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

Advancing Animal Models of Human Type 1 Diabetes

Multiple rodent models have been developed to study the basis of type 1 diabetes (T1D). However, nonobese diabetic (NOD) mice and derivative strains still provide the gold standard for dissecting the basis of the autoimmune responses underlying T1D. Here, we review the developmental origins of NOD mice, and how they and derivative strains have been used over the past several decades to dissect the genetic and immunopathogenic basis of T1D. Also discussed are ways in which the immunopathogenic basis of T1D in NOD mice and humans are similar or differ. Additionally reviewed are efforts to "humanize" NOD mice and derivative strains to provide improved models to study autoimmune responses contributing to T1D in human patients.

Toll-like receptor 7 deficiency suppresses type 1 diabetes development by modulating B-cell differentiation and function

Innate immunity mediated by Toll-like receptors (TLRs), which can recognize pathogen molecular patterns, plays a critical role in type 1 diabetes development. TLR7 is a pattern recognition receptor that senses single-stranded RNAs from viruses and host tissue cells; however, its role in type 1 diabetes development remains unclear. In our study, we discovered that Tlr7-deficient (Tlr7-/-) nonobese diabetic (NOD) mice, a model of human type 1 diabetes, exhibited a significantly delayed onset and reduced incidence of type 1 diabetes compared with Tlr7-sufficient (Tlr7+/+) NOD mice. Mechanistic investigations showed that Tlr7 deficiency significantly altered B-cell differentiation and immunoglobulin production. Moreover, Tlr7-/- NOD B cells were found to suppress diabetogenic CD4+ T-cell responses and protect immunodeficient NOD mice from developing diabetes induced by diabetogenic T cells. In addition, we found that Tlr7 deficiency suppressed the antigen-presenting functions of B cells and inhibited cytotoxic CD8+ T-cell activation by downregulating the expression of both nonclassical and classical MHC class I (MHC-I) molecules on B cells. Our data suggest that TLR7 contributes to type 1 diabetes development by regulating B-cell functions and subsequent interactions with T cells. Therefore, therapeutically targeting TLR7 may prove beneficial for disease protection.

Altered Systemic and Intestinal IgA Immune Responses in Individuals With Type 1 Diabetes

OBJECTIVE

Increasing evidence supports the observation that immunoglobulin A (IgA) exerts a critical effect on the susceptibility to autoimmunity by modulating gut homeostasis and subsequent host immunity. We hypothesized that the IgA immunity is altered in individuals with type 1 diabetes. To test our hypothesis, we investigated intestinal, oral, and peripheral IgA immune responses in individuals with type 1 diabetes.

METHODS

We collected stool, oral cavity, and blood samples from participants diagnosed with type 1 diabetes (within 1 year and more than 1 year) and healthy control individuals. Serum islet autoantibody titers were detected by radioligand assays. IgA-bound bacteria and IgA-expressing B cells were studied by flow cytometry. Oral free IgA level was measured by enzyme-linked immunosorbent assay. Serum and stool free IgA concentrations were determined by immune-turbidimetry method.

RESULTS

Individuals diagnosed with type 1 diabetes within 1 year had an increased proportion of stool IgA-bound bacteria compared with healthy control individuals. The proportion of stool IgA-bound bacteria was positively associated with glutamic acid decarboxylase autoantibody titer. Moreover, individuals with a longer disease duration displayed a higher level of IgA-bound bacteria than those diagnosed within 1 year. In contrast to healthy control individuals, type 1 diabetes patients had increased serum IgA concentrations.

CONCLUSIONS

Individuals with type 1 diabetes display altered IgA immunity, especially increased stool IgA-bound bacteria, which is likely to contribute to β-cell autoimmunity and the disease development, and thus, might be considered as a novel therapeutic target for the treatment of type 1 diabetes.

Antigen-specific immunotherapy combined with a regenerative drug in the treatment of experimental type 1 diabetes

Type 1 diabetes is an autoimmune disease caused by the destruction of the insulin-producing β-cells. To revert type 1 diabetes, the suppression of the autoimmune attack should be combined with a β-cell replacement strategy. It has been previously demonstrated that liraglutide, a glucagon-like peptide-1 receptor agonist, restores β-cell mass in type 1 diabetes, via α-cell transdifferentiation and neogenesis. We report here that treatment with liraglutide does not prevent type 1 diabetes in the spontaneous non-obese diabetic (NOD) mouse model, but it tends to reduce leukocytic islet infiltration. However, in combination with an immunotherapy based on tolerogenic liposomes, it is effective in ameliorating hyperglycaemia in diabetic NOD mice. Importantly, liraglutide is not detrimental for the tolerogenic effect that liposomes exert on dendritic cells from patients with type 1 diabetes in terms of membrane expression of molecules involved in antigen presentation, immunoregulation and activation. Moreover, the in vivo effect of the combined therapy was tested in mice humanised with peripheral blood mononuclear cells from patients with type 1 diabetes, showing no adverse effects in leukocyte subsets. In conclusion, the combination therapy with liraglutide and a liposome-based immunotherapy is a promising candidate strategy for type 1 diabetes.

Gut microbial metabolites alter IgA immunity in type 1 diabetes

The incidence of type 1 diabetes (T1D) has been increasing among children and adolescents, in which environmental factors, including gut microbiota, play an important role. However, the underlying mechanisms are yet to be determined. Here, we show that patients with newly diagnosed T1D displayed not only a distinct profile of gut microbiota associated with decreased short-chain fatty acids (SCFAs) production, but also an altered IgA-mediated immunity compared with healthy control subjects. Using germ-free NOD mice, we demonstrate that gut microbiota from patients with T1D promoted different IgA-mediated immune responses compared with healthy control gut microbiota. Treatment with the SCFA, acetate, reduced gut bacteria-induced IgA response accompanied by decreased severity of insulitis in NOD mice. We believe our study provides new insights into the functional effects of gut microbiota on inducing IgA immune response in T1D, suggesting that SCFAs might be potential therapeutic agents in T1D prevention and/or treatment.

