Human enterovirus RNA in monthly fecal samples and islet autoimmunity in Norwegian children with high genetic risk for type 1 diabetes: the MIDIA study

Enteroviruses and risk of islet autoimmunity or type 1 diabetes: systematic review and meta-analysis of controlled observational studies detecting viral nucleic acids and proteins

BACKGROUND

Enteroviruses are routinely detected with molecular methods within large cohorts that are at risk of type 1 diabetes. We aimed to examine the association between enteroviruses and either islet autoimmunity or type 1 diabetes.

METHODS

For this systematic review and meta-analysis, we searched PubMed and Embase for controlled observational studies from inception until Jan 1, 2023. Cohort or case-control studies were eligible if enterovirus RNA or protein were detected in individuals with outcomes of islet autoimmunity or type 1 diabetes. Studies in pregnancy or other types of diabetes were excluded. Data extraction and appraisal involved author contact and deduplication, which was done independently by three reviewers. Study quality was assessed with the Newcastle-Ottawa Scale and National Health and Medical Research Council levels of evidence. Pooled and subgroup meta-analyses were done in RevMan version 5.4, with random effects models and Mantel-Haenszel odds ratios (ORs; 95% CIs). The study is registered with PROSPERO, CRD42021278863.

FINDINGS

The search returned 3266 publications, with 897 full texts screened. Following deduplication, 113 eligible records corresponded to 60 studies (40 type 1 diabetes; nine islet autoimmunity; 11 both), comprising 12077 participants (5981 cases; 6096 controls). Study design and quality varied, generating substantial statistical heterogeneity. Meta-analysis of 56 studies showed associations between enteroviruses and islet autoimmunity (OR 2·1, 95% CI 1·3-3·3; p=0·002; n=18; heterogeneity χ²/df 2·69; p=0·0004; I²=63%), type 1 diabetes (OR 8·0, 95% CI 4·9-13·0; p<0·0001; n=48; χ²/df 6·75; p<0·0001; I²=85%), or within 1 month of type 1 diabetes (OR 16·2, 95% CI 8·6-30·5; p<0·0001; n=28; χ²/df 3·25; p<0·0001; I²=69%). Detection of either multiple or consecutive enteroviruses was associated with islet autoimmunity (OR 2·0, 95% CI 1·0-4·0; p=0·050; n=8). Detection of Enterovirus B was associated with type 1 diabetes (OR 12·7, 95% CI 4·1-39·1; p<0·0001; n=15).

INTERPRETATION

These findings highlight the association between enteroviruses and islet autoimmunity or type 1 diabetes. Our data strengthen the rationale for vaccine development targeting diabetogenic enterovirus types, particularly those within Enterovirus B. Prospective studies of early life are needed to elucidate the role of enterovirus timing, type, and infection duration on the initiation of islet autoimmunity and the progression to type 1 diabetes.

FUNDING

Environmental Determinants of Islet Autoimmunity, European Association for the Study of Diabetes, JDRF, Australian National Health and Medical Research Council, and University of New South Wales.

The virome in early life and childhood and development of islet autoimmunity and type 1 diabetes: A systematic review and meta-analysis of observational studies

Viruses are postulated as primary candidate triggers of islet autoimmunity (IA) and type 1 diabetes (T1D), based on considerable epidemiological and experimental evidence. Recent studies have investigated the association between all viruses (the 'virome') and IA/T1D using metagenomic next-generation sequencing (mNGS). Current associations between the early life virome and the development of IA/T1D were analysed in a systematic review and meta-analysis of human observational studies from Medline and EMBASE (published 2000-June 2020), without language restriction. Inclusion criteria were as follows: cohort and case-control studies examining the virome using mNGS in clinical specimens of children ≤18 years who developed IA/T1D. The National Health and Medical Research Council level of evidence scale and Newcastle-Ottawa scale were used for study appraisal. Meta-analysis for exposure to specific viruses was performed using random-effects models, and the strength of association was measured using odds ratios (ORs) and 95% confidence intervals (CIs). Eligible studies (one case-control, nine nested case-control) included 1,425 participants (695 cases, 730 controls) and examined IA (n = 1,023) or T1D (n = 402). Meta-analysis identified small but significant associations between IA and number of stool samples positive for all enteroviruses (OR 1.14, 95% CI 1.00-1.29, p = 0.05; heterogeneity χ2  = 1.51, p = 0.68, I2  = 0%), consecutive positivity for enteroviruses (1.55, 1.09-2.20, p = 0.01; χ2  = 0.19, p = 0.91, I2  = 0%) and number of stool samples positive specifically for enterovirus B (1.20, 1.01-1.42, p = 0.04; χ2  = 0.03, p = 0.86, I2  = 0%). Virome analyses to date have demonstrated associations between enteroviruses and IA that may be clinically significant. However, larger prospective mNGS studies with more frequent sampling and follow-up from pregnancy are required to further elucidate associations between early virus exposure and IA/T1D.

