Dissecting autoimmune diabetes through genetic manipulation of non-obese diabetic mice

Experimental diabetic animal models to study diabetes and diabetic complications

Diabetes is an endocrine illness involving numerous physiological systems. To understand the intricated pathophysiology and disease progression in diabetes, small animals are still the most relevant model systems, despite the availability and progression in numerous invitro and insilico research methods in recent years. In general, experimental diabetes is instigated mainly due to the effectiveness of animal models in illuminating disease etiology. Most diabetes trials are conducted on rodents, while some research is conducted on larger animals. This review will discuss the methodology and mechanisms in detail for preparing diabetic animal models, considering the following important points. The exact pathophysiology of the disease may or may not be replicated in animal models, the correct induction doses must be given and the combination of different approaches for the models is recommended to get desired results.•Animal models are essential to understand diabetes etiology and pathophysiology.•Diabetic models can be developed in both rodents and non-rodents.•Chemically induced and genetic models of diabetes are widely used to study diabetes and diabetic complications.

Polyploidy and nuclear phenotype characteristics of cardiomyocytes from diabetic adult and normoglycemic aged mice

The frequency of polyploid nuclei in the aging human heart is in sharp contrast with that in the human liver. An inverse pattern exists between the mouse heart and liver cells. Ploidy degrees in mouse hepatocytes under hyperglycemic conditions are elevated to higher levels than those in aged hepatocytes. In this study, image analysis cytometry was used to investigate the effect of diabetes and aging on Feulgen-DNA quantities, ploidy degrees, nuclear shapes and chromatin texture in mouse cardiomyocytes compared to previously reported data for mouse hepatocytes. Adult, non-obese diabetic (NOD) hyperglycemic and normoglycemic females and 56-week-old normoglycemic BALB/c females were used. A small percentage (∼7%) of the cardiomyocyte nuclei in severely hyperglycemic NOD adult mice possessed higher ploidy values than those in the 8-week-old normoglycemic mice. Surprisingly, the Feulgen-DNA values and the frequency of nuclei belonging to the 4C and 8C ploidy classes were even higher (∼6%) in normoglycemic NOD specimens than in age-matched hyperglycemic NOD specimens. Additionally, a pronounced elongated nuclear shape was observed especially in adult normoglycemic NOD mice. In conclusion, NOD mice, irrespective of their glycemic level, exhibit a moderate increase in ploidy degrees within cardiomyocyte nuclei during the adult lifetime. As expected, aging did not affect the Feulgen-DNA values and the ploidy degrees of cardiomyocytes in BALB/c mice. The differences in ploidy degrees and chromatin textures such as absorbance variability and entropy, between adult NOD and aged BALB/c mice are consistent with other reports, indicating dissimilarities in chromatin functions between diabetes and aging.

Changes in liver cell DNA methylation status in diabetic mice affect its FT-IR characteristics

Background

Lower levels of cytosine methylation have been found in the liver cell DNA from non-obese diabetic (NOD) mice under hyperglycemic conditions. Because the Fourier transform-infrared (FT-IR) profiles of dry DNA samples are differently affected by DNA base composition, single-stranded form and histone binding, it is expected that the methylation status in the DNA could also affect its FT-IR profile.

Methodology/Principal Findings

The DNA FT-IR signatures obtained from the liver cell nuclei of hyperglycemic and normoglycemic NOD mice of the same age were compared. Dried DNA samples were examined in an IR microspectroscope equipped with an all-reflecting objective (ARO) and adequate software.

Conclusions/Significance

Changes in DNA cytosine methylation levels induced by hyperglycemia in mouse liver cells produced changes in the respective DNA FT-IR profiles, revealing modifications to the vibrational intensities and frequencies of several chemical markers, including ν_as –CH₃ stretching vibrations in the 5-methylcytosine methyl group. A smaller band area reflecting lower energy absorbed in the DNA was found in the hyperglycemic mice and assumed to be related to the lower levels of –CH₃ groups. Other spectral differences were found at 1700–1500 cm⁻¹ and in the fingerprint region, and a slight change in the DNA conformation at the lower DNA methylation levels was suggested for the hyperglycemic mice. The changes that affect cytosine methylation levels certainly affect the DNA-protein interactions and, consequently, gene expression in liver cells from the hyperglycemic NOD mice.

