Infection with viruses from several families triggers autoimmune diabetes in LEW*1WR1 rats: prevention of diabetes by maternal immunization

An Early Islet Transcriptional Signature Is Associated With Local Inflammation in Autoimmune Diabetes

Identifying the early islet cellular processes of autoimmune type 1 diabetes (T1D) in humans is challenging given the absence of symptoms during this period and the inaccessibility of the pancreas for sampling. In this article, we study temporal events in pancreatic islets in LEW.1WR1 rats, in which autoimmune diabetes can be induced with virus infection, by performing transcriptional analysis of islets harvested during the prediabetic period. Single-cell RNA-sequencing and differential expression analyses of islets from prediabetic rats reveal subsets of β- and α-cells under stress as evidenced by heightened expression, over time, of a transcriptional signature characterized by interferon-stimulated genes, chemokines including Cxcl10, major histocompatibility class I, and genes for the ubiquitin-proteasome system. Mononuclear phagocytes show increased expression of inflammatory markers. RNA-in situ hybridization of rat pancreatic tissue defines the spatial distribution of Cxcl10+ β- and α-cells and their association with CD8+ T cell infiltration, a hallmark of insulitis and islet destruction. Our studies define early islet transcriptional events during immune cell recruitment to islets and reveal spatial associations between stressed β- and α-cells and immune cells. Insights into such early processes can assist in the development of therapeutic and prevention strategies for T1D.

The missing heritability in type 1 diabetes

Type 1 diabetes (T1D) is a complex autoimmune disease characterized by an absolute deficiency of insulin. It affects more than 20 million people worldwide and imposes an enormous financial burden on patients. The underlying pathogenic mechanisms of T1D are still obscure, but it is widely accepted that both genetics and the environment play an important role in its onset and development. Previous studies have identified more than 60 susceptible loci associated with T1D, explaining approximately 80%-85% of the heritability. However, most identified variants confer only small increases in risk, which restricts their potential clinical application. In addition, there is still a so-called 'missing heritability' phenomenon. While the gap between known heritability and true heritability in T1D is small compared with that in other complex traits and disorders, further elucidation of T1D genetics has the potential to bring novel insights into its aetiology and provide new therapeutic targets. Many hypotheses have been proposed to explain the missing heritability, including variants remaining to be found (variants with small effect sizes, rare variants and structural variants) and interactions (gene-gene and gene-environment interactions; e.g. epigenetic effects). In the following review, we introduce the possible sources of missing heritability and discuss the existing related knowledge in the context of T1D.

Modeling human T1D-associated autoimmune processes

BACKGROUND

Type 1 diabetes (T1D) is an autoimmune disease characterized by impaired immune tolerance to β-cell antigens and progressive destruction of insulin-producing β-cells. Animal models have provided valuable insights for understanding the etiology and pathogenesis of this disease, but they fall short of reflecting the extensive heterogeneity of the disease in humans, which is contributed by various combinations of risk gene alleles and unique environmental factors. Collectively, these factors have been used to define subgroups of patients, termed endotypes, with distinct predominating disease characteristics.

SCOPE OF REVIEW

Here, we review the gaps filled by these models in understanding the intricate involvement and regulation of the immune system in human T1D pathogenesis. We describe the various models developed so far and the scientific questions that have been addressed using them. Finally, we discuss the limitations of these models, primarily ascribed to hosting a human immune system (HIS) in a xenogeneic recipient, and what remains to be done to improve their physiological relevance.

MAJOR CONCLUSIONS

To understand the role of genetic and environmental factors or evaluate immune-modifying therapies in humans, it is critical to develop and apply models in which human cells can be manipulated and their functions studied under conditions that recapitulate as closely as possible the physiological conditions of the human body. While microphysiological systems and living tissue slices provide some of these conditions, HIS mice enable more extensive analyses using in vivo systems.

Environmental Triggering of Type 1 Diabetes Autoimmunity

Type 1 diabetes (T1D) is a chronic autoimmune disease in which pancreatic islet β cells are destroyed by immune cells, ultimately leading to overt diabetes. The progressive increase in T1D incidence over the years points to the role of environmental factors in triggering or accelerating the disease process which develops on a highly multigenic susceptibility background. Evidence that environmental factors induce T1D has mostly been obtained in animal models. In the human, associations between viruses, dietary habits or changes in the microbiota and the development of islet cell autoantibodies or overt diabetes have been reported. So far, prediction of T1D development is mostly based on autoantibody detection. Future work should focus on identifying a causality between the different environmental risk factors and T1D development to improve prediction scores. This should allow developing preventive strategies to limit the T1D burden in the future.

