from those of male NOD mice. The only observed difference was that islet inflammation progressed at an increased rate in female compared to male NOD mice. There was no difference in the composition of islet infiltrates in male and female NOD mice. Unexpectedly, the ratio of CD4(+):CD8(+) T cells was tightly controlled in the islets throughout diabetogenesis. The frequency of IL-4(+) CD4(+) T cells started high but quickly fell to 3% of the population that was maintained with increasing inflammation. A significant portion of the CD8(+) T cells were islet-specific glucose-6-phosphatase catalytic subunit-related protein specific in both male and female NOD mice and this population was antigen experienced and increased at high levels of islet inflammation. Surprisingly, a large pool of antigen inexperienced naïve T cells was detected in the islets. We conclude the underlying immunological processes in both male and female NOD mice are similar while the rates differ and the presence of naïve T cell in the islets may contribute to epitope spreading.

Control of type 1 diabetes by CD4+Foxp3+ regulatory T cells: lessons from mouse models and implications for human disease

In recent years, there has been a revival of the concept of CD4(+) regulatory T (T(reg)) cells as being a central control point in various immune responses, including autoimmune responses and immunity to transplants, allergens, tumours and infectious microbes. The current literature suggests that T(reg) cells are diverse in their phenotype and mechanism(s) of action, and as such, may constitute a myriad of naturally occurring and induced T cell precursors with variable degrees of regulatory potential. In this review, we summarize research from various laboratories, including our own, showing that CD4(+)Foxp3(+) T(reg) cells are critical in the control of type 1 diabetes (T1D) in mouse models and humans. In this review, we also discuss cellular and molecular determinants that impact CD4(+)Foxp3(+) T(reg) cell development and function and consequential resistance to organ-specific autoimmune disease. Recent advances in the use of CD4(+)Foxp3(+) T(reg) cellular therapy to promote immunological tolerance in the absence of long-term generalized immunosuppression are also presented.

Progress in understanding autoimmune exocrinopathy using the non-obese diabetic mouse: an update

Sjögren's Syndrome (SS) is a chronic autoimmune disease characterized by histological and functional alterations of salivary and lacrimal glands that result in a severe dryness of the mouth and the eyes. The etiology of SS has remained undefined despite investigators' significant efforts to identify the mechanisms of initiation. Based on histopathology, several animal models are available--such as MRL/lpr, NZW/NZB, NFS/sld, graft vs. host, transgenic mouse expressing viral surface antigen, and the non-obese diabetic (NOD) mouse--for investigation of the etiology of SS. Biochemical and immunological similarities between human SS and autoimmune exocrinopathy (AEC) in the NOD mouse, including the loss of secretory function, establish the NOD mouse as an appropriate model to unravel the underlying pathophysiology of SS. Recently, several NOD congenic partner strains have been developed to investigate the roles of genetic intervals, cytokines, and autoantibodies in the disease pathogenesis. Studies on NOD-scid suggest that the pathogenesis of SS occurs in two phases: an asymptomatic phase, in which epithelial cells of exocrine tissues undergo dedifferentiation accompanied by elevated apoptosis; and a second phase in which autoaggression is mounted against target organ autoantigens, resulting in the activation of T- and B-cells, and the generation of autoantibodies. The presence of autoantibodies on the cell-surface signaling receptor, the muscarinic(3) receptor, in both SS patients and the NOD mice correlates with the hallmark clinical symptom of secretory dysfunction. Additionally, the NOD mouse model provides an important example of how both Th1 and Th2 cytokines, as well as non-immune genetic loci, are involved in the maintenance of and progression to the overt disease state. Ultimately, analysis of these data provides insight into potentially novel therapeutic interventions.

Resistance of the target islet tissue to autoimmune destruction contributes to genetic susceptibility in Type 1 diabetes

Type 1 diabetes occurs when self-reactive T lymphocytes destroy the insulin-producing islet beta cells of the pancreas. The defects causing this disease have often been assumed to occur exclusively in the immune system. We present evidence that genetic variation at the Idd9 diabetes susceptibility locus determines the resilience of the targets of autoimmunity, the islets, to destruction. Susceptible islets exhibit hyper-responsiveness to inflammatory cytokines resulting in enhanced cell death and increased expression of the death receptor Fas. Fas upregulation in beta cells is mediated by TNFR2, and colocalization of TNFR2 with the adaptor TRAF2 in NOD beta cells is altered. TNFR2 lies within the candidate Idd9 interval and the diabetes-associated variant contains a mutation adjacent to the TRAF2 binding site. A component of diabetes susceptibility may therefore be determined by the target of the autoimmune response, and protective TNFR2 signaling in islets inhibit early cytokine-induced damage required for the development of destructive autoimmunity.

REVIEWERS

This article was reviewed by Matthiasvon Herrath, HaraldVon Boehmer, and Ciriaco Piccirillo (nominated by Ethan Shevach).

