Enteroviruses, type 1 diabetes and hygiene: a complex relationship

Inflammatory perturbations in early life long-lastingly shape the transcriptome and TCR repertoire of the first wave of regulatory T cells

The first wave of Foxp3⁺ regulatory T cells (Tregs) generated in neonates is critical for the life-long prevention of autoimmunity. Although it is widely accepted that neonates are highly susceptible to infections, the impact of neonatal infections on this first wave of Tregs is completely unknown. Here, we challenged newborn Treg fate-mapping mice (Foxp3^eGFPCreERT2xROSA26^STOP-eYFP) with the Toll-like receptor (TLR) agonists LPS and poly I:C to mimic inflammatory perturbations upon neonatal bacterial or viral infections, respectively, and subsequently administrated tamoxifen during the first 8 days of life to selectively label the first wave of Tregs. Neonatally-tagged Tregs preferentially accumulated in non-lymphoid tissues (NLTs) when compared to secondary lymphoid organs (SLOs) irrespective of the treatment. One week post challenge, no differences in the frequency and phenotypes of neonatally-tagged Tregs were observed between challenged mice and untreated controls. However, upon aging, a decreased frequency of neonatally-tagged Tregs in both NLTs and SLOs was detected in challenged mice when compared to untreated controls. This decrease became significant 12 weeks post challenge, with no signs of altered Foxp3 stability. Remarkably, this late decrease in the frequency of neonatally-tagged Tregs only occurred when newborns were challenged, as treating 8-days-old mice with TLR agonists did not result in long-lasting alterations of the first wave of Tregs. Combined single-cell T cell receptor (TCR)-seq and RNA-seq revealed that neonatal inflammatory perturbations drastically diminished TCR diversity and long-lastingly altered the transcriptome of neonatally-tagged Tregs, exemplified by lower expression of Tigit, Foxp3, and Il2ra. Together, our data demonstrate that a single, transient encounter with a pathogen in early life can have long-lasting consequences for the first wave of Tregs, which might affect immunological tolerance, prevention of autoimmunity, and other non-canonical functions of tissue-resident Tregs in adulthood.

Novel Biomarkers of Inflammation for the Management of Diabetes: Immunoglobulin-Free Light Chains

Virus infection, inflammation and genetic factors are important factors in the pathogenesis of diabetes mellitus. The nuclear factor-kappa B (NF-κB) is a family of transcription factors that bind the enhancer of the κ light chain gene of B cell immunoglobulin. NF-κB plays an essential role in the activation and development of B cells, and the activation of NF-κB is critical in the inflammation and development of diabetes mellitus. Recently, immunoglobulin-free light chain (FLC) λ was found to be increased in the sera of patients with diabetes mellitus, and the FLC λ and κ/λ ratios are more specific and sensitive markers for the diagnosis of diabetes relative to glycated hemoglobin A1c. Thus, FLCs may be promising biomarkers of inflammation that could relate to the activation of NF-κB. We suggest that NF-κB could be a target for an anti-inflammatory strategy in preventing and treating diabetes when FLCs are modified. FLCs could be a surrogate endpoint in the management of diabetes. In this review, the role of inflammation in the pathogenesis of diabetes, as well as the novel inflammatory biomarkers of FLCs for the management of diabetes, are discussed.

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.

Type 1 Diabetes: Interferons and the Aftermath of Pancreatic Beta-Cell Enteroviral Infection

Enteroviruses (EVs) have long been implicated in the pathogenesis of type 1 diabetes (T1D), and accumulating evidence has associated virus-induced autoimmunity with the loss of pancreatic beta cells in T1D. Inflammatory cytokines including interferons (IFN) form a primary line of defence against viral infections, and their chronic elevation is a hallmark feature of many autoimmune diseases. IFNs play a key role in activating and regulating innate and adaptive immune responses, and to do so they modulate the expression of networks of genes and transcription factors known generically as IFN stimulated genes (ISGs). ISGs in turn modulate critical cellular processes ranging from cellular metabolism and growth regulation to endoplasmic reticulum (ER) stress and apoptosis. More recent studies have revealed that IFNs also modulate gene expression at an epigenetic as well as post-transcriptional and post-translational levels. As such, IFNs form a key link connecting the various genetic, environmental and immunological factors involved in the initiation and progression of T1D. Therefore, gaining an improved understanding of the mechanisms by which IFNs modulate beta cell function and survival is crucial in explaining the pathogenesis of virally-induced T1D. This should provide the means to prevent, decelerate or even reverse beta cell impairment.

