The prevalence of enteroviral capsid protein vp1 immunostaining in pancreatic islets in human type 1 diabetes

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

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

Type 1 diabetes alters lipid handling and metabolism in human fibroblasts and peripheral blood mononuclear cells

Triggers of the autoimmune response that leads to type 1 diabetes (T1D) remain poorly understood. A possibility is that parallel changes in both T cells and target cells provoke autoimmune attack. We previously documented greater Ca²⁺ transients in fibroblasts from T1D subjects than non-T1D after exposure to fatty acids (FA) and tumor necrosis factor α (TNFα). These data indicate that metabolic and signal transduction defects present in T1D can be elicited ex vivo in isolated cells. Changes that precede T1D, including inflammation, may activate atypical responses in people that are genetically predisposed to T1D. To identify such cellular differences in T1D, we quantified a panel of metabolic responses in fibroblasts and peripheral blood cells (PBMCs) from age-matched T1D and non-T1D subjects, as models for non-immune and immune cells, respectively. Fibroblasts from T1D subjects accumulated more lipid, had higher LC-CoA levels and converted more FA to CO₂, with less mitochondrial proton leak in response to oleate alone or with TNFα, using the latter as a model of inflammation. T1D-PBMCs contained and also accumulated more lipid following FA exposure. In addition, they formed more peroxidized lipid than controls following FA exposure. We conclude that both immune and non-immune cells in T1D subjects differ from controls in terms of responses to FA and TNFα. Our results suggest a differential sensitivity to inflammatory insults and FA that may precede and contribute to T1D by priming both immune cells and their targets for autoimmune reactions.

Presence of Human Herpesvirus 6B in the Pancreas of Subjects With and Without Type 1 Diabetes

OBJECTIVES

The aims of this study were to investigate the presence of human herpesvirus 6 (HHV6) A and B in human pancreata and to search for signs of active infection in this organ of subjects with and without type 1 diabetes (T1D).

METHODS

Pancreata from brain-dead organ donors with and without T1D were examined for the presence of HHV6 genomic sequences by polymerase chain reaction (PCR), transcripts by reverse transcriptase-PCR, and protein by immunohistochemistry. Quantitative PCR of isolated pancreatic islets and exocrine cell clusters was used to determine the intrapancreatic location of HHV6 DNA.

RESULTS

Human herpesvirus 6B genomic sequences were present in 1 of 2 donors who died of acute-onset T1D, 4 of 6 donors with long-standing T1D, and 9 of 12 nondiabetic donors. Higher copy numbers of HHV6B DNA were present in isolated islets than in exocrine tissue from the same donors. No signs of active HHV6 transcription were found. Human herpesvirus 6A was not present in any tested pancreas.

CONCLUSIONS

The herein presented data demonstrate, for the first time, the presence of a latent HHV6B infection in the pancreas and islets of Langerhans. Whether this virus can contribute to disease in the pancreas remains to be determined.

Enteroviruses in blood of patients with type 1 diabetes detected by integrated cell culture and reverse transcription quantitative real-time PCR

AIMS

Enteroviruses (EV) have been associated with type 1 diabetes (T1D), but EV RNA detection has been reported in only a small proportion of T1D patients. We studied whether integrated cell culture and reverse transcription real-time PCR could improve EV detection in blood samples from patients with T1D.

METHODS

Blood was collected from 13 patients with T1D. The presence of EV RNA in blood was investigated by using real-time RT-PCR. In addition, plasma and white blood cells (WBC) were inoculated to BGM and Vero cell line cultures. Culture supernatants and cells collected on day 7 and day 14 were tested for EV RNA by real-time RT-PCR. Enterovirus identification was performed through sequencing of the VP4/VP2 region.

RESULTS

Enterovirus RNA was detected in blood by using real-time RT-PCR in only one out of 13 patients. The detection of EV RNA in cultures inoculated with clinical samples (plasma and/or WBC) gave positive results in five other patients. The viral loads were low, ranging from 45 to 4420 copies/ng of total RNA. One isolate was successfully identified as coxsackievirus B1.

CONCLUSIONS

Integrated cell culture and reverse transcription real-time PCR can improve the detection rate of EV in blood samples of patients with T1D and can be useful to investigate further the relationship between EV and the disease.

Marker of coxsackievirus-B4 infection in saliva of patients with type 1 diabetes

BACKGROUND

Coxsackieviruses B (CV-B) are enteroviruses that have been reported to play a role in the pathogenesis of type 1 diabetes. Enteroviral RNA was detected in the gut mucosa of patients. The mucosal immunity is an interconnected network; therefore, the response to enteroviruses possibly present in the gastrointestinal mucosa can be reflected by specific antibodies in the saliva. In the present study, the anti-CV-B neutralizing activity of saliva samples from patients with type 1 diabetes was investigated.

METHODS

Saliva samples were collected from patients and controls of 3 countries, and plasma was obtained from some of them. The anti-CV-B activity of clinical samples was determined by neutralization of the cytopathic effect induced by challenging viruses in vitro and expressed as titre value.