B-Lymphocyte Phenotype Determines T-Lymphocyte Subset Differentiation in Autoimmune Diabetes

Previous studies indicate that B-lymphocytes play a key role activating diabetogenic T-lymphocytes during the development of autoimmune diabetes. Recently, two transgenic NOD mouse models were generated: the NOD-PerIg and the 116C-NOD mice. In NOD-PerIg mice, B-lymphocytes acquire an activated proliferative phenotype and support accelerated autoimmune diabetes development. In contrast, in 116C-NOD mice, B-lymphocytes display an anergic-like phenotype delaying autoimmune diabetes onset and decreasing disease incidence. The present study further evaluates the T- and B-lymphocyte phenotype in both models. In islet-infiltrating B-lymphocytes (IIBLs) from 116C-NOD mice, the expression of H2-K^d and H2-A^g7 is decreased, whereas that of BAFF, BAFF-R, and TACI is increased. In contrast, IIBLs from NOD-PerIg show an increase in CD86 and FAS expression. In addition, islet-infiltrating T-lymphocytes (IITLs) from NOD-PerIg mice exhibit an increase in PD-1 expression. Moreover, proliferation assays indicate a high capacity of B-lymphocytes from NOD-PerIg mice to secrete high amounts of cytokines and induce T-lymphocyte activation compared to 116C B-lymphocytes. This functional variability between 116C and PerIg B-lymphocytes ultimately results in differences in the ability to shape T-lymphocyte phenotype. These results support the role of B-lymphocytes as key regulators of T-lymphocytes in autoimmune diabetes and provide essential information on the phenotypic characteristics of the T- and B-lymphocytes involved in the autoimmune response in autoimmune diabetes.

Targeting Type 1 Diabetes: Selective Approaches for New Therapies

The clinical onset of type 1 diabetes is characterized by the destruction of the insulin-producing β cells of the pancreas and is caused by autoantigen-induced inflammation (insulitis) of the islets of Langerhans. The current standard of care for type 1 diabetes mellitus patients allows for management of the disease with exogenous insulin, but patients eventually succumb to many chronic complications such as limb amputation, blindness, and kidney failure. New therapeutic approaches now on the horizon are looking beyond glycemic management and are evaluating new strategies from protecting and regenerating endogenous islets to treating the underlying autoimmunity through selective modulation of key immune cell populations. Currently, there are no effective treatments for the autoimmunity that causes the disease, and strategies that aim to delay or prevent the onset of the disease will play an important role in the future of diabetes research. In this review, we summarize many of the key efforts underway that utilize molecular approaches to selectively modulate this disease and look at new therapeutic paradigms that can transform clinical treatment.

CD19+IgM+ cells demonstrate enhanced therapeutic efficacy in type 1 diabetes mellitus

We describe a protective effect on autoimmune diabetes and reduced destructive insulitis in NOD.scid recipients following splenocyte injections from diabetic NOD donors and sorted CD19+ cells compared with NOD.scid recipients receiving splenocytes alone. This protective effect was age specific (only CD19+ cells from young NOD donors exerted this effect; P < 0.001). We found that the CD19+IgM+ cell is the primary subpopulation of B cells that delayed transfer of diabetes mediated by diabetogenic T cells from NOD mice (P = 0.002). Removal of IgM+ cells from the CD19+ pool did not result in protection. Notably, protection conferred by CD19+IgM+ cotransfers were not dependent on the presence of Tregs, as their depletion did not affect their ability to delay onset of diabetes. Blockade of IL-10 with neutralizing antibodies at the time of CD19+ cell cotransfers also abrogated the therapeutic effect, suggesting that IL-10 secretion was an important component of protection. These results were strengthened by ex vivo incubation of CD19+ cells with IL-5, resulting in enhanced proliferation and IL-10 production and equivalently delayed diabetes progression (P = 0.0005). The potential to expand CD19+IgM+ cells, especially in response to IL-5 stimulation or by pharmacologic agents, may be a new therapeutic option for type 1 diabetes.

Anti-Insulin B Cells Are Poised for Antigen Presentation in Type 1 Diabetes

Early breaches in B cell tolerance are central to type 1 diabetes progression in mouse and man. Conventional BCR transgenic mouse models (VH125.Tg NOD) reveal the power of B cell specificity to drive disease as APCs. However, in conventional fixed IgM models, comprehensive assessment of B cell development is limited. To provide more accurate insight into the developmental and functional fates of anti-insulin B cells, we generated a new NOD model (V_H125^SDNOD) in which anti-insulin VDJH125 is targeted to the IgH chain locus to generate a small (1-2%) population of class switch-competent insulin-binding B cells. Tracking of this rare population in a polyclonal repertoire reveals that anti-insulin B cells are preferentially skewed into marginal zone and late transitional subsets known to have increased sensitivity to proinflammatory signals. Additionally, IL-10 production, characteristic of regulatory B cell subsets, is increased. In contrast to conventional models, class switch-competent anti-insulin B cells proliferate normally in response to mitogenic stimuli but remain functionally silent for insulin autoantibody production. Diabetes development is accelerated, which demonstrates the power of anti-insulin B cells to exacerbate disease without differentiation into Ab-forming or plasma cells. Autoreactive T cell responses in V_H125^SDNOD mice are not restricted to insulin autoantigens, as evidenced by increased IFN-γ production to a broad array of diabetes-associated epitopes. Together, these results independently validate the pathogenic role of anti-insulin B cells in type 1 diabetes, underscore their diverse developmental fates, and demonstrate the pathologic potential of coupling a critical β cell specificity to predominantly proinflammatory Ag-presenting B cell subsets.

Genetic and Small Molecule Disruption of the AID/RAD51 Axis Similarly Protects Nonobese Diabetic Mice from Type 1 Diabetes through Expansion of Regulatory B Lymphocytes

B lymphocytes play a key role in type 1 diabetes (T1D) development by serving as a subset of APCs preferentially supporting the expansion of autoreactive pathogenic T cells. As a result of their pathogenic importance, B lymphocyte-targeted therapies have received considerable interest as potential T1D interventions. Unfortunately, the B lymphocyte-directed T1D interventions tested to date failed to halt β cell demise. IgG autoantibodies marking humans at future risk for T1D indicate that B lymphocytes producing them have undergone the affinity-maturation processes of class switch recombination and, possibly, somatic hypermutation. This study found that CRISPR/Cas9-mediated ablation of the activation-induced cytidine deaminase gene required for class switch recombination/somatic hypermutation induction inhibits T1D development in the NOD mouse model. The activation-induced cytidine deaminase protein induces genome-wide DNA breaks that, if not repaired through RAD51-mediated homologous recombination, result in B lymphocyte death. Treatment with the RAD51 inhibitor 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid also strongly inhibited T1D development in NOD mice. The genetic and small molecule-targeting approaches expanded CD73⁺ B lymphocytes that exert regulatory activity suppressing diabetogenic T cell responses. Hence, an initial CRISPR/Cas9-mediated genetic modification approach has identified the AID/RAD51 axis as a target for a potentially clinically translatable pharmacological approach that can block T1D development by converting B lymphocytes to a disease-inhibitory CD73⁺ regulatory state.