Type 1 diabetes pathogenesis and the role of inhibitory receptors in islet tolerance

Type 1 diabetes (T1D) affects over a million Americans, and disease incidence is on the rise. Despite decades of research, there is still no cure for this disease. Exciting beta cell replacement strategies are being developed, but in order for such approaches to work, targeted immunotherapies must be designed. To selectively halt the autoimmune response, researchers must first understand how this response is regulated and which tolerance checkpoints fail during T1D development. Herein, we discuss the current understanding of T1D pathogenesis in humans, genetic and environmental risk factors, presumed roles of CD4+ and CD8+ T cells as well as B cells, and implicated autoantigens. We also highlight studies in non-obese diabetic mice that have demonstrated the requirement for CD4+ and CD8+ T cells and B cells in driving T1D pathology. We present an overview of central and peripheral tolerance mechanisms and comment on existing controversies in the field regarding central tolerance. Finally, we discuss T cell- and B cell-intrinsic tolerance mechanisms, with an emphasis on the roles of inhibitory receptors in maintaining islet tolerance in humans and in diabetes-prone mice, and strategies employed to date to harness inhibitory receptor signaling to prevent or reverse T1D.

Viruses and Autoimmunity: A Review on the Potential Interaction and Molecular Mechanisms

For a long time, viruses have been shown to modify the clinical picture of several autoimmune diseases, including type 1 diabetes (T1D), systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), Sjögren’s syndrome (SS), herpetic stromal keratitis (HSK), celiac disease (CD), and multiple sclerosis (MS). Best examples of viral infections that have been proposed to modulate the induction and development of autoimmune diseases are the infections with enteric viruses such as Coxsackie B virus (CVB) and rotavirus, as well as influenza A viruses (IAV), and herpesviruses. Other viruses that have been studied in this context include, measles, mumps, and rubella. Epidemiological studies in humans and experimental studies in animal have shown that viral infections can induce or protect from autoimmunopathologies depending on several factors including genetic background, host-elicited immune responses, type of virus strain, viral load, and the onset time of infection. Still, data delineating the clear mechanistic interaction between the virus and the immune system to induce autoreactivity are scarce. Available data indicate that viral-induced autoimmunity can be activated through multiple mechanisms including molecular mimicry, epitope spreading, bystander activation, and immortalization of infected B cells. Contrarily, the protective effects can be achieved via regulatory immune responses which lead to the suppression of autoimmune phenomena. Therefore, a better understanding of the immune-related molecular processes in virus-induced autoimmunity is warranted. Here we provide an overview of the current understanding of viral-induced autoimmunity and the mechanisms that are associated with this phenomenon.

Mining the Virome for Insights into Type 1 Diabetes

Type 1 diabetes (T1D) is characterized by the autoimmune destruction of insulin-producing pancreatic beta cells. Although environmental factors interplay with genetic susceptibility to promote immune dysregulation and disease, it remains unclear as to which potential environmental factors are causative and not simply correlative. Despite many hints that the microbiome can have a profound effect on T1D, significant changes in bacterial gut flora and diversity appear to emerge only after the detection of early signs of T1D. Surprisingly, we recently found significant differences in the gut virome preceding the initial signs of T1D, raising the tantalizing possibility that the state of the virome may influence or predict whether susceptible individuals progress on the path to disease. The challenge will be to discern whether there is likely a causative relationship between detected virome differences and T1D.

Enterovirus and type 1 diabetes: What is the matter?

A complex interaction of genetic and environmental factors can trigger the immune-mediated mechanism responsible for type 1 diabetes mellitus (T1DM) establishment. Environmental factors may initiate and possibly sustain, accelerate, or retard damage to β-cells. The role of environmental factors in this process has been exhaustive studied and viruses are among the most probable ones, especially enteroviruses. Improvements in enterovirus detection methods and randomized studies with patient follow-up have confirmed the importance of human enterovirus in the pathogenesis of T1DM. The genetic risk of T1DM and particular innate and acquired immune responses to enterovirus infection contribute to a tolerance to T1DM-related autoantigens. However, the frequency, mechanisms, and pathways of virally induced autoimmunity and β-cell destruction in T1DM remain to be determined. It is difficult to investigate the role of enterovirus infection in T1DM because of several concomitant mechanisms by which the virus damages pancreatic β-cells, which, consequently, may lead to T1DM establishment. Advances in molecular and genomic studies may facilitate the identification of pathways at earlier stages of autoimmunity when preventive and therapeutic approaches may be more effective.