Visceral Adipose Tissue: A New Target Organ in Virus-Induced Type 1 Diabetes

Type 1 diabetes (T1D) is a proinflammatory pathology that leads to the specific destruction of insulin producing β-cells and hyperglycaemia. Much of the knowledge about type 1 diabetes (T1D) has focused on mechanisms of disease progression such as adaptive immune cells and the cytokines that control their function, whereas mechanisms linked with the initiation of the disease remain unknown. It has been hypothesized that in addition to genetics, environmental factors play a pivotal role in triggering β-cell autoimmunity. The BioBreeding Diabetes Resistant (BBDR) and LEW1.WR1 rats have been used to decipher the mechanisms that lead to virus-induced T1D. Both animals develop β-cell inflammation and hyperglycemia upon infection with the parvovirus Kilham Rat Virus (KRV). Our earlier in vitro and in vivo studies indicated that KRV-induced innate immune upregulation early in the disease course plays a causal role in triggering β-cell inflammation and destruction. Furthermore, we recently found for the first time that infection with KRV induces inflammation in visceral adipose tissue (VAT) detectable as early as day 1 post-infection prior to insulitis and hyperglycemia. The proinflammatory response in VAT is associated with macrophage recruitment, proinflammatory cytokine and chemokine upregulation, endoplasmic reticulum (ER) and oxidative stress responses, apoptosis, and downregulation of adipokines and molecules that mediate insulin signaling. Downregulation of inflammation suppresses VAT inflammation and T1D development. These observations are strikingly reminiscent of data from obesity and type 2 diabetes (T2D) in which VAT inflammation is believed to play a causal role in disease mechanisms. We propose that VAT inflammation and dysfunction may be linked with the mechanism of T1D progression.

Epigenetic regulation of Toll-like receptors and its roles in type 1 diabetes

The immune system can be divided into adaptive immunity and innate immunity. Adaptive immunity has been confirmed to be involved in the pathogenesis of autoimmune diseases, including type 1 diabetes (T1D). However, the role of innate immunity in T1D has only been studied recently. T1D is caused by selective autoimmune destruction of pancreatic islet β cells. A series of studies have suggested that TLRs play a critical role in the pathogenesis of T1D. Aberrant TLR signaling will change immune homeostasis and result in immunopathological conditions such as endotoxin shock and autoimmune responses. Thus, TLR signaling pathways are supposed to be strictly and finely regulated. Epigenetics has recently been proven to be a new regulator of TLR expression. DNA methylation, histone modification, and microRNAs are the three main epigenetic modifications. This review will mainly focus on these epigenetic mechanisms of regulation of TLRs and the role of TLRs in the pathogenesis of T1D.

Modulation of the diet and gastrointestinal microbiota normalizes systemic inflammation and β-cell chemokine expression associated with autoimmune diabetes susceptibility

Environmental changes associated with modern lifestyles may underlie the rising incidence of Type 1 diabetes (T1D). Our previous studies of T1D families and the BioBreeding (BB) rat model have identified a peripheral inflammatory state that is associated with diabetes susceptibility, consistent with pattern recognition receptor ligation, but is independent of disease progression. Here, compared to control strains, islets of spontaneously diabetic BB DRlyp/lyp and diabetes inducible BB DR+/+ weanlings provided a standard cereal diet expressed a robust proinflammatory transcriptional program consistent with microbial antigen exposure that included numerous cytokines/chemokines. The dependence of this phenotype on diet and gastrointestinal microbiota was investigated by transitioning DR+/+ weanlings to a gluten-free hydrolyzed casein diet (HCD) or treating them with antibiotics to alter/reduce pattern recognition receptor ligand exposure. Bacterial 16S rRNA gene sequencing revealed that these treatments altered the ileal and cecal microbiota, increasing the Firmicutes:Bacteriodetes ratio and the relative abundances of lactobacilli and butyrate producing taxa. While these conditions did not normalize the inherent hyper-responsiveness of DR+/+ rat leukocytes to ex vivo TLR stimulation, they normalized plasma cytokine levels, plasma TLR4 activity levels, the proinflammatory islet transcriptome, and β-cell chemokine expression. In lymphopenic DRlyp/lyp rats, HCD reduced T1D incidence, and the introduction of gluten to this diet induced islet chemokine expression and abrogated protection from diabetes. Overall, these studies link BB rat islet-level immunocyte recruiting potential, as measured by β-cell chemokine expression, to a genetically controlled immune hyper-responsiveness and innate inflammatory state that can be modulated by diet and the intestinal microbiota.

