Islet-infiltrating lymphocytes from prediabetic NOD mice rapidly transfer diabetes to NOD-scid/scid mice

New Perspectives in Studying Type 1 Diabetes Susceptibility Biomarkers

Type 1 diabetes (T1D) is generally viewed as an etiologic subtype of diabetes caused by the autoimmune destruction of the insulin-secreting β-cells. It has been known that autoreactive T cells unfortunately destroy healthy β-cells. However, there has been a notion of etiologic heterogeneity around the world implicating a varying incidence of a non-autoimmune subgroup of T1D related to insulin deficiency associated with decreased β cell mass, in which the β-cell is the key contributor to the disease. Beta cell dysfunction, reduced mass, and apoptosis may lead to insufficient insulin secretion and ultimately to the development of T1D. Interestingly, Korean as well as other ethnic genetic results have also suggested that genes related with insulin deficiency, let alone those of immune regulation, were associated with the risk of T1D in the young. Genes related with insulin secretion may influence the phenotype of diabetes differentially and different genes may be working on different steps of T1D development. Although we admit the consensus that islet autoimmunity is an essential component in the pathogenesis of T1D, however, dysfunction might occur not only in the immune system but also in the β-cells, the defect of which may induce further dysfunction of the immune system. These arguments stem from the fact that the β-cell might be the trigger of an autoimmune response. This emergent view has many parallels with the fact that by their nature and function, β-cells are prone to biosynthetic stress with limited measures for self-defense. Beta cell stress may induce an immune attack that has considerable negative effects on the production of a vital hormone, insulin. If then, both β-cell stress and islet autoimmunity can be harnessed as targets for intervention strategies. This also may explain why immunotherapy at best delays the progression of T1D and suggests the use of alternative therapies to expand β-cells, in combination with immune intervention strategies, to reverse the disease. Future research should extend to further investigate β-cell biology, in addition to studies of immunologic areas, to find appropriate biomarkers of T1D susceptibility. This will help to decipher β-cell characteristics and the factors regulating their function to develop novel therapeutic approaches.

Exploring lncRNAs associated with human pancreatic islet cell death induced by transfer of adoptive lymphocytes in a humanized mouse model

Background

Long noncoding RNA (lncRNA)-mediated posttranscriptional and epigenetic landscapes of gene regulation are associated with numerous human diseases. However, the regulatory mechanisms governing human β-cell function and survival remain unknown. Owing to technical and ethical constraints, studying the direct role of lncRNAs in β-cell function and survival in humans in vivo is difficult. Therefore, we utilized humanized mice with human islets to investigate lncRNA expression using whole transcriptome shotgun sequencing. Our study aimed to characterize lncRNAs that may be crucial for human islet cell function and survival.

Methods

Human β-cell death was induced in humanized mice engrafted with functional human islets. Using these humanized mice harboring human islets with induced β-cell death, we investigated lncRNA expression through whole transcriptome shotgun sequencing. Additionally, we systematically identified, characterized, and explored the regulatory functions of lncRNAs that are potentially important for human pancreatic islet cell function and survival.

Results

Human islet cell death was induced in humanized mice engrafted with functional human islets. RNA sequencing analysis of isolated human islets, islet grafts from humanized mice with and without induced cell death, revealed aberrant expression of a distinct set of lncRNAs that are associated with the deregulated mRNAs important for cellular processes and molecular pathways related to β-cell function and survival. A total of 10 lncRNA isoforms (SCYL1-1:22, POLG2-1:1, CTRB1-1:1, SRPK1-1:1, GTF3C5-1:1, PPY-1:1, CTRB1-1:5, CPA5-1:1, BCAR1-2:1, and CTRB1-1:4) were identified as highly enriched and specific to human islets. These lncRNAs were deregulated in human islets from donors with different BMIs and with type 2 diabetes (T2D), as well as in cultured human islets with glucose stimulation and induced cell death induced by cytokines. Aberrant expression of these lncRNAs was detected in the exosomes from the medium used to culture islets with cytokines.

Conclusion

Islet-enriched and specific human lncRNAs are deregulated in human islet grafts and cultured human islets with induced cell death. These lncRNAs may be crucial for human β-cell function and survival and could have an impact on identifying biomarkers for β-cell loss and discovering novel therapeutic targets to enhance β-cell function and survival.

The relationship between Schistosoma and glycolipid metabolism

Diabetes and obesity have become the most popular metabolic diseases in the world. A large number of previous studies have shown that glucose and lipid metabolism disorder is an important risk factor and a main cause of diabetes and obesity. Schistosoma is a parasite transmitted by freshwater snails. It can induce a series of inflammatory and immune reactions after infecting the human body, causing schistosomiasis. However, in recent years, studies have found that Schistosoma infection or Schistosoma related products can improve or prevent some immune and inflammatory diseases, such as severe asthma, inflammatory bowel disease, diabetes and so on. Further experiments have also revealed that Schistosoma can promote the secretion of anti-inflammatory factors and regulate the glucose and lipid metabolism in the host body by polarizing immune cells such as T cells, B cells and dendritic cells (DCs). In this review, we summarize studies that investigated Schistosoma and Schistosoma-derived products and their relationship with glycolipid metabolism and related diseases, highlighting potential protective mechanisms.