Luminex and other multiplex high throughput technologies for the identification of, and host response to, environmental triggers of type 1 diabetes

Complex interactions between a series of environmental factors and genes result in progression to clinical type 1 diabetes in genetically susceptible individuals. Despite several decades of research in the area, these interactions remain poorly understood. Several studies have yielded associations of certain foods, infections, and immunizations with the onset and progression of diabetes autoimmunity, but most findings are still inconclusive. Environmental triggers are difficult to identify mainly due to (i) large number and complex nature of environmental exposures, including bacteria, viruses, dietary factors, and environmental pollutants, (ii) reliance on low throughput technology, (iii) less efforts in quantifying host response, (iv) long silent period between the exposure and clinical onset of T1D which may lead to loss of the exposure fingerprints, and (v) limited sample sets. Recent development in multiplex technologies has enabled systematic evaluation of different classes of molecules or macroparticles in a high throughput manner. However, the use of multiplex assays in type 1 diabetes research is limited to cytokine assays. In this review, we will discuss the potential use of multiplex high throughput technologies in identification of environmental triggers and host response in type 1 diabetes.

Enteroviruses as causative agents in type 1 diabetes: loose ends or lost cause?

Considerable evidence implies that an enteroviral infection may accelerate or precipitate type 1 diabetes (T1D) in some individuals. However, causality is not proven. We present and critically assess evidence suggesting that islet β cells can become infected with enterovirus, and argue that this may result in one of several consequences. Occasionally, a fully lytic infection may arise and this culminates in fulminant diabetes. Alternatively, an atypical persistent infection develops which can be either benign or promote islet autoimmunity. We propose a model in which the 'strength' of the β cell response to the establishment of a persistent enteroviral infection determines the final disease outcome.

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.

Coxsackievirus can persist in murine pancreas by deletion of 5' terminal genomic sequences

Enterovirus infections are generally acute and rapidly cleared by the host immune response. Enteroviruses can at times persist in immunologically intact individuals after the rise of the type-specific neutralizing immune response. The mechanism of enterovirus persistence was shown in group B coxsackieviruses (CVB) to be due to naturally-occurring deletions at the 5' terminus of the genome which variably impact the stem-loop secondary structure called domain I. These deletions result in much slower viral replication and a loss of measurable cytopathic effect when such 5' terminally deleted (TD) viruses are assayed in cell culture. The existence and persistence of CVB-TD long after the acute phase of infection has been documented in hearts of experimentally inoculated mice and naturally infected humans but to date, the existence of TD enteroviral populations have not been documented in any other organ. Enteroviral infections have been shown to impact type 1 diabetes (T1D) onset in humans as well as in the non-obese diabetic mouse model of T1D. The first step to studying the potential impact of CVB-TD on T1D etiology is to determine whether CVB-TD populations can arise in the pancreas. After inoculation of NOD diabetic mice with CVB, viral RNA persists in the absence of cytopathic virus in pancreas weeks past the acute infectious period. Analysis of viral genomic 5' termini by RT-PCR showed CVB-TD populations displace the parental population during persistent replication in murine pancreata.

Enteroviral pathogenesis of type 1 diabetes: queries and answers

PURPOSE OF REVIEW

Type 1 diabetes (T1D) results from interplay between genetic predisposition, immune system, and environmental factors. Epidemiological and experimental data strongly suggest a role for enteroviruses in the development of T1D, but a lot of controversies and unanswered questions remained. This review focuses on issues that are fueling debate.

RECENT FINDINGS

Beyond HLA genes, which provide genetic susceptibility for T1D, other loci have been identified to be associated with the disease. There is a link between T1D and single-nucleotide polymorphisms (SNPs) in the interferon-induced helicase 1 (IFIH1) gene that encodes melanoma differentiation-associated protein 5 (MDA5). This protein is a cytoplasmic sensor for viruses especially coxsackieviruses B, the most incriminated enteroviruses in T1D pathogenesis. Upon viral infection, MDA5 stimulates the production of mediators of the innate antiviral immune response, which is believed to play a role in a 'bystander activation' scenario. Rare variants of IFIH1 through a lost or reduced expression of the protein are protective against T1D, whereas common IFIH1 SNPs are associated with the disease. However, a clear association has not been yet established between T1D-associated IFIH1 polymorphisms and enterovirus detection.

SUMMARY

Literature have accumulated a lot of evidence supporting that enteroviruses can contribute, at least in some patients, to the pathogenesis of T1D through various mechanisms. But it is still a challenge to date to prove a causal relationship between enteroviruses and T1D. Future studies may lead to a better understanding of this relationship and ultimately can help toward disease prevention.

Intrafamilial spread of enterovirus infections at the clinical onset of type 1 diabetes

BACKGROUND

At the clinical onset of type 1 diabetes mellitus (T1D), enterovirus (EV) infections are suspected to play a role. EVs in blood are seen as a possible biomarker of T1D. EV infections may occur in temporal and geographic clusters and may spread within families.