A Critical Role for the Type I Interferon Receptor in Virus-Induced Autoimmune Diabetes in Rats

The pathogenesis of human type 1 diabetes, characterized by immune-mediated damage of insulin-producing β-cells of pancreatic islets, may involve viral infection. Essential components of the innate immune antiviral response, including type I interferon (IFN) and IFN receptor-mediated signaling pathways, are candidates for determining susceptibility to human type 1 diabetes. Numerous aspects of human type 1 diabetes pathogenesis are recapitulated in the LEW.1WR1 rat model. Diabetes can be induced in LEW.1WR1 weanling rats challenged with virus or with the viral mimetic polyinosinic:polycytidylic acid (poly I:C). We hypothesized that disrupting the cognate type I IFN receptor (type I IFN α/β receptor [IFNAR]) to interrupt IFN signaling would prevent or delay the development of virus-induced diabetes. We generated IFNAR1 subunit-deficient LEW.1WR1 rats using CRISPR-Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) genome editing and confirmed functional disruption of the Ifnar1 gene. IFNAR1 deficiency significantly delayed the onset and frequency of diabetes and greatly reduced the intensity of insulitis after poly I:C treatment. The occurrence of Kilham rat virus-induced diabetes was also diminished in IFNAR1-deficient animals. These findings firmly establish that alterations in innate immunity influence the course of autoimmune diabetes and support the use of targeted strategies to limit or prevent the development of type 1 diabetes.

Innate inflammation in type 1 diabetes

Type 1 diabetes mellitus (T1D) is an autoimmune disease often diagnosed in childhood that results in pancreatic β-cell destruction and life-long insulin dependence. T1D susceptibility involves a complex interplay between genetic and environmental factors and has historically been attributed to adaptive immunity, although there is now increasing evidence for a role of innate inflammation. Here, we review studies that define a heightened age-dependent innate inflammatory state in T1D families that is paralleled with high fidelity by the T1D-susceptible biobreeding rat. Innate inflammation may be driven by changes in interactions between the host and environment, such as through an altered microbiome, intestinal hyperpermeability, or viral exposures. Special focus is put on the temporal measurement of plasma-induced transcriptional signatures of recent-onset T1D patients and their siblings as well as in the biobreeding rat as it defines the natural history of innate inflammation. These sensitive and comprehensive analyses have also revealed that those who successfully managed T1D risk develop an age-dependent immunoregulatory state, providing a possible mechanism for the juvenile nature of T1D. Therapeutic targeting of innate inflammation has been proven effective in preventing and delaying T1D in rat models. Clinical trials of agents that suppress innate inflammation have had more modest success, but efficacy may be improved by the addition of combinatorial approaches that target other aspects of T1D pathogenesis. An understanding of innate inflammation and mechanisms by which this susceptibility is both potentiated and mitigated offers important insight into T1D progression and avenues for therapeutic intervention.

Enteroviruses, hygiene and type 1 diabetes: toward a preventive vaccine

Enteroviruses and humans have long co-existed. Although recognized in ancient times, poliomyelitis and type 1 diabetes (T1D) were exceptionally rare and not epidemic, due in large part to poor sanitation and personal hygiene which resulted in repeated exposure to fecal-oral transmitted viruses and other infectious agents and viruses and the generation of a broad protective immunity. As a function of a growing acceptance of the benefits of hygienic practices and microbiologically clean(er) water supplies, the likelihood of exposure to diverse infectious agents and viruses declined. The effort to vaccinate against poliomyelitis demonstrated that enteroviral diseases are preventable by vaccination and led to understanding how to successfully attenuate enteroviruses. Type 1 diabetes onset has been convincingly linked to infection by numerous enteroviruses including the group B coxsackieviruses (CVB), while studies of CVB infections in NOD mice have demonstrated not only a clear link between disease onset but an ability to reduce the incidence of T1D as well: CVB infections can suppress naturally occurring autoimmune T1D. We propose here that if we can harness and develop the capacity to use attenuated enteroviral strains to induce regulatory T cell populations in the host through vaccination, then a vaccine could be considered that should function to protect against both autoimmune as well as virus-triggered T1D. Such a vaccine would not only specifically protect from certain enterovirus types but more importantly, also reset the organism's regulatory rheostat making the further development of pathogenic autoimmunity less likely.