Male sex chromosomal complement exacerbates the pathogenicity of Th17 cells in a chronic model of central nervous system autoimmunity

Sex differences in multiple sclerosis (MS) incidence and severity have long been recognized. However, the underlying cellular and molecular mechanisms for why male sex is associated with more aggressive disease remain poorly defined. Using a T cell adoptive transfer model of chronic experimental autoimmune encephalomyelitis (EAE), we find that male Th17 cells induce disease of increased severity relative to female Th17 cells, irrespective of whether transferred to male or female recipients. Throughout the disease course, a greater frequency of male Th17 cells produce IFNγ, a hallmark of pathogenic Th17 responses. Intriguingly, XY chromosomal complement increases the pathogenicity of male Th17 cells. An X-linked immune regulator, Jarid1c, is downregulated in pathogenic male murine Th17 cells, and functional experiments reveal that it represses the severity of Th17-mediated EAE. Furthermore, Jarid1c expression is downregulated in CD4⁺ T cells from MS-affected individuals. Our data indicate that male sex chromosomal complement critically regulates Th17 cell pathogenicity.

Identification and Characterization of microRNAs Associated With Human β-Cell Loss in a Mouse Model

Currently there is no effective approach for monitoring early β-cell loss during islet graft rejection following human islet transplantation (HIT). Due to ethical and technical constraints, it is difficult to directly study biomarkers of islet destruction in humans. Here, we established a humanized mouse model with induced human β-cell death using adoptive lymphocyte transfer (ALT). Human islet grafts of ALT-treated mice had perigraft lymphocyte infiltration, fewer insulin⁺ β cells, and increased β-cell apoptosis. Islet-specific miR-375 was used to validate our model, and expression of miR-375 was significantly decreased in the grafts and increased in the circulation of ALT-treated mice before hyperglycemia. A NanoString expression assay was further used to profile 800 human miRNAs in the human islet grafts, and the results were validated using quantitative real-time polymerase chain reaction. We found that miR-4454 and miR-199a-5p were decreased in the human islet grafts following ALT and increased in the circulation prior to hyperglycemia. These data demonstrate that our in vivo model of induced human β-cell destruction is a robust method for identifying and characterizing circulating biomarkers, and suggest that miR-4454 and miR-199a-5p can serve as novel biomarkers associated with early human β-cell loss following HIT.

Role of ITGAE in the development of autoimmune diabetes in non-obese diabetic mice

There is compelling evidence that autoreactive CD8(+)T cells play a central role in precipitating the development of autoimmune diabetes in non-obese diabetic (NOD) mice, but the underlying mechanisms remain unclear. Given that ITGAE (CD103) recognizes an islet-restricted ligand (E-cadherin), we postulated that its expression is required for initiation of disease. We herein use a mouse model of autoimmune diabetes (NOD/ShiLt mice) to test this hypothesis. We demonstrate that ITGAE is expressed by a discrete subset of CD8(+)T cells that infiltrate pancreatic islets before the development of diabetes. Moreover, we demonstrate that development of diabetes in Itgae-deficient NOD mice is significantly delayed at early but not late time points, indicating that ITGAE is preferentially involved in early diabetes development. To rule out a potential contribution by closely linked loci to this delay, we treated WT NOD mice beginning at 2 weeks of age through 5 weeks of age with a depleting anti-ITGAE mAb and found a decreased incidence of diabetes following anti-ITGAE mAb treatment compared with mice that received isotype control mAbs or non-depleting mAbs to ITGAE. Moreover, a histological examination of the pancreas of treated mice revealed that NOD mice treated with a depleting mAb were resistant to immune destruction. These results indicate that ITGAE(+) cells play a key role in the development of autoimmune diabetes and are consistent with the hypothesis that ITGAE(+)CD8(+)T effectors initiate the disease process.

Polymorphism in the innate immune receptor SIRPα controls CD47 binding and autoimmunity in the nonobese diabetic mouse

The signal regulatory protein (SIRP) locus encodes a family of paired receptors that mediate both activating and inhibitory signals and is associated with type 1 diabetes (T1D) risk. The NOD mouse model recapitulates multiple features of human T1D and enables mechanistic analysis of the impact of genetic variations on disease. In this study, we identify Sirpa encoding an inhibitory receptor on myeloid cells as a gene in the insulin-dependent diabetes locus 13.2 (Idd13.2) that drives islet inflammation and T1D. Compared to T1D-resistant strains, the NOD variant of SIRPα displayed greater binding to its ligand CD47, as well as enhanced T cell proliferation and diabetogenic potency. Myeloid cell-restricted expression of a Sirpa transgene accelerated disease in a dose-dependent manner and displayed genetic and functional interaction with the Idd5 locus to potentiate insulitis progression. Our study demonstrates that variations in both SIRPα sequence and expression level modulate T1D immunopathogenesis. Thus, we identify Sirpa as a T1D risk gene and provide insight into the complex mechanisms by which disease-associated variants act in concert to drive defined stages in disease progression.

CD4+ T cells recognize diverse epitopes within GAD65: implications for repertoire development and diabetes monitoring

Type 1 diabetes is associated with T-cell responses to β-cell antigens such as GAD65. Single T-cell epitopes have been investigated for immune monitoring with some success, but multiple epitopes may be required to fully characterize responses in all subjects. We used a systematic approach to examine the diversity of the GAD65-specific T-cell repertoire in subjects with DRB1*04:01 haplotypes. Using class II tetramers, we observed responses to 15 GAD65 epitopes, including five novel epitopes. The majority were confirmed to be processed and presented. Upon stimulation with peptides, GAD-specific responses were equally broad in subjects with diabetes and healthy controls in the presence or absence of CD25(+) T cells, suggesting that a susceptible HLA is sufficient to generate a potentially autoreactive repertoire. Without depleting CD25(+) cells, GAD(113-132) and GAD(265-284) responses were significantly stronger in subjects with diabetes. Although nearly every individual responded to at least one GAD65 epitope, most were seen in less than half of the subjects tested, suggesting that multiple epitopes are recommended for immune monitoring.