The use of animal models in diabetes research

Diabetes is a disease characterized by a relative or absolute lack of insulin, leading to hyperglycaemia. There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Type 1 diabetes is due to an autoimmune destruction of the insulin-producing pancreatic beta cells, and type 2 diabetes is caused by insulin resistance coupled by a failure of the beta cell to compensate. Animal models for type 1 diabetes range from animals with spontaneously developing autoimmune diabetes to chemical ablation of the pancreatic beta cells. Type 2 diabetes is modelled in both obese and non-obese animal models with varying degrees of insulin resistance and beta cell failure. This review outlines some of the models currently used in diabetes research. In addition, the use of transgenic and knock-out mouse models is discussed. Ideally, more than one animal model should be used to represent the diversity seen in human diabetic patients.

Polyploidy and chromatin remodeling in hepatocytes from insulin-dependent diabetic and normoglycemic aged mice

Changes in polyploidization, chromatin supraorganization, and chromatin accessibility were investigated in hepatocytes collected from adult, nonobese diabetic (NOD) mice with increasing hyperglycemia and compared with adult normoglycemic controls and 56-week-old normoglycemic BALB/c mice. Our goal was to determine the changes in ploidy degrees and chromatin characteristics in mouse hepatocytes that are associated with insulin-dependent diabetes and to detect similarities in these aspects with those verified with aging, with greater accuracy than previous studies. Image analysis of Feulgen-stained nuclei revealed changes in ploidy degrees and chromatin supraorganization. Chromatin accessibility was assessed with micrococcal nuclease (MNase) digestion. Increased polyploidy was associated with increasing levels of glycemia, and this trend toward polyploidy was found even under normoglycemic conditions in NOD mice. Although high degrees of ploidy were also detected in aged BALB/c mice, the magnitude of polyploidy was not the same magnitude as that in the diabetic mice. While there was increased homogeneity of chromatin packaging with increasing polyploidy under conditions of severe hyperglycemia (and even under conditions of normoglycemia) in NOD mice, an inverse relationship was observed in aged BALB/c mice. Chromatin accessibility to MNase increased under severe hyperglycemia and advanced age, but it was much higher in the diabetic mice. In conclusion, although similarities in polyploidy were observed between the hepatocytes from increasingly hyperglycemic adult mice and those from normoglycemic aged mice, the relationship between chromatin remodeling and increases in ploidy degrees was not the same between the hepatocytes of these two groups. These findings demonstrate that strict similarities between diabetes and aging are not always true at the cellular level. This discordance is likely due to differences in the metabolic state of mouse hepatocytes during aging and diabetic conditions consequent to specificities in their gene regulatory programs.

Innate stimulation of B1a cells enhances the autoreactive IgM repertoire in the NOD mouse: implications for type 1 diabetes

AIMS/HYPOTHESIS

We sought to determine whether the presence of natural autoreactive antibodies of B1a cell origin would play a role in the initiation of type 1 diabetes.

METHODS

We compared IgM repertoires and B1a cell compartments in NOD and C57BL/6 mice. Serum IgM autoreactivity profiles were determined by ELISA and the secretory properties and activation status of B1a cells were characterised by enzyme-linked immunosorbent spot (ELISPOT) assay and flow cytometry. B1a cell response to innate activation was analysed by gene expression assays, ELISA and [(3)H]thymidine incorporation. The effect of NOD IgM produced by B1a cells on NOD.severe combined immunodeficient (SCID) beta cells was examined in co-cultures: IgM binding was measured by flow cytometry and real-time PCR was used to study oxidative stress responses.