Diversity in the preimmune immunoglobulin repertoire of SHR lines susceptible and resistant to end-organ injury

We used next-generation sequencing to identify IGH genetic variation in two closely related hypertensive rat lines that differ in susceptibility to end-organ disease (SHR-A3 and SHR-B2). The two SHR lines differ extensively at the IGH locus from the rat reference genome sequence (RRGS) and from each other, creating 306 sequence unique IGH genes. Compared to IGH genes mapped in the RRGS, 98 are null gene alleles (31 are null in both SHR lines, 45 are null in SHR-A3 only, and 23 are null in SHR-B2 only). Of the 306 divergent gene sequences, 126 result in amino acid substitution and, among these, SHR-A3 and SHR-B2 differ from one another at the amino acid level in 96 segments. Twelve pseudogenes in the RRGS had changes displacing the stop codon and creating probable functional genes in either or both SHR-A3 and SHR-B2. A further 5 alleles that encoded functional RRGS genes or open reading frames were converted to pseudogenes in either or both SHR-A3 and SHR-B2. These studies reveal that the pre-immune immunoglobulin repertoire is highly divergent among SHR lines differing in end organ injury susceptibility and this may modify immune mechanisms in hypertensive renal injury.

Autoantigen-induced focusing of Vβ13+ T cells precedes onset of autoimmune diabetes in the LEW.1WR1 rat

The earliest events leading to autoimmune type 1 diabetes (T1D) are not known in any species. A T-cell receptor (TCR)-variable region, TCR-Vβ13, is required for susceptibility to autoimmune diabetes in rats, and selective depletion of Vβ13(+) T cells with an allele-specific monoclonal antibody prevents disease in multiple rat strains. To investigate the role of Vβ13 early in diabetes, we examined islet T-cell transcripts in susceptible (LEW.1WR1) and resistant (LEW.1W and Wistar Furth) strains induced with polyinosinic:polycytidylic acid. Vβ13(+) T cells displayed antigenic focusing in LEW.1WR1 islets 5 days postinduction and were characterized by a substantial decrease in complementarity determining region 3 diversity. This occurred prior to significant islet T-cell accumulation (day 7) or frank diabetes (days 10-14). Vβ13(+) transcripts increased in LEW.1WR1 islets during diabetes progression, but not in resistant rats. We also analyzed transcript clonality of rat TCR-Vα5, an ortholog of the dominant TCR-Vα chain found on insulin B:9-23-reactive T cells in nonobese diabetic rat islets. We observed clonal expansion of Vα5(+) transcripts in prediabetic LEW.1WR1 islets, suggesting that rat Vα5 is also an important component of islet autoantigen recognition. These data provide additional evidence that genome-encoded TCR sequences are important determinants of genetic susceptibility to T1D.

Testing agents for prevention or reversal of type 1 diabetes in rodents

We report the results of an independent laboratory's tests of novel agents to prevent or reverse type 1 diabetes (T1D) in the non-obese diabetic (NOD) mouse, BioBreeding diabetes prone (BBDP) rat, and multiple autoimmune disease prone (MAD) rat models. Methods were developed to better mimic human clinical trials, including: prescreening, randomization, blinding, and improved glycemic care of the animals. Agents were suggested by the research community in an open call for proposals, and selected for testing by an NIDDK appointed independent review panel. Agents selected for testing to prevent diabetes at later stages of progression in a rodent model were a STAT4 antagonist (DT22669), alpha1 anti-trypsin (Aralast NP), celastrol (a natural product with anti-inflammatory properties), and a Macrophage Inflammatory Factor inhibitor (ISO-092). Agents tested for reversal of established T1D in rodent models were: alpha1 anti-trypsin (Aralast NP), tolerogenic peptides (Tregitopes), and a long-acting formulation of GLP-1 (PGC-GLP-1). None of these agents were seen to prevent or reverse type 1 diabetes, while the positive control interventions were effective: anti-CD3 treatment provided disease reversal in the NOD mouse, dexamethasone prevented T1D induction in the MAD rat, and cyclosporin prevented T1D in the BBDP rat. For some tested agents, details of previous formulation, delivery, or dosing, as well as laboratory procedure, availability of reagents and experimental design, could have impacted our ability to confirm prior reports of efficacy in preclinical animal models. In addition, the testing protocols utilized here provided detection of effects in a range commonly used in placebo controlled clinical trials (for example, 50% effect size), and thus may have been underpowered to observe more limited effects. That said, we believe the results compiled here, showing good control and repeatability, confirm the feasibility of screening diverse test agents in an independent laboratory.

