Requirements for viral-mediated autoimmune diabetes: beta-cell damage and immune infiltration

COVID-19 in two children with new-onset diabetes: case reports

Delayed diagnosis, low socioeconomic status and infection have been associated with diabetic ketoacidosis (DKA) at type 1 diabetes mellitus presentation. A teenager from a low socioeconomic status family, with longstanding weight loss, polyphagia, polyuria, vomiting and abdominal pain, attended the emergency department, also complaining of anosmia and odynophagia. He was diagnosed with COVID-19 and new-onset DKA. The second child had 2 weeks of diabetes symptoms and was admitted with new-onset mild DKA. SARS-CoV-2 RT-PCR test was positive, although asymptomatic. Persistent hyperglycaemia with high insulin requirements was a common feature to both patients. Both cases support that SARS-CoV-2 may have an association with rapidly increasing insulin daily needs. In case one, not only fear of COVID-19 delayed hospital attendance but also the setting of a low socioeconomic status family appears to have enhanced the risk for late diagnosis and challenging disease management.

Toll-Like Receptor 3 Is Critical to the Pancreatic Islet Milieu That Is Required for Coxsackievirus B4-Induced Type 1 Diabetes in Female Nonobese Diabetic Mice

OBJECTIVE

Genetic and environmental influences play a role as triggers of type 1 diabetes mellitus (T1DM). Female nonobese diabetic (NOD) mice are useful for studying T1DM as they spontaneously develop T1DM, which can be accelerated by some viruses. Toll-like receptor 3 (TLR3) is believed to play a critical role in viral-induced T1DM and β-cell destruction, because female Tlr3 knockout (Tlr3-/-) NOD mice are protected from Coxsackievirus B4 (CVB4)-induced acceleration of T1DM. However, the exact role(s) TLR3 plays in the pathogenesis of CVB4-induced T1DM remain unknown.

METHODS

This longitudinal study used immunostaining, laser capture microdissection, and reverse transcription real-time polymerase chain reaction of islets from female uninfected and CVB4-infected Tlr3+/+ and Tlr3-/- NOD mice.

RESULTS

Islets isolated from female Tlr3+/+ NOD mice 4 to 8 weeks of age had higher amounts of insulitis, Cxcl10, Il1b, Tnfa, and Tgfb1 expression compared with Tlr3-/- NOD mice. After CVB4 infection, Tlr3+/+ NOD mice had higher amounts of insulitis and T-cell infiltration at 3 days after infection compared with Tlr3-/- CVB4-infected NOD mice.

CONCLUSIONS

Toll-like receptor 3 is necessary for establishment of a pancreatic islet inflammatory microenvironment by increasing insulitis and cytokine expression that facilitates CVB4-induced T1DM in female NOD mice.

Redox-Sensitive Innate Immune Pathways During Macrophage Activation in Type 1 Diabetes

SIGNIFICANCE

Type 1 diabetes (T1D) is an autoimmune disease resulting in β-cell destruction mediated by islet-infiltrating leukocytes. The role of oxidative stress in human and murine models of T1D is highly significant as these noxious molecules contribute to diabetic complications and β-cell lysis, but their direct impact on dysregulated autoimmune responses is highly understudied. Pro-inflammatory macrophages play a vital role in the initiation and effector phases of T1D by producing free radicals and pro-inflammatory cytokines to facilitate β-cell destruction and to present antigen to autoreactive T cells. Recent Advances: Redox modulation of macrophage functions may play critical roles in autoimmunity. These include enhancing pro-inflammatory innate immune signaling pathways in response to environmental triggers, enforcing an M1 macrophage differentiation program, controlling antigen processing, and altering peptide recognition by oxidative post-translational modification. Therefore, an oxidative environment may act on multiple macrophage functions to orchestrate T1D pathogenesis.

CRITICAL ISSUES

Mechanisms involved in the initiation of T1D remain unclear, making preventive and early therapeutics difficult to develop. Although many of these advances in the redox regulation of macrophages are in their infancy, they provide insight into how oxidative stress aids in the precipitating event of autoimmune activation.

FUTURE DIRECTIONS

Future studies should be aimed at mechanistically determining which redox-regulated macrophage functions are pertinent in T1D pathogenesis, as well as at investigating potential targetable therapeutics to halt and/or dampen innate immune activation in T1D.

The proinflammatory effects of macrophage-derived NADPH oxidase function in autoimmune diabetes

Type 1 diabetes (T1D) is an autoimmune disease culminating in the destruction of insulin-producing pancreatic β-cells. While ultimately a T cell-mediated disease, macrophages play an indispensable role in disease initiation and progression. Infiltrating macrophages generate an inflammatory environment by releasing NADPH oxidase-derived superoxide and proinflammatory cytokines. The synthesis of reactive oxygen species (ROS) is acknowledged as putative factors contributing to autoimmunity and β-cell damage in T1D. In addition to direct lysis, free radicals collectively participate in β-cell destruction by providing a redox-dependent third signal necessary for islet-reactive CD4 and CD8 T cell maturation and by inducing oxidative post-translational modifications of β-cell epitopes to further exacerbate autoimmune responses. This review will provide an overview of macrophage function and a synergistic cross-talk with redox biology that contributes to autoimmune dysregulation in T1D.