Type I interferons as key players in pancreatic β-cell dysfunction in type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease characterized by pancreatic islet inflammation (insulitis) and specific pancreatic β-cell destruction by an immune attack. Although the precise underlying mechanisms leading to the autoimmune assault remain poorly understood, it is well accepted that insulitis takes place in the context of a conflicting dialogue between pancreatic β-cells and the immune cells. Moreover, both host genetic background (i.e., candidate genes) and environmental factors (e.g., viral infections) contribute to this inadequate dialogue. Accumulating evidence indicates that type I interferons (IFNs), cytokines that are crucial for both innate and adaptive immune responses, act as key links between environmental and genetic risk factors in the development of T1D. This chapter summarizes some relevant pathways involved in β-cell dysfunction and death, and briefly reviews how enteroviral infections and genetic susceptibility can impact insulitis. Moreover, we present the current evidence showing that, in β-cells, type I IFN signaling pathway activation leads to several outcomes, such as long-lasting major histocompatibility complex (MHC) class I hyperexpression, endoplasmic reticulum (ER) stress, epigenetic changes, and induction of posttranscriptional as well as posttranslational modifications. MHC class I overexpression, when combined with ER stress and posttranscriptional/posttranslational modifications, might lead to sustained neoantigen presentation to immune system and β-cell apoptosis. This knowledge supports the concept that type I IFNs are implicated in the early stages of T1D pathogenesis. Finally, we highlight the promising therapeutic avenues for T1D treatment directed at type I IFN signaling pathway.

Prospective virome analyses in young children at increased genetic risk for type 1 diabetes

Viruses are implicated in autoimmune destruction of pancreatic islet β cells, which results in insulin deficiency and type 1 diabetes (T1D)1-4. Certain enteroviruses can infect β cells in vitro5, have been detected in the pancreatic islets of patients with T1D6 and have shown an association with T1D in meta-analyses4. However, establishing consistency in findings across studies has proven difficult. Obstacles to convincingly linking RNA viruses to islet autoimmunity may be attributed to rapid viral mutation rates, the cyclical periodicity of viruses7 and the selection of variants with altered pathogenicity and ability to spread in populations. β cells strongly express cell-surface coxsackie and adenovirus receptor (CXADR) genes, which can facilitate enterovirus infection8. Studies of human pancreata and cultured islets have shown significant variation in enteroviral virulence to β cells between serotypes and within the same serotype9,10. In this large-scale study of known eukaryotic DNA and RNA viruses in stools from children, we evaluated fecally shed viruses in relation to islet autoimmunity and T1D. This study showed that prolonged enterovirus B rather than independent, short-duration enterovirus B infections may be involved in the development of islet autoimmunity, but not T1D, in some young children. Furthermore, we found that fewer early-life human mastadenovirus C infections, as well as CXADR rs6517774, independently correlated with islet autoimmunity.

Enterovirus as trigger of coeliac disease: nested case-control study within prospective birth cohort

OBJECTIVE

To determine whether infection with human enterovirus or adenovirus, both common intestinal viruses, predicts development of coeliac disease.

DESIGN

Case-control study nested within Norwegian birth cohort recruited between 2001 and 2007 and followed to September 2016.

SETTING

Norwegian population.

PARTICIPANTS

Children carrying the HLA genotype DR4-DQ8/DR3-DQ2 conferring increased risk of coeliac disease.

EXPOSURES

Enterovirus and adenovirus detected using real time polymerase chain reaction in monthly stool samples from age 3 to 36 months.

MAIN OUTCOME MEASURE

Coeliac disease diagnosed according to standard criteria. Coeliac disease antibodies were tested in blood samples taken at age 3, 6, 9, and 12 months and then annually. Adjusted odds ratios from mixed effects logistic regression model were used to assess the relation between viral infections before development of coeliac disease antibodies and coeliac disease.

RESULTS

Among 220 children, and after a mean of 9.9 (SD 1.6) years, 25 children were diagnosed as having coeliac disease after screening and were matched to two controls each. Enterovirus was found in 370 (17%) of 2135 samples and was significantly more frequent in samples collected before development of coeliac disease antibodies in cases than in controls (adjusted odds ratio 1.49, 95% confidence interval 1.07 to 2.06; P=0.02). The association was restricted to infections after introduction of gluten. High quantity samples (>100 000 copies/μL) (adjusted odds ratio 2.11, 1.24 to 3.60; P=0.01) and long lasting infections (>2 months) (2.16, 1.16 to 4.04; P=0.02) gave higher risk estimates. Both the commonly detected enterovirus species Enterovirus A and Enterovirus B were significantly associated with coeliac disease. The association was not found for infections during or after development of coeliac disease antibodies. Adenovirus was not associated with coeliac disease.

CONCLUSIONS

In this longitudinal study, a higher frequency of enterovirus, but not adenovirus, during early childhood was associated with later coeliac disease. The finding adds new information on the role of viral infections in the aetiology of coeliac disease.

Stem-cell based organ-on-a-chip models for diabetes research

Diabetes mellitus (DM) ranks among the severest global health concerns of the 21st century. It encompasses a group of chronic disorders characterized by a dysregulated glucose metabolism, which arises as a consequence of progressive autoimmune destruction of pancreatic beta-cells (type 1 DM), or as a result of beta-cell dysfunction combined with systemic insulin resistance (type 2 DM). Human cohort studies have provided evidence of genetic and environmental contributions to DM; yet, these studies are mostly restricted to investigating statistical correlations between DM and certain risk factors. Mechanistic studies, on the other hand, aimed at re-creating the clinical picture of human DM in animal models. A translation to human biology is, however, often inadequate owing to significant differences between animal and human physiology, including the species-specific glucose regulation. Thus, there is an urgent need for the development of advanced human in vitro models with the potential to identify novel treatment options for DM. This review provides an overview of the technological advances in research on DM-relevant stem cells and their integration into microphysiological environments as provided by the organ-on-a-chip technology.