Using stem cells to study and possibly treat type 1 diabetes

Stem cells with the potential to form many different cell types are actively studied for their possible use in cell replacement therapies for several diseases. In addition, the differentiated derivatives of stem cells are being used as reagents to test for drugs that slow or correct disease phenotypes found in several degenerative diseases. This paper explores these approaches in the context of type 1 or juvenile diabetes, pointing to recent successes as well as the technical and theoretical challenges that lie ahead in the path to new treatments and cures.

Mouse Models for Type 1 Diabetes

Our understanding of the genetics, aetiology and pathogenesis of Type 1 Diabetes (T1D) was propelled by the discovery of animal models of T1D in the late 1970s and early 1980s, particularly the non-obese diabetic (NOD) mouse. Since then, transgenic and gene-targeting technologies allowed the generation of many models with reduced genetic and pathogenic complexity. These models allowed researchers to zoom in on specific aspects of this complex disease. In this review, we provide an overview of currently available mouse models for T1D.

Suppression of autoimmune diabetes by soluble galectin-1

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that targets the beta-cells of the pancreas. We investigated the ability of soluble galectin-1 (gal-1), an endogenous lectin that promotes T cell apoptosis, to down-regulate the T cell response that destroys the pancreatic beta-cells. We demonstrated that in nonobese diabetic (NOD) mice, gal-1 therapy reduces significantly the amount of Th1 cells, augments the number of T cells secreting IL-4 or IL-10 specific for islet cell Ag, and causes peripheral deletion of beta-cell-reactive T cells. Administration of gal-1 prevented the onset of hyperglycemia in NOD mice at early and subclinical stages of T1D. Preventive gal-1 therapy shifted the composition of the insulitis into an infiltrate that did not invade the islets and that contained a significantly reduced number of Th1 cells and a higher percentage of CD4(+) T cells with content of IL-4, IL-5, or IL-10. The beneficial effects of gal-1 correlated with the ability of the lectin to trigger apoptosis of the T cell subsets that cause beta-cell damage while sparing naive T cells, Th2 lymphocytes, and regulatory T cells in NOD mice. Importantly, gal-1 reversed beta-cell autoimmunity and hyperglycemia in NOD mice with ongoing T1D. Because gal-1 therapy did not cause major side effects or beta-cell toxicity in NOD mice, the use of gal-1 to control beta-cell autoimmunity represents a novel alternative for treatment of subclinical or ongoing T1D.

The use of rodent models to investigate host-bacteria interactions related to periodontal diseases

Even though animal models have limitations, they are often superior to in vitro or clinical studies in addressing mechanistic questions and serve as an essential link between hypotheses and human patients. Periodontal disease can be viewed as a process that involves four major stages: bacterial colonization, invasion, induction of a destructive host response in connective tissue and a repair process that reduces the extent of tissue breakdown. Animal studies should be evaluated in terms of their capacity to test specific hypotheses rather than their fidelity to all aspects of periodontal disease initiation and progression. Thus, each of the models described below can be adapted to test discrete components of these four major steps, but not all of them. This review describes five different animal models that are appropriate for examining components of host-bacteria interactions that can lead to breakdown of hard and soft connective tissue or conditions that limit its repair as follows: the mouse calvarial model, murine oral gavage models with or without adoptive transfer of human lymphocytes, rat ligature model and rat Aggregatibacter actinomycetemcomitans feeding model.

The use of CD3-specific antibodies in autoimmune diabetes: a step toward the induction of immune tolerance in the clinic

CD3-specific monoclonal antibodies were the first rodent monoclonals introduced in clinical practice in the mid 1980s as approved immunosuppressants to prevent and treat organ allograft rejection. Since then compelling evidence has been accumulated to suggest that in addition to their immunosuppressive properties, CD3-specific antibodies can also afford inducing immune tolerance especially in the context of ongoing immune responses. Thus, they are highly effective at restoring self-tolerance in overt autoimmunity, a capacity first demonstrated in the experimental setting, which was recently transferred to the clinic with success.

Mapping of the murine type 1 diabetes locus Idd20 by genetic interaction

In the nonobese diabetes mouse, the murine type 1 diabetes susceptibility locus Idd20 interacts genetically with the diabetes resistance locus Idd19. Both Idds are located on distal mouse Chromosome 6, and previous studies on NOD.C3H congenic strains have shown that C3H alleles at Idd20 can suppress the disease-promoting effects of C3H alleles at Idd19 in both spontaneous and cyclophosphamide-induced diabetes. In this article we present the construction of novel congenic strains which, while maintaining the C3H alleles at Idd19, have allowed the candidate interval of Idd20 to be reduced from 4 to 1.8 cM. The analysis of these strains shows that Idd20 controls the progression of insulitis. Idd20 also increases the suppressive but not the pathogenic activity of splenocytes in diabetes transfer experiments. Our results suggest that the two Chromosome 6 susceptibility loci, Idd6 and Idd20, interact with the resistance locus Idd19 by regulating the activity of suppressor cells in the peripheral immune system.