Superoxide Production by NADPH Oxidase Intensifies Macrophage Antiviral Responses during Diabetogenic Coxsackievirus Infection

Coxsackievirus B infections are suspected environmental triggers of type 1 diabetes (T1D) and macrophage antiviral responses may provide a link to virus-induced T1D. We previously demonstrated an important role for NADPH oxidase (NOX)-derived superoxide production during T1D pathogenesis, as NOX-deficient NOD mice (NOD.Ncf1m1J ) were protected against T1D due, in part, to impaired proinflammatory TLR signaling in NOD.Ncf1m1J macrophages. Therefore, we hypothesized that loss of NOX-derived superoxide would dampen diabetogenic antiviral macrophage responses and protect from virus-induced diabetes. Upon infection with a suspected diabetogenic virus, Coxsackievirus B3 (CB3), NOD.Ncf1m1J mice remained resistant to virus-induced autoimmune diabetes. A concomitant decrease in circulating inflammatory chemokines, blunted antiviral gene signature within the pancreas, and reduced proinflammatory M1 macrophage responses were observed. Importantly, exogenous superoxide addition to CB3-infected NOD.Ncf1m1J bone marrow-derived macrophages rescued the inflammatory antiviral M1 macrophage response, revealing reduction-oxidation-dependent mechanisms of signal transducer and activator of transcription 1 signaling and dsRNA viral sensors in macrophages. We report that superoxide production following CB3 infection may exacerbate pancreatic β cell destruction in T1D by influencing proinflammatory M1 macrophage responses, and mechanistically linking oxidative stress, inflammation, and diabetogenic virus infections.

Environmental Factors Contribute to β Cell Endoplasmic Reticulum Stress and Neo-Antigen Formation in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease in which immune-mediated targeting and destruction of insulin-producing pancreatic islet β cells leads to chronic hyperglycemia. There are many β cell proteins that are targeted by autoreactive T cells in their native state. However, recent studies have demonstrated that many β cell proteins are recognized as neo-antigens following posttranslational modification (PTM). Although modified neo-antigens are well-established targets of pathology in other autoimmune diseases, the effects of neo-antigens in T1D progression and the mechanisms by which they are generated are not well understood. We have demonstrated that PTM occurs during endoplasmic reticulum (ER) stress, a process to which β cells are uniquely susceptible due to the high rate of insulin production in response to dynamic glucose sensing. In the context of genetic susceptibility to autoimmunity, presentation of these modified neo-antigens may activate autoreactive T cells and cause pathology. However, inherent β cell ER stress and protein PTM do not cause T1D in every genetically susceptible individual, suggesting the contribution of additional factors. Indeed, many environmental factors, such as viral infection, chemicals, or inflammatory cytokines, are associated with T1D onset, but the mechanisms by which these factors lead to disease onset remain unknown. Since these environmental factors also cause ER stress, exposure to these factors may enhance production of neo-antigens, therefore boosting β cell recognition by autoreactive T cells and exacerbating T1D pathogenesis. Therefore, the combined effects of physiological ER stress and the stress that is induced by environmental factors may lead to breaks in peripheral tolerance, contribute to antigen spread, and hasten disease onset. This Hypothesis and Theory article summarizes what is currently known about ER stress and protein PTM in autoimmune diseases including T1D and proposes a role for environmental factors in breaking immune tolerance to β cell antigens through neo-antigen formation.

Environmental risk factors for type 1 diabetes

The incidence of type 1 diabetes has risen considerably in the past 30 years due to changes in the environment that have been only partially identified. In this Series paper, we critically discuss candidate triggers of islet autoimmunity and factors thought to promote progression from autoimmunity to overt type 1 diabetes. We revisit previously proposed hypotheses to explain the growth in the incidence of type 1 diabetes in light of current data. Finally, we suggest a unified model in which immune tolerance to β cells can be broken by several environmental exposures that induce generation of hybrid peptides acting as neoautoantigens.