Virus genotyping by massive parallel amplicon sequencing: adenovirus and enterovirus in the Norwegian MIDIA study

OBJECTIVES

Direct genotyping of adenovirus or enterovirus from clinical material using polymerase chain reaction (PCR) followed by Sanger sequencing is often difficult due to the presence of multiple virus types in a sample, or due to varying efficacy of PCR amplifying the capsid gene on the background of foreign nucleic acids. Here we present a simple protocol for virus genotyping using massive parallel amplicon sequencing.

METHODS

The protocol utilized a set of 16 tailed degenerate primers flanking the seventh hypervariable region of the adenovirus hexon gene and 9 tailed degenerate primers targeted to the proximal portion of the enterovirus VP1 gene. Subsequent addition of dual indices enabled simultaneous sequencing of 384 different samples on an Illumina MiSeq instrument. Downstream bioinformatic analysis was based on remapping to a set of references representative of the presently known repertoire of virus types.

RESULTS

After validation with known virus types, the sequencing method was applied on 301 adenovirus-positive samples and 350 enterovirus-positive samples from a longitudinally collected series of stools from 83 children aged 3 to 36 months. We detected 7 different adenovirus types and 27 different enterovirus types. There were 37 (6.2%) samples containing more than one genotype of the same viral genus. At least one dual infection was experienced by 23 of 83 (28%) of the children observed over the 3 years' observation period.

CONCLUSIONS

Amplicon sequencing with a multiplex set of degenerate primers seems to be a rapid and reliable technical solution for genotyping of large collections of samples where simultaneous infections with multiple strains can be expected.

Developing a vaccine for type 1 diabetes by targeting coxsackievirus B

INTRODUCTION

Virus infections have long been considered as a possible cause of type 1 diabetes (T1D). One virus group, enteroviruses (EVs), has been studied extensively, and clinical development of a vaccine against T1D-associated EV types has started.

AREAS COVERED

Epidemiological studies have indicated an association between EVs and T1D. These viruses have a strong tropism for insulin-producing β-cells; the destruction of these cells leads to T1D. The exact mechanisms by which EVs could cause T1D are not known, but direct infection of β-cells and virus-induced inflammation may play a role. Recent studies have narrowed down the epidemiological association to a subset of EVs: group B coxsackieviruses (CVBs). These findings have prompted efforts to develop vaccines against CVBs. Prototype CVB vaccines have prevented both infection and CVB-induced diabetes in mice. This review summarizes recent progress in the field and the specifics of what could constitute the first human vaccine developed for a chronic autoimmune disease.

EXPERT COMMENTARY

Manufacturing of a clinical CVB vaccine as well as preclinical studies are currently in progress in order to enable clinical testing of the first CVB vaccine. Ongoing scientific research projects can significantly facilitate this effort by providing insights into the mechanisms of the CVB-T1D association.

Molecular epidemiology of enteroviruses in young children at increased risk of type 1 diabetes

Background

Young children are susceptible to enterovirus (EV) infections, which cause significant morbidity in this age group. However, the current knowledge regarding the epidemiology of EVs and the circulating virus strains is mostly based on viruses detected in children with severe diseases leading to contact with the health care system, while the vast reservoir of EVs that circulate in the general population is less characterized.

Methodology

The present study investigates the types and the prevalence of EVs circulating in the young children of the background population in Georgia, Colorado, and Washington State in the USA, and Germany, Sweden, and Finland in Europe.

A total of 4018 stool samples, collected monthly from 300 healthy and non-hospitalized children at the age of 3–18 months in 2005–2009, were analyzed for the presence of EVs using RT-PCR, followed by sequencing of the VP1-2A region of the viral genome to type the EV(s) present. All of the children carried type HLA-DQ2 or -DQ8 alleles associated with type 1 diabetes.

Principal findings

Altogether 201 children (67%) were found to be EV positive. The prevalence was much lower in Finnish children (26%) than in the children of the other counties combined (75%). Infections increased by age and showed a nadir during the winter months. Children who carried both the HLA-DQ2 and -DQ8 alleles had less infections than children who were homozygous for these alleles. Coxsackieviruses type A were the most frequently detected viruses in all geographical regions. Coxsackievirus type A4, Echovirus type 18, and Echovirus type 25 were shed for longer time periods than the other EV types.

Conclusions

Compared to prevalence data from symptomatic patients requiring medical attention, this study provides a better view of EVs circulating in young children in the USA and in Europe. The observations may prove useful for the selection of strategies for designing EV vaccines in the future. The study also confirms our previous serological findings suggesting that EV infections are relatively rare in Finland.

Detection of enteroviruses in stools precedes islet autoimmunity by several months: possible evidence for slowly operating mechanisms in virus-induced autoimmunity

AIMS/HYPOTHESIS

This case-control study was nested in a prospective birth cohort to evaluate whether the presence of enteroviruses in stools was associated with the appearance of islet autoimmunity in the Type 1 Diabetes Prediction and Prevention study in Finland.

METHODS

Altogether, 1673 longitudinal stool samples from 129 case children who turned positive for multiple islet autoantibodies and 3108 stool samples from 282 matched control children were screened for the presence of enterovirus RNA using RT-PCR. Viral genotype was detected by sequencing.

RESULTS

Case children had more enterovirus infections than control children (0.8 vs 0.6 infections per child). Time-dependent analysis indicated that this excess of infections occurred more than 1 year before the first detection of islet autoantibodies (6.3 vs 2.1 infections per 10 follow-up years). No such difference was seen in infections occurring less than 1 year before islet autoantibody seroconversion or after seroconversion. The most frequent enterovirus types included coxsackievirus A4 (28% of genotyped viruses), coxsackievirus A2 (14%) and coxsackievirus A16 (11%).