Virus infections in type 1 diabetes

The precise etiology of type 1 diabetes (T1D) is still unknown, but viruses have long been suggested as a potential environmental trigger for the disease. However, despite decades of research, the body of evidence supporting a relationship between viral infections and initiation or acceleration of islet autoimmunity remains largely circumstantial. The most robust association with viruses and T1D involves enterovirus species, of which some strains have the ability to induce or accelerate disease in animal models. Several hypotheses have been formulated to mechanistically explain how viruses may affect islet autoimmunity and β-cell decay. The recent observation that certain viral infections, when encountered at the right time and infectious dose, can prevent autoimmune diabetes illustrates that potential relationships may be more complex than previously thought. Here, we provide a concise summary of data obtained in mouse models and humans, and identify future avenues toward a better characterization of the association between viruses and T1D.

Temporal induction of immunoregulatory processes coincides with age-dependent resistance to viral-induced type 1 diabetes

The dilute plasma cytokine milieu associated with type 1 diabetes (T1D), while difficult to measure directly, is sufficient to drive transcription in a bioassay that uses healthy leukocytes as reporters. Previously, we reported disease-associated, partially IL-1 dependent, transcriptional signatures in both T1D patients and the BioBreeding (BB) rat model. Here, we examine temporal signatures in congenic BBDR.lyp/lyp rats that develop spontaneous T1D, and BBDR rats where T1D progresses only after immunological perturbation in young animals. After weaning, the BBDR temporal signature showed early coincident induction of transcription related to innate inflammation as well as IL-10- and TGF-β-mediated regulation. BBDR plasma cytokine levels mirrored the signatures showing early inflammation, followed by induction of a regulated state that correlated with failure of virus to induce T1D in older rats. In contrast, the BBDR.lyp/lyp temporal signature exhibited asynchronous dynamics, with delayed induction of inflammatory transcription and later, weaker induction of regulatory transcription, consistent with their deficiency in regulatory T cells. Through longitudinal analyses of plasma-induced signatures in BB rats and a human T1D progressor, we have identified changes in immunoregulatory processes that attenuate a preexisting innate inflammatory state in BBDR rats, suggesting a mechanism underlying the decline in T1D susceptibility with age.

Previous maternal infection protects offspring from enterovirus infection and prevents experimental diabetes development in mice

AIMS/HYPOTHESIS

Enterovirus (e.g. Coxsackie B virus serotypes [CVBs]) infections may be associated with development of type 1 diabetes. Studies conducted in several European countries have, however, shown an inverse correlation between the incidence of type 1 diabetes and the prevalence of enterovirus infections. These findings could in part be explained by an extension of the poliovirus hypothesis, suggesting that the absence of maternally transferred antibodies protecting offspring from early infection increases the risk for diabetes development. Experimental evidence supporting this hypothesis in type 1 diabetes is, however, lacking. As maternally transferred protection from infection is a crucial component of the extended poliovirus hypothesis, we here tested the hypothesis that previously infected females transfer protection against infection and diabetes to offspring.

METHODS

The induction of CVB-specific maternal antibodies and transfer of protection from virus infection, replication and development of virus-induced diabetes to offspring was assessed using NOD and Socs1-transgenic NOD mice.

RESULTS

Infected mice produced neutralising antibodies to CVB. Offspring from infected females were positive for neutralising antibodies and were strongly protected from both infection and experimental diabetes.

CONCLUSIONS/INTERPRETATION

Our study shows that maternally transferred antibodies protect offspring from enterovirus infection and virus-induced diabetes. This suggests that the absence of maternally provided protection increases the risk for severe outcomes after an enterovirus infection in offspring. Moreover, our findings may have implications for the design of prospective studies aimed at investigating the possible role of enterovirus infections in the aetiology of human type 1 diabetes.