Dendritic Cells Expressing Transgenic Galectin-1 Delay Onset of Autoimmune Diabetes in Mice

Type 1 diabetes (T1D) is a disease caused by the destruction of the beta cells of the pancreas by activated T cells. Dendritic cells (DC) are the APC that initiate the T cell response that triggers T1D. However, DC also participate in T cell tolerance, and genetic engineering of DC to modulate T cell immunity is an area of active research. Galectin-1 (gal-1) is an endogenous lectin with regulatory effects on activated T cells including induction of apoptosis and down-regulation of the Th1 response, characteristics that make gal-1 an ideal transgene to transduce DC to treat T1D. We engineered bone marrow-derived DC to synthesize transgenic gal-1 (gal-1-DC) and tested their potential to prevent T1D through their regulatory effects on activated T cells. NOD-derived gal-1-DC triggered rapid apoptosis of diabetogenic BDC2.5 TCR-transgenic CD4+ T cells by TCR-dependent and -independent mechanisms. Intravenously administered gal-1-DC trafficked to pancreatic lymph nodes and spleen and delayed onset of diabetes and insulitis in the NODrag1(-/-) lymphocyte adoptive transfer model. The therapeutic effect of gal-1-DC was accompanied by increased percentage of apoptotic T cells and reduced number of IFN-gamma-secreting CD4+ T cells in pancreatic lymph nodes. Treatment with gal-1-DC inhibited proliferation and secretion of IFN-gamma of T cells in response to beta cell Ag. Unlike other DC-based approaches to modulate T cell immunity, the use of the regulatory properties of gal-1-DC on activated T cells might help to delete beta cell-reactive T cells at early stages of the disease when the diabetogenic T cells are already activated.

IFN beta accelerates autoimmune type 1 diabetes in nonobese diabetic mice and breaks the tolerance to beta cells in nondiabetes-prone mice

Genetic and environmental factors are decisive in the etiology of type 1 diabetes. Viruses have been proposed as a triggering environmental event and some evidences have been reported: type I IFNs exist in the pancreata of diabetic patients and transgenic mice expressing these cytokines in beta cells develop diabetes. To determine the role of IFNbeta in diabetes, we studied transgenic mice expressing human IFNbeta in the beta cells. Autoimmune features were found: MHC class I islet hyperexpression, T and B cells infiltrating the islets and transfer of the disease by lymphocytes. Moreover, the expression of beta(2)-microglobulin, preproinsulin, and glucagon in the thymus was not altered by IFNbeta, thus suggesting that the disease is caused by a local effect of IFNbeta, strong enough to break the peripheral tolerance to beta cells. This is the first report of the generation of NOD (a model of spontaneous autoimmune diabetes) and nonobese-resistant (its homologous resistant) transgenic mice expressing a type I IFN in the islets: transgenic NOD and nonobese-resistant mice developed accelerated autoimmune diabetes with a high incidence of the disease. These results indicate that the antiviral cytokine IFNbeta breaks peripheral tolerance to beta cells, influences the insulitis progression and contributes to autoimmunity in diabetes and nondiabetes- prone mice.

What can the HLA transgenic mouse tell us about autoimmune diabetes?

Type 1 diabetes mellitus is a polygenic disease strongly associated with the class II molecules DR3, 4 and the linked DQ2, 8 alleles. These molecules play an important role in presentation of peptide antigens after intracellular processing to CD4 T lymphocytes. A number of in vitro approaches have been used to elucidate the molecular basis for the association of particular HLA alleles with susceptibility to or protection from Type 1 diabetes mellitus. These have focused on the structure of the antigen-presenting molecules, together with their peptides. Binding studies, peptide elution, molecular modelling and crystallisation of the peptide MHC complex have between them made it possible to define the peptide-binding regions and to examine the stability of binding of peptides from putative autoantigens. It is difficult to study the role of these molecules in vivo in humans, and HLA transgenic mice have been generated to overcome this problem. Studies of mice expressing the HLA class II alleles associated with diabetes have shown that the presence of HLA molecules alone does not cause disease except in the presence of an islet "insult", even when this "insult" would in itself be insufficient to precipitate disease in the absence of the HLA class II transgene. HLA transgenic mice offer a way to elucidate the in vivo role of these molecules, and could help the development of targeted immunotherapy.

CD25+ CD4+ T cells, expanded with dendritic cells presenting a single autoantigenic peptide, suppress autoimmune diabetes

In the nonobese diabetic (NOD) mouse model of type 1 diabetes, the immune system recognizes many autoantigens expressed in pancreatic islet β cells. To silence autoimmunity, we used dendritic cells (DCs) from NOD mice to expand CD25⁺ CD4⁺ suppressor T cells from BDC2.5 mice, which are specific for a single islet autoantigen. The expanded T cells were more suppressive in vitro than their freshly isolated counterparts, indicating that DCs from autoimmune mice can increase the number and function of antigen-specific, CD25⁺ CD4⁺ regulatory T cells. Importantly, only 5,000 expanded CD25⁺ CD4⁺ BDC2.5 T cells could block autoimmunity caused by diabetogenic T cells in NOD mice, whereas 10⁵ polyclonal, CD25⁺ CD4⁺ T cells from NOD mice were inactive. When islets were examined in treated mice, insulitis development was blocked at early (3 wk) but not later (11 wk) time points. The expanded CD25⁺ CD4⁺ BDC2.5 T cells were effective even if administered 14 d after the diabetogenic T cells. Our data indicate that DCs can generate CD25⁺ CD4⁺ T cells that suppress autoimmune disease in vivo. This might be harnessed as a new avenue for immunotherapy, especially because CD25⁺ CD4⁺ regulatory cells responsive to a single autoantigen can inhibit diabetes mediated by reactivity to multiple antigens.