CONCLUSIONS/INTERPRETATION

The results suggest that enterovirus infections diagnosed by detecting viral RNA in stools are associated with the development of islet autoimmunity with a time lag of several months.

Beta-cell Specific Autoantibodies: Are they Just an Indicator of Type 1 Diabetes?

BACKGROUND

Autoantibodies (AAbs) against islet autoantigens (AAgs) are used for type 1 diabetes (T1D) diagnosis and prediction. Islet-specific AAbs usually appear early in life and may fluctuate in terms of number and titer sometimes for over 20 years before T1D develops. Whereas their predictive power is high for pediatric subjects with high genetic risk who rapidly progress to multiple AAb positivity, they are less reliable for children with low genetic risk, single AAb positivity and slow disease progression.

OBJECTIVE

It is unknown how AAbs develop and whether they are involved in T1D pathogenesis. So far an increase in AAb number seems to only indicate AAg spreading and progression towards clinical T1D. The goal of this review is to shed light on the possible involvement of AAbs in T1D development.

METHOD

We thoroughly review the current literature and discuss possible mechanisms of AAb development and the roles they may play in disease pathogenesis.

RESULTS

Genetic and environmental factors instigate changes at the molecular and cellular levels that promote AAb development. Although direct involvement of AAbs in T1D is less clear, autoreactive B cells are clearly involved in various immune and autoimmune responses via antigen presentation, immunoregulation and cytokine production.

CONCLUSION

Our analysis suggests that understanding the mechanisms that lead to islet-specific AAb development and the diabetogenic processes that autoreactive B cells promote may uncover additional biomarkers and therapeutic targets.

The viral paradigm in type 1 diabetes: Who are the main suspects?

Type 1 diabetes (T1D) is an autoimmune disease characterized by the loss of pancreatic beta cells in the islets of Langerhans. Although genetic predisposition plays an important role in T1D development, studies of identical twins suggest that environmental factors such as viruses and other pathogens may be critical triggers either through direct cytolytic effect and gradual beta cell destruction, or by bystander activation of the immune system. In addition, viruses may circumvent the host immune response and have the capacity to establish chronic lifelong infections. The association of various viral infections with the induction of T1D has been extensively studied at the serological and epidemiological level. However, there is still little evidence from studies of human pancreas to confirm their presence or a causal role in disease pathogenesis. In this review, we identify possible suspects for viral triggers of disease and explain their potential roles in the "viral paradigm" of T1D.

Prolonged Shedding of Human Parechovirus in Feces of Young Children after Symptomatic Infection

After symptomatic human parechovirus (HPeV) infection in infants, the duration of (mostly asymptomatic) shedding in feces was 2-24 weeks (median 58 days). HPeV cycle threshold value could neither differentiate between symptomatic disease and asymptomatic shedding nor between severe and mild disease as high cycle threshold values (indicating low viral loads) were observed in HPeV3-infected children with severe disease.

Saffold Virus, a Human Cardiovirus, and Risk of Persistent Islet Autoantibodies in the Longitudinal Birth Cohort Study MIDIA

The aim of this study was to describe the frequency and distribution of Saffold virus in longitudinal stool samples from children, and test for association with development of persistent autoantibodies predictive of type 1 diabetes. A cohort of Norwegian children carrying the HLA genotype associated with highest risk of type 1 diabetes (“DR4-DQ8/DR3-DQ2”) was followed with monthly stool samples from 3 to 35 months of age. Blood samples were tested for autoantibodies to insulin, glutamic acid decarboxylase₆₅ and Islet Antigen-2. 2077 stool samples from 27 children with ≥2 repeatedly positive islet autoantibodies (cases), and 53 matched controls were analysed for Saffold virus genomic RNA by semi-quantitative real-time reverse transcriptase PCR. Saffold virus was found in 53 of 2077 (2.6%) samples, with similar proportions between cases (2.5%) and controls (2.6%). The probability of being infected by 3 years of age was 28% (95% CI 0.18–0.40). Viral quantities ranged from <1 to almost 10⁵ copies/μl. Estimated odds ratio between islet autoimmunity and infection episodes prior to seroconversion was 1.98 (95% CI: 0.57–6.91, p = 0.29). Saffold virus had no statistically significant association with islet autoimmunity.

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.

Environmental trigger(s) of type 1 diabetes: why so difficult to identify?

Type 1 diabetes (T1D) is one of the most common chronic diseases with childhood onset, and the disease has increased two- to fivefold over the past half century by as yet unknown means. T1D occurs when the body's immune system turns against itself so that, in a very specific and targeted way, it destroys the pancreatic β-cells. T1D results from poorly defined interactions between susceptibility genes and environmental determinants. In contrast to the rapid progress in finding T1D genes, identification and confirmation of environmental determinants remain a formidable challenge. This review article will focus on factors which have to be evaluated and decision to take before starting a new prospective cohort study. Considering all the large ongoing prospective studies, new and more conclusive data than that obtained so far should instead come from international collaboration on the ongoing cohort studies.