Toll-like receptor 3 is critical for coxsackievirus B4-induced type 1 diabetes in female NOD mice

Group B coxsackieviruses (CVBs) are involved in triggering some cases of type 1 diabetes mellitus (T1DM). However, the molecular mechanism(s) responsible for this remain elusive. Toll-like receptor 3 (TLR3), a receptor that recognizes viral double-stranded RNA, is hypothesized to play a role in virus-induced T1DM, although this hypothesis is yet to be substantiated. The objective of this study was to directly investigate the role of TLR3 in CVB-triggered T1DM in nonobese diabetic (NOD) mice, a mouse model of human T1DM that is widely used to study both spontaneous autoimmune and viral-induced T1DM. As such, we infected female wild-type (TLR3(+/+)) and TLR3 knockout (TLR3(-/-)) NOD mice with CVB4 and compared the incidence of diabetes in CVB4-infected mice with that of uninfected counterparts. We also evaluated the islets of uninfected and CVB4-infected wild-type and TLR3 knockout NOD mice by immunohistochemistry and insulitis scoring. TLR3 knockout mice were markedly protected from CVB4-induced diabetes compared with CVB4-infected wild-type mice. CVB4-induced T-lymphocyte-mediated insulitis was also significantly less severe in TLR3 knockout mice compared with wild-type mice. No differences in insulitis were observed between uninfected animals, either wild-type or TLR3 knockout mice. These data demonstrate for the first time that TLR3 is 1) critical for CVB4-induced T1DM, and 2) modulates CVB4-induced insulitis in genetically prone NOD mice.

Type I diabetes mellitus: genetic factors and presumptive enteroviral etiology or protection

We review type 1 diabetes and host genetic components, as well as epigenetics and viruses associated with type 1 diabetes, with added emphasis on the enteroviruses, which are often associated with triggering the disease. Genus Enterovirus is classified into twelve species of which seven (Enterovirus A, Enterovirus B, Enterovirus C, and Enterovirus D and Rhinovirus A, Rhinovirus B, and Rhinovirus C) are human pathogens. These viruses are transmitted mainly by the fecal-oral route; they may also spread via the nasopharyngeal route. Enterovirus infections are highly prevalent, but these infections are usually subclinical or cause a mild flu-like illness. However, infections caused by enteroviruses can sometimes be serious, with manifestations of meningoencephalitis, paralysis, myocarditis, and in neonates a fulminant sepsis-like syndrome. These viruses are often implicated in chronic (inflammatory) diseases as chronic myocarditis, chronic pancreatitis, and type 1 diabetes. In this review we discuss the currently suggested mechanisms involved in the viral induction of type 1 diabetes. We recapitulate current basic knowledge and definitions.

Protection against type 1 diabetes upon Coxsackievirus B4 infection and iNKT-cell stimulation: role of suppressive macrophages

Invariant natural killer T (iNKT) cells belong to the innate immune system and exercise a dual role as potent regulators of autoimmunity and participate in responses against different pathogens. They have been shown to prevent type 1 diabetes development and to promote antiviral responses. Many studies in the implication of environmental factors on the etiology of type 1 diabetes have suggested a link between enteroviral infections and the development of this disease. This study of the pancreatropic enterovirus Coxsackievirus B4 (CVB4) shows that although infection accelerated type 1 diabetes development in a subset of proinsulin 2-deficient NOD mice, the activation of iNKT cells by a specific agonist, α-galactosylceramide, at the time of infection inhibited the disease. Diabetes development was associated with the infiltration of pancreatic islets by inflammatory macrophages, producing high levels of interleukin (IL)-1β, IL-6, and tumor necrosis factor-α and activation of anti-islet T cells. On the contrary, macrophages infiltrating the islets after CVB4 infection and iNKT-cell stimulation expressed a number of suppressive enzymes, among which indoleamine 2,3-dioxygenase was sufficient to inhibit anti-islet T-cell response and to prevent diabetes. This study highlights the critical interaction between virus and the immune system in the acceleration or prevention of type 1 diabetes.

Induction of an antiviral state and attenuated coxsackievirus replication in type III interferon-treated primary human pancreatic islets

Type III interferons (IFNs), also called lambda interferons (IFN-λ), comprise three isoforms, IFN-λ1 (interleukin-29 [IL-29]), IFN-λ2 (IL-28A), and IFN-λ3 (IL-28B). Only limited information is available on their expression and biological functions in humans. Type I and type II IFNs protect human pancreatic islets against coxsackievirus infection, and this is important since such viruses have been proposed to play a role in the development of human type 1 diabetes. Here we investigated whether type III IFN is expressed during infection of human islet cells with coxsackievirus and if type III IFN regulates permissiveness to such infections. We show that human islets respond to a coxsackievirus serotype B3 (CVB3) infection by inducing the expression of type III IFNs. We also demonstrate that islet endocrine cells from nondiabetic individuals express the type III IFN receptor subunits IFN-λR1 and IL-10R2. Pancreatic alpha cells express both receptor subunits, while pancreatic beta cells express only IL-10R2. Type III IFN stimulation elicited a biological response in human islets as indicated by the upregulated expression of antiviral genes as well as pattern recognition receptors. We also show that type III IFN significantly reduces CVB3 replication. Our studies reveal that type III IFNs are expressed during CVB3 infection and that the expression of the type III IFN receptor by the human pancreatic islet allows this group of IFNs to regulate the islets' permissiveness to infection. Our novel observations suggest that type III IFNs may regulate viral replication and thereby contribute to reduced tissue damage and promote islet cell survival during coxsackievirus infection.