RESULTS

NOD mice displayed increased levels of serum anti-insulin IgM that were independent of the H2 locus, that were maintained up to prediabetic stages and that correlated with the NOD B1a cell secretion profile. NOD B1a cells had a naturally increased pattern of activation, expressed higher levels of toll-like-receptors (Tlrs) and responded to TLR stimulation in vitro with higher proliferation and increased capacity to secrete anti-type-1-diabetes-related IgM, but produced lower amounts of IL10. IgM of NOD B1a cell origin was able to bind to pancreatic beta cells in vitro and induce expression of inducible nitric oxide synthase (Nos2).

CONCLUSIONS/INTERPRETATION

NOD B1a cells had a lower innate activation threshold for secretion of autoreactive IgM capable of triggering oxidative stress responses on binding to pancreatic beta cells; this provides an early mechanism that contributes to diabetes in a mouse model of type 1 diabetes.

Autoimmunity triggers in the NOD mouse: a role for natural auto-antibody reactivities in type 1 diabetes

The nonobese diabetic mouse (NOD) is widely used as a model to study human type 1 diabetes (T1D). In the NOD mouse T1D is a T cell-mediated autoimmune disease of complex etiology in which B cells play an essential role. One of the major unresolved issues in T1D is the genetic and/or environmental factors that trigger the autoimmune reaction. In the NOD mouse, as in humans, auto-antibodies to pancreatic islets are present at early ages and are highly correlated to diabetes progression, but their etiological role has long been disputed. NOD auto-antibodies have the characteristics of a natural repertoire, and B1 cells, the main natural antibody producers, exhibit functional differences in this strain that could have consequences for disease determination. Using a genetic approach, we propose to test if the NOD natural auto-antibody repertoire includes innate reactivities that participate in diabetes pathogenesis by promoting insulitis initiation.

Coxsackievirus B4 and type 1 diabetes pathogenesis: contribution of animal models

The role of enteroviruses, in particular type B coxsackieviruses (CV-B), in type 1 diabetes (T1D) pathogenesis is supported by epidemiological, clinical and experimental observations.The investigation of T1D pathogenesis benefits from the contribution of animal models called spontaneously diabetic. Among these animals the non-obese diabetic (NOD) mouse and the bio-breeding diabetes-prone (BBDP) rat present a genetic susceptibility manifested by the expression of an autoimmune diabetes similar to the pathology observed in human beings. Other models whose genetic predisposition is less known are of considerable contribution as well. Numerous major observations relative to several aspects of T1D pathogenesis in the context of CV-B infections, such as susceptibility, diabetogenicity, pancreatotropism, mechanisms of beta cells destruction and others, have been deduced thanks to investigations with animal models. Despite their limits, these models are necessary in improving our knowledge of the role of enteroviruses, like CV-B4, in the pathogenesis of T1D, and the recent advances ensuing from their contribution may have important therapeutic and preventive spin-offs.

DNA content, chromatin supraorganization, nuclear glycoproteins and RNA amounts in hepatocytes of mice expressing insulin-dependent diabetes

Chromatin supraorganization and extensibility and nuclear glycoprotein content have been reported to change in hepatocytes from mice during development and aging, as well as under starvation and refeeding conditions. In non-obese diabetic (NOD) mice, the expression of insulin-dependent diabetes may be accompanied by metabolic changes in the liver. These changes are likely to be similar to those involved in the aging processes of non-diabetic animals. Therefore, we hypothesized that the chromatin organization, as well as the physical properties and compositions of hepatocyte nuclei would also be affected in NOD mice in the same way as those in aged non-diabetic mice. Nuclear image parameters were evaluated by image analysis of Feulgen-stained preparations. Chromatin extensibility in response to gravity was observed with polarized light after lysis and toluidine blue staining. The Con-A response of nuclear glycoproteins was evaluated with scanning microspectrophotometry. These characteristics were assessed using hepatocyte imprints from female NOD mice after a 28-day period of diabetes expression. Observations and measurements were made in comparison to healthy BALB/c mice. Total RNA amounts were determined for livers of NOD and BALB/c mice. Enhanced polyploidy levels, a decrease in chromatin higher-order packing states, an increased frequency of extended chromatin fiber formation, and deeper Con-A-responsive chromatin areas were observed in the hepatocytes of the NOD mice expressing insulin-dependent diabetes. Reduced amounts of total RNA were also found in the livers of these mice. Our findings for NOD mice expressing insulin-dependent diabetes are consistent with previously reported data for old-aged mice of the inbred strain A/Uni and may reflect changes in transcriptional activities associated with the stressful physiological demands on the liver during the expression of diabetes.