Transforming growth factor-beta and T-cell-mediated immunoregulation in the control of autoimmune diabetes

It is now well-established that CD4+ regulatory T cells are instrumental in controlling immune responses both to self-antigens and to non-self-antigens. However, the precise modalities involved in their differentiation and survival, their mode of action and their antigen specificity are only partially understood. We have been particularly interested in the study of regulatory T cells controlling autoimmune insulin-dependent diabetes. Here, we provide evidence to support the phenotypic and functional diversity of regulatory T cells mediating transferable 'active' or 'dominant' peripheral tolerance in the non-obese diabetic mouse model (NOD). They include natural and adaptive regulatory T cells that are operational both in unmanipulated NOD mice and in animals undergoing treatments aimed at inducing/restoring tolerance to self-beta-cell antigens. At least in our hands, the differential cytokine-dependency appears as a major distinctive feature of regulatory T cells subsets. Among immunoregulatory cytokines, transforming growth factor-beta(TGF-beta) appeared to play a key role. Herein we discuss these results and the working hypothesis they evoke in the context of the present literature, where the role of TGF-beta-dependent T-cell-mediated immunoregulation is still debated.

Resetting the functional capacity of regulatory T cells: a novel immunotherapeutic strategy to promote immune tolerance

Over the last few years, there has been a re-emergence of the concept of suppressor/regulatory T cells among the central players of immune mechanisms controlling a wide variety of immune responses from physiological autoreactivity (i.e., response to self-antigens) to responses to transplants, tumours and infectious antigens. Regulatory T cells are diverse in their phenotypes, antigen specificity, mode of action and immunopathological relevance. This review briefly summarises studies from the authors' group showing that specialised subsets of regulatory T cells are instrumental in the control of autoimmune diseases and more specifically of Type 1 diabetes. In addition, this review will provide evidence supporting the notion that CD3-specific monoclonal antibodies are representatives of a new category of immunotherapeutic agents that possess the unique capacity to promote immunological tolerance (an antigen-specific unresponsiveness in the absence of long-term generalised immunosuppression) through their ability to induce immunoregulatory T cells.

Autoimmune destruction of pancreatic beta cells

Type 1 diabetes results from the destruction of insulin-producing pancreatic beta cells by a beta cell-specific autoimmune process. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes have been shown to be involved in the pathogenesis of autoimmune diabetes. Beta cell autoantigens are thought to be released from beta cells by cellular turnover or damage and are processed and presented to T helper cells by antigen-presenting cells. Macrophages and dendritic cells are the first cell types to infiltrate the pancreatic islets. Naive CD4+ T cells that circulate in the blood and lymphoid organs, including the pancreatic lymph nodes, may recognize major histocompatibility complex and beta cell peptides presented by dendritic cells and macrophages in the islets. These CD4+ T cells can be activated by interleukin (IL)-12 released from macrophages and dendritic cells. While this process takes place, beta cell antigen-specific CD8+ T cells are activated by IL-2 produced by the activated TH1 CD4+ T cells, differentiate into cytotoxic T cells and are recruited into the pancreatic islets. These activated TH1 CD4+ T cells and CD8+ cytotoxic T cells are involved in the destruction of beta cells. In addition, beta cells can also be damaged by granzymes and perforin released from CD8+ cytotoxic T cells and by soluble mediators such as cytokines and reactive oxygen molecules released from activated macrophages in the islets. Thus, activated macrophages, TH1 CD4+ T cells, and beta cell-cytotoxic CD8+ T cells act synergistically to destroy beta cells, resulting in autoimmune type 1 diabetes.

Control of Type 1 Autoimmune Diabetes by Naturally Occurring CD4+CD25+Regulatory T Lymphocytes in Neonatal NOD Mice

Nonobese diabetic (NOD) mice serve as a model of spontaneous type 1 diabetes (T1D), a T cell-mediated autoimmune disease leading to the destruction of pancreatic insulin-producing beta islet cells. A possible deficiency in regulatory T (T(reg)) cell development or function may promote the activation, expansion, and recruitment of autoreactive T cells and the onset of T1D. Naturally occurring CD4(+)CD25(+) T(reg) (nT(reg)) cells, which typically display potent inhibitory effects on T cell functions in vitro and in vivo, may be defective at controlling autoimmunity in T1D. We have examined the relative contribution of CD4(+)CD25(+) nT(reg) cells in the immune regulation of T1D in the NOD mouse model. CD4(+)CD25(+) T cells represent 5-10% of CD4(+) thymocytes or peripheral T cells from prediabetic neonatal NOD mice, are anergic to TCR signals, and potently suppress activated T cells in a contact-dependent and cytokine-independent fashion in vitro. Unlike total CD4(+) T cells, prediabetic CD25(+)-depleted CD4(+) T cells are potently diabetogenic when transferred in immunodeficient NOD mice. Co-transfer of CD4(+)CD25(+) T cells from thymocytes or peripheral lymphoid tissues of neonatal NOD mice dramatically halts disease development and beta-islet cell lymphocytic infiltration, even when T1D is induced by CD4(+) T cells from BDC2.5 transgenic or diabetic NOD mice. Finally, we show that CD4(+)CD25(+) T(reg) preferentially accumulate in inflamed pancreatic environments, where they potently inhibit the antigen-specific expansion and cytokine effector functions of diabetogenic T cells. Thus, CD4(+)CD25(+) T cell-mediated regulation is operative in the prediabetic neonatal T cell repertoire and can suppress the diabetogenic process and control the onset of T1D.