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.

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.

Immunology in the clinic review series; focus on type 1 diabetes and viruses: the enterovirus link to type 1 diabetes: critical review of human studies

The hypothesis that under some circumstances enteroviral infections can lead to type 1 diabetes (T1D) was proposed several decades ago, based initially on evidence from animal studies and sero-epidemiology. Subsequently, enterovirus RNA has been detected more frequently in serum of patients than in control subjects, but such studies are susceptible to selection bias and reverse causality. Here, we review critically recent evidence from human studies, focusing on longitudinal studies with potential to demonstrate temporal association. Among seven longitudinal birth cohort studies, the evidence that enterovirus infections predict islet autoimmunity is quite inconsistent in our interpretation, due partially, perhaps, to heterogeneity in study design and a limited number of subjects studied. An association between enterovirus and rapid progression from autoimmunity to T1D was reported by one longitudinal study, but although consistent with evidence from animal models, this novel observation awaits replication. It is possible that a potential association with initiation and/or progression of islet autoimmunity can be ascribed to a subgroup of the many enterovirus serotypes, but this has still not been investigated properly. There is a need for larger studies with frequent sample intervals and collection of specimens of sufficient quality and quantity for detailed characterization of enterovirus. More research into the molecular epidemiology of enteroviruses and enterovirus immunity in human populations is also warranted. Ultimately, this knowledge may be used to devise strategies to reduce the risk of T1D in humans.

Group B coxsackieviruses and autoimmunity: focus on Type 1 diabetes

Group B coxsackieviruses (CVB) and/or their components have been found in the blood and pancreas of patients with Type 1 diabetes (T1D). CVB infections lead to the activation of the innate and adaptive immune systems, which can result in the induction or aggravation of autoimmune processes. Persistent and/or repeated infections of pancreas islet β cells with CVB and the resulting production of IFN-α and inflammatory mediators, combined with a predisposed genetic background, may induce bystander activation of autoimmune effector T cells and an autoreactive response to islet self-antigens through molecular mimicry. Moreover, the antibody-dependent enhancement of CVB infection of monocytes, as well as infection of the thymus can intervene in the pathogenesis of T1D. In contrast with the deleterious effect of CVB, it has been shown that these viruses can protect against the development of T1D under certain experimental conditions. The role of CVB in autoimmunity is complex, and therefore a better understanding of the inducer versus protective effects of these viruses in T1D will help to design new strategies to treat and prevent the disease.

Parasites or cohabitants: cruel omnipresent usurpers or creative "éminences grises"?

This paper presents many types of interplays between parasites and the host, showing the history of parasites, the effects of parasites on the outcome of wars, invasions, migrations, and on the development of numerous regions of the globe, and the impact of parasitic diseases on the society and on the course of human evolution. It also emphasizes the pressing need to change the look at the parasitism phenomenon, proposing that the term “cohabitant” is more accurate than parasite, because every living being, from bacteria to mammals, is a consortium of living beings in the pangenome. Even the term parasitology should be replaced by cohabitology because there is no parasite alone and host alone: both together compose a new adaptive system: the parasitized-host or the cohabitant-cohabited being. It also suggests switching the old paradigm based on attrition and destruction, to a new one founded on adaptation and living together.

Type 1 Diabetes: Etiology, Immunology, and Therapeutic Strategies

Type 1 diabetes (T1D) is a chronic autoimmune disease in which destruction or damaging of the beta-cells in the islets of Langerhans results in insulin deficiency and hyperglycemia. We only know for sure that autoimmunity is the predominant effector mechanism of T1D, but may not be its primary cause. T1D precipitates in genetically susceptible individuals, very likely as a result of an environmental trigger. Current genetic data point towards the following genes as susceptibility genes: HLA, insulin, PTPN22, IL2Ra, and CTLA4. Epidemiological and other studies suggest a triggering role for enteroviruses, while other microorganisms might provide protection. Efficacious prevention of T1D will require detection of the earliest events in the process. So far, autoantibodies are most widely used as serum biomarker, but T-cell readouts and metabolome studies might strengthen and bring forward diagnosis. Current preventive clinical trials mostly focus on environmental triggers. Therapeutic trials test the efficacy of antigen-specific and antigen-nonspecific immune interventions, but also include restoration of the affected beta-cell mass by islet transplantation, neogenesis and regeneration, and combinations thereof. In this comprehensive review, we explain the genetic, environmental, and immunological data underlying the prevention and intervention strategies to constrain T1D.