Lentivectors encoding immunosuppressive proteins genetically engineer pancreatic beta-cells to correct diabetes in allogeneic mice

The effectiveness of genetic engineering with lentivectors to protect transplanted cells from allogeneic rejection was examined using, as a model, type 1 diabetes treatment with beta-cell transplantation, whose widespread use has been limited by the requirement for sustained immunosuppressive treatment to prevent graft rejection. We examined whether lentivectors expressing select immunosuppressive proteins encoded by the adenoviral genome early region 3 (AdE3) would protect transplanted beta-cells from an alloimmune attack. The insulin-producing beta-cell line beta TC-tet (C3HeB/FeJ-derived) was transduced with lentiviruses encoding the AdE3 proteins gp19K and RID alpha/beta. The efficiency of lentiviral transduction of beta TC-tet cells exceeded 85%. Lentivector expression of gp19K decreased surface class I major histocompatibility complex expression by over 90%, whereas RID alpha/beta expression inhibited cytokine-induced Fas upregulation by over 75%. beta TC-tet cells transduced with gp19K and RID alpha/beta lentivectors, but not with a control lentivector, provided prolonged correction of hyperglycemia after transplantation into diabetic BALB/c severe combined immunodeficient mice reconstituted with allogeneic immune effector cells or into diabetic allogeneic BALB/c mice. Thus, genetic engineering of beta-cells using gp19K- and RID alpha/beta-expressing lentiviral vectors may provide an alternative that has the potential to eliminate or reduce treatment with the potent immunosuppressive agents necessary at present for prolonged engraftment with transplanted islets.

PD-1 deficiency reveals various tissue-specific autoimmunity by H-2b and dose-dependent requirement of H-2g7 for diabetes in NOD mice

Although many autoimmune diseases are associated with particular HLA/H-2 haplotypes, the mechanisms through which specific HLA/H-2 haplotypes afford autoimmune susceptibility remain enigmatic. Here, we analyzed the effects of the diabetes-associated (H-2(g7)) and an antidiabetogenic (H-2(b)) H-2 haplotypes in NOD mice deficient for programmed cell death-1 (PD-1, Pdcd1), a unique model of type 1 diabetes that confers complete penetrance and rapid onset of the disease. NOD-H2(b/b)Pdcd1(-/-) mice were completely protected from diabetes, confirming that H-2(g7) is indispensable for diabetes even in the absence of PD-1. However, NOD-H2(b/b)Pdcd1(-/-) mice developed autoimmune inflammation in multiple tissues including peripheral nerves, stomachs, and exocrine tissues, demonstrating that autoreactive T cells are generated in the context of H-2(b). These autoreactive T cells damaged target tissues only in the absence of PD-1, confirming that PD-1 deficiency unravels the hidden autoimmune susceptibility of the strain by reducing the threshold of T cell activation. Transfer experiments revealed that CD4 T cells are the effector cells of neuritis, and nerve-infiltrating CD4 T cells are strongly deviated toward Th1. Interestingly, neuritogenic T cells were also generated in the context of H-2(g7), in sharp contrast to the strict requirement of H-2(g7) for diabetes. In addition, 60% of the NOD-H2(b/g7)Pdcd1(-/-) mice developed diabetes, suggesting that H-2(b) does not dominantly suppress diabetes and that H-2(g7) induces diabetes in a dose-dependent fashion.