B-lymphocytes expressing an Ig specificity recognizing the pancreatic ß-cell autoantigen peripherin are potent contributors to type 1 diabetes development in NOD mice

While the autoimmune destruction of pancreatic ß-cells underlying type 1 diabetes (1D) development is ultimately mediated by T-cells in NOD mice and also likely humans, B-lymphocytes play an additional key pathogenic role. It appears expression of plasma membrane bound immunoglobulin (Ig) molecules that efficiently capture ß-cell antigens allows autoreactive B-lymphocytes bypassing normal tolerance induction processes to be the subset of antigen presenting cells most efficiently activating diabetogenic T-cells. NOD mice transgenically expressing Ig molecules recognizing antigens that are (insulin) or not (hen egg lysozyme; HEL) expressed by ß-cells have proven useful in dissecting the developmental basis of diabetogenic B-lymphocytes. However, these transgenic Ig specificities were originally selected for their ability to recognize insulin or HEL as foreign, rather than autoantigens. Thus, we generated and characterized NOD mice transgenically expressing an Ig molecule representative of a large proportion of naturally occurring islet-infiltrating B-lymphocytes in NOD mice recognizing the neuronal antigen peripherin. Transgenic peripherin autoreactive B-lymphocytes infiltrate NOD pancreatic islets, acquire an activated proliferative phenotype, and potently support accelerated T1D development. These results support the concept of neuronal autoimmunity as a pathogenic feature of T1D, and targeting such responses could ultimately provide an effective disease intervention approach.

The importance of the Non Obese Diabetic (NOD) mouse model in autoimmune diabetes

Type 1 Diabetes (T1D) is an autoimmune disease characterized by the pancreatic infiltration of immune cells resulting in T cell-mediated destruction of the insulin-producing beta cells. The successes of the Non-Obese Diabetic (NOD) mouse model have come in multiple forms including identifying key genetic and environmental risk factors e.g. Idd loci and effects of microorganisms including the gut microbiota, respectively, and how they may contribute to disease susceptibility and pathogenesis. Furthermore, the NOD model also provides insights into the roles of the innate immune cells as well as the B cells in contributing to the T cell-mediated disease. Unlike many autoimmune disease models, the NOD mouse develops spontaneous disease and has many similarities to human T1D. Through exploiting these similarities many targets have been identified for immune-intervention strategies. Although many of these immunotherapies did not have a significant impact on human T1D, they have been shown to be effective in the NOD mouse in early stage disease, which is not equivalent to trials in newly-diagnosed patients with diabetes. However, the continued development of humanized NOD mice would enable further clinical developments, bringing T1D research to a new translational level. Therefore, it is the aim of this review to discuss the importance of the NOD model in identifying the roles of the innate immune system and the interaction with the gut microbiota in modifying diabetes susceptibility. In addition, the role of the B cells will also be discussed with new insights gained through B cell depletion experiments and the impact on translational developments. Finally, this review will also discuss the future of the NOD mouse and the development of humanized NOD mice, providing novel insights into human T1D.

Distortion of the Major Histocompatibility Complex Class I Binding Groove to Accommodate an Insulin-derived 10-Mer Peptide

The non-obese diabetic mouse model of type 1 diabetes continues to be an important tool for delineating the role of T-cell-mediated destruction of pancreatic β-cells. However, little is known about the molecular mechanisms that enable this disease pathway. We show that insulin reactivity by a CD8(+) T-cell clone, known to induce type 1 diabetes, is characterized by weak T-cell antigen receptor binding to a relatively unstable peptide-MHC. The structure of the native 9- and 10-mer insulin epitopes demonstrated that peptide residues 7 and 8 form a prominent solvent-exposed bulge that could potentially be the main focus of T-cell receptor binding. The C terminus of the peptide governed peptide-MHC stability. Unexpectedly, we further demonstrate a novel mode of flexible peptide presentation in which the MHC peptide-binding groove is able to "open the back door" to accommodate extra C-terminal peptide residues.

Development of type 1 diabetes mellitus in nonobese diabetic mice follows changes in thymocyte and peripheral T lymphocyte transcriptional activity

As early as one month of age, nonobese diabetic (NOD) mice feature pancreatic infiltration of autoreactive T lymphocytes, which destruct insulin-producing beta cells, producing autoimmune diabetes mellitus (T1D) within eight months. Thus, we hypothesized that during the development of T1D, the transcriptional modulation of immune reactivity genes may occur as thymocytes mature into peripheral T lymphocytes. The transcriptome of thymocytes and peripheral CD3⁺ T lymphocytes from prediabetic or diabetic mice analyzed through microarray hybridizations identified 2,771 differentially expressed genes. Hierarchical clustering grouped mice according to age/T1D onset and genes according to their transcription profiling. The transcriptional activity of thymocytes developing into peripheral T lymphocytes revealed sequential participation of genes involved with CD4⁺/CD8⁺ T-cell differentiation (Themis), tolerance induction by Tregs (Foxp3), and apoptosis (Fasl) soon after T-cell activation (IL4), while the emergence of T1D coincided with the expression of cytotoxicity (Crtam) and inflammatory response genes (Tlr) by peripheral T lymphocytes.

B cell depletion in autoimmune diabetes: insights from murine models

INTRODUCTION

The incidence of type 1 diabetes (T1D) is rising for reasons that largely elude us. New strategies aimed at halting the disease process are needed. One type of immune cell thought to contribute to T1D is the B lymphocyte. The first Phase II trial of B cell depletion in new onset T1D patients indicated that this slowed the destruction of insulin-producing pancreatic beta cells. The mechanistic basis of the beneficial effects remains unclear.

AREAS COVERED

Studies of B cell depletion and deficiency in animal models of T1D. How B cells can influence T cell-dependent autoimmune diabetes in animal models. The heterogeneity of B cell populations and current evidence for the potential contribution of specific B cell subsets to diabetes, with emphasis on marginal zone B cells and B1 B cells.

EXPERT OPINION

B cells can influence the T cell response to islet antigens and B cell depletion or genetic deficiency is associated with decreased insulitis in animal models. New evidence suggests that B1 cells may contribute to diabetes pathogenesis. A better understanding of the roles of individual B cell subsets in disease will permit fine-tuning of therapeutic strategies to modify these populations.

Beta cell apoptosis in diabetes

Apoptosis of beta cells is a feature of both type 1 and type 2 diabetes as well as loss of islets after transplantation. In type 1 diabetes, beta cells are destroyed by immunological mechanisms. In type 2 diabetes abnormal levels of metabolic factors contribute to beta cell failure and subsequent apoptosis. Loss of beta cells after islet transplantation is due to many factors including the stress associated with islet isolation, primary graft non-function and allogeneic graft rejection. Irrespective of the exact mediators, highly conserved intracellular pathways of apoptosis are triggered. This review will outline the molecular mediators of beta cell apoptosis and the intracellular pathways activated.