Relationship between beta cell mass of NOD donors and diabetes development of NOD-scid recipients in adoptive transfer system

BACKGROUND

There is controversy about the way the beta cell mass is reduced in type 1 diabetes. One view is that a gradual fall in beta cell mass begins soon after the onset of insulitis. Another view is that a sudden wave of beta cell destruction occurs just before the onset of diabetes. To clarify how the beta cell mass is reduced, we performed adoptive transfer experiments and examined the relationship between the pancreatic status of NOD donors and the time taken to transfer diabetes into NOD-scid recipients.

METHODS

We killed 18-week-old female NOD mice (n = 20), removed their spleen, and transferred splenocytes into 5-week-old female NOD-scid mice (n = 60). The relationship between the pancreatic status of donors and the time taken to transfer diabetes into recipients was assessed. As pancreatic status, we measured insulin content and severity of insulitis.

RESULTS

There was no linear correlation between the pancreatic status of donors and the time taken to transfer diabetes into recipients. NOD donors who needed 7 or more weeks to transfer diabetes in NOD-scid recipients had similar levels of insulin content or severity of insulitis as those of NOD donors who could not transfer diabetes. On the other hand, NOD donors who needed 6 or less weeks to transfer diabetes in recipients had similar levels of insulin content or severity of insulitis as those of diabetic NOD mice.

CONCLUSIONS

According to our observations, beta cell mass seems to be preserved until just before the onset of diabetes and decreased dramatically within a few weeks.

Mechanisms of accelerated immune-mediated diabetes resulting from islet beta cell expression of a Fas ligand transgene

Nonobese diabetic (NOD) mice transgenic for Fas ligand (FasL) on islet beta cells (HIPFasL mice) exhibit an accelerated diabetes distinct from the normal autoimmune diabetes of NOD mice. This study was undertaken to define the mechanism underlying accelerated diabetes development in HIPFasL mice. It was found that diabetes in HIPFasL mice is dependent on the NOD genetic background, as HIPFasL does not cause diabetes when crossed into other mice strains and is lymphocyte dependent, as it does not develop in HIPFasL(SCID) mice. Diabetes development in NOD(SCID) recipients of diabetic HIPFasL splenocytes is slower than when using splenocytes from diabetic NOD mice. Beta cells from HIPFasL mice are more susceptible to cytokine-induced apoptosis than wild-type NOD beta cells, and this can be blocked with anti-FasL Ab. HIPFasL islets are more rapidly destroyed than wild-type islets when transplanted into nondiabetic NOD mice. This confirms that FasL(+) islets do not obtain immune privilege, and instead NOD beta cells constitutively expressing FasL are more susceptible to apoptosis induced by Fas-FasL interaction. These findings are consistent with the accelerated diabetes of young HIPFasL mice being a different disease process from the autoimmune diabetes of wild-type NOD mice. The data support a mechanism by which cytokines produced by the insulitis lesion mediate up-regulation of beta cell Fas expression, resulting in suicide or fratricide of HIPFasL beta cells that overexpress FasL.

Molecular aspects of type 1 diabetes

Type 1 diabetes is a T cell mediated autoimmune disease, characterised by the selective destruction of pancreatic beta cells, and susceptibility is determined by a combination of genetic and environmental factors. The environmental agents implicated include viruses and dietary factors, although none has yet been shown to be directly responsible for triggering beta cell autoimmunity. The genetic factors that influence disease risk have been subjected to more intensive study and two gene regions of major importance have been identified: the human leucocyte antigen locus and the insulin gene. This review will focus on the mechanisms by which these genes might influence the risk of developing type 1 diabetes.

The subpopulation of CD4+CD25+ splenocytes that delays adoptive transfer of diabetes expresses L-selectin and high levels of CCR7

Recently, CD4(+)CD25(+) T cells have been implicated in the control of diabetes, suggesting that the inflamed islets of Langerhans in prediabetic NOD mice are under peripheral immune surveillance. Here we show that CD4(+)CD25(+) splenocytes inhibit diabetes in cotransfer with islet-infiltrating cells. Furthermore, CD62L expression is necessary for this disease-delaying effect of CD4(+)CD25(+) cells in vivo, but not for their suppressor function in vitro. We demonstrate that the CD4(+)CD25(+)CD62L(+) splenocytes express CCR7 at high levels and migrate toward secondary lymphoid tissue chemokine and ELC (macrophage-inflammatory protein-3beta), lymphoid chemokines, whereas CD4(+)CD25(+)CD62L(-) splenocytes preferentially express CCR2, CCR4, and CXCR3 and migrate toward the corresponding inflammatory chemokines. These data demonstrate that CD4(+)CD25(+)CD62L(+), but not CD4(+)CD25(+)CD62L(-), splenocytes delay diabetes transfer, and that CD4(+)CD25(+) suppressor T cells are comprised of at least two subpopulations that behave differently in cotransfer in vivo and express distinct chemokine receptor and chemotactic response profiles despite demonstrating equivalent suppressor functions in vitro.