Enteroviruses and type 1 diabetes: towards a better understanding of the relationship

Environmental factors, especially viruses, are involved in the initiation or the acceleration of type 1 diabetes (T1D) pathogenesis. Epidemiological data strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), can be associated with T1D. It has been demonstrated that enterovirus infections were significantly more prevalent in at risk individuals, such as siblings of diabetic patients, when they developed anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients strengthened the hypothesis of a relationship between the virus and the disease. Studies performed in vitro and in vivo in animal models helped to discover mechanisms of the infection of pancreas and other tissues, potentially able to play a role in the pathogenesis of T1D. Interestingly, it cannot be excluded that enteroviruses behave as half-devil half-angel since experimental studies suggest that, in certain conditions, these agents would be able to protect individuals against the disease. All of the plausible mechanisms by which enterovirus may be related to T1D will be reviewed here.

Enterovirus infection and progression from islet autoimmunity to type 1 diabetes: the Diabetes and Autoimmunity Study in the Young (DAISY)

OBJECTIVE

To investigate whether enterovirus infections predict progression to type 1 diabetes in genetically predisposed children repeatedly positive for islet autoantibodies.

RESEARCH DESIGN AND METHODS

Since 1993, the Diabetes and Autoimmunity Study in the Young (DAISY) has followed 2,365 genetically predisposed children for islet autoimmunity and type 1 diabetes. Venous blood and rectal swabs were collected every 3-6 months after seroconversion for islet autoantibodies (against GAD, insulin, or insulinoma-associated antigen-2 [IA-2]) until diagnosis of diabetes. Enteroviral RNA in serum or rectal swabs was detected using reverse transcriptase PCR with primers specific for the conserved 5' noncoding region, detecting essentially all enterovirus serotypes.

RESULTS

Of 140 children who seroconverted to repeated positivity for islet autoantibodies at a median age of 4.0 years, 50 progressed to type 1 diabetes during a median follow-up of 4.2 years. The risk of progression to clinical type 1 diabetes in the sample interval following detection of enteroviral RNA in serum (three diabetes cases diagnosed among 17 intervals) was significantly increased compared with that in intervals following a negative serum enteroviral RNA test (33 cases diagnosed among 1,064 intervals; hazard ratio 7.02 [95% CI 1.95-25.3] after adjusting for number of autoantibodies). Results remained significant after adjustment for ZnT8-autoantibodies and after restriction to various subgroups. Enteroviral RNA in rectal swabs was not predictive of progression to type 1 diabetes. No evidence for viral persistence was found.

CONCLUSIONS

This novel observation suggests that progression from islet autoimmunity to type 1 diabetes may increase after an enterovirus infection characterized by the presence of viral RNA in blood.

Virus infections: lessons from pancreas histology

Type 1 diabetes mellitus is a chronic autoimmune disease resulting from the progressive immune-mediated destruction of pancreatic beta cells in genetically susceptible individuals, with the likely contribution of environmental factors, among which viruses have been extensively studied. The pathologic hallmark of the disease is insulitis-a process characterized by islet infiltration of immunocompetent cells that has been well characterized in animal models of islet autoimmunity, and to a lesser extent, in humans. Insulitis characterization has provided valuable information to gain insights into the disease pathogenesis. We review the recent literature on the viral contribution to beta-cell destruction and dysfunction in type 1 diabetes, with particular reference to the pathology of the pancreatic islet in humans and in animal models of the disease.

Pathogenesis of type 1 diabetes mellitus: interplay between enterovirus and host

Enteroviruses are believed to contribute to the pathogenesis of type 1 diabetes mellitus (T1DM). In this Review, the interplay between infection with enteroviruses, the immune system and host genes is discussed. Data from retrospective and prospective epidemiological studies strongly suggest the involvement of enteroviruses, such as coxsackievirus B, in the development of T1DM. Enteroviral RNA and/or proteins can be detected in tissues of patients with T1DM. Isolation of coxsackievirus B4 from the pancreas of patients with T1DM or the presence of enteroviral components in their islets strengthens the hypothesis of a relationship between the virus and the disease. Enteroviruses can play a part in the early phase of T1DM through the infection of beta cells and the activation of innate immunity and inflammation. In contrast with its antiviral role, virus-induced interferon alpha can be deleterious, acting as an initiator of the autoimmunity directed against beta cells. Enteroviruses, through persistent and/or successive infections, can interact with the adaptive immune system. Host genes, such as IFIH1, that influence susceptibility to T1DM are associated with antiviral activities. An increased activity of the IFIH1 protein may promote the development of T1DM. An improved knowledge of the pathogenic mechanisms of enterovirus infections should help to uncover preventive strategies for T1DM.

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

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

Role of coxsackievirus B4 in the pathogenesis of type 1 diabetes

Environmental factors, especially viruses, are thought to play an important role in the initiation or acceleration of the pathogenesis of type 1 diabetes (T1D). Data from retrospective and prospective epidemiological studies strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), may be associated with the development of T1D. It has also been shown that enterovirus infections are significantly more prevalent in at-risk individuals such as the siblings of diabetic patients, when they develop anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients supports the hypothesis of a relationship between the virus and the disease. Furthermore, studies performed in vitro and in vivo in animal models have increased our knowledge of the role of CV-B4 in T1D by helping to clarify the pathogenic mechanisms of the infection that can lead to beta-cell destruction, including direct virus-induced beta-cell lysis, molecular mimicry, 'bystander activation' and viral persistence. The role of enteroviruses as the sole agents in T1D, and a causal link between these agents and T1D, have not yet been established, although arguments that support such a role for these viruses in the pathogenesis of the disease cannot be ignored.