A dual role for interferon-gamma in the pathogenesis of Sjogren's syndrome-like autoimmune exocrinopathy in the nonobese diabetic mouse

Sjogren's syndrome-like autoimmune exocrinopathy (AEC) in the nonobese diabetic (NOD) mouse progresses from a preimmune phase to an immune phase, resulting in dry mouth and/or dry eyes. In the present study, the impact of the prototypical T-helper type 1 cytokine, interferon-gamma (IFN-gamma), on the onset of AEC was investigated using both the IFN-gamma and the IFN-gamma receptor gene knockout mice, NOD.IFN-gamma(-/-) and NOD.IFN-gammaR(-/-), respectively. Neither the NOD.IFN-gamma(-/-) nor the NOD.IFN-gammaR(-/-) mice exhibited increased acinar cell apoptosis and abnormal salivary protein expression, typically observed in parental NOD mice prior to disease. Without these preimmune phase abnormalities, NOD.IFN-gamma(-/-) and NOD.IFN-gammaR(-/-) mice showed no subsequent autoimmune responses against the salivary glands at 20 weeks. Interestingly, real-time polymerase chain reaction and electrophoretic gel mobility shift assays suggested that IFN-gamma and STAT1, as well as the transcriptional activity of STAT1 in NOD glands, were increased at birth. Unlike the neonatal submandibular glands of NOD or NOD-scid mice that show abnormal glandular morphogenesis at birth, the submandibular glands of the newly constructed congenic strain, NOD-scid.IFN-gamma(-/-), were found to be normal. Taken together, IFN-gamma appears to play a critical role not only during the later immune phase of AEC, but also the early preimmune phase, independent of effector functions of immune cells. How exactly IFN-gamma functions during this period remains speculative.

Satisfaction (not) guaranteed: re-evaluating the use of animal models of type 1 diabetes

Without a doubt, rodent models have been instrumental in describing pathways that lead to pancreatic beta-cell destruction, evaluating potential causes of type 1 diabetes and providing proof-of-principle for the potential of immune-based interventions. However, despite more than two decades of productive research, we are still yet to define an initiating autoantigen for the human disease, to determine the precise mechanisms of beta-cell destruction in humans and to design interventions that prevent or cure type 1 diabetes. In this Perspective article, we propose that a major philosophical change would benefit this field, a proposition that is based on evaluation of situations in which rodent models have provided useful guidance and in which they have led to disappointments.

A Sudden Decline in Active Membrane-Bound TGF-β Impairs Both T Regulatory Cell Function and Protection against Autoimmune Diabetes

Autoimmunity presumably manifests as a consequence of a shortfall in the maintenance of peripheral tolerance by CD4(+)CD25(+) T regulatory cells (Tregs). However, the mechanism underlying the functional impairment of Tregs remains largely undefined. In this study a glutamic acid decarboxylase (GAD) diabetogenic epitope was expressed on an Ig to enhance tolerogenic function, and the resulting Ig-GAD expanded Tregs in both young and older insulitis-positive, nonobese diabetic (NOD) mice, but delayed autoimmune diabetes only in the former. Interestingly, Tregs induced at 4 wk of age had significant active membrane-bound TGF-beta (mTGF-beta) and sustained protection against diabetes, whereas Tregs expanded during insulitis had minimal mTGF-beta and could not protect against diabetes. The Tregs probably operate suppressive function through mTGF-beta, because Ab blockade of mTGF-beta nullifies protection against diabetes. Surprisingly, young Tregs that modulated pathogenic T cells maintained stable frequency over time in the protected animals, but decreased their mTGF-beta at the age of 8 wk. More strikingly, these 8-wk-old mTGF-beta-negative Tregs, which were previously protective, became unable to confer resistance against diabetes. Thus, a developmental decline in active mTGF-beta nullifies Treg function, leading to a break in tolerance and the onset of diabetes.

Coxsackievirus B3 infection and type 1 diabetes development in NOD mice: insulitis determines susceptibility of pancreatic islets to virus infection

Group B coxsackieviruses (CVB) are believed to trigger some cases of human type 1 diabetes (T1D), although the mechanism by which this may occur has not been shown. We demonstrated previously that inoculation of young nonobese diabetic (NOD) mice with any of several different CVB strains reduced T1D incidence. We also observed no evidence of CVB replication within islets of young NOD mice, suggesting no role for CVB in T1D induction in the NOD mouse model. The failure to observe CVB replication within islets of young NOD mice has been proposed to be due to interferon expression by insulin-producing beta cells or lack of expression of the CVB receptor CAR. We found that CAR protein is detectable within islets of young and older NOD mice and that a CVB3 strain, which expresses murine IL-4, can replicate in islets. Mice inoculated with the IL-4 expressing CVB3 chimeric strain were better protected from T1D onset than were mock-infected control mice despite intraislet viral replication. Having demonstrated that CVB can replicate in healthy islets of young NOD mice when the intraislet environment is suitably altered, we asked whether islets in old prediabetic mice were resistant to CVB infection. Unlike young mice in which insulitis is not yet apparent, older NOD mice demonstrate severe insulitis in all islets. Inoculating older prediabetic mice with different pathogenic CVB strains caused accelerated T1D onset relative to control mice, a phenomenon that was preceded by detection of virus within islets. Together, the results suggest a model for resolving conflicting data regarding the role of CVB in human T1D etiology.