Expression of transgene encoded TGF-beta in islets prevents autoimmune diabetes in NOD mice by a local mechanism

To analyse the effects of TGF-beta in insulin dependent diabetes mellitus (IDDM), we have developed non-obese diabetic (NOD) transgenic mice expressing TGF-beta under the control of the rat insulin II promoter. Pancreata of TGF-beta transgenic mice were roughly one twentieth of the size of pancreata of wild-type NOD mice and showed small clusters of micro-islets rather than normal adult islets. However, these islets produced sufficient levels of insulin to maintain normal glucose levels and mice were protected from the diabetes, which developed in their negative littermates. A massive fibrosis was seen in the transgenic pancreata that was accompanied with infiltration of mononuclear cells that decreased with age. Interestingly, these mice showed normal anti-islet immune response in their spleens and remained susceptible to adoptive transfer of IDDM by mature cloned CD8 effector cells. TUNEL assays revealed increased apoptosis of invading cells when compared to non-transgenic NOD mice. Taken together, these results suggest that TGF-beta protects islets by a local event.

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.

Characterization of peripheral regulatory CD4+ T cells that prevent diabetes onset in nonobese diabetic mice

The period that precedes onset of insulin-dependent diabetes mellitus corresponds to an active dynamic state in which pathogenic autoreactive T cells are kept from destroying beta cells by regulatory T cells. In prediabetic nonobese diabetic (NOD) mice, CD4+ splenocytes were shown to prevent diabetes transfer in immunodeficient NOD recipients. We now demonstrate that regulatory splenocytes belong to the CD4+ CD62Lhigh T cell subset that comprises a vast majority of naive cells producing low levels of IL-2 and IFN-gamma and no IL-4 and IL-10 upon in vitro stimulation. Consistently, the inhibition of diabetes transfer was not mediated by IL-4 and IL-10. Regulatory cells homed to the pancreas and modified the migration of diabetogenic to the islets, which resulted in a decreased insulitis severity. The efficiency of CD62L+ T cells was dose dependent, independent of sex and disease prevalence. Protection mechanisms did not involve the CD62L molecule, an observation that may relate to the fact that CD4+ CD62Lhigh lymph node cells were less potent than their splenic counterparts. Regulatory T cells were detectable after weaning and persist until disease onset, sustaining the notion that diabetes is a late and abrupt event. Thus, the CD62L molecule appears as a unique marker that can discriminate diabetogenic (previously shown to be CD62L-) from regulatory T cells. The phenotypic and functional characteristics of protective CD4+ CD62L+ cells suggest they are different from Th2-, Tr1-, and NK T-type cells, reported to be implicated in the control of diabetes in NOD mice, and may represent a new immunoregulatory population.

CD4 T cells and major histocompatibility complex class II expression influence worm expulsion and increased intestinal muscle contraction during Trichinella spiralis infection

Expulsion of intestinal nematode parasites and the associated increased contraction by intestinal muscle are T cell dependent, since both are attenuated in athymic rodents. The CD4 T-cell subset has been strongly associated with worm expulsion; however, the relationship between these cells, antigen presentation, and worm expulsion is not definitive and the role of these factors in intestinal muscle hypercontractility has not been defined. We infected C57BL/6, athymic, CD4-deficient, CD8alpha-deficient, and major histocompatibility complex class II (MHC II)-deficient (C2d) mice with Trichinella spiralis larvae. We examined intestinal worm numbers, longitudinal muscle contraction, and MHC II expression. Numerous MHC II-positive cells were identified within the muscularis externa of infected but not uninfected C57BL/6 mice. C57BL/6 and CD8alpha-deficient mice developed large increases in muscle contraction, expelling the parasite by day 21. Athymic and C2d mice exhibited much smaller increases in muscle contraction and delayed parasite expulsion. CD4-deficient mice exhibited intermediate levels of muscle contraction and delayed parasite expulsion. To further examine the role of MHC II and CD4 T cells, we irradiated C2d mice and reconstituted them with C57BL/6 bone marrow alone or with C57BL/6 CD4 T cells. C57BL/6 bone marrow alone did not affect muscle function or worm expulsion in recipient C2d mice. Partial CD4 T-cell reconstitution was sufficient to restore increased muscle contraction but not worm expulsion. Thus, hematopoietic MHC II expression alone is insufficient for the development of muscle hypercontractility and worm expulsion, but the addition of even small numbers of CD4 T cells was sufficient to induce intestinal muscle pathophysiology.

Update on the genetics and pathophysiology of type I diabetes mellitus

Type I diabetes mellitus results from the genetically predetermined autoimmune destruction of pancreatic beta-cells, resulting in gradual, but complete, loss of insulin secretion. There are strong associations with specific HLA haplotypes, but environmental triggers are also required to initiate beta-cell autoimmunity. These could possibly include enteroviral infection, early weaning from breastfeeding, early exposure to cow's milk antigens, and free radical damage. Once initiated, beta-cell autoimmunity does not always lead to clinical diabetes, suggesting that immunomodulators may be important in the control of beta-cell destruction. Current interventions designed to prevent type I diabetes mellitus are based on attempts to alter this immune response and to preserve beta-cell function. It is important for the pediatrician to understand the background of these trials and to be able to answer parents' questions regarding study participation.