OBJECTIVE

We checked whether EVs were present in the blood of newly diagnosed diabetic probands and of their consenting siblings and parents. We aimed at evaluating the frequency of EV infection, whether infections were spreading within families, and which EV species were involved.

SUBJECTS AND METHODS

Blood was drawn from 24 newly diagnosed diabetic children/adolescents and their family members (20 siblings and 41 parents). Blood donors and non-diabetic children/adolescents diagnosed with overweight/short stature were used as controls. RNA was extracted from plasma/leukocytes. Reverse-transcription polymerase chain reaction assays capable of detecting virtually all EV types and of giving preliminary species identification were used.

RESULTS AND CONCLUSIONS

EV genomes were found in the blood of 19 of 24 (79%) diabetics, 12 of 20 (60%) non-diabetic siblings, 26 of 41 (63%) parents, and 1 of 29 (3%) pediatric controls. EVs of the A, B, C, and D species were detected, with the B and C species more prevalent. Probands and virus-positive members of each family consistently shared the same EV species. During follow-up, 4 of 20 (20%) siblings of diabetic probands developed T1D with a latency of 3-25 months. In conclusion, infection by different EV species is highly prevalent at the clinical onset and extends to family members. EV may represent a precipitating factor of T1D. However, the disease only develops in a subset of infected individuals.

Viruses and type 1 diabetes: a new look at an old story

Epidemiological data suggesting an infectious origin of diabetes pre-date the discovery of insulin; indeed it was the variation in mortality rates from diabetes that led Gunderson to hypothesise that a virus with 'selective affinity for the pancreas' may cause 'acute diabetes' in youth (1). He noted an increase in deaths from diabetes in young people aged 10-20 yr in Norway from 1900 to 1921 following epidemics of parotitis, with a lag time of 3-4 yr between infection and death. In Norway, Denmark,France, and America, the increase in deaths from diabetes exceeded the expected number based on population growth; lending further weight to the proposal that diabetes was caused by infection. Since that time,a large body of epidemiological, clinical and experimental research, in humans, cellular and animal models, has provided further insights into the contribution of infections in the development of type 1 diabetes.Epidemiological evidence for a viral aetiology of diabetes A substantial body of epidemiological data point to a significant contribution of the environment in the development of type 1 diabetes,although much of the evidence is not specific to viruses per se. These data include rising rates of type 1 diabetes in both developed and developing countries in recent decades (2, 3) and a reduced contribution of high risk human leucocyte antigen (HLA) genotypes (4, 5), indicating that non-genetic factors are important. Similarly, the pairwise concordance between monozygotic twins for type 1 diabetes of less than 40%, and the observation that the incidence of diabetes in migrant children reflects that of their adopted country (6, 7), provide circumstantial evidence that environmental agents contribute to the disease. Space-time clustering in the presentation of type 1 diabetes (8-10) and clustering of births in children who subsequently develop diabetes (11) support a direct role for infections in the initiation and acceleration of the disease process.

Influence of the vitamin D plasma level and vitamin D-related genetic polymorphisms on the immune status of patients with type 1 diabetes: a pilot study

Vitamin D (VD) has been implicated in type 1 diabetes (T1D) by genetic and epidemiological studies. Individuals living in regions with low sunlight exposure have an increased T1D risk and VD supplementation reduced the risk in human individuals and mouse models. One possibility of how VD influences the pathogenesis of T1D is its immunomodulatory effect on dendritic cells (DC), which then preferentially activate regulatory T cells (T(regs) ). In the present pilot study, we collected blood samples from a small cohort of patients with T1D at baseline and months 6 and 12. VD-deficient patients were advised to supplement with 1000 IU/day VD. We found a considerable variation in the VD plasma level at baseline and follow-up. However, with higher VD plasma levels, a lower frequency of interleukin (IL)-4-producing CD8 T cells was observed. We further performed a comprehensive genotyping of 13 VD-related polymorphisms and found an association between VD plasma level and the genotype of the VD binding protein (DBP). The frequency of DC and T cell subsets was variable in patients of all subgroups and in individual patients over time. Nevertheless, we found some significant associations, including the 1,25-dihydroxyvitamin D(3) hydroxylase (CYP27B1) genotype with the frequency of DC subtypes. In summary, our preliminary results indicate only a limited influence of the VD plasma level on the immune balance in patients with T1D. Nevertheless, our pilot study provides a basis for a follow-up study with a larger cohort of patients.