Activating Fc gamma receptors participate in the development of autoimmune diabetes in NOD mice

Type 1 diabetes mellitus (T1D) in humans is an organ-specific autoimmune disease in which pancreatic islet beta cells are ruptured by autoreactive T cells. NOD mice, the most commonly used animal model of T1D, show early infiltration of leukocytes in the islets (insulitis), resulting in islet destruction and diabetes later. NOD mice produce various islet beta cell-specific autoantibodies, although it remains a subject of debate regarding whether these autoantibodies contribute to the development of T1D. Fc gammaRs are multipotent molecules that play important roles in Ab-mediated regulatory as well as effector functions in autoimmune diseases. To investigate the possible role of Fc gammaRs in NOD mice, we generated several Fc gammaR-less NOD lines, namely FcR common gamma-chain (Fc Rgamma)-deficient (NOD.gamma(-/-)), Fc gammaRIII-deficient (NOD.III(-/-)), Fc gammaRIIB-deficient (NOD.IIB(-/-)), and both Fc Rgamma and Fc gammaRIIB-deficient NOD (NOD.null) mice. In this study, we show significant protection from diabetes in NOD.gamma(-/-), NOD.III(-/-), and NOD.null, but not in NOD.IIB(-/-) mice even with grossly comparable production of autoantibodies among them. Insulitis in NOD.gamma(-/-) mice was also alleviated. Adoptive transfer of bone marrow-derived dendritic cells or NK cells from NOD mice rendered NOD.gamma(-/-) animals more susceptible to diabetes, suggesting a possible scenario in which activating Fc gammaRs on dendritic cells enhance autoantigen presentation leading to the activation of autoreactive T cells, and Fc gammaRIII on NK cells trigger Ab-dependent effector functions and inflammation. These findings highlight the critical roles of activating Fc gammaRs in the development of T1D, and indicate that Fc gammaRs are novel targets for therapies for T1D.

Oxidant stress, immune dysregulation, and vascular function in type I diabetes

Although high glucose is an important contributor to diabetic vasculopathies, complications still occur in spite of tight glycemic control, suggesting that some critical event prior to or concurrent with hyperglycemia may contribute to early vascular changes. Utilizing previously published and new experimental evidence, this review will discuss how prior to the hyperglycemic state, an imbalance between oxidants and antioxidants may contribute to early vascular dysfunction and set in motion proinflammatory insults that are further amplified as the diabetes develops. This imbalance results from the resetting of the equilibrium between vessel superoxide/H(2)O(2) production and/or decreased antioxidant defenses. Such an imbalance may cause endothelial dysfunction, characterized by abnormal endothelium-dependent vasoreactivity, as the first sign of blood vessel damage, followed by morphological changes of the vessel wall and inflammation. As such, increased oxidant stress in preglycemic states may be a critically central initiating event that underlies the pathogenesis of life-threatening vascular diseases in autoimmune diabetes. This review focuses on the relationship between oxidative stress, immune dysregulation, and vascular injury in type 1 diabetes, and how the discovery of novel pathways of vascular disease in nonobese diabetic mice may direct future studies in patients with type 1 diabetes.

Genes within the Idd5 and Idd9/11 diabetes susceptibility loci affect the pathogenic activity of B cells in nonobese diabetic mice

Autoreactive T cells clearly mediate the pancreatic beta cell destruction causing type 1 diabetes (T1D). However, studies in NOD mice indicate that B cells also contribute to pathogenesis because their ablation by introduction of an Igmunull mutation elicits T1D resistance. T1D susceptibility is restored in NOD.Igmunull mice that are irradiated and reconstituted with syngeneic bone marrow plus NOD B cells, but not syngeneic bone marrow alone. Thus, we hypothesized some non-MHC T1D susceptibility (Idd) genes contribute to disease by allowing development of pathogenic B cells. Supporting this hypothesis was the finding that unlike those from NOD donors, engraftment with B cells from H2g7 MHC-matched, but T1D-resistant, nonobese-resistant (NOR) mice failed to restore full disease susceptibility in NOD.Igmunull recipients. T1D resistance in NOR mice is mainly encoded within the Idd13, Idd5.2, and Idd9/11 loci. B cells from NOD congenic stocks containing Idd9/11 or Idd5.1/5.2-resistance loci, respectively, derived from the NOR or C57BL/10 strains were characterized by suppressed diabetogenic activity. Immature autoreactive B cells in NOD mice have an impaired ability to be rendered anergic upon Ag engagement. Interestingly, both Idd5.1/5.2 and Idd9/11-resistance loci were found to normalize this B cell tolerogenic process, which may represent a mechanism contributing to the inhibition of T1D.