Autoimmune diseases as the loss of active "self-control"

Converging experimental evidence indicates that the clinical expression of autoimmunity is under the control of T cell-mediated immunoregulatory circuits. Several types of suppressor T cells have been described. Some of them are closely dependent upon cytokines such as TH2 cells and Tr1 cells. Others appear to rely more on cell-cell contact (such as CD25+ CD62L+ T cells), although some cytokines, notably TGF-beta, may be involved in their growth or their mode of action. It is tempting to separate suppressor cells that appear spontaneously, such as CD25+ T cells and NKT cells (innate immunoregulation), from those that are only observed after antigen administration, such as TH2 cells and Tr1 cells (adaptive immunoregulation). The role of these diverse cell types in the control of the onset or the progression of autoimmune diseases is likely, but still a matter of debate. A central question is to determine whether immune dysregulation precedes the burst of pathogenic autoimmunity.

TGF-beta-dependent mechanisms mediate restoration of self-tolerance induced by antibodies to CD3 in overt autoimmune diabetes

CD3-specific antibodies have the unique capacity to restore self-tolerance in established autoimmunity. They induce long-term remission of overt diabetes in nonobese diabetic (NOD) mice and in human type I diabetes. The underlying mechanisms had been unclear until now. Here we report that treatment with CD3epsilon-specific antibodies induces transferable T-cell-mediated tolerance involving CD4+CD25+ cells. However, these CD4+CD25+ T cells are distinct from naturally occurring regulatory T cells that control physiological autoreactivity. CD3-specific antibody treatment induced remission in NOD Cd28-/- mice that were devoid of such regulatory cells. Remission of diabetes was abrogated by coadministration of a neutralizing transforming growth factor (TGF)-beta-specific antibody. The central role of TGF-beta was further suggested by its increased, long-lasting production by CD4+ T cells from tolerant mice. These data explain the intriguing tolerogenic effect of CD3-specific antibodies and position them as the first clinically applicable pharmacological stimulant of TGF-beta-producing regulatory CD4+ T cells.

Induction of autoantigen-specific Th2 and Tr1 regulatory T cells and modulation of autoimmune diabetes

Autoantigen-based immunotherapy can modulate autoimmune diabetes, perhaps due to the activation of Ag-specific regulatory T cells. Studies of these regulatory T cells should help us understand their roles in diabetes and aid in designing a more effective immunotherapy. We have used class II MHC tetramers to isolate Ag-specific T cells from nonobese diabetic (NOD) mice and BALB/c mice treated with glutamic acid decarboxylase 65 peptides (p206 and p221). Based on their cytokine secretion profiles, immunization of NOD mice with the same peptide induced different T cell subsets than in BALB/c mice. Treatment of NOD mice induced not only Th2 cells but also IFN-gamma/IL-10-secreting T regulatory type 1 (Tr1) cells. Adoptive transfer experiments showed that isolated tetramer(+) T cells specific for p206 or p221 could inhibit diabetes development. These cells were able to suppress the in vitro proliferation of other NOD mouse T cells without cell-cell contact. They performed their regulatory functions probably by secreting cytokines, and Abs against these cytokines could block their suppressive effect. Interestingly, the presence of both anti-IL-10 and anti-IFN-gamma could enhance the target cell proliferation, suggesting that Tr1 cells play an important role. Further in vivo experiments showed that the tetramer(+) T cells could block diabetogenic T cell migration into lymph nodes. Therefore, treatment of NOD mice with autoantigen could induce Th2 and Tr1 regulatory cells that can suppress the function and/or block the migration of other T cells, including diabetogenic T cells, and inhibit diabetes development.

A role for innate immunity in type 1 diabetes?

Two arms of the immune system, innate and adaptive immunity, differ in their mode of immune recognition. The innate immune system recognizes a few highly conserved structures on a broad range of microorganisms. On the other hand, recognition of self or autoreactivity is generally confined to the adaptive immune response. Whilst autoimmune features are relatively common, they should be distinguished from autoimmune disease that is infrequent. Type 1 diabetes is an immune-mediated disease due to the destruction of insulin secreting cells mediated by aggressive immune responses, including activation of the adaptive immune system following genetic and environmental interaction. Hypotheses for the cause of the immune dysfunction leading to type 1 diabetes include self-reactive T-cell clones that (1) escape deletion in the thymus, (2) escape from peripheral tolerance or (3) escape from homeostatic control with an alteration in the immune balance leading to autoimmunity. Evidence, outlined in this review, raises the possibility that changes in the innate immune system could lead to autoimmunity, by either priming or promoting aggressive adaptive immune responses. Hostile microorganisms are identified by genetically determined surface receptors on innate effector cells, thereby promoting clearance of these invaders. These innate effectors include a few relatively inflexible cell populations such as monocytes/macrophages, dendritic cells (DC), natural killer (NK) cells, natural killer T (NKT) cells and gammadelta T cells. Recent studies have identified abnormalities in some of these cells both in patients with type 1 diabetes and in those at risk of the disease. However, it remains unclear whether these abnormalities in innate effector cells predispose to autoimmune disease. If they were to do so, then modulation of the innate immune system could be of therapeutic value in preventing immune-mediated diseases such as type 1 diabetes.