Absence of significant Th2 response in diabetes-prone non-obese diabetic (NOD) mice

Accumulating evidence suggests that Th1 T cells play a pivotal role in the development of autoimmune diabetes. Conversely, promoting a Th2 response inhibits disease progression. However, it has not been determined whether Th2 cells are regulatory T cells that fail at the time of diabetes development in naive non-diabetic NOD mice. Therefore, in order to evaluate cytokine secretion by spleen and islet infiltrating T cells in NOD mice at different stages of the autoimmune process, we developed an ELISPOT assay that detects IL-2, IL-4, and interferon-gamma (IFN-gamma) secretion in vitro at the single-cell level. We showed that, whatever the age considered, IFN-gamma is predominantly secreted, and that no IL-4-secreting cells are detected in the islets of male and female NOD mice. Spleen cells from 8-week-old female NOD mice, which include regulatory suppressor T cells, do not secrete IL-4, either upon presentation of islet cell antigens in vitro, or after transfer in vivo, but do secrete IFN-gamma. IFN-gamma secretion by T cells from diabetic mice results from CD4 but not CD8 T cells in transfer experiments into NOD/severe combined immunodeficient (SCID) recipients. These results suggest that (i) detection of regulatory CD4 T cells in NOD mice is not paralleled by a Th2 response; (ii) beta cell destruction does not depend on a switch from a Th2 to a Th1-type response; and (iii) CD8 T cells do not participate in induction of diabetes by secreting IFN-gamma.

Contribution of T cells to the development of autoimmune diabetes in the NOD mouse model

The nonobese diabetic (NOD) mouse spontaneously develops an autoimmune diabetes that shares many immunogenetic features with human insulin-dependent diabetes mellitus (IDDM), type 1 diabetes. The mononuclear cell infiltrates in the islet, which results in the development of insulitis (a prerequisite step for the development of diabetes) are primarily composed of T cells. It is now well accepted that these T cells play important roles in initiating and propagating an autoimmune process, which in turn destroys insulin-producing islet beta cells in the pancreas. T cells are subdivided into CD4+ helper T cells and CD8+ cytotoxic T cells. CD4+ T cells are further subdivided into Th1 and Th2 cells based on profiles of cytokine production, and these two T-cell populations counterregulate each other. Because many autoimmune diseases are Th1 T-cell mediated, current studies have focused on manipulating the Th1/Th2 imbalance to suppress the autoimmune process in the NOD model. Furthermore, the incidence of disease is much higher in females than that in males, suggesting an involvement of sex-steroid hormones in the development of diabetes. Understanding insights of the mechanism of immune-mediated islet cell destruction and the interaction between the immune and the neuroendocrine system may, therefore, provide new therapeutic means of preventing this chronic debilitating disease.

The role of lymphocyte subsets in accelerated diabetes in nonobese diabetic-rat insulin promoter-B7-1 (NOD-RIP-B7-1) mice

B7-1 transgene expression on the pancreatic islets in nonobese diabetic (NOD) mice leads to accelerated diabetes, with >50% of animals developing diabetes before 12 wk of age. The expression of B7-1 directly on the pancreatic beta cells, which do not normally express costimulator molecules, converts the cells into effective antigen-presenting cells leading to an intensified autoimmune attack. The pancreatic islet infiltrate in diabetic mice consists of CD8 T cells, CD4 T cells, and B cells, similar to diabetic nontransgenic NOD mice. To elucidate the relative importance of each of the subsets of cells, the NOD-rat insulin promoter (RIP)-B7-1 animals were crossed with NOD.beta2microglobulin -/- mice which lack major histocompatibility complex class I molecules and are deficient in peripheral CD8 T cells, NOD.CD4 -/- mice which lack T cells expressing CD4, and NOD.muMT -/- mice which lack B220-positive B cells. These experiments showed that both CD4 and CD8 T cells were necessary for the accelerated onset of diabetes, but that B cells, which are needed for diabetes to occur in normal NOD mice, are not required. It is possible that B lymphocytes play an important role in the provision of costimulation in NOD mice which is unnecessary in the NOD-RIP-B7-1 transgenic mice.

GAD-reactive CD4+ Th1 cells induce diabetes in NOD/SCID mice

Although glutamic acid decarboxylase (GAD) has been implicated in IDDM, there is no direct evidence showing GAD-reactive T cells are diabetogenic in vivo. To address this issue, 3-wk-old NOD mice received two injections of purified rat brain GAD; one mouse rapidly developed diabetes 3 wk later. Splenocytes from this mouse showed a proliferative response to purified GAD, and were used to generate a CD4+ T cell line, designated 5A, that expresses TCRs encoding Vbeta2 and Vbeta12. 5A T cells exhibit a MHC restricted proliferative response to purified GAD, as well as GAD65 peptide 524-543. After antigen-specific stimulation, 5A T cells secrete IFNgamma and TNFalpha/beta, but not IL-4. They are also cytotoxic against NOD-derived hybridoma cells (expressing I-Ag7) that were transfected with rat GAD65, but not nontransfected hybridoma cells. Adoptive transfer of 5A cells into NOD/SCID mice produced insulitis in all mice. Diabetes occurred in 83% of the mice. We conclude that GAD injection in young NOD mice may, in some cases, provoke diabetes due to the activation of diabetogenic T cells reactive to GAD65 peptides. Our data provide direct evidence that GAD65 autoimmunity may be a critical event in the pathogenesis of IDDM.