Rotavirus acceleration of murine type 1 diabetes is associated with a T helper 1-dependent specific serum antibody response and virus effects in regional lymph nodes

AIMS/HYPOTHESIS

Rotavirus infection in at-risk children correlates with production of serum autoantibodies indicative of type 1 diabetes progression. Oral infection with rhesus monkey rotavirus (RRV) accelerates diabetes onset in mice. This relates to their rotavirus-specific serum antibody titre and local pro-inflammatory cytokine induction without pancreatic infection. Our aim was to further investigate the roles of serum antibodies and viral extra-intestinal spread in diabetes acceleration by rotavirus.

METHODS

Rotavirus-specific serum antibody production was detected by ELISA in diabetes-prone mice given either inactivated or low-dose RRV, in relation to their diabetes development. Serum anti-rotavirus antibody titres and infectious virus in lymph nodes were measured in mice given RRV or porcine rotavirus CRW-8. In lymph node cells, rotavirus antigen presence and immune activation were determined by flow cytometry, in conjunction with cytokine mRNA levels.

RESULTS

Acceleration of diabetes by RRV required virus replication, which correlated with antibody presence. CRW-8 induced similar specific total immunoglobulin and IgA titres to those induced by RRV, but did not accelerate diabetes. RRV alone elicited specific serum IgG antibodies with a T helper (Th)1 bias, spread to regional lymph nodes and activated antigen-presenting cells at these sites. RRV increased Th1-specific cytokine expression in pancreatic lymph nodes. Diabetes onset was more rapid in the RRV-infected mice with the greater Th1 bias.

CONCLUSIONS/INTERPRETATION

Acceleration of murine diabetes by rotavirus is virus strain-specific and associated with virus spread to regional lymph nodes, activation of antigen-presenting cells at these sites and induction of a Th1-dominated antibody and cytokine response.

Helminth mediated modulation of Type 1 diabetes (T1D)

Type 1 diabetes is increasing dramatically in incidence in the developed world. While there may be several reasons for this, improved sanitation and public health measures have altered our interactions with certain infectious agents such as helminths. There is increasing interest in the use of helminths or their products to alleviate inflammatory or allergic conditions. Using rodent models of diabetes, it has been possible to explore the therapeutic potential of both live infections as well as helminth-derived products on the development of autoimmunity. This review provides an overview of the findings from animal models and additionally explores the potential for translation to the clinic.

Why is type 1 diabetes increasing?

A series of studies have reported a constant global rise in the incidence of type 1 diabetes. Epidemiological and immunological studies have demonstrated that environmental factors may influence the pathogenesis, leading to a cell-mediated pancreatic β-cell destruction associated with humoral immunity. The search for the triggering factor(s) has been going on for the past century, and yet they are still unknown. This review provides an overview of some of the most well-known theories found in the literature: hygiene, viral, vitamin D deficiency, breast milk and cow's milk hypotheses. Although the hygiene hypothesis appears to be the most promising, positive evidence from animal, human and epidemiological studies precludes us from completely discarding any of the other hypotheses. Moreover, due to contrasting evidence in the literature, a single factor is unlikely to cause an increase in the incidence of diabetes all over the world, which suggests that a multifactorial process might be involved. Although the immunological mechanisms are still unclear, there seems to be some overlap between the various hypotheses. It is thought that the emphasis should be shifted from a single to a multifactorial process and that perhaps the 'balance shift' model should be considered as a possible explanation for the rise in the incidence of type 1 diabetes.

Expression of the enteroviral capsid protein VP1 in the islet cells of patients with type 1 diabetes is associated with induction of protein kinase R and downregulation of Mcl-1

AIMS/HYPOTHESIS

Immunohistochemical staining reveals that the enteroviral capsid protein VP1 is present at higher frequency in the insulin-containing islets of patients with recent-onset type 1 diabetes than in controls. This is consistent with epidemiological evidence suggesting that enteroviral infection may contribute to the autoimmune response in type 1 diabetes. However, immunostaining of VP1 is not definitive since the antibody widely used to detect the protein (Clone 5D8/1) might also cross-react with additional proteins under some conditions. Therefore, we sought to verify that VP1 immunopositivity correlates with additional markers of viral infection.

METHODS

Antigen immunoreactivity was examined in formalin-fixed, paraffin-embedded, pancreases from two different collections of type 1 diabetes and control cases: a historical collection from the UK and the nPOD (network of Pancreatic Organ donors with Diabetes) cohort from the USA.

RESULTS

VP1 immunoreactivity was present in ~20% of insulin-containing islets of both cohorts under stringent conditions but was absent from insulin-deficient islets. The presence of VP1 was restricted to beta cells but only a minority of these contained the antigen. The innate viral sensor, protein kinase R (PKR) was upregulated selectively in beta cells that were immunopositive for VP1. The anti-apoptotic protein myeloid cell leukaemia sequence-1 (Mcl-1) was abundant in beta cells that were immunonegative for VP1 but Mcl-1 was depleted in cells containing VP1.