Regulatory T-cells protect from type 1 diabetes after induction by coxsackievirus infection in the context of transforming growth factor-beta

OBJECTIVE

Coxsackievirus infections have long been associated with the induction of type 1 diabetes. Infection with coxsackievirus B4 (CB4) enhances type 1 diabetes onset in NOD mice by accelerating the presentation of beta-cell antigen to autoreactive T-cells. It has been reported that a progressive defect in regulatory T-cell (Treg) function is, in part, responsible for type 1 diabetes onset in NOD mice. This defect may contribute to susceptibility to viral-induced type 1 diabetes. We asked whether the immune response after CB4 infection could be manipulated to reestablish peripheral tolerance while maintaining the immune response to virus.

RESEARCH DESIGN AND METHODS

NOD mice expressing transforming growth factor-beta (TGF-beta) specifically in the beta-cells were infected with CB4, and the functional role of Tregs in disease protection was measured. Systemic treatments with TGF-beta were used to assess its therapeutic potential.

RESULTS

Here, we report that Tregs induced after CB4 infection in the presence of TGF-beta prevented type 1 diabetes. The capacity to directly infect pancreatic beta-cells correlated with increased numbers of pancreatic Tregs, suggesting that presentation of beta-cell antigen is integral to induction of diabetogenic protective Tregs. Furthermore, the presence of these viral induced Tregs correlated with protection from type 1 diabetes without altering the antiviral response. Finally, when TGF-beta was administered systemically to NOD mice after infection, the incidence of type 1 diabetes was reduced, thereby signifying a potential therapeutic role for TGF-beta.

CONCLUSIONS

We demonstrate manipulations of the immune response that result in Treg-mediated protection from type 1 diabetes without concomitant loss of the capacity to control viral infection.

Interferons induce an antiviral state in human pancreatic islet cells

Enterovirus infections, in particular those with Coxsackieviruses, have been linked to the development of type 1 diabetes (T1D). Although animal models have demonstrated that interferons (IFNs) regulate virus-induced T1D by acting directly on the beta cell, little is known on the human pancreatic islet response to IFNs. Here we show that human islet cells respond to IFNs by expressing signature genes of antiviral defense. We also demonstrate that they express three intracellular sensors for viral RNA, the toll like receptor 3 (TLR3) gene, the retinoic acid-inducible gene I (RIG-I) and the melanoma differentiation-associated gene-5 (MDA-5), which induce type I IFN production in infected cells. Finally, we show for the first time that the IFN-induced antiviral state provides human islets with a powerful protection from the replication of Coxsackievirus. This may be critical for beta cell survival and protection from virus-induced T1D in humans.

Expression of IGF-I in pancreatic islets prevents lymphocytic infiltration and protects mice from type 1 diabetes

Type 1 diabetic patients are diagnosed when beta-cell destruction is almost complete. Reversal of type 1 diabetes will require beta-cell regeneration from islet cell precursors and prevention of recurring autoimmunity. IGF-I expression in beta-cells of streptozotocin (STZ)-treated transgenic mice regenerates the endocrine pancreas by increasing beta-cell replication and neogenesis. Here, we examined whether IGF-I also protects islets from autoimmune destruction. Expression of interferon (IFN)-beta in beta-cells of transgenic mice led to islet beta(2)-microglobulin and Fas hyperexpression and increased lymphocytic infiltration. Pancreatic islets showed high insulitis, and these mice developed overt diabetes when treated with very-low doses of STZ, which did not affect control mice. IGF-I expression in IFN-beta-expressing beta-cells of double-transgenic mice reduced beta(2)-microglobulin, blocked Fas expression, and counteracted islet infiltration. This was parallel to a decrease in beta-cell death by apoptosis in islets of STZ-treated IGF-I+IFN-beta-expressing mice. These mice were normoglycemic, normoinsulinemic, and showed normal glucose tolerance. They also presented similar pancreatic insulin content and beta-cell mass to healthy mice. Thus, local expression of IGF-I prevented islet infiltration and beta-cell death in mice with increased susceptibility to diabetes. These results indicate that pancreatic expression of IGF-I may regenerate and protect beta-cell mass in type 1 diabetes.