Type 1 diabetes epidemic in Finland is triggered by zinc-containing amorphous silica nanoparticles

Type 1 diabetes (T1D), an autoimmune disease, breaks out in some of the children who has genetic susceptibility to T1D. Besides genetic susceptibility some environmental factor(s) are required to trigger the disease. The incidence of T1D in Finland is highest in the world, so we must seek an environmental factor, that is typical for Finland and can declare many aspects of T1D epidemiology and biology. In the literature most popular trigger has been enterovirus infections. It is difficult however to find why enteroviruses would be in this role in Finland in contrary to neighbouring countries e.g. Sweden. Colloidal amorphous silica (ASi) is typical for Finnish environment in consequency of the geohistory of Finland, great part of Finland is an ancient lake and sea bottom. ASi concentrations in natural waters are high in April-June and in November, only traces can be found in the rest of months. Pure colloidal ASi is not a strong trigger for T1D, but ASi particle which has surface adsorbed tetrahedrally coordinated zinc (ASiZn) is probably the trigger which has kept it's secret up to date. Zn functions as address label which conducts the ASiZn particle to the beta cell, whose content of zinc is highest in the body. ASi particle adheres to membrane proteins distorting their tertiary structure revealing new epitopes. If the fetus has not met these epitopes at proper time during intrauterine development, the consequence is that the negative selection of lymphocytes in the thymus and bone marrow and fetal liver is not perfect. When a child later in postnatal life becomes predisposed to ASiZn particles the immune system reacts to these as to nonself proteins. As a consequence the insulin producing beta cells are destroyed. Many observations from diabetes research support the hypothesis, some to mentioned. 1. Three common autoantigens (ZnT8, ICA512/IA-2, GAD65) are membrane proteins whose function zinc regulates. 2. Geographical variation in Finland is convergent with surface water manganese concentrations. Manganese is the principal Zn scavenger and high manganese in water reduces ASiZn particle formation and the incidence of T1D. 3. The incidence of T1D depends of drinking water pH. The highest incidence can be found within water pH 6.2-6.9. Zn coordination changes from octahedral (unphysiologic) to tetrahedral (physiologic) at pH 6.56. In the text are presented five more supporting observations e.g. the similarity between the soils in Sardinia and Finland in respect to ASi.

Enterovirus RNA in longitudinal blood samples and risk of islet autoimmunity in children with a high genetic risk of type 1 diabetes: the MIDIA study

AIMS/HYPOTHESIS

Only a few longitudinal molecular studies of enterovirus and islet autoimmunity have been reported, and positive results seem to be limited to Finland. We aimed to investigate an association between enterovirus RNA in blood and islet autoimmunity in the MIDIA study from Norway, a country which largely shares environmental and economic features with Finland.

METHODS

We analysed serial blood samples collected at ages 3, 6, and 9 months and then annually from 45 children who developed confirmed positivity for at least two autoantibodies (against insulin, GAD65 and IA-2) and 92 matched controls, all from a cohort of children with a single high-risk HLA-DQ-DR genotype. Enterovirus was tested in RNA extracted from frozen blood cell pellets, using real-time RT-PCR with stringent performance control.

RESULTS

Out of 807 blood samples, 72 (8.9%) were positive for enterovirus. There was no association between enterovirus RNA and islet autoimmunity in samples obtained strictly before (7.6% cases, 10.0% controls, OR 0.75 [95% CI 0.36, 1.57]), or strictly after the first detection of islet autoantibodies (10.5% case, 5.8% controls, OR 2.00 [95% CI 0.64, 6.27]). However, there was a tendency towards a higher frequency of enterovirus detection in the first islet autoantibody-positive sample (15.8%) compared with the corresponding time point in matched controls (3.2%, OR 8.7 [95% CI 0.97, 77]). Neither of these results was changed by adjusting for potential confounders, restricting to various time intervals or employing various definitions of enterovirus positivity.

CONCLUSIONS/INTERPRETATION

Positivity for enterovirus RNA in blood did not predict the later induction of islet autoantibodies, but enterovirus tended to be detected more often at the islet autoantibody seroconversion stage.

Potential viral pathogenic mechanism in human type 1 diabetes

In type 1 diabetes, as a result of as yet unknown triggering events, auto-aggressive CD8(+) T cells, together with a significant number of other inflammatory cells, including CD8(+) T lymphocytes with unknown specificity, infiltrate the pancreas, leading to insulitis and destruction of the insulin-producing beta cells. Type 1 diabetes is a multifactorial disease caused by an interactive combination of genetic and environmental factors. Viruses are major environmental candidates with known potential effects on specific key points in the pathogenesis of type 1 diabetes and recent findings seem to confirm this presumption. However, we still lack well-grounded mechanistic explanations for how exactly viruses may influence type 1 diabetes aetiology. In this review we provide a summary of experimentally defined viral mechanisms potentially involved in the ontology of type 1 diabetes and discuss some novel hypotheses of how viruses may affect the initiation and natural history of the disease.

Developing a vaccine for Type 1 diabetes through targeting enteroviral infections

Type 1 diabetes (T1D) is a chronic disease caused by the destruction of insulin producing β-cells in the pancreas. Studies carried out during the past decades have implied that enteroviruses could be an important causative agent. These findings have generated efforts aiming at developing vaccines against these viruses and testing their efficacy against T1D in clinical trials. Extensive work has been carried out to define the serotype of enteroviruses which are linked to T1D and which should be included in the vaccine, and experimental vaccines have been shown to be effective and safe in mouse models. Large-scale studies are currently in progress to increase the confidence in the scientific concept of the enterovirus-diabetes association, paralleling the efforts aimed at starting the clinical development of the vaccine. This review summarizes recent progress in this field and the scenarios regarding this development process.