Damage control, rather than unresponsiveness, effected by protective DX5+ T cells in autoimmune diabetes

The progression of autoimmune diabetes is regulated. We examined here the cellular controls exerted on disease that developed in the BDC2.5 T cell receptor-transgenic model. We found that all BDC2.5 mice with a monoclonal, beta cell-reactive, T cell repertoire developed diabetes before 4 weeks of age; transfer of splenocytes from young standard NOD (nonobese diabetic) mice into perinatal monoclonal BDC2.5 animals protected them from diabetes. The protective activity was generated by CD4+ alphabeta T cells, which operated for a short time at disease initiation, could be partitioned according to DX5 cell surface marker expression and split into two components. Protection did not involve clonal deletion or anergy of the autoreactive BDC2.5 cells, permitting their full activation and attack of pancreatic islets; rather, it tempered the aggressiveness of the insulitic lesion and the extent of beta cell destruction.

Plasmid vaccination with insulin B chain prevents autoimmune diabetes in nonobese diabetic mice

The insulin B (InsB) chain bears major type 1 diabetes-associated epitopes of significance for disease in humans and nonobese diabetic (NOD) mice. Somatic expression of InsB chain initiated early in life by plasmid inoculation resulted in substantial protection of female NOD mice against disease. This was associated with a T2 shift in spleen, expansion of IL-4-producing and, to a lesser extent, of IFN-gamma-secreting T cells in pancreatic lymph nodes, as well as intermolecular Th2 epitope spreading to glutamic acid decarboxylase determinants. A critical role of IL-4 for the Ag-specific protective effect triggered by plasmid administration was revealed in female IL-4(-/-) NOD mice that developed diabetes and higher Th1 responses. Coadministration of IL-4-expressing plasmid or extension of the vaccination schedule corrected the unfavorable response of male NOD mice to DNA vaccination with InsB chain. Thus, plasmid-mediated expression of the InsB chain early in diabetes-prone mice has the potential to prevent transition to full-blown disease depending on the presence of IL-4.

T lymphocytes need IL-7 but not IL-4 or IL-6 to survive in vivo

The role of IL-4, -6 and -7 in the survival of T lymphocytes was studied in vivo. The decay of polyclonal populations of CD4(+) and CD8(+) T cells was monitored in thymectomized anti-cytokine receptor mAb-treated and/or cytokine-deficient mice. The lack of IL-4 or -6 did not have any detectable effect on T cell survival, but IL-7 played an important role in the survival of the naive T cell compartment, especially of naive CD4(+) T cells.

CD1-restricted NK T cells protect nonobese diabetic mice from developing diabetes

NK T cells are a unique subset of T cells that recognize lipid antigens presented by CD1d. After activation, NK T cells promptly produce large amounts of cytokines, which may modulate the upcoming immune responses. Previous studies have documented an association between decreased numbers of NK T cells and the progression of some autoimmune diseases, suggesting that NK T cells may control the development of autoimmune diseases. To investigate the role of NK T cells in autoimmune diabetes, we crossed CD1 knockout (CD1KO) mutation onto the nonobese diabetic (NOD) genetic background. We found that male CD1KO NOD mice exhibited significantly higher incidence and earlier onset of diabetes compared with the heterozygous controls. The diabetic frequencies in female mice showed a similar pattern; however, the differences were less profound between female CD1KO and control mice. Early treatment of NOD mice with alpha-galactosylceramide, a potent NK T cell activator, reduced the severity of autoimmune diabetes in a CD1-dependent manner. Our results not only suggest a protective role of CD1-restricted NK T cells in autoimmune diabetes but also reveal a causative link between the deficiency of NK T cells and the induction of insulin-dependent diabetes mellitus.

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.

Non-Th2 regulatory T-cell control of Th1 autoimmunity

The Th1/Th2 concept brought an attractive explanation of the active self tolerance which appears to control the onset of pathogenic autoimmunity. New data coming from various independent horizons indicate that self immunoregulation could also depend to a large extent on non-Th2 cells. Original data derived from the day-3-thymectomy model, selective T-cell lymphocytopenia and nonobese diabetic mice are discussed in an effort to analyze similarities and differences in phenotype (CD25, CD62L and CD45RB) and cytokine pattern (notably interleukin (IL)-4, IL-10 and transforming growth factor (TGF)beta) of regulatory cells involved in these models. The relationship of these cells with Th3, Tr1 and natural killer (NK) T cells are also discussed. The hypothesis is proposed that CD25 CD62L T cells mediate the physiologic regulation of self regulation whereas Th2 and Th3 cells are essentially induced following sensitization against autoantigens.

A Glutamic Acid Decarboxylase 65-Specific Th2 Cell Clone Immunoregulates Autoimmune Diabetes in Nonobese Diabetic Mice

Several studies have provided indirect evidence in support of a role for beta cell-specific Th2 cells in regulating insulin-dependent diabetes (IDDM). Whether a homogeneous population of Th2 cells having a defined beta cell Ag specificity can prevent or suppress autoimmune diabetes is still unclear. In fact, recent studies have demonstrated that beta cell-specific Th2 cell clones can induce IDDM. In this study we have established Th cell clones specific for glutamic acid decarboxylase 65 (GAD65), a known beta cell autoantigen, from young unimmunized nonobese diabetic (NOD) mice. Adoptive transfer of a GAD65-specific Th2 cell clone (characterized by the secretion of IL-4, IL-5, and IL-10, but not IFN-gamma or TGF-beta) into 2- or 12-wk-old NOD female recipients prevented the progression of insulitis and subsequent development of overt IDDM. This prevention was marked by the establishment of a Th2-like cytokine profile in response to a panel of beta cell autoantigens in cultures established from the spleen and pancreatic lymph nodes of recipient mice. The immunoregulatory function of a given Th cell clone was dependent on the relative levels of IFN-gamma vs IL-4 and IL-10 secreted. These results provide direct evidence that beta cell-specific Th2 cells can indeed prevent and suppress autoimmune diabetes in NOD mice.