RESULTS

Overall prevalence and levels of anti-CV-B4 activity of saliva were higher in patients (n = 181) than in controls (n = 135; P = .0002; titre values ≥ 16: odds ratio = 4.22 95% CI: 1.90-9.38 P = .0002). It has been shown that IgA1 played a role in this activity. There was no correlation between the saliva and the plasma anti-CV-B4 neutralizing activity. The neutralizing activity of saliva against CV-B1, CV-B2, CV-B3, and CV-B5 existed rarely, if at all. Increased levels of anti-CV-B4 activity were observed all along a 4 year follow-up period in patients but not in matched controls (P = .01).

CONCLUSION

There is an anti-CV-B4 activity in saliva of patients with type 1 diabetes that may be a useful marker to study the role of CV-B in the pathogenesis of the disease.

Respiratory infections are temporally associated with initiation of type 1 diabetes autoimmunity: the TEDDY study

AIMS/HYPOTHESIS

Respiratory infections and onset of islet autoimmunity are reported to correlate positively in two small prospective studies. The Environmental Determinants of Diabetes in the Young (TEDDY) study is the largest prospective international cohort study on the environmental determinants of type 1 diabetes that regularly monitors both clinical infections and islet autoantibodies. The aim was to confirm the influence of reported respiratory infections and to further characterise the temporal relationship with autoantibody seroconversion.

METHODS

During the years 2004-2009, 8676 newborn babies with HLA genotypes conferring an increased risk of type 1 diabetes were enrolled at 3 months of age to participate in a 15 year follow-up. In the present study, the association between parent-reported respiratory infections and islet autoantibodies at 3 month intervals up to 4 years of age was evaluated in 7869 children. Time-dependent proportional hazard models were used to assess how the timing of respiratory infections related to persistent confirmed islet autoimmunity, defined as autoantibody positivity against insulin, GAD and/or insulinoma antigen-2, concordant at two reference laboratories on two or more consecutive visits.

RESULTS

In total, 87,327 parent-reported respiratory infectious episodes were recorded while the children were under study surveillance for islet autoimmunity, and 454 children seroconverted. The number of respiratory infections occurring in a 9 month period was associated with the subsequent risk of autoimmunity (p < 0.001). For each 1/year rate increase in infections, the hazard of islet autoimmunity increased by 5.6% (95% CI 2.5%, 8.8%). The risk association was linked primarily to infections occurring in the winter (HR 1.42 [95% CI 1.16, 1.74]; p < 0.001). The types of respiratory infection independently associated with autoimmunity were common cold, influenza-like illness, sinusitis, and laryngitis/tracheitis, with HRs (95% CI) of 1.38 (1.11, 1.71), 2.37 (1.35, 4.15), 2.63 (1.22, 5.67) and 1.76 (1.04, 2.98), respectively.

CONCLUSIONS/INTERPRETATION

Recent respiratory infections in young children correlate with an increased risk of islet autoimmunity in the TEDDY study. Further studies to identify the potential causative viruses with pathogen-specific assays should focus especially on the 9 month time window leading to autoantibody seroconversion.

Targeting Innate Immunity for Type 1 Diabetes Prevention

PURPOSE OF REVIEW

Despite immense research efforts, type 1 diabetes (T1D) remains an autoimmune disease without a known trigger or approved intervention. Over the last three decades, studies have primarily focused on delineating the role of the adaptive immune system in the mechanism of T1D. The discovery of Toll-like receptors in the 1990s has advanced the knowledge on the role of the innate immune system in host defense as well as mechanisms that regulate adaptive immunity including the function of autoreactive T cells.

RECENT FINDINGS

Recent investigations suggest that inflammation plays a key role in promoting a large number of autoimmune disorders including T1D. Data from the LEW1.WR1 rat model of virus-induced disease and the RIP-B7.1 mouse model of diabetes suggest that innate immune signaling plays a key role in triggering disease progression. There is also evidence that innate immunity may be involved in the course of T1D in humans; however, a small number of clinical trials have shown that interfering with the function of the innate immune system following disease onset exerts only a modest effect on β-cell function. The data implying that innate immune pathways are linked with mechanisms of islet autoimmunity hold great promise for the identification of novel disease pathways that may be harnessed for clinical intervention. Nevertheless, more work needs to be done to better understand mechanisms by which innate immunity triggers β-cell destruction and assess the therapeutic value in blocking innate immunity for diabetes prevention.

The Four-Way Stop Sign: Viruses, 12-Lipoxygenase, Islets, and Natural Killer Cells in Type 1 Diabetes Progression

Natural killer (NK) cells represent an important effector arm against viral infection, and mounting evidence suggests that viral infection plays a role in the development of type 1 diabetes (T1D) in at least a portion of patients. NK cells recognize their target cells through a delicate balance of inhibitory and stimulatory receptors on their surface. If unbalanced, NK cells have great potential to