Role of viruses and other microbes in the pathogenesis of type 1 diabetes

Type 1 diabetes is caused by an immune-mediated destruction of insulin producing beta-cells in the pancreas. The risk of the disease is determined by interactions between more than 40 different susceptibility genes and yet unidentified environmental factors. The rapidly increasing incidence indicates that these environmental agents have a significant role in the pathogenesis. Microbes have associated with both increased and decreased risk reflecting their possible role as risk or protective factors. Two main hypotheses have been proposed to explain these effects: the hygiene hypothesis suggests that microbial exposures in early childhood stimulate immunoregulatory mechanisms which control autoimmune reactions (analogy with allergy), while the triggering hypothesis suggests that specific microbes damage insulin producing cells. Certain viruses, particularly enteroviruses, are currently the main candidates for such risk microbes. Enteroviruses cause diabetes in animals and have associated with increased risk of type 1 diabetes in epidemiological studies. They have also been detected in the pancreas of diabetic patients. Possible protective effect of microbes has been studied in animal models and in epidemiological studies, where certain enteral microbes (e.g. hepatitis A virus and Helicobacter pylori) and patterns of gut microbiome have associated with low risk of type 1 diabetes. In conclusion, these microbial effects offer attractive possibilities for the development of preventive interventions for type 1 diabetes based on the elimination of triggering agents (e.g. enterovirus vaccines) or use of protective microbes as probiotics.

Diagnosis and classification of autoimmune diabetes mellitus

Diabetes mellitus is increasing in prevalence worldwide. The economic costs and burden of the disease are considerable given the cardiovascular complications and co-morbidities that it may entail. Two major groups of diabetes mellitus have been defined, type 1, or immune-based, and type 2. In recent years, other subgroups have been described in-between these major groups. Correct classification of the disease is crucial in order to ascribe the most efficient preventive, diagnostic and treatment strategies for each patient. In the present review, we discuss the epidemiology, etiopathogenesis, diagnostic criteria and clinical classification of what is currently known as autoimmune diabetes. In addition, the other groups of diabetes mellitus will be regarded in relation to their pathogenesis and potential autoimmunity features.

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.

Environmental determinants of islet autoimmunity (ENDIA): a pregnancy to early life cohort study in children at-risk of type 1 diabetes

BACKGROUND

The incidence of type 1 diabetes has increased worldwide, particularly in younger children and those with lower genetic susceptibility. These observations suggest factors in the modern environment promote pancreatic islet autoimmunity and destruction of insulin-producing beta cells. The Environmental Determinants of Islet Autoimmunity (ENDIA) Study is investigating candidate environmental exposures and gene-environment interactions that may contribute to the development of islet autoimmunity and type 1 diabetes.

METHODS/DESIGN

ENDIA is the only prospective pregnancy/birth cohort study in the Southern Hemisphere investigating the determinants of type 1 diabetes in at-risk children. The study will recruit 1,400 unborn infants or infants less than six months of age with a first-degree relative (i.e. mother, father or sibling) with type 1 diabetes, across five Australian states. Pregnant mothers/infants will be followed prospectively from early pregnancy through childhood to investigate relationships between genotype, the development of islet autoimmunity (and subsequently type 1 diabetes), and prenatal and postnatal environmental factors. ENDIA will evaluate the microbiome, nutrition, bodyweight/composition, metabolome-lipidome, insulin resistance, innate and adaptive immune function and viral infections. A systems biology approach will be used to integrate these data. Investigation will be by 3-monthly assessments of the mother during pregnancy, then 3-monthly assessments of the child until 24 months of age and 6-monthly thereafter. The primary outcome measure is persistent islet autoimmunity, defined as the presence of autoantibodies to one or more islet autoantigens on consecutive tests.

DISCUSSION

Defining gene-environment interactions that initiate and/or promote destruction of the insulin-producing beta cells in early life will inform approaches to primary prevention of type 1 diabetes. The strength of ENDIA is the prospective, comprehensive and frequent systems-wide profiling from early pregnancy through to early childhood, to capture dynamic environmental exposures that may shape the development of islet autoimmunity.

TRIAL REGISTRATION

Australia New Zealand Clinical Trials Registry ACTRN12613000794707.

Virus infections among young children--the first year of the INDIS study

The frequencies of early childhood infections were studied in healthy children with increased genetic risk for type 1 diabetes participating in the ongoing prospective high intensive infection follow-up Study, INDIS, started in 2009 in Turku, Finland. Here the results obtained from 160 stool to 160 nasal swab specimens collected in parallel at times of infectious symptoms in 2009-2010 from 45 children at the age of 24 months or younger are reported. The specimens were analyzed for enteric (human enterovirus, norovirus, rotavirus, sapovirus, astrovirus) and respiratory RNA viruses (human enterovirus and rhinovirus) common in early childhood, respectively, using highly validated virus-specific real-time PCR methods. According to the results 96% of the children had at least one virus infection during the study period and one or several viral agents were detected in 76% of sample sets. The most prevalent viral agents were human rhinovirus, enterovirus, parechovirus, and norovirus (genotype GII) with positive specimens 57.5%, 28.8%, 19.4%, and 6.9%, respectively. Other intestinal viruses were found in less than 2% of stool specimens. Single infections covered 40.0% of the specimens while multiple infections with two or more infectious agents were detected in 36.3% of specimens and altogether 11 combinations of viruses were included in the mixed infections. Although human enterovirus is known to be a frequent finding in stool specimens, especially during early childhood, it was found in this study more frequently in nasal swab specimens. Whether this is true, more general, in countries with the high hygiene level remains to be shown.