Antigen-specific mediated suppression of beta cell autoimmunity by plasmid DNA vaccination

In this study, we have investigated the use of plasmid DNA (pDNA) vaccination to elicit Th2 effector cell function in an Ag-specific manner and in turn prevent insulin-dependent diabetes mellitus (IDDM) in nonobese diabetic (NOD) mice. pDNA recombinants were engineered encoding a secreted fusion protein consisting of a fragment of glutamic acid decarboxylase 65 (GAD65) linked to IgGFc, and IL-4. Intramuscular injection of pDNA encoding GAD65-IgGFc and IL-4 effectively prevented diabetes in NOD mice treated at early or late preclinical stages of IDDM. This protection was GAD65-specific since NOD mice immunized with pDNA encoding hen egg lysozyme-IgGFc and IL-4 continued to develop diabetes. Furthermore, disease prevention correlated with suppression of insulitis and induction of GAD65-specific regulatory Th2 cells. Importantly, GAD65-specific immune deviation was dependent on pDNA-encoded IL-4. In fact, GAD65-specific Th1 cell reactivity was significantly enhanced in animals immunized with pDNA encoding only GAD65-IgGFc. Finally, NOD.IL4(null) mice treated with pDNA encoding GAD65-IgGFc and IL-4 continued to develop diabetes, indicating that endogenous IL-4 was also required for disease prevention. These results demonstrate that pDNA vaccination is an effective strategy to elicit beta cell-specific Th2 regulatory cell function for the purpose of preventing IDDM even at a late stage of disease development.

Th1 to Th2 cytokine shifts in nonobese diabetic mice: sometimes an outcome, rather than the cause, of diabetes resistance elicited by immunostimulation

Numerous immunostimulatory protocols inhibit the development of T cell-mediated autoimmune insulin-dependent diabetes mellitus (IDDM) in the nonobese diabetic (NOD) mouse model. Many of these protocols, including treatment with the nonspecific immunostimulatory agents CFA or bacillus Calmette-Guérin (BCG) vaccine, have been reported to mediate protection by skewing the pattern of cytokines produced by pancreatic beta-cell autoreactive T cells from a Th1 (IFN-gamma) to a Th2 (IL-4 and IL-10) profile. However, most of these studies have documented associations between such cytokine shifts and disease protection rather than a cause/effect relationship. To partially address this issue we produced NOD mice genetically deficient in IFN-gamma, IL-4, or IL-10. Elimination of any of these cytokines did not significantly alter the rate of spontaneous IDDM development. Additional experiments using these mice confirmed that CFA- or BCG-elicited diabetes protection is associated with a decreased IFN-gamma to IL-4 mRNA ratio within T cell-infiltrated pancreatic islets, but this is a secondary consequence rather than the cause of disease resistance. Unexpectedly, we also found that the ability of BCG and, to a lesser extent, CFA to inhibit IDDM development in standard NOD mice is actually dependent upon the presence of the Th1 cytokine, IFN-gamma. Collectively, our studies demonstrate that while Th1 and Th2 cytokine shifts may occur among beta-cell autoreactive T cells of NOD mice protected from overt IDDM by various immunomodulatory therapies, it cannot automatically be assumed that this is the cause of their disease resistance.

Relative diabetogenic properties of islet-specific Tc1 and Tc2 cells in immunocompetent hosts

CD8(+) T cells are important effectors, as well as regulators, of organ-specific autoimmunity. Compared with Tc1-type CD8(+) cells, Tc2 cells have impaired anti-viral and anti-tumor effector functions, although no data are yet available on their pathogenic role in autoimmunity. Our aim was to explore the role of autoreactive Tc1 and Tc2 cells in autoimmune diabetes. We set up an adoptive transfer model in which the recipients were transgenic mice expressing influenza virus hemagglutinin (HA) specifically in their pancreatic ss islet cells (rat insulin promoter-HA mice) and islet-specific Tc1 and Tc2 cells were generated in vitro from HA-specific CD8(+) cells of TCR transgenic mice (CL4-TCR mice). One million Tc1 cells, differentiated in vitro in the presence of IL-12, transferred diabetes in 100% of nonirradiated adult rat insulin promoter-HA recipients; the 50% diabetogenic dose was 5 x 10(5). Highly polarized Tc2 cells generated in the presence of IL-4, IL-10, and anti-IFN-gamma mAb had a relatively low, but definite, diabetogenic potential. Thus, 5 x 10(6) Tc2 cells caused diabetes in 6 of 18 recipients, while the same dose of naive CD8(+) cells did not cause diabetes. Looking for the cause of the different diabetogenic potential of Tc1 and Tc2 cells, we found that Tc2 cells are at least as cytotoxic as Tc1 cells but their accumulation in the pancreas is slower, a possible consequence of differential chemokine receptor expression. The diabetogenicity of autoreactive Tc2 cells, most likely caused by their cytotoxic activity, precludes their therapeutic use as regulators of autoimmunity.