Maternal environment affects endogenous virus induction in the offspring of type 1 diabetes model non-obese diabetic mice

Type 1 diabetes results from the destruction of pancreatic b-cells (insulitis). It is a multifactorial disease involving genetic and environmental factors, including the maternal environment. Viruses have also been implicated in the pathogenesis of human type 1 diabetes as well as in its model non-obese diabetic (NOD) mice during the perinatal period, as endogenous viruses and/or as infectious agents vertically transmitted from mothers. However, the role of virus as genetic or environmental factor and its interaction with other maternal factors remain unclear. In a series of experiments, we transplanted preimplantation-stage NOD embryos into the uterus of recipient Institute of Cancer Research (ICR) mice, which are without diabetic genetic predisposition, and NOD mice, which did not exhibit overt diabetes during the experiment, and designated offspring as NOD/ICR and NOD/NOD, respectively. We previously observed that NOD/ICR offspring developed insulitis significantly earlier than NOD/NOD offspring. To assess the role of viruses in the development of insulitis, we examined the appearance of viral particles and expression of retroviruses between NOD/ICR and NOD/NOD. NOD/ICR showed earlier expression of env region of the xenotropic type C retrovirus by polymerase chain reaction analysis than NOD/NOD, while the retrovirus-like particles were observed in the islet b-cells similarly in both groups by electron microscopy. Serum corticosterone level, which is suggested to enhance retroviral induction, was significantly higher in the ICR than in the NOD surrogate mothers. These findings suggest that the observed virus is endogenous and that maternal environmental factors, including hormone levels, affect the induction of endogenous viruses and cause the earlier onset of insulitis.

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

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

Lack of islet neogenesis plays a key role in beta-cell depletion in mice infected with a diabetogenic variant of coxsackievirus B4

Group B coxsackieviruses (CVBs) have a well-established association with type 1 diabetes but the mechanism of depletion of beta-cell mass following infection has not yet been defined. In this report we show that the major difference in pathogenesis between the E2 diabetogenic strain of CVB4 and the prototypic JVB strain in SJL mice is not in tropism for islet cells but in the degree of damage inflicted on the exocrine pancreas and the resulting capacity for regeneration of both acinar and islet tissue by the host. Both strains replicated to a high titre in acinar tissue up to day 3 post-infection (p.i.), while the islets of Langerhans were largely spared. However, the pancreas in the JVB-infected animals then regenerated and many small islets were seen throughout the tissue by day 10 p.i. In contrast, the acinar tissue in E2-infected mice became increasingly necrotic until all that remained by day 21 p.i. were large islets containing varying numbers of dead cells, caught up in strands of connective tissue. Surviving beta cells were found to synthesize little insulin, although islet amyloid polypeptide was detected and glucagon synthesis in alpha cells appeared normal or enhanced. Our results suggest that the key to CVB-E2-induced damage lies in the exocrine tissue and prevention of islet neogenesis rather than from direct effects on existing islets.

Toward testing the hypothesis that group B coxsackieviruses (CVB) trigger insulin-dependent diabetes: inoculating nonobese diabetic mice with CVB markedly lowers diabetes incidence

Insulin-dependent (type 1) diabetes mellitus (T1D) onset is mediated by individual human genetics as well as undefined environmental influences such as viral infections. The group B coxsackieviruses (CVB) are commonly named as putative T1D-inducing agents. We studied CVB replication in nonobese diabetic (NOD) mice to assess how infection by diverse CVB strains affected T1D incidence in a model of human T1D. Inoculation of 4- or 8-week-old NOD mice with any of nine different CVB strains significantly reduced the incidence of T1D by 2- to 10-fold over a 10-month period relative to T1D incidences in mock-infected control mice. Greater protection was conferred by more-pathogenic CVB strains relative to less-virulent or avirulent strains. Two CVB3 strains were employed to further explore the relationship of CVB virulence phenotypes to T1D onset and incidence: a pathogenic strain (CVB3/M) and a nonvirulent strain (CVB3/GA). CVB3/M replicated to four- to fivefold-higher titers than CVB3/GA in the pancreas and induced widespread pancreatitis, whereas CVB3/GA induced no pancreatitis. Apoptotic nuclei were detected by TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) assay in CVB3/M-infected pancreata but not in CVB3/GA-infected pancreata. In situ hybridization detected CVB3 RNA in acinar tissue but not in pancreatic islets. Although islets demonstrated inflammatory infiltrates in CVB3-protected mice, insulin remained detectable by immunohistochemistry in these islets but not in those from diabetic mice. Enzyme-linked immunosorbent assay-based examination of murine sera for immunoglobulin G1 (IgG1) and IgG2a immunoreactivity against diabetic autoantigens insulin and HSP60 revealed no statistically significant relationship between CVB3-protected mice or diabetic mice and specific autoimmunity. However, when pooled sera from CVB3/M-protected mice were used to probe a Western blot of pancreatic proteins, numerous proteins were detected, whereas only one band was detected by sera from CVB3/GA-protected mice. No proteins were detected by sera from diabetic or normal mice. Cumulatively, these data do not support the hypothesis that CVB are causative agents of T1D. To the contrary, CVB infections provide significant protection from T1D onset in NOD mice. Possible mechanisms by which this virus-induced protection may occur are discussed.