CD8(+) T cells specific for beta cells encounter their cognate antigens in the islets of NOD mice

CD8(+) T cells play a key role in the initiation of insulitis. However, the site(s) where naive CD8(+) T cells encounter beta-cell antigens and the mechanism(s) by which beta-cell autoimmunity is initiated remain to be determined. In the current study, an adoptive transfer model was employed assessing the initial site of priming and the nature of antigen recognition by naive beta-cell-specific CD8(+) T cells. Temporal analysis demonstrated that unlike CD4(+) T cells that are primed in the draining pancreatic lymph nodes, initial proliferation of transferred CD8(+) T cells was detected in the islets. These results indicate that in our model, naive beta-cell-specific CD8(+) T cells encounter beta-cell antigens in the islets. Furthermore, ectopic expression of CD80 by beta cells accelerated the onset of insulitis mediated by beta-cell-specific CD8(+) T cells, but had no effect on CD4(+) T-cell-mediated diabetes, suggesting an antigenic interaction between beta cells and naive CD8(+) T cells. However, it remains to be determined whether the initiation of insulitis in spontaneous diabetes is the result of a cognate interaction between naive CD8(+) T cells and islet beta cells.

Active CD4+ helper T cells directly stimulate CD8+ cytotoxic T lymphocyte responses in wild-type and MHC II gene knockout C57BL/6 mice and transgenic RIP-mOVA mice expressing islet beta-cell ovalbumin antigen leading to diabetes

CD4+ helper T (Th) cells play crucial role in priming, expansion and survival of CD8+ cytotoxic T lymphocytes (CTLs). However, how CD4+ Th cell's help is delivered to CD8+ T cells in vivo is still unclear. We previously demonstrated that CD4+ Th cells can acquire ovalbumin (OVA) peptide/major histocompatibility complex (pMHC I) and costimulatory CD80 by OVA-pulsed DC (DC(OVA)) stimulation, and then stimulate OVA-specific CD8+ CTL responses in C57BL/6 mice. In this study, we further investigated CD4+ Th cell's effect on stimulation of CD8 CTL responses in major histocompatibility complex (MHC II) gene knockout (KO) mice and transgenic rat insulin promoter (RIP)-mOVA mice with moderate expression of self OVA by using CD4+ Th cells or Th cells with various gene deficiency. We demonstrated that the in vitro DC(OVA)-activated CD4+ Th cells (3 x 10(6) cells/mouse) can directly stimulate OVA-specific CD8+ T-cell responses in wild-type C57BL/6 mice and MHC II gene KO mice lacking CD4+ T cells. A large amount of CD4+ Th cells (12 x 10(6) cells/mouse) can even overcome OVA-specific immune tolerance in transgenic RIP-mOVA mice, leading to CD8+ CTL-mediated mouse pancreatic islet destruction and diabetes. The stimulatory effect of CD4+ Th cells is mediated by its IL-2 secretion and CD40L and CD80 costimulations, and is specifically delivered to OVA-specific CD8+ T cells in vivo via its acquired pMHC I complexes. Therefore, the above elucidated principles for CD4+ Th cells will have substantial implications in autoimmunity and antitumor immunity, and regulatory T-cell-dependent immune suppression.

Distinct local immunogenic stimuli dictate differential requirements for CD4+ and CD8+ T cell subsets in the pathogenesis of spontaneous autoimmune diabetes

The strong MHC class II association in human as well as murine Type 1 diabetes (T1D) suggests a central role for CD4+T cells in the disease pathogenesis. Nonetheless, CD8+T cells also play a role in the pathogenic process. We describe how CD4+ or CD8+T cells can contribute differentially to the pathogenesis of T1D using the HLA-DQ8 transgenic mouse models. HLA-DQ8 transgenic mice expressing the costimulatory molecule, B7.1 (RIP.B7.1), or the proinflammatory cytokine, TNF-alpha (RIP.TNF) or both (RIP.B7.RIP.TNF) under the control of rat insulin promoter (RIP) were used. Our observations indicate that in the RIP-B7 model, CD4+T cells were absolutely required for diabetes to occur. However, when CD8+ T cells were also present, the incidence of diabetes increased. On the other hand, in the RIP-TNF model, CD8+T cells were absolutely required for diabetes to occur. Interestingly, when CD4+T cells were also present, the incidence of diabetes decreased. In the RIP-B7.RIP-TNF double transgenic mouse model, either CD4+ or CD8+T cells were sufficient to precipitate diabetes in 100% of the animals. Thus, the relative roles of CD4+ or CD8+T cells in the pathogenesis of T1D are possibly determined by the local inflammatory stimuli.

Treatment with CD20-specific antibody prevents and reverses autoimmune diabetes in mice

The precise roles of B cells in promoting the pathogenesis of type 1 diabetes remain undefined. Here, we demonstrate that B cell depletion in mice can prevent or delay diabetes, reverse diabetes after frank hyperglycemia, and lead to the development of cells that suppress disease. To determine the efficacy and potential mechanism of therapeutic B cell depletion, we generated a transgenic NOD mouse expressing human CD20 (hCD20) on B cells. A single cycle of treatment with an antibody specific for hCD20 temporarily depleted B cells and significantly delayed and/or reduced the onset of diabetes. Furthermore, disease established to the point of clinical hyperglycemia could be reversed in over one-third of diabetic mice. Why B cell depletion is therapeutic for a variety of autoimmune diseases is unclear, although effects on antibodies, cytokines, and antigen presentation to T cells are thought to be important. In B cell-depleted NOD mice, we identified what we believe is a novel mechanism by which B cell depletion may lead to long-term remission through expansion of Tregs and regulatory B cells. Our results demonstrate clinical efficacy even in established disease and identify mechanisms for therapeutic action that will guide design and evaluation of parallel studies in patients.

CD86 has sustained costimulatory effects on CD8 T cells

CD80 and CD86 both costimulate T cell activation. Their individual effects in vivo are difficult to study as they are coordinately up-regulated on APCs. We have studied mice expressing rat insulin promoter (RIP)-CD80 and RIP-CD86 on the NOD and NOD.scid genetic background to generate in vivo models, using diabetes as a readout for cytotoxic T cell activation. Accelerated spontaneous diabetes onset was observed in NOD-RIP-CD80 mice and the transfer of diabetes from 6-wk-old NOD mice to NOD.scid-RIP-CD80 mice was greater compared with NOD-RIP-CD86 and NOD.scid-RIP-CD86 mice, respectively. However, the secondary in vivo response was maintained if T cells were activated through CD86 costimulation compared with CD80. This was demonstrated by greater ability to cause recurrent diabetes in NOD-RIP-CD86 diabetic mice transplanted with 6-wk-old NOD islets and adoptively transferred diabetes from diabetic NOD-RIP-CD86 mice to NOD.scid mice. In vitro, CD80 costimulation enhanced cytotoxicity, proliferation, and cytokine secretion in activated CD8 T cells compared with CD86 costimulation. We demonstrated increased CTLA-4 and programmed death-1 inhibitory molecule expression following costimulation by both CD80 and CD86 (CD80 > CD86). Furthermore, T cells stimulated by CD80 were more susceptible to inhibition by CD4(+)CD25(+) T cells. Overall, while CD86 does not stimulate an initial response as strongly as CD80, there is greater sustained activity that is seen even in the absence of continued costimulation. These functions have implications for the engineered use of costimulatory molecules in altering immune responses in a therapeutic setting.