Altered major histocompatibility complex class II peptide loading in H2-O-deficient mice

The biosynthesis of MHC class II/peptide complexes involves classical, cell surface MHC products as well as the intracellular component H2-M, required for the removal of invariant chain-derived CLIP and for peptide loading. The function of another intracellular class II heterodimer, H2-O, is the matter of some controversy. The physical association of H2-O with H2-M and co-localization in class II+ vesicles suggest a related function in peptide exchange. Furthermore, the distinctive thymic distribution of H2-O raises the possibility of a specialized role in T cell thymic selection. To investigate the role of H2-O in vivo we generated mice carrying a targeted disruption in the H2-Oa gene. No evidence was obtained for a defect in removal of CLIP. However, the array of endogenous peptides bound by class II was altered and a defect in antigen presentation through H2-A to T cells was seen on the 129/Sv/ C57BL/6 mixed strain background but not in 129/Sv pure strain mice. Furthermore, H2-O-null mice showed enhanced selection of CD4+ single positive thymocytes. The findings indicate that H2-O interacts with H2-M in peptide editing but that the genetic background in which H2-O deficiency is manifest is also important. Overall, the experiments indicate that H2-O/HLA-DO should be regarded as neither up-regulating nor down-regulating the DM-dependent release of CLIP, but as a modulator of peptide editing, determining the presenting cell type specific peptide profile able to retain stability in the class II groove.

IL-10 deficiency does not inhibit insulitis and accelerates cyclophosphamide-induced diabetes in the nonobese diabetic mouse

IL-10 exterts profound immunostimulatory and immunoinhibitory effects. To explore the role of IL-10 in autoimmune diabetes of nonobese diabetic (NOD) mice, we generated IL-10-deficient NOD mice. In contrast to our previous results with neutralizing antibodies to IL-10, IL-10-deficient NOD mice developed insulitis and their splenocytes readily responded to islet antigen glutamic acid decarboxylase 65. IL-10-deficient NOD mice did not develop accelerated spontaneous diabetes. On the other hand, IL-10-deficient NOD mice developed accelerated disease following cyclophosphamide (CYP) injection. These findings demonstrate that IL-10 is dispensable for autoimmune diabetes. IL-10's absence fails to accelerate endogenous diabetes but potentiates CYP-induced diabetes.

Cellular and molecular roles of beta cell autoantigens, macrophages and T cells in the pathogenesis of autoimmune diabetes

Type I diabetes, also known as insulin-dependent diabetes mellitus (IDDM) results from the destruction of insulin-producing pancreatic beta cells by a progressive beta cell-specific autoimmune process. The pathogenesis of autoimmune IDDM has been extensively studied for the past two decades using animal models such as the non-obese diabetic (NOD) mouse and the BioBreeding (BB) rat. However, the initial events that trigger the immune responses leading to the selective destruction of the beta cells are poorly understood. It is thought that beta cell autoantigens are involved in the triggering of beta cell-specific autoimmunity. Among a dozen putative beta cell autoantigens, glutamic acid decarboxylase (GAD) has been proposed as perhaps the strongest candidate in both humans and the NOD mouse. In the NOD mouse, GAD, as compared with other beta cell autoantigens, provokes the earliest T cell proliferative response. The suppression of GAD expression in the beta cells results in the prevention of autoimmune diabetes in NOD mice. In addition, the major populations of cells infiltrating the islets during the early stage of insulitis in BB rats and NOD mice are macrophages and dendritic cells. The inactivation of macrophages in NOD mice results in the prevention of T cell mediated autoimmune diabetes. Macrophages are primary contributors to the creation of the immune environment conducive to the development and activation of beta cell-specific Th1-type CD4+ T cells and CD8+ cytotoxic T cells that cause autoimmune diabetes in NOD mice. CD4+ and CD8+ T cells are both believed to be important for the destruction of beta cells. These cells, as final effectors, can kill the insulin-producing beta cells by the induction of apoptosis. In addition, CD8+ cytotoxic T cells release granzyme and cytolysin (perforin), which are also toxic to beta cells. In this way, macrophages, CD4+ T cells and CD8+ T cells act synergistically to kill the beta cells in conjunction with beta cell autoantigens and MHC class I and class II antigens, resulting in the onset of autoimmune type I diabetes.

Failure of exogenously administered interferon-gamma or blockage of endogenous interleukin-4 with specific inhibitors to augment the incidence of autoimmune diabetes in male NOD mice

Interferon (IFN)-gamma and interleukin (IL)-4 are prototypic type 1 and type 2 cytokines which are known to play pathogenetic and protective roles, respectively, in NOD mouse IDDM. The capacity of male NOD mice to produce more IL-4 and less IFN-gamma within the insulitic lesions than females has been suggested to contribute to their lower incidence of diabetes. In this study we have tested the effects of prolonged prophylactic treatment of male NOD mice with rat IFN-gamma, mouse IFN-gamma, anti-IL-4 monoclonal antibody (mAb) and recombinant murine soluble IL-4 receptor (smIL-4R) on the diabetogenic events leading to insulitis and diabetes. None of these treatments influenced spontaneous and/or cyclophosphamide-induced autoimmune diabetogenesis in male NOD mice. Control mice exhibited comparable histological signs of insulitis and incidence of diabetes to those treated with either mouse/rat IFN-gamma or specific IL-4 inhibitors. On the contrary, both clinical and histological signs of diabetes were suppressed by prophylactic treatment with anti-IFN-gamma mAb. These findings indicate that the autoimmune diathesis of male NOD mice towards IDDM cannot be augmented by manipulation of endogenous IFN-gamma or IL-4.