Viruses and autoimmunity: an affair but not a marriage contract

Viruses are considered as causative agents and contributors to lesion expression in autoimmune disease, notions best supported by studies in animal model systems. This review discusses relationships between virus infection and autoimmunity focusing on mechanisms by which they could induce autoreactivity. The popular idea of molecular mimicry is viewed skeptically with the reviewers taking the viewpoint that viruses contribute to autoimmunity mainly by inducing several nonspecific inflammatory events that together are sufficient to trigger autoreactivity in genetically receptive hosts.

Enterovirus infections and type 1 diabetes

Type 1 (insulin-dependent) diabetes is a typical organ-specific autoimmune disease where insulin-producing beta cells are destroyed by immune mediated mechanisms. The risk of the disease is modulated by genetic factors, mainly genes coding for human leukocyte antigens (HLA), but environmental factors are needed to trigger the process in genetically susceptible individuals. Possible viral triggers of the disease have been sought for years but their identification has been very difficult. Recently, considerable progress has been made by employing new research methods which have supported the idea that the group of enteroviruses may be particularly important in the pathogenesis. An association between enterovirus infections and type 1 diabetes was first reported 30 years ago and since then evaluated in several studies. Recent molecular studies have considerably strengthened this hypothesis by showing that enterovirus genome is present in the blood of diabetic patients. In addition, the first prospective studies have suggested that enterovirus infections may initiate the beta-cell damaging process several years before clinical diabetes is diagnosed. Ecological studies have also indicated similarities in the epidemiology of type 1 diabetes and poliomyelitis - a well-known enterovirus disease. Experimental models, like enterovirus-infected mice or in vitro-cultured beta cells, have provided important information about possible mechanisms, but still it is not known how beta cells are destroyed in human beings. The ongoing prospective studies will answer many open questions, and should the association still hold true, intervention trials will be needed to confirm causality. Even if enterovirus infections were not associated with all diabetes cases but rather with a subgroup of them, this would offer attractive possibilities to prevent the disease or part of it, for example, by an enterovirus vaccine.

ICA69(null) nonobese diabetic mice develop diabetes, but resist disease acceleration by cyclophosphamide

ICA69 (islet cell Ag 69 kDa) is a diabetes-associated autoantigen with high expression levels in beta cells and brain. Its function is unknown, but knockout of its Caenorhabditis elegans homologue, ric-19, compromised neurotransmission. We disrupted the murine gene, ica-1, in 129-strain mice. These animals aged normally, but speed-congenic ICA69(null) nonobese diabetic (NOD) mice developed mid-life lethality, reminiscent of NOD-specific, late lethal seizures in glutamic acid decarboxylase 65-deficient mice. In contrast to wild-type and heterozygous animals, ICA69(null) NOD congenics fail to generate, even after immunization, cross-reactive T cells that recognize the dominant Tep69 epitope in ICA69, and its environmental mimicry Ag, the ABBOS epitope in BSA. This antigenic mimicry is thus driven by the endogenous self Ag, and not initiated by the environmental mimic. Insulitis, spontaneous, and adoptively transferred diabetes develop normally in ICA69(null) NOD congenics. Like glutamic acid decarboxylase 65, ICA69 is not an obligate autoantigen in diabetes. Unexpectedly, ICA69(null) NOD mice were resistant to cyclophosphamide (CY)-accelerated diabetes. Transplantation experiments with hemopoietic and islet tissue linked CY resistance to ICA69 deficiency in islets. CY-accelerated diabetes involves not only ablation of lymphoid cells, but ICA69-dependent drug toxicity in beta cells that boosts autoreactivity in the regenerating lymphoid system.

Presented antigen from damaged pancreatic beta cells activates autoreactive T cells in virus-mediated autoimmune diabetes

The induction of autoimmunity by viruses has been attributed to numerous mechanisms. In mice, coxsackievirus B4 (CB4) induces insulin-dependent diabetes mellitus (IDDM) resembling the final step of disease progression in humans. The immune response following the viral insult clearly precipitates IDDM. However, the molecular pathway between viral infection and the subsequent activation of T cells specific for islet antigen has not been elucidated. These T cells could become activated through exposure to sequestered antigens released by damaged beta cells, or they could have responded to factors secreted by the inflammatory response itself. To distinguish between these possibilities, we treated mice harboring a diabetogenic T cell repertoire with either the islet-damaging agent streptozotocin (STZ) or poly I:C, which nonspecifically activates T cells. Significantly, only treatment of mice with STZ resulted in IDDM and mimicked the effects observed following CB4 infection. Furthermore, antigen-presenting cells from STZ-treated mice were shown to directly activate autoreactive T cells and induce diabetes. Therefore, the primary role of CB4 in the precipitation of IDDM is to damage tissue, causing release and presentation of sequestered islet antigen. These events stimulate autoreactive T cells and thereby initiate disease.