Lessons on autoimmune diabetes from animal models

T1DM (Type I diabetes mellitus) results from selective destruction of the insulin-producing beta-cells of the pancreas by the immune system, and is characterized by hyperglycaemia and vascular complications arising from suboptimal control of blood glucose levels. The discovery of animal models of T1DM in the late 1970s and early 1980s, particularly the NOD (non-obese diabetic) mouse and the BB (BioBreeding) diabetes-prone rat, had a fundamental impact on our ability to understand the genetics, aetiology and pathogenesis of this disease. NOD and BB diabetes-prone rats spontaneously develop a form of diabetes that closely resembles the human counterpart. Early studies of these animals quickly led to the realization that T1DM is caused by autoreactive T-lymphocytes and revealed that the development of T1DM is controlled by numerous polymorphic genetic elements that are scattered throughout the genome. The development of transgenic and gene-targeting technologies during the 1980s allowed the generation of models of T1DM of reduced genetic and pathogenic complexity, and a more detailed understanding of the immunogenetics of T1DM. In this review, we summarize the contribution of studies in animal models of T1DM to our current understanding of four fundamental aspects of T1DM: (i) the nature of genetic elements affording T1DM susceptibility or resistance; (ii) the mechanisms underlying the development and recruitment of pathogenic autoreactive T-cells; (iii) the identity of islet antigens that contribute to the initiation and/or progression of islet inflammation and beta-cell destruction; and (iv) the design of avenues for therapeutic intervention that are rooted in the knowledge gained from studies of animal models. Development of new animal models will ensure continued progress in these four areas.

Insulin--a primary autoantigen in type 1 diabetes?

Two recently published papers highlight the importance of insulin as a major autoantigenic target of the T cell autoimmune attack in the non-obese diabetic mouse model of diabetes and in type 1 diabetes in humans. Knowledge of the major targets of the autoimmune attack will enable us specifically to focus on these to develop treatments that could alter the ability of pathogenic T cells to cause diabetes. Targeting these T cells could be a strategy for the prevention and cure of the diabetes in the future.

Diabetes Resistance/Susceptibility in T Cells of Nonobese Diabetic Mice Conferred by MHC and MHC-Linked Genes

Polymorphism of MHC and MHC-linked genes is tightly associated with susceptibility to type 1 diabetes (T1D) in human and animal models. Despite the extensive studies, however, the role of MHC and MHC-linked genes expressed by T cells on T1D susceptibility remains unclear. Because T cells develop from TCR(-) thymic precursor (pre-T) cells that undergo MHC restriction mediated by thymic stroma cells, we reconstituted the T cell compartment of NOD.scid-RIP-B7.1 mice using pre-T cells isolated from NOD, NOR, AKR, and C57BL/6 (B6) mice. T1D developed rapidly in the mice reconstituted with pre-T cells derived from NOD or NOR donors. In contrast, most of the NOD.scid-RIP-B7.1 mice reconstituted with pre-T cells from AKR or B6 donors were free of T1D. Further analysis revealed that genes within MHC locus of AKR or B6 origin reduced incidence of T1D in the reconstituted NOD.scid-RIP-B7.1 mice. The expression of MHC class I genes of k, but not b haplotype, in T cells conferred T1D resistance. Replacement of an interval near the distal end of the D region in T cells of B6 origin with an identical allele of 129.S6 origin resulted in T1D development in the reconstituted mice. These results provide evidence that the expression of MHC class I and MHC-linked genes in T cells of NOD mice indeed contributes to T1D susceptibility, while expression of specific resistance alleles of MHC or MHC-linked genes in T cells alone would effectively reduce or even prevent T1D.