Neonatal activation of CD28 signaling overcomes T cell anergy and prevents autoimmune diabetes by an IL-4-dependent mechanism

Optimal T cell responsiveness requires signaling through the T cell receptor (TCR) and CD28 costimulatory receptors. Previously, we showed that T cells from autoimmune nonobese diabetic (NOD) mice display proliferative hyporesponsiveness to TCR stimulation, which may be causal to the development of insulin-dependent diabetes mellitus (IDDM). Here, we demonstrate that anti-CD28 mAb stimulation restores complete NOD T cell proliferative responsiveness by augmentation of IL-4 production. Whereas neonatal treatment of NOD mice with anti-CD28 beginning at 2 wk of age inhibits destructive insulitis and protects against IDDM by enhancement of IL-4 production by islet-infiltrating T cells, administration of anti-CD28 beginning at 5-6 wk of age does not prevent IDDM. Simultaneous anti-IL-4 treatment abrogates the preventative effect of anti-CD28 treatment. Thus, neonatal CD28 costimulation during 2-4 wk of age is required to prevent IDDM, and is mediated by the generation of a Th2 cell-enriched nondestructive environment in the pancreatic islets of treated NOD mice. Our data support the hypothesis that a CD28 signal is requisite for activation of IL-4-producing cells and protection from IDDM.

Diabetes results from a late change in the autoimmune response of NOD mice

IDDM in the NOD mouse is the result of a chronic autoimmune process. NOD mice are shown to express benign autoimmunity that converts to a state of malignant autoimmunity and the development of IDDM. Young disease-prone NOD mice are in a state of benign autoimmunity that is correlated with a non-destructive response to islet tissue and the preservation of insulin-containing beta-cells. A proportion of mice with benign autoimmunity convert to having malignant autoimmunity. Clinical diabetes is diagnosed approximately 3 weeks from the development of malignant autoimmunity which is correlated with a destructive response to grafted islet tissue and extensive beta-cell destruction. We conclude that the development of clinical disease is correlated with a change in the state of autoimmunity, that is, from benign to malignant autoimmunity.

Analysis of pathogenesis of autoimmune insulitis in NOD mice: adoptive transfer experiments of insulitis in ILI and NOD nude mice

In an effort to study the pathophysiological events in the development of insulitis in NOD mice, we have developed ILI- and NOD-nu/nu mice. ILI mice are a nondiabetic inbred strain but are derived from the same JcI:ICR mouse as NOD mice and share the same H-2 allotype with NOD mice. Splenocytes and CD4+ cells from diabetic NOD mice appeared to transfer insulitis to ILI-nu/nu mice, suggesting that ILI mice already express autoantigen(s) responsible for insulitis. But reciprocal thymic grafts from NOD mice into ILI-nu/ nu mice and those from ILI mice into NOD-nu/nu mice failed to allow the development of insulitis, implying that ILI mice possess neither precursor T cells nor the thymic environment responsible for the development of insulitis. In addition, splenocytes from ILI mice appeared to contain regulatory cells which suppress the development of diabetes but not that of insulitis in NOD mice. The use of these nude mice should provide more information on the products of insulitis-susceptibility genes of NOD mice.

Breaking self-tolerance in nonobese diabetic mice

Unresponsiveness to self is maintained through two mechanisms of immune regulation: thymic-negative selection and peripheral tolerance. Although thymic-negative selection is a major mechanism to eliminate self-reactive T cells, normal mice have readily detectable populations of T cells reactive to self-proteins but do not exhibit autoimmune responses. It has been postulated that autoimmune disease results from breakdown or loss of peripheral tolerance. We present data that demonstrate that peripheral tolerance or unresponsiveness to self can be broken in nonobese diabetic (NOD) mice. Immunization of NOD mice (but not of conventional mice) with self-peptides caused an immune response to self-peptide with resultant autoproliferation of peripheral lymphocytes. Autoproliferation of self-reactive T cells in NOD mice resulted from the recognition and proliferation of the activated T cells to endogenously processed and presented self-antigens. This loss of self-tolerance demonstrated in vitro may well be the basis of NOD autoimmune disease in vivo.

Monoclonal T cells identified in early NOD islet infiltrates

To examine the hypothesis that a single initiating antigen was recognized by a monoclonal T cell population leading to subsequent inflammatory insulitis in non-obese (NOD) mouse islets, we examined the T cell receptor TCR V beta repertoire of islet-infiltrating T cells in very young (2-week-old) NOD mice. In independent experiments, we repeatedly identified one monoclonal TCR V-beta 8.2 gene product expressed by T lymphocytes infiltrating the islets of NOD mice at 2 weeks of age. The resultant inflammatory response quickly obscures the monoclonal nature of the initiating event. These data suggest that autoimmune diabetes in NOD mice may be initiated by recognition of a single autoantigen.

CD8 T cell clones from young nonobese diabetic (NOD) islets can transfer rapid onset of diabetes in NOD mice in the absence of CD4 cells

T cells play an important role in the pathogenesis of diabetes in the nonobese diabetic (NOD) mouse. CD8 cytotoxic T cell lines and clones were generated from the lymphocytic infiltrate in the islets of Langerhans of young (7-wk-old). NOD mice by growing them on (NOD x B6-RIP-B7-1)F1 islets. These cells proliferate specifically to NOD islets and kill NOD islets in vitro. The cells are restricted by H-2Kd, and all bear T cell antigen receptor encoded by V beta 6. When these CD8 T cell lines and clones are adoptively transferred to irradiated female NOD, young NOD-SCID, and CB17-SCID mice, diabetes occurs very rapidly, within 10 d of transfer and without CD4 T cells.