CONCLUSIONS/INTERPRETATION

The presence of immunoreactive VP1 within beta cells in type 1 diabetes is associated with a cellular phenotype consistent with the activation of antiviral response pathways and enhanced sensitivity to apoptosis. However, definitive studies confirming whether viral infections are causal to beta cell loss in human diabetes are still awaited.

Rodent models for investigating the dysregulation of immune responses in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease mediated by T cells that selectively destroy the insulin-producing β cells. Previous reports based on epidemiological and animal studies have demonstrated that both genetic factors and environmental parameters can either promote or attenuate the progression of autoimmunity. In recent decades, several inbred rodent strains that spontaneously develop diabetes have been applied to the investigation of the pathogenesis of T1D. Because the genetic manipulation of mice is well developed (transgenic, knockout, and conditional knockout/transgenic), most studies are performed using the nonobese diabetic (NOD) mouse model. This paper will focus on the use of genetically manipulated NOD mice to explore the pathogenesis of T1D and to develop potential therapeutic approaches.

A case-crossover study of infectious diseases and new diagnosis of type 1 diabetes

BACKGROUND

Infectious diseases have been associated with increased risk of type 1 diabetes (T1D). The objective of this case-crossover was to quantify the role of infectious diseases as triggers for T1D, 1 and 2 yr preceding disease diagnosis.

METHODS

All children aged 2-18 yr diagnosed with T1D between 2004 and 2009 among a two million member Israeli healthcare organization were identified (n = 368). For each patient, visits to physicians with symptomatic infectious diseases during 1 and 2 yr before T1D diagnosis were collected and compared. A similar analysis was conducted in a population of non-diabetic members matched on exact date of birth, sex and socioeconomic status (n = 307).

RESULTS

The rate of systemic viral infections was significantly higher in the year before T1D onset, as compared to the prior year [27 vs. 7%, respectively, odds ratio (OR) = 4.7, 95% confidence intervals (CI): 2.9-8.2]. This difference was most significant among patients diagnosed with T1D at the age of 2 to 6 (5 vs. 46%, respectively, OR = 27.0, 95% CI: 4.5-1105.4). Among non-T1D patients of the same age group, no difference was found in the proportion of patients with viral diseases 1 and 2 yr prior to T1D diagnosis (44 vs. 49%, respectively, OR = 0.8, 95% CI: 0.4-1.6). This unique association was limited only to viral diseases and to patients diagnosed with T1D at young age.

CONCLUSIONS

Our results indicate that T1D occurring in toddlers is characterized with a relatively low incidence of viral disease 2 yr prior to diagnosis and a much higher incidence in the subsequent year.

The association between enteroviruses and type 1 diabetes

The hypothesis that under some circumstances enteroviral infections can lead to type1 diabetes (T1D) was proposed several decades ago, based initially on evidence fromanimal studies and sero-epidemiology. The mechanisms leading to the diseaseinvolve complex interactions between the virus, host target tissue (pancreas) and theimmune system. The following article is intended as a review of several recentinformation of the topic based on human studies that try to establish a connectionbetween a viral infection and Type 1 diabetes. Through understanding better thisassociation and it’s implications in the onset of T1D potential new ways ofprevention and treatment may emerge.

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.

Animal models as tools to investigate antidiabetic and anti-inflammatory plants

Plants have been historically used for diabetes treatment and related anti-inflammatory activity throughout the world; few of them have been validated by scientific criteria. Recently, a large diversity of animal models has been developed for better understanding the pathogenesis of diabetes mellitus and its underlying inflammatory mechanism and new drugs have been introduced in the market to treat this disease. The aim of this work is to review the available animal models of diabetes and anti-inflammatory activity along with some in vitro models which have been used as tools to investigate the mechanism of action of drugs with potential antidiabetic properties and related anti-inflammatory mechanism. At present, the rigorous procedures for evaluation of conventional antidiabetic medicines have rarely been applied to test raw plant materials used as traditional treatments for diabetes; and natural products, mainly derived from plants, have been tested in chemically induced diabetes model. This paper contributes to design new strategies for the development of novel antidiabetic drugs and its related inflammatory activity in order to treat this serious condition which represents a global public health problem.