B cells in autoimmune diabetes

Autoantibodies have been used as good markers for the prediction of future development of type 1 diabetes mellitus (T1DM), but are not thought to be pathogenic in this disease. The role of B cells that produce autoantibodies in the pathogenesis of human T1DM is largely unknown. In the non-obese diabetic (NOD) mouse model of autoimmune diabetes, it has been shown that B cells may contribute multifariously to the pathogenesis of the disease. Some aspects of deficiencies of B cell tolerance may lead to the circulation of autoreactive B cells. In addition, the antigen-presenting function of autoantigen specific B cells is likely to be particularly important, and autoantibodies are also considered to play a critical role. This review discusses the possible aspects of B cells involved in the development of autoimmune diabetes.

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.

Regulatory T cells and autoimmune disease

Although T-cell clones bearing T-cell receptors with high affinity for self-peptide major histocompatibility complex (MHC) products are generally eliminated in the thymus (recessive tolerance), the peripheral T-cell repertoire remains strongly biased toward self-peptide MHC complexes and includes autoreactive T cells. A search for peripheral T cells that might exert dominant inhibitory effects on autoreactivity has implicated a subpopulation of CD4(+)CD25(+) T cells called regulatory T cells (Tregs). Here, we discuss the role of cytokines and costimulatory molecules in the generation, maintenance, and function of Tregs. We also summarize evidence for the involvement of Tregs in controlling autoimmune diseases, including type 1 diabetes, experimental autoimmune encephalomyelitis, and inflammatory bowel disease. Last, we discuss our recent definition of the potential role of B7 expressed on activated T-effector cells as a target molecule for Treg-dependent suppression. These observations suggest that the engagement of B7 on effector T cells transmits an inhibitory signal that blocks or attenuates effector T-cell function. We restrict our comments to the suppression mediated by cells within the CD4 lineage; the impact of the cells within the CD8 lineage that may suppress via engagement of Qa-1 on effector T cells is not addressed in this review.

The influence of the major histocompatibility complex on development of autoimmune diabetes in RIP-B7.1 mice

The most important genetic susceptibility factor for type 1 diabetes is encoded in the major histocompatibility complex (MHC). The nonobese diabetic (NOD) mouse, which develops spontaneous diabetes, expresses H-2g7 comprising the MHC class I molecules Kd and Db and the MHC class II molecule I-Ag7. However, neither B6.H-2g7 mice, in which H-2g7 is expressed on the C57BL/6 genetic background, nor the nonobese resistant (NOR) mouse, in which H-2g7 is expressed on a genetic background that is 88% similar to NOD mice, develop diabetes. Immune tolerance can be broken in these diabetes-resistant mice expressing H-2g7 if the costimulatory molecule B7.1 is present on the islet beta cells. This does not occur if only single MHC class I components of the H-2g7 haplotype are present, such as Kd in BALB/c mice or Db in C57BL/6 mice, both of which develop only a low level of diabetes when B7.1 is expressed. The presence of I-Ag7 leads to the development of an autoimmune T-cell repertoire, and local costimulation of CD8 T-cells precipitates aggressive diabetes. This implies that a major role of the MHC class II molecules in diabetes is the development of an autoreactive T-cell repertoire.

Targeting the local tumor microenvironment with vaccinia virus expressing B7.1 for the treatment of melanoma

Immunotherapy for the treatment of metastatic melanoma remains a major clinical challenge. The melanoma microenvironment may lead to local T cell tolerance in part through downregulation of costimulatory molecules, such as B7.1 (CD80). We report the results from the first clinical trial, to our knowledge, using a recombinant vaccinia virus expressing B7.1 (rV-B7.1) for monthly intralesional vaccination of accessible melanoma lesions. A standard 2-dose-escalation phase I clinical trial was conducted with 12 patients. The approach was well tolerated with only low-grade fever, myalgias, and fatigue reported and 2 patients experiencing vitiligo. An objective partial response was observed in 1 patient and disease stabilization in 2 patients, 1 of whom is alive without disease 59 months following vaccination. All patients demonstrated an increase in postvaccination antibody and T cell responses against vaccinia virus. Systemic immunity was tested in HLA-A*0201 patients who demonstrated an increased frequency of gp100 and T cells specific to melanoma antigen recognized by T cells 1 (MART-1), also known as Melan-A, by ELISPOT assay following local rV-B7.1 vaccination. Local immunity was evaluated by quantitative real-time RT-PCR, which suggested that tumor regression was associated with increased expression of CD8 and IFN-gamma. The local delivery of vaccinia virus expressing B7.1 was well tolerated and represents an innovative strategy for altering the local tumor microenvironment in patients with melanoma.

A functional CD40 receptor is expressed in pancreatic beta cells

AIMS/HYPOTHESIS

Despite differences in function and embryonic origin, pancreatic islet cells and neurons express proteins belonging to the tumour necrosis factor receptor superfamily. While neurons express the CD40 receptor, it is unknown whether islet cells also express it. We investigated CD40 expression in human and mouse pancreatic islets as well as in NIT-1 insulinoma cells.

METHODS

CD40 expression was studied by reverse transcriptase polymerase chain reaction, flow cytometry, immunohistochemistry and western blot. Responses mediated by CD40 were assessed by a luciferase gene reporter assay following stimulation with a CD40 agonist antibody.

RESULTS

We found that CD40 is expressed in mouse and human pancreatic islet cells. CD40 is expressed by beta cells, and its expression is upregulated by proinflammatory cytokines (IL-1beta, IFN-gamma and TNF-alpha). CD40 signalling in NIT-1 insulinoma cells activates nuclear factor kappa-B, demonstrating that CD40 is functional.

CONCLUSIONS/INTERPRETATION

We present evidence that, in addition to immune cell types, mouse and human pancreatic beta cells express CD40. Its expression is upregulated by proinflammatory stimuli, and signalling through this receptor activates NF-kappaB. We suggest that the effects of inflammatory stimuli that affect beta cell function and survival may be also mediated by signalling through the CD40 receptor. Thus, CD40 may have a role in processes associated with islet autoimmunity and transplantation.