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

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

Establishment of NOD-Pdcd1-/- mice as an efficient animal model of type I diabetes

Mice deficient in programmed cell death 1 (PD-1, Pdcd1), an immunoinhibitory receptor belonging to the CD28/cytotoxic T lymphocyte-associated antigen-4 family, spontaneously develop lupus-like autoimmune disease and autoimmune dilated cardiomyopathy on C57BL/6 and BALB/c backgrounds, respectively. However, how PD-1 deficiency induces different forms of autoimmune diseases on these two strains was unknown. Here, we report that PD-1 deficiency specifically accelerates the onset and frequency of type I diabetes in NOD (nonobese diabetic) mice, with strong T helper 1 polarization of T cells infiltrating into islets. These results suggest that PD-1 deficiency accelerates autoimmune predisposition of the background strain, leading to the induction of different forms of autoimmune diseases depending on the genetic background of the strain. Using NOD-Pdcd1-/- mice as an efficient animal model of type I diabetes, we screened diabetes-susceptible loci by genetic linkage analysis. The diabetic incidence of NOD-Pdcd1-/- mice was controlled by five genetic loci, including three known recessive loci [Idd (insulin-dependent diabetes) 1, Idd17, and Idd20] and two previously unidentified dominant loci [Iddp (Idd under PD-1 deficiency) 1 and Iddp2].

The good turned ugly: immunopathogenic basis for diabetogenic CD8+ T cells in NOD mice

Type 1 diabetes (T1D) in both humans and nonobese diabetic (NOD) mice is a T-cell-mediated autoimmune disease in which the insulin-producing pancreatic islet beta-cells are selectively eliminated. As a result, glucose metabolism cannot be regulated unless exogenous insulin is administered. Both the CD4(+) and the CD8(+) T-cell subsets are required for T1D development. Approximately 20 years ago, an association between certain class II major histocompatibility complex (MHC) alleles and susceptibility to T1D was reported. This finding led to enormous interest in the CD4(+) T cells participating in the development of T1D, while the CD8(+) subset was relatively ignored. However, the isolation of beta-cell-autoreactive CD8(+) T-cell clones from the islets of NOD mice helped to generate interest in the pathogenic role of this subset, as has accumulating evidence that certain class I MHC alleles are additional risk factors for T1D development in humans. Three distinct diabetogenic CD8(+) T-cell populations have now been characterized in NOD mice. Here, we review recent investigations exploring their selection, activation, trafficking, and antigenic specificities. As CD8(+) T cells are suspected contributors to beta-cell demise in humans, continued exploration of these critical areas could very possibly lead to tangible benefits for T1D patients and at-risk individuals.

Toll-like receptor engagement converts T-cell autoreactivity into overt autoimmune disease

Autoimmune diabetes mellitus in humans is characterized by immunological destruction of pancreatic beta islet cells. We investigated the circumstances under which CD8(+) T cells specific for pancreatic beta-islet antigens induce disease in mice expressing lymphocytic choriomeningitis virus (LCMV) glycoprotein (GP) as a transgene under the control of the rat insulin promoter. In contrast to infection with LCMV, immunization with LCMV-GP derived peptide did not induce autoimmune diabetes despite large numbers of autoreactive cytotoxic T cells. Only subsequent treatment with Toll-like receptor ligands elicited overt autoimmune disease. This difference was critically regulated by the peripheral target organ itself, which upregulated class I major histocompatibility complex (MHC) in response to systemic Toll-like receptor-triggered interferon-alpha production. These data identify the 'inflammatory status' of the target organ as a separate and limiting factor determining the development of autoimmune disease.