The Missing Heritability in T1D and Potential New Targets for Prevention

Type 1 diabetes (T1D) is a T cell-mediated disease. It is strongly associated with susceptibility haplotypes within the major histocompatibility complex, but this association accounts for an estimated 50% of susceptibility. Other studies have identified as many as 50 additional susceptibility loci, but the effect of most is very modest (odds ratio (OR) <1.5). What accounts for the "missing heritability" is unknown and is often attributed to environmental factors. Here we review new data on the cognate ligand of MHC molecules, the T cell receptor (TCR). In rats, we found that one allele of a TCR variable gene, V β 13A, is strongly associated with T1D (OR >5) and that deletion of V β 13+ T cells prevents diabetes. A role for the TCR is also suspected in NOD mice, but TCR regions have not been associated with human T1D. To investigate this disparity, we tested the hypothesis in silico that previous studies of human T1D genetics were underpowered to detect MHC-contingent TCR susceptibility. We show that stratifying by MHC markedly increases statistical power to detect potential TCR susceptibility alleles. We suggest that the TCR regions are viable candidates for T1D susceptibility genes, could account for "missing heritability," and could be targets for prevention.

Prevention or acceleration of type 1 diabetes by viruses

Type 1 diabetes is an autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells. Even though extensive scientific research has yielded important insights into the immune mechanisms involved in pancreatic β-cell destruction, little is known about the events that trigger the autoimmune process. Recent epidemiological and experimental data suggest that environmental factors are involved in this process. In this review, we discuss the role of viruses as an environmental factor on the development of type 1 diabetes, and the immune mechanisms by which they can trigger or protect against this pathology.

Viral infections and diabetes

Type 1 diabetes mellitus (T1DM) is a multi-factorial autoimmune disease determined by the interaction of genetic, environmental and immunologic factors. One of the environmental risk factors identified by a series of independent studies is represented by viral infection, with strong evidence showing that viruses can indeed infect pancreatic beta cells with consequent effects ranging from functional damage to cell death. In this chapter we review the data obtained both in man and in experimental animal models in support of the potential participation of viral infections to Type 1 diabetes pathogenesis, with a particular emphasis on virus-triggered islet inflammation, beta-cell dysfunction and autoimmunity.

Infection as a cause of type 1 diabetes?

PURPOSE OF REVIEW

It is the current opinion that pathogens, such as viruses, are contributing to the development of type 1 diabetes (T1D) in susceptible individuals. This opinion is based on epidemiological associations, direct isolation of pathogens from the islets of Langerhans, as well as a large amount of data from various experimental animal models. Human enteroviruses have dominated the literature associated with the etiology of T1D. However, virus infections have also been reported to protect from autoimmune disorders.

RECENT FINDINGS

Here we review the evidence for virus infections to be involved in the pathogenesis of T1D and discuss potential mechanisms of how such infections could accelerate the destruction of insulin-producing β-cells. In addition, we will review evidence from epidemiologic and experimental animal studies showing that virus infections could also have protective properties.

SUMMARY

Virus infections play an important role in the pathogenesis of T1D by inducing or accelerating the autodestructive process, but also by protecting from autoimmunity. Thus, multiple sequential infections might shape the autoreactive immune repertoire and the pathogenesis of T1D in a complex fashion.

Prevention of type 1 diabetes in the rat with an allele-specific anti-T-cell receptor antibody: Vβ13 as a therapeutic target and biomarker

In earlier studies of the Iddm14 diabetes susceptibility locus in the rat, we identified an allele of the T-cell receptor (TCR) β-chain, Tcrb-V13S1A1, as a candidate gene. To establish its importance, we treated susceptible rats with a depleting anti-rat Vβ13 monoclonal antibody and then exposed them to either polyinosinic:polycytidylic acid or a diabetogenic virus to induce diabetes. The overall frequency of diabetes in the controls was 74% (n = 50), compared with 17% (n = 30) in the anti-Vβ13-treated animals, with minimal islet pathology in nondiabetic treated animals. T cells isolated from islets on day 5 after starting induction showed a greater proportion of Vβ13(+) T cells than did peripheral lymph node T cells. Vβ13 transcripts recovered from day 5 islets revealed focused Jβ usage and less CDR3 diversity than did transcripts from peripheral Vβ13(+) T cells. CDR3 usage was not skewed in control Vβ16 CDR3 transcripts. Anti-rat Vβ13 antibody also prevented spontaneous diabetes in BBDP rats. The Iddm14 gene is likely to be Tcrb-V13, indicating that TCR β-chain usage is a determinant of susceptibility to autoimmune diabetes in rats. It may be possible to prevent autoimmune diabetes by targeting a limited element of the T-cell repertoire.