Dysregulated B7-1 and B7-2 Expression on Nonobese Diabetic Mouse B Cells Is Associated with Increased T Cell Costimulation and the Development of Insulitis

Little is known about the pathogenic role of B cell dysfunction in T cell-mediated autoimmune disease. We previously reported that B cell hyper-responsiveness, resistance to apoptosis, and accumulation in islets occur during the onset of insulitis, but not in type 1 diabetes (T1D), in NOD mice. In this study we extended these studies to further determine how islet-infiltrated B cells contribute to this inflammatory insulitis. We demonstrate the presence of an increased percentage of B7-1(+) and a decreased percentage of B7-2(+) B cells in the spleen of autoimmune disease-prone NOD and nonobese diabetes-resistant mice compared with the spleen of nonautoimmune disease-prone C57BL/6 and BALB/c mice. An age-dependent differential expression of B7-1 and B7-2 was associated with the development of insulitis and CD4(+)CD25(+) T cell deficiency in autoimmune disease-prone mice. Whereas BCR and LPS stimulation increased B7-2 expression on B cells from autoimmune disease-prone and nonautoimmune disease-prone mice, LPS-induced B7-1 expression was higher on NOD than C57BL/6 B cells. Interestingly, increased expression of B7-1 and B7-2 was found on islet-infiltrated B cells, and this increase was associated with enhanced T cell costimulation. Islet-infiltrated B cells were shown to be a source of TNF-alpha production in islets. B7 blockade of BCR-stimulated NOD B cells by anti-B7-1 and anti-B7-2 mAbs during coadoptive transfer with diabetogenic T cells into NOD.scid mice protected these recipients from T1D. These results suggest that increased B7-1 and B7-2 expression on islet-infiltrated NOD B cells is associated with increased T cell costimulation and the development of inflammatory insulitis in NOD mice.

Somatostatin receptors and autoimmune-mediated diabetes

Somatostatin (SST) peptide is produced by various SST-secreting cells throughout the body and acts as a neurotransmitter or paracrine/autocrine regulator in response to ions, nutrients, peptides hormones and neurotransmitters. SST is also widely distributed in the periphery to regulate the inflammatory and immune cells in response to hormones, growth factors, cytokines and other secretive molecules. SST peptides are considered the most important physiologic regulator of the islet cell, gastrointestinal cell and immune cell functions, and the importance of SST production levels has been implicated in several diseases including diabetes. The expression of SST receptors has also been found in T lymphocytes and primary immunologic organs. Interaction of SST and its receptors is also involved in T-cell proliferation and thymocyte selection. SSTR gene-ablated mice developed diabetes with morphologic, physiologic and immunologic alterations in the endocrine pancreas. Increased levels of mononuclear cell infiltration of the islets are associated with the increased levels of antigen-presenting cells located in the islets and peripancreatic lymph nodes. Increased levels of SST were also found in antigen-presenting cells and are associated with a significant increase of CD8 expression levels on CD4(+)/CD8(+) immature thymocytes. These findings highlight the crucial role of this neuroendocrine peptide and its receptors in regulating autoimmune functions.

Investigation of the role of B-cells in type 1 diabetes in the NOD mouse

B-cells are important in the development of type 1 diabetes, but their role is not completely defined. Although B-cells produce autoantibodies, these are not thought to be pathogenic; however, their antigen-presenting function is postulated to be critical. To examine the relative importance of these functions of B-cells, we have generated nonobese diabetic (NOD) B-cell-deficient mice that express a transgene encoding a mutant heavy chain immunoglobulin transgene on the cell surface but cannot secrete immunoglobulins (mIgs). This allowed us to dissect the importance of the relative roles of antigen presentation, dissociated from antibody production. We found that the expression of the mIg transgene increased insulitis and the incidence of diabetes compared with transgene-negative NOD B-cell-deficient mice, indicating that the ability to produce antibodies is not necessary for B-cells to have some effect on the development of diabetes. However, diabetes was not restored to the level seen in normal NOD mice. This may relate to reduced ability to activate an islet-specific T-cell repertoire, presumably due to the reduced islet-specific B-cell repertoire. Our results implicate a specific antigen-presenting function for B-cells.

Expression of the B7.1 costimulatory molecule on pancreatic beta cells abrogates the requirement for CD4 T cells in the development of type 1 diabetes

Although HLA-DQ8 has been implicated as a key determinant of genetic susceptibility to human type 1 diabetes, spontaneous diabetes has been observed in HLA-DQ8 transgenic mice that lack expression of murine MHC class II molecules (mII(-/-)) only when the potent costimulatory molecule, B7.1, is transgenically expressed on pancreatic beta cells. To study the contribution of HLA-DQ8 to the development of diabetes in this model, we crossed RIP-B7.1mII(-/-) mice with a set of transgenic mouse lines that differed in their HLA-DQ8 expression patterns on APC subpopulations, in particular dendritic cells and cortical thymic epithelial cells. Surprisingly, we found that even in the absence of HLA-DQ8 and CD4 T cells, a substantial fraction of the RIP-B7.1mII(-/-) mice developed diabetes. This disease process was remarkable for not only showing insulitis, but also inflammatory destruction of the exocrine pancreas with diffusely up-regulated expression of MHC class I and ICAM-1 molecules. Expression of HLA-DQ8 markedly increased the kinetics and frequency of diabetes, with the most severe disease in the lines with the highest levels of HLA-DQ8 on cortical thymic epithelial cells and the largest numbers of CD4 T cells. However, the adoptive transfer of diabetes was not HLA-DQ8-dependent and disease could be rapidly induced with purified CD8 T cells alone. Expression of B7.1 in the target tissue can thus dramatically alter the cellular and molecular requirements for the development of autoimmunity.

The role of t/b lymphocyte collaboration in the regulation of autoimmune and alloimmune responses

The present review highlights the two areas of research pursuit in our laboratory: (1). the regulation of the autoimmune T cell response to pancreatic islet beta cells using the nonobese diabetic (NOD) mouse model of type 1 diabetes and (2). the regulation the T cell response to alloantigens. Our work has established a central role for B lymphocytes in driving both autoimmune and allo-immmune T cell responses. Our studies indicate that: (1). B cell-deficient NOD mice are protected from autoimmune diabetes; (2). targeted disruption of cognate T/B cell collaboration via major histocompatibility complex (MHC) class II prevents both T cell-mediated islet destruction and allograft rejection; and (3). maternal transmission of islet-reactive autoantibodies potentiates the activation of diabetogenic T cells, highlighting the important role of B cells in the early targeting of islet beta cells.