The microbiology of human hygiene and its impact on type 1 diabetes

The incidence of type 1 diabetes (T1D), as with several other autoimmune diseases and conditions, began to notably rise in the latter half of the last century. Most cases of T1D are not solely attributable to genetics and therefore, environmental influences are proposed to account for the difference. Humans live today in general under much more hygienic conditions than their ancestors. Although human enteroviruses (HEV) have been strongly implicated as causative environmental agents of T1D, recent work has shown that the bacterial genera in the gut of diabetics compared with non-diabetics, can vary significantly. Here, we consider these data in light of our non-hygienic human past in order to discuss a possible relationship between the resident bacterial biome and acute infectious events by HEV, suggesting how this may have influenced T1D incidences in the past and the risk for developing T1D today.

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.

Immunology in the clinic review series: focus on type 1 diabetes and viruses: the role of viruses in type 1 diabetes: a difficult dilemma

Convincing evidence now indicates that viruses are associated with type 1 diabetes (T1D) development and progression. Human enteroviruses (HEV) have emerged as prime suspects, based on detection frequencies around clinical onset in patients and their ability to rapidly hyperglycaemia trigger in the non-obese diabetic (NOD) mouse. Whether or not HEV can truly cause islet autoimmunity or, rather, act by accelerating ongoing insulitis remains a matter of debate. In view of the disease's globally rising incidence it is hypothesized that improved hygiene standards may reduce the immune system's ability to appropriately respond to viral infections. Arguments in favour of and against viral infections as major aetiological factors in T1D will be discussed in conjunction with potential pathological scenarios. More profound insights into the intricate relationship between viruses and their autoimmunity-prone host may lead ultimately to opportunities for early intervention through immune modulation or vaccination.

Immunology in the clinic review series: focus on type 1 diabetes and viruses: the role of viruses in type 1 diabetes: a difficult dilemma

Convincing evidence now indicates that viruses are associated with type 1 diabetes (T1D) development and progression. Human enteroviruses (HEV) have emerged as prime suspects, based on detection frequencies around clinical onset in patients and their ability to rapidly hyperglycaemia trigger in the non-obese diabetic (NOD) mouse. Whether or not HEV can truly cause islet autoimmunity or, rather, act by accelerating ongoing insulitis remains a matter of debate. In view of the disease's globally rising incidence it is hypothesized that improved hygiene standards may reduce the immune system's ability to appropriately respond to viral infections. Arguments in favour of and against viral infections as major aetiological factors in T1D will be discussed in conjunction with potential pathological scenarios. More profound insights into the intricate relationship between viruses and their autoimmunity-prone host may lead ultimately to opportunities for early intervention through immune modulation or vaccination.

Dysregulated TLR3-dependent signaling and innate immune activation in superoxide-deficient macrophages from nonobese diabetic mice

In type 1 diabetes (T1D), reactive oxygen species (ROS) and proinflammatory cytokines produced by macrophages and other innate immune cells destroy pancreatic β cells while promoting autoreactive T cell maturation. Superoxide-deficient nonobese diabetic mice (NOD.Ncf1(m1J)) are resistant to spontaneous diabetes, revealing the integral role of ROS signaling in T1D. Here, we evaluate the innate immune activation state of bone marrow-derived macrophages (BM-Mϕ) from NOD and NOD.Ncf1(m1J) mice after poly(I:C)-induced Toll-like receptor 3 (TLR3) signaling. We show that ROS synthesis is required for efficient activation of the NF-κB signaling pathway and concomitant expression of TLR3 and the cognate adaptor molecule, TRIF. Poly(I:C)-stimulated NOD.Ncf1(m1J) BM-Mϕ exhibited a 2- and 10-fold decrease in TNF-α and IFN-β proinflammatory cytokine synthesis, respectively, in contrast to NOD BM-Mϕ. Optimal expression of IFN-α/β is not solely dependent on superoxide synthesis, but requires p47(phox) to function in a NOX-independent manner to mediate type I interferon synthesis. Interestingly, MHC-II I-A(g7) expression necessary for CD4 T cell activation is increased 2-fold relative to NOD, implicating a role for superoxide in I-A(g7) downregulation. These findings suggest that defective innate immune-pattern-recognition receptor activation and subsequent decrease in TNF-α and IFN-β proinflammatory cytokine synthesis necessary for autoreactive T cell maturation may contribute to the T1D protection observed in NOD.Ncf1(m1J) mice.

Enteroviruses and type 1 diabetes

BACKGROUND

Human enteroviruses, which are transmitted via a faecal-oral route, have long been associated with type 1 diabetes onset. Increased hygiene in the 20th century may now be responsible for a decreased chance of enterovirus exposure from an early age onward. Infections with enteroviruses may also be more likely to occur at a later age; the recurrent poliomyelitis epidemics in the 20th century were linked to increased hygiene, consistent with this hypothesis. The association of fewer enterovirus exposures and increased diabetes rates may seem at first non-intuitive but may be explained using a combination of human observations and data from experimental coxsackie B virus infections in nonobese diabetic mice.