Susceptibility of human pancreatic β cells for cytomegalovirus infection and the effects on cellular immunogenicity

OBJECTIVES

Human cytomegalovirus (HCMV) infection has been suggested to be a causal factor in the development of type 1 diabetes, posttransplantation diabetes, and the failure of islet allografts. This effect of CMV has been interpreted as an indirect effect on the immune system rather than direct infection-induced cell death. In the present study, we investigated (i) the susceptibility of β cells to HCMV infection, (ii) regulation of immune cell-activating ligands, (iii) release of proinflammatory cytokines, and (iv) the effects on peripheral blood mononuclear cell (PBMC) activation.

METHODS

CM insulinoma cells and primary β cells were HCMV-infected in vitro using a laboratory and a clinical HCMV strain. The susceptibility to infection was measured by the expression of viral genes and proteins. Furthermore, expression levels of Major Histocompatibility Complex I, Intracellular Adhesion Molecule-1, and Lymphocyte Function Associated Antigen-3 and the release of proinflammatory cytokines were determined. In addition, PBMC activation to HCMV-infected β cells was determined.

RESULTS

β Cells were susceptible to HCMV infection. Moreover, the infection increased the cellular immunogenicity, as demonstrated by an increased MHC I and ICAM-1 expression and an increased proinflammatory cytokine release. Human cytomegalovirus-infected CM cells potently activated PBMCs. The infection-induced effects were dependent on both viral "sensing" and viral replication.

CONCLUSIONS

In vivo β-cell HCMV infection and infection-enhanced cellular immunogenicity may have important consequences for native or transplanted β-cell survival.

Haptoglobin as an early serum biomarker of virus-induced autoimmune type 1 diabetes in biobreeding diabetes resistant and LEW1.WR1 rats

Proteomic profiling of serum is a powerful technique to identify differentially expressed proteins that can serve as biomarkers predictive of disease onset. In this study, we utilized two-dimensional (2D) gel analysis followed by matrix-assisted-laser desorption/ionization time-of-flight mass spectrometry analysis to identify putative serum biomarkers for autoimmune type 1 diabetes (T1D) in biobreeding diabetes resistant (BBDR) rats induced to express the disease. Treatment with toll-like receptor 3 ligand, polyinosinic:polycytidilic acid (pIC), plus infection with Kilham rat virus (KRV), a rat parvovirus, results in nearly 100% of young BBDR rats becoming diabetic within 11-21 d. Sera collected from prediabetic rats at early time points following treatment with pIC + KRV were analyzed by 2D gel electrophoresis and compared with sera from control rats treated with phosphate-buffered saline, pIC alone or pIC + H1, a non-diabetogenic parvovirus. None of the latter three control treatments precipitates T1D. 2D gel analysis revealed that haptoglobin, an acute phase and hemoglobin scavenger protein, was differentially expressed in the sera of rats treated with pIC + KRV relative to control groups. These results were confirmed by Western blot and enzyme-linked immunosorbent assay studies, which further validated haptoglobin levels as being differentially increased in the sera of pIC + KRV-treated rats relative to controls during the first week following infection. Early elevations in serum haptoglobin were also observed in LEW1.WR1 rats that became diabetic following infection with rat cytomegalovirus. The identification and validation of haptoglobin as a putative serum biomarker for autoimmune T1D in rats now affords us the opportunity to test the validity of this protein as a biomarker for human T1D, particularly in those situations where viral infection is believed to precede the onset of disease.

Immune cell crosstalk in type 1 diabetes

The development of type 1 diabetes involves a complex interaction between pancreatic beta-cells and cells of both the innate and adaptive immune systems. Analyses of the interactions between natural killer (NK) cells, NKT cells, different dendritic cell populations and T cells have highlighted how these different cell populations can influence the onset of autoimmunity. There is evidence that infection can have either a potentiating or inhibitory role in the development of type 1 diabetes. Interactions between pathogens and cells of the innate immune system, and how this can influence whether T cell activation or tolerance occurs, have been under close scrutiny in recent years. This Review focuses on the nature of this crosstalk between the innate and the adaptive immune responses and how pathogens influence the process.