Viruses and Type 1 diabetes: a dynamic labile equilibrium

Type 1 diabetes (T1D) results from the specific immune-mediated destruction of the insulin-producing β-cells of the pancreas. In genetically susceptible individuals, a still undetermined initiating 'hit' triggers a cascade of events that eventually leads to autoreactive CD8 T cells infiltrating the pancreatic islets and, subsequently, destroying them. There is increasing evidence that viruses, especially enteroviruses, are major environmental candidates; however, despite decades of investigation, we still lack certainty with regard to the causation of T1D. Moreover, studies in animal models of diabetes suggest a protective role of certain enteroviral infections upon diabetes contraction, making the quest for viral involvement in T1D even more difficult. Analyzing the foundation and the results of the most current work in the field, this article gives a brief overview of current knowledge, as well as providing an outlook for future directions.

Virus infections as potential targets of preventive treatments for type 1 diabetes

Environmental factors play an important role in the pathogenesis of type 1 diabetes, and are attractive targets for preventive interventions. Several studies have shown that viruses can cause diabetes in animals, indicating their potential as candidates for environmental triggering agents. However, human studies have been hampered by the complex nature of the disease pathogenesis, leaving the question of viral etiology unanswered. Significant progress has recently been made in this field by searching for viruses within pancreatic tissue samples, and by carrying out prospective studies. Consequently, there is increasing evidence for a group of enteroviruses acting as possible environmental key triggers. In past studies, these viruses have been linked to type 1 diabetes. Recent studies have shown that they exert tropism to pancreatic islets, and that they are associated with the start of the beta-cell damaging process. Also, polymorphisms of the gene coding for the innate immune system sensor for enteroviruses (IFIH1) were found to modulate the risk of diabetes. Based on these findings, interest in the possible development of vaccines against these viruses has increased. However, even if enterovirus vaccines (polio vaccines) are effective and safe, we currently lack necessary information for the development of a vaccine against diabetogenic enteroviruses, e.g. regarding the identification of their specific serotypes and the causal relationship between these viruses and diabetes initiation. Ongoing research projects are currently addressing these questions, and will hopefully increase the consensus in this field. Also, new sequencing technologies will provide additional information about the whole virome, which could enable the discovery of new candidate viruses.

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.

No evidence of enteroviruses in the intestine of patients with type 1 diabetes

AIMS/HYPOTHESIS

The purpose of this study was to investigate whether the gut mucosa is a reservoir for enterovirus persistence in patients with type 1 diabetes.

METHODS

Small intestine biopsy samples from 25 individuals at different stages of type 1 diabetes, 21 control individuals and 27 individuals with coeliac disease were analysed for the presence of enterovirus RNA by using both radioactive in-situ hybridisation and real-time RT-PCR and for the presence of enterovirus proteins by immunostaining with antibodies against VP1 and VP4-2-3 capsid proteins and virus polymerase. Lymphocytic enteropathy and serum anti-VP1 antibodies were also evaluated at the time of biopsy. Moreover, high-throughput sequencing was performed to identify viral transcripts or genomes.

RESULTS

Enterovirus was not detected by in-situ hybridisation or RT-PCR in any of the individuals tested. Immunohistology revealed a few stained cells in the intestinal epithelium in a low number of individuals, with no difference between diabetic and non-diabetic individuals. Levels of serum IgG against VP1 did not differ between control individuals and those with diabetes or coeliac disease and no evidence of diabetes-related lymphocytic enteropathy was detected. High-throughput sequencing did not reveal specific enterovirus sequences in the gut mucosa of individuals with type 1 diabetes.

CONCLUSIONS/INTERPRETATION

Prolonged/persistent enterovirus infections in gut mucosa are not common in patients with type 1 diabetes.

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.

Is the origin of type 1 diabetes in the gut?

In type 1 diabetes, insulin-producing beta-cells in the pancreas are destroyed by immune-mediated mechanisms. The manifestation of the disease is preceded by the so-called pre-diabetic period that may last several years and is characterized by the appearance of circulating autoantibodies against beta-cell antigens. The role of the gut as a regulator of type 1 diabetes was suggested in animal studies, in which changes affecting the gut immune system modulated the incidence of diabetes. Dietary interventions, alterations in the intestinal microbiota and exposure to enteric pathogens, regulate the development of autoimmune diabetes in animal models. It has been demonstrated that these modulations affect the gut barrier mechanisms and intestinal immunity. Because the pancreas and the gut belong to the same intestinal immune system, the link between autoimmune diabetes and the gut is not unexpected. The gut hypothesis in the development of type 1 diabetes is also supported by the observations made in human type 1 diabetes. Early diet could modulate the development of beta-cell autoimmunity; weaning to hydrolysed casein formula decreased the risk of beta-cell autoimmunity by age 10 in the infants at genetic risk. Increased gut permeability, intestinal inflammation with impaired regulatory mechanisms and dysregulated oral tolerance have been observed in children with type 1 diabetes. The factors that contribute to these intestinal alterations are not known, but interest is focused on the microbial stimuli and function of innate immunity. It is likely that our microbial environment does not support the healthy maturation of the gut and tolerance in the gut, and this leads to the increasing type 1 diabetes as well as other immune-mediated diseases regulated by intestinal immune system. Thus, the interventions, aiming to prevent or treat type 1 diabetes in humans, should be targeting the gut immune system.

Human enterovirus infections in children at increased risk for type 1 diabetes: the Babydiet study

AIMS/HYPOTHESIS

The aim of this study was to examine human enteroviruses (HEVs) and other intestinal viruses derived from children who participated in the Babydiet intervention study and to analyse the findings according to the appearance of islet autoantibodies, dietary intervention, maternal type 1 diabetes and clinical symptoms.

METHODS

In the Babydiet study the influence of first gluten exposure (6 or 12 months) on the development of islet autoimmunity was investigated in 150 children with increased genetic and familial risk for type 1 diabetes. Blood and stool samples were collected at 3 monthly intervals until the age of 3 years and yearly thereafter. Infections and clinical symptoms were recorded daily for the first year. In the present study, 339 stool samples collected from 104 children during the first year of life were analysed for HEVs and a certain proportion of the samples were analysed for other intestinal viruses.

RESULTS

HEV was detected in 32 (9.4%) samples from 24 (23.1%) children. Altogether 13 serotypes were identified, with HEV-A species being the most common. Children with gastrointestinal symptoms had norovirus (3/11) and sapovirus (1/11) infections in addition to HEV (1/11). Of the 104 children, 22 developed islet autoantibodies. HEV infections were detected in 18% (4/22) and 24% (20/82) of islet-autoantibody-positive and -negative children, respectively (p = 0.5). The prevalence of HEV was similar in the gluten-exposed groups and in children from mothers with type 1 diabetes or from affected fathers and/or siblings (p = 1.0 and 0.6, respectively).

CONCLUSIONS/INTERPRETATION

No correlation was found between the presence of HEV in the first year of life and the development of islet autoantibodies. There was no association between HEV infections and dietary intervention, maternal diabetes or clinical symptoms.

Polymorphisms in the innate immune IFIH1 gene, frequency of enterovirus in monthly fecal samples during infancy, and islet autoimmunity

Interferon induced with helicase C domain 1 (IFIH1) senses and initiates antiviral activity against enteroviruses. Genetic variants of IFIH1, one common and four rare SNPs have been associated with lower risk for type 1 diabetes. Our aim was to test whether these type 1 diabetes-associated IFIH1 polymorphisms are associated with the occurrence of enterovirus infection in the gut of healthy children, or influence the lack of association between gut enterovirus infection and islet autoimmunity.

After testing of 46,939 Norwegian newborns, 421 children carrying the high risk genotype for type 1 diabetes (HLA-DR4-DQ8/DR3-DQ2) as well as 375 children without this genotype were included for monthly fecal collections from 3 to 35 months of age, and genotyped for the IFIH1 polymorphisms. A total of 7,793 fecal samples were tested for presence of enterovirus RNA using real time reverse transcriptase PCR.

We found no association with frequency of enterovirus in the gut for the common IFIH1 polymorphism rs1990760, or either of the rare variants of rs35744605, rs35667974, rs35337543, while the enterovirus prevalence marginally differed in samples from the 8 carriers of a rare allele of rs35732034 (26.1%, 18/69 samples) as compared to wild-type homozygotes (12.4%, 955/7724 samples); odds ratio 2.5, p = 0.06. The association was stronger when infections were restricted to those with high viral loads (odds ratio 3.3, 95% CI 1.3–8.4, p = 0.01). The lack of association between enterovirus frequency and islet autoimmunity reported in our previous study was not materially influenced by the IFIH1 SNPs.

We conclude that the type 1 diabetes-associated IFIH1 polymorphisms have no, or only minor influence on the occurrence, quantity or duration of enterovirus infection in the gut. Its effect on the risk of diabetes is likely to lie elsewhere in the pathogenic process than in the modification of gut infection.

The gut as a regulator of early inflammation in type 1 diabetes

PURPOSE OF REVIEW

Several studies indicate that factors affecting the gut are capable of modulating the development of autoimmune diabetes. This review discusses the recent research on these mechanisms, which may reveal novel pathogenic pathways and new possibilities for prevention of type 1 diabetes (T1D).

RECENT FINDINGS

The role of the gut as a regulator of T1D is mainly based on animal studies in which changes affecting the gut immune system have been shown to modulate the immune-mediated destruction of insulin-producing beta-cells. Dietary interventions, alterations in the intestinal microbiota and exposure to enteral pathogens regulate the development of autoimmune diabetes in animal models. In several studies, it has been demonstrated that these modulations affect the gut barrier mechanisms and intestinal immunity. Also, in humans, increased gut permeability and intestinal inflammation are associated with T1D. A recent report of dietary intervention study in infants at genetic risk of T1D showed that early diet could modulate the development of beta-cell autoimmunity in humans; weaning to hydrolyzed casein formula decreased the risk of beta-cell autoimmunity by age 10.

SUMMARY

The gut modulation affecting permeability, inflammation and microbiota is evidently associated with the regulation of the inflammation leading to beta-cell destruction. Although the mechanisms of action are not fully understood, the recent research points out the lines of approach for the prevention of T1D.

The epidemic of type 1 diabetes: what is it telling us?

PURPOSE OF REVIEW

Type 1 diabetes (T1D) is an autoimmune disorder which affects millions around the world. The incidence of T1D in children is increasing worldwide at a rate that cannot be explained by genetics alone. This review explores the recent research regarding possible causes of this epidemic.

RECENT FINDINGS

Investigation into T1D epidemiology has recently focused on several hypotheses. These theories include the role of infections, early childhood diet, vitamin D exposure, environmental pollutants, increased height velocity, obesity, and insulin resistance in the risk for T1D. Over the past year, the evidence has strengthened for early childhood infections, dietary proteins, and insulin resistance as risk factors for T1D, but not for vitamin D exposure or environmental pollutants.

SUMMARY

Investigation into the source of the current epidemic of T1D has shed light on several possible causes, but has not provided definitive answers, yet.