Pancreatic IL-4 Expression Results in Islet-Reactive Th2 Cells That Inhibit Diabetogenic Lymphocytes in the Nonobese Diabetic Mouse

When immunological tolerance breaks down, autoimmune destruction of insulin-producing β cells in the pancreas can cause insulin-dependent diabetes mellitus. We previously showed that transgenic nonobese diabetic (NOD) mice expressing IL-4 in the pancreas (NOD-IL-4 mice) were protected from insulitis and diabetes. Here we have characterized the avoidance of pathological autoimmunity in these mice. The absence of disease did not result from a lack of T cell priming, because T cells responding to dominant islet Ags were present. These islet Ag-specific T cells displayed a Th2 phenotype, indicating that Th2 responses could account for the observed tolerance. Interestingly, islet Ag-specific Th1 T cells were present and found to be functional, because neutralization of the Th2 effector cytokines IL-4 and IL-10 resulted in diabetes. Histological examination revealed that NOD-IL-4 splenocytes inhibited diabetogenic T cells in cotransfer experiments by limiting insulitis and delaying diabetes. Neutralization of IL-4 in this system abrogated the ability of NOD-IL-4 splenocytes to delay the onset of diabetes. These results indicate that IL-4 expressed in the islets does not prevent the generation of pathogenic islet responses but induces islet Ag-specific Th2 T cells that block the action of diabetogenic T cells in the pancreas.

Induction of Glutamic Acid Decarboxylase 65-Specific Th2 Cells and Suppression of Autoimmune Diabetes at Late Stages of Disease Is Epitope Dependent

Peptide-based immunotherapy is one strategy by which to selectively suppress the T cell-mediated destruction of β cells and treat insulin-dependent diabetes mellitus (IDDM). Here, we investigated whether a panel of T cell epitopes derived from the β cell autoantigen glutamic acid decarboxylase 65 (GAD65) differ in their capacity to induce Th2 cell function in nonobese diabetic (NOD) mice and in turn prevent overt IDDM at different preclinical stages of disease development. The panel consists of GAD65-specific peptides spanning aa 217–236 (p217), 247–265 (p247), 290–309 (p290), and 524–543 (p524). Our studies revealed that all of the peptides effectively prevented insulitis and diabetes when administered to NOD mice before the onset of insulitis. In contrast, only a mixture of p217 and p290 prevented progression of insulitis and overt IDDM in NOD mice exhibiting extensive β cell autoimmunity. Immunization with the GAD65-specific peptides did not block IDDM development in NOD mice deficient in IL-4 expression. These findings demonstrate that GAD65-specific peptide immunotherapy effectively suppresses progression to overt IDDM, requires the production of IL-4, and is dependent on the epitope targeted and the extent of preexisting β cell autoimmunity in the recipient.

Establishment of an embryonic stem (ES) cell line derived from a non-obese diabetic (NOD) mouse: in vivo differentiation into lymphocytes and potential for germ line transmission

A non-obese diabetic (NOD) mouse-derived embryonic stem (ES) cell line has been stably maintained in an undifferentiated state with a characteristic ES cell-like morphology, expressing the stem cell marker alkaline phosphatase, and displaying a normal diploid karyotype. After injecting the NOD-ES cells into blastocysts, chimeric mice were obtained. Small but significant numbers of lymphocytes expressed the NOD-derived MHC allele. When a chimeric mouse was mated with C57BL/6 mice, an agouti mouse was obtained, having the NOD-derived H-2 I-A(beta)g7 haplotype. Thus, an NOD-ES cell line which can differentiate into lymphocytes with potential for germ line transmission was successfully established.

Dissecting the role of CD4+ T cells in autoimmune diabetes through the use of TCR transgenic mice

Insulin-dependent diabetes mellitus (IDDM) is an immunological disorder wherein autoimmune-mediated destruction of islet cells in the pancreas results in persistent hyperglycemia. The non-obese diabetic mouse model of IDDM has revealed the importance of multiple factors that impact upon the disease process; however, understanding of primary immune mechanisms leading to IDDM remains elusive. The emergence of transgenic mouse models for IDDM has made important contributions towards clarifying many of these factors, including the cell types, the various effector molecules and the genetic elements involved in the pathogenesis of IDDM. In this review, we will focus on the primary mechanism and mediators of islet beta-cell death, the impact of T-helper lymphocytes on disease progression and the potential role of major histocompatibility complex class II molecules in conferring susceptibility to IDDM.

Transgenes and knockout mutations in animal models of type 1 diabetes and multiple sclerosis

In this article, we will examine the roles of transgenic and knockout animals that aid us in understanding two autoimmune diseases-type 1 (insulin-dependent) diabetes and multiple sclerosis. The first sections will focus on studies in type 1 diabetes to show how genetically altered animals have given insight into the role of various immune cell types, autoantigens, co-stimulatory molecules, cytokines and, finally, the role of various effector pathways in the pathogenesis of diabetes. The second section concentrating on the animal model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE), will show how animals that express a T-cell receptor derived from a clone able to cause disease have given insight into the pathogenesis of EAE.