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

Type 1 diabetes results from a genetically and immunologically complex autoimmune process that is specifically directed against the pancreatic beta cells. Non-obese diabetic mice spontaneously develop a form of autoimmune diabetes closely resembling the disease in humans. This happens because, like human diabetic patients, non-obese diabetic mice have an unfortunate combination of apparently normal alleles at numerous loci associated with Type 1 diabetes. In isolation, each of these allelic variants affords a small degree of susceptibility to diabetes. In combination, however, they set in motion a series of immunological events that lead to islet inflammation and overt diabetes. Type 1 diabetes is associated with defects in self-tolerance and immunoregulation. It involves presentation of beta cell antigens to autoreactive T lymphocytes by professional antigen-presenting cells, the recruitment of antigen-activated T cells into pancreatic islets, and the differentiation of these antigen-activated lymphocytes into beta cell killers. Understanding the precise sequence of events in the pathogenesis of Type 1 diabetes has been, and remains, a challenging task. Much of our understanding of the immunology of the disease stems from studies of genetically engineered, non-obese diabetic mice. These mice provide reductionist systems, with which the contribution of individual cellular elements, molecules or genes to the disease process can be dissected. This review focuses on the lessons that have been learned through studies of these mice.

Beneficial effect of orally administered myelin basic protein in EAE-susceptible Lewis rats in a model of acute CNS degeneration

Axonal injury in the central nervous system (CNS) results in the degeneration of directly damaged fibers and also in the secondary degeneration of fibers that escaped the primary insult. Studies have shown that a protective T cell-mediated autoimmunity directed against myelin-related self-antigens is a physiological response to CNS insult, spontaneously elicited in strains that are constitutionally resistant to experimental autoimmune encephalomyelitis (EAE) but not in EAE-susceptible strains. The protective response following axonal injury can be induced in susceptible rats and boosted in resistant rats by passive or active immunization with myelin-related antigens. Here we show that oral administration of low-dose myelin basic protein (MBP) over a 5-day period is beneficial for post-traumatic survival of neurons in Lewis (EAE-susceptible) rats. Protection was accompanied by increased expression of the costimulatory molecule B7.2 in the traumatized nerves, similar to that seen after passive transfer of MBP-specific T cells. These results support the contention that properly controlled autoimmunity is the body's defense mechanism against non-infective insults. Oral immunization with MBP can be viewed as a way to control the autoimmunity capable of fighting off the consequences of CNS injury in EAE-susceptible strains.

Development of new strategies to prevent type 1 diabetes: the role of animal models

Type 1 diabetes is an immune-mediated disease typically preceded by a long preclinical stage during which a growing number of islet-cell-specific autoantibodies appear in the serum. Although antigen-specific T lymphocytes and cytokines rather than these autoantibodies are the likely executors of beta-cell-destruction, these autoantibodies reflect the existence of autoimmunity that targets islet beta-cells. Abrogation of this autoimmunity during the preclinical stage would be the key to the prevention of type 1 diabetes. However, the quest of protecting islet-cells from the immune attack requires detailed knowledge of mechanisms that control islet-inflammation and beta-cell-destruction, and of mechanisms that control immune tolerance to peripheral self-antigens in general. This knowledge can only be obtained through further innovative research in experimental animal models. In this review, we will first examine how research in non-obese diabetic mice has already led to promising new strategies of diabetes prevention now being tested in human clinical trials. Thereafter, we will discuss how recent advances in understanding the mechanisms that control immune response to peripheral self-antigens such as beta-cell antigens may help to develop even more selective and effective strategies to prevent diabetes in the future.

Role of stromal-cell derived factor-1 in the development of autoimmune diseases in non-obese diabetic mice

The chemokine stromal-cell derived factor-1 (SDF-1) controls maturation, trafficking, and homing of certain subsets, lymphoid cells including immunogenic B and T cells, as a ligand of the CXCR4 chemokine receptor. Insulin-dependent diabetes mellitus (IDDM) and Sjögren's syndrome (SS), both highly regulated autoimmune diseases, develop spontaneously in non-obese diabetic (NOD) mice. To investigate the role of SDF-1 in the development of autoimmune diseases, we injected groups of NOD female mice with antibodies to SDF-1 (anti-SDF-1), which resulted in a 30% reduction of diabetes up to 30 weeks of age, delayed average diabetes onset by 10 weeks, and suppressed insulitis. Autoimmune sialoadenitis was evident in anti-SDF-1-injected mice (SDF-1-Ig group) at the same level as in all groups of mice, whether injected with non-specific antibodies or not. In addition, in the SDF-1-Ig group, a greater number of immunoglobulin M (IgM)- IgD- B220(low) CD38+ CD43+ CD23- progenitor B cells and IgM+ IgD+ B220(high) CD43- CD38+ CD24+ CD23+ mature B cells remained in the bone marrow, whereas infiltration of mature IgM+ B cells was less extensive in peripheral tissues. Our results suggested that anti-SDF-1 antibodies injection was effective in inhibiting diabetes and insulitis without affecting autoimmune sialoadenitis or SS in NOD mice. SDF-1 may be an essential chemokine for trafficking and migration of autoreactive B cells in the development of diabetes.

Pathophysiology of immune-mediated (type 1) diabetes mellitus: potential for immunotherapy

Type 1 diabetes mellitus is a chronic T cell-mediated disease resulting from autoimmune destruction of pancreatic beta-cells. This process leads to progressive and irreversible failure of insulin secretion. Development of the disease involves both genetic and environmental factors. Genetic predisposition is mainly connected with the human leucocyte antigen (HLA) region, which encodes structures responsible for antigen presentation. A comprehensive molecular understanding of the pathogenesis of the disease is essential for the design of rational and well tolerated means of prevention. This paper describes recent experimental and clinical findings and elucidates the current possibilities for immunotherapy of type 1 diabetes. The nature of breakdown of self-tolerance and the mechanisms involved in its recovery are discussed.

The regulatory role of DR4 in a spontaneous diabetes DQ8 transgenic model

MHC class II molecules are critical determinants of genetic susceptibility to human type 1 diabetes. In patients, the most common haplotype contains the DRA1*0101-DRB1*0401 (DR4) and DQA1*0301-DQB1*0302 (DQ8) loci. To assess directly the relative roles of HLA-DQ8 and DR4 for diabetes development in vivo, we generated C57BL/6 transgenic mice that lack endogenous mouse MHC class II molecules but express HLA-DQ8 and/or DR4. Neither HLA-DQ nor HLA-DR transgenic mice developed insulitis or spontaneous diabetes. However, when they were crossed to transgenic mice (C57BL/6) expressing the B7.1 costimulatory molecules on pancreatic beta cells that do not normally develop diabetes, T cells from these double transgenic mice were no longer tolerant to islet autoantigens. The majority of DQ8/RIP-B7 mice developed spontaneous diabetes, whereas only 25% of DR4/RIP-B7 mice did so. Interestingly, when DQ8 and DR4 were coexpressed (DQ8DR4/RIP-B7), only 23% of these mice developed diabetes, an incidence indistinguishable from the DR4/RIP-B7 mice. T cells from both DR4/RIP-B7 and DQ8DR4/RIP-B7 mice, unlike those from DQ8/RIP-B7 mice, exhibited a Th2-like phenotype. Thus, the expression of DR4 appeared to downregulate DQ8-restricted autoreactive T cells in DQ8DR4/RIP-B7 mice. Our data suggest that although both DQ8 and DR4 can promote spontaneous diabetes in mice with a non-autoimmune-prone genetic background, the diabetogenic effect of the DQ8 allele is much greater, whereas DR4 expression downregulates the diabetogenic effect of DQ8, perhaps by enhancing Th2-like immune responses.

The role of self-recognition in receptor repertoire development. Members of the Janeway Laboratory

The role of self-antigen recognition in the development of T and B cells of the adaptive immune system has been studied in several different ways. We have shown that CD4 T cells are selected on self-peptide:self-MHC class II ligands, and in the periphery, they are sustained by contact with the same or similar ligands. We have also observed that B cells are positively selected on unknown and presumed self-ligands. We have used this information to explore autoimmune diseases as well. Finally, we have recently identified the innate immune system as playing a crucial role in regulating expression of costimulatory molecules that are required for induction of adaptive immune responses.

Impaired CD4 T cell activation due to reliance upon B cell-mediated costimulation in nonobese diabetic (NOD) mice

Diabetes in nonobese diabetic (NOD) mice results from the activation of I-A(g7)-restricted, islet-reactive T cells. This study delineates several characteristics of NOD CD4 T cell activation, which, independent of I-A(g7), are likely to promote a dysregulated state of peripheral T cell tolerance. NOD CD4 T cell activation was found to be resistant to antigenic stimulation via the TCR complex, using the progression of cell division as a measure. The extent of NOD CD4 T cell division was highly sensitive to changes in Ag ligand density. Moreover, even upon maximal TCR complex-mediated stimulation, NOD CD4 T cell division prematurely terminated. Maximally stimulated NOD CD4 T cells failed to achieve the threshold number of division cycles required for optimal susceptibility to activation-induced death, a critical mechanism for the regulation of peripheral T cell tolerance. Importantly, these aberrant activation characteristics were not T cell-intrinsic but resulted from reliance on B cell costimulatory function in NOD mice. Costimulation delivered by nonautoimmune strain APCs normalized NOD CD4 T cell division and the extent of activation-induced death. Thus, by disrupting the progression of CD4 T cell division, polarization of APC costimulatory function to the B cell compartment could allow the persistence and activation of diabetogenic cells in NOD mice.

Cutting edge: B cells promote CD8+ T cell activation in MRL-Fas(lpr) mice independently of MHC class I antigen presentation

Spontaneous CD8+ T cell activation in MRL-Faslpr mice is B cell dependent. It is unclear whether this B-dependent activation is mediated by direct Ag presentation via MHC class I proteins (i.e., cross-presentation) or whether activation occurs by an indirect mechanism, e.g., via effects on CD4+ cells. To determine how CD8+ T cell activation is promoted by B cells, we created mixed bone marrow chimeras where direct MHC class I Ag presentation by B cells was abrogated while other leukocyte compartments could express MHC class I. Surprisingly, despite the absence of B cell class I-restricted Ag presentation, CD8+ T cell activation was intact in the chimeric mice. Therefore, the spontaneous B cell-dependent CD8+ T cell activation that occurs in systemic autoimmunity is not due to direct presentation by B cells to CD8+ T cells.

In vivo evidence for the contribution of human histocompatibility leukocyte antigen (HLA)-DQ molecules to the development of diabetes

Although DQA1*0301/DQB1*0302 is the human histocompatibility leukocyte antigen (HLA) class II gene most commonly associated with human type 1 diabetes, direct in vivo experimental evidence for its diabetogenic role is lacking. Therefore, we generated C57BL/6 transgenic mice that bear this molecule and do not express mouse major histocompatibility complex (MHC) class II molecules (DQ8(+)/mII(-)). They did not develop insulitis or spontaneous diabetes. However, when DQ8(+)/mII(-) mice were bred with C57BL/6 mice expressing costimulatory molecule B7-1 on beta cells (which normally do not develop diabetes), 81% of the DQ8(+)/mII(-)/B7-1(+) mice developed spontaneous diabetes. The diabetes was accompanied by severe insulitis composed of both T cells (CD4(+) and CD8(+)) and B cells. T cells from the diabetic mice secreted large amounts of interferon gamma, but not interleukin 4, in response to DQ8(+) islets and the putative islet autoantigens, insulin and glutamic acid decarboxylase (GAD). Diabetes could also be adoptively transferred to irradiated nondiabetic DQ8(+)/mII(-)/B7-1(+) mice. In striking contrast, none of the transgenic mice in which the diabetes protective allele (DQA1*0103/DQB1*0601, DQ6 for short) was substituted for mouse MHC class II molecules but remained for the expression of B7-1 on pancreatic beta cells (DQ6(+)/mII(-)/B7-1(+)) developed diabetes. Only 7% of DQ(-)/mII(-)/B7-1(+) mice developed diabetes at an older age, and none of the DQ(-)/mII(+)/B7-1(+) mice or DQ8(+)/mII(+)/B7-1(+) mice developed diabetes. In conclusion, substitution of HLA-DQA1*0301/DQB1*0302, but not HLA-DQA1*0103/DQB1*0601, for murine MHC class II provokes autoimmune diabetes in non-diabetes-prone rat insulin promoter (RIP).B7-1 C57BL/6 mice. Our data provide direct in vivo evidence for the diabetogenic effect of this human MHC class II molecule and a unique "humanized" animal model of spontaneous diabetes.

Transgenic overexpression of human Bcl-2 in islet beta cells inhibits apoptosis but does not prevent autoimmune destruction

Insulin-dependent diabetes mellitus results when > 90% of the insulin-producing beta cells in the pancreatic islets are killed as a result of autoimmune attack by T cells. During the progression to diabetes, islet beta cells die as a result of different insults from the immune system. Agents such as perforin and granzymes, CD95 ligand and tumor necrosis factor-alpha, or cytokines and free-radicals have all been shown to cause beta cell apoptosis. The anti-apoptotic protein, Bcl-2, might protect against some of these stimuli. We have therefore generated transgenic mice expressing human Bcl-2 in their islet beta cells. Although Bcl-2 was able to prevent apoptosis induced by cytotoxic agents against beta cells in vitro, Bcl-2 alone could not prevent or ameliorate cytotoxic or autoimmune beta cell damage in vivo.