METHODS

Network for Pancreatic Organ Donors with Diabetes samples were examined for the presence of detectable enteroviral RNA by RT-PCR.

RESULTS

Viral RNA was not detected.

CONCLUSIONS

A role for enteroviruses in the aetiology of human type 1 diabetes is hard to refute but in order to definitively link enteroviruses in general, and specific viruses in particular, with the disease, pancreas biopsy tissue must become available at the time of disease diagnosis.

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.

Viral infection prevents diabetes by inducing regulatory T cells through NKT cell-plasmacytoid dendritic cell interplay

Type 1 diabetes (T1D) is an autoimmune disease resulting from T cell-mediated destruction of insulin-producing β cells, and viral infections can prevent the onset of disease. Invariant natural killer T cells (iNKT cells) exert a regulatory role in T1D by inhibiting autoimmune T cell responses. As iNKT cell-plasmacytoid dendritic cell (pDC) cooperation controls viral replication in the pancreatic islets, we investigated whether this cellular cross talk could interfere with T1D development during viral infection. Using both virus-induced and spontaneous mouse models of T1D, we show that upon viral infection, iNKT cells induce TGF-β-producing pDCs in the pancreatic lymph nodes (LNs). These tolerogenic pDCs convert naive anti-islet T cells into Foxp3(+) CD4(+) regulatory T cells (T reg cells) in pancreatic LNs. T reg cells are then recruited into the pancreatic islets where they produce TGF-β, which dampens the activity of viral- and islet-specific CD8(+) T cells, thereby preventing T1D development in both T1D models. These findings reveal a crucial cooperation between iNKT cells, pDCs, and T reg cells for prevention of T1D by viral infection.

Protection against or triggering of Type 1 diabetes? Different roles for viral infections

The emergence of autoreactivity that ultimately destroys insulin-producing β-cells and causes Type 1 diabetes (T1D) is a result of genetic susceptibility and environmental factors, such as viral infections. The ability to induce strong cellular immune responses and to cause inflammation in the target organ makes viral infections prime candidates for the initiation of islet autoreactivity. Indeed, certain viruses have been linked to the occurrence of T1D based on epidemiological, serological and histological findings; and several rodent studies clearly demonstrate that viral infections can trigger autoimmunity. However, viruses have also been shown to efficiently prevent autoimmunity, which underlines the beneficial aspects of exposure to microbial agents as suggested by the hygiene hypothesis. Here, we will try to untangle some aspects of the complex interplay between viruses and the immune system and we will recapitulate by what rationale certain viruses have been associated with T1D.

Do viral infections protect from or enhance type 1 diabetes and how can we tell the difference?

Virus infections have been implicated in both initiation of and protection from autoimmune diseases, such as type 1 diabetes (T1D). In this review we intend to reflect on recent evidence how viruses might on the one hand be involved in the pathogenesis of T1D and on the other hand induce a state of protection from autoimmune-mediated damage. It is important to acknowledge that human individuals encounter more than just one virus infection in their lifetime. Therefore, it is important to integrate more than just one possible environmental triggering factor for autoimmune diseases to occur.

Enterovirus RNA in blood is linked to the development of type 1 diabetes

OBJECTIVE

To assess whether the detection of enterovirus RNA in blood predicts the development of clinical type 1 diabetes in a prospective birth cohort study. Further, to study the role of enteroviruses in both the initiation of the process and the progression to type 1 diabetes.

RESEARCH DESIGN AND METHODS

This was a nested case-control study where all case children (N = 38) have progressed to clinical type 1 diabetes. Nondiabetic control children (N = 140) were pairwise matched for sex, date of birth, hospital district, and HLA-DQ-conferred genetic susceptibility to type 1 diabetes. Serum samples, drawn at 3- to 12-month intervals, were screened for enterovirus RNA using RT-PCR.

RESULTS

Enterovirus RNA-positive samples were more frequent among the case subjects than among the control subjects. A total of 5.1% of the samples (17 of 333) in the case group were enterovirus RNA-positive compared with 1.9% of the samples (19 of 993) in the control group (P < 0.01). The strongest risk for type 1 diabetes was related to enterovirus RNA positivity during the 6-month period preceding the first autoantibody-positive sample (odds ratio 7.7 [95% CI 1.9-31.5]). This risk effect was stronger in boys than in girls.

CONCLUSIONS

The present study supports the hypothesis that enteroviruses play a role in the pathogenesis of type 1 diabetes, especially in the initiation of the β-cell damaging process. The enterovirus-associated risk for type 1 diabetes may be stronger in boys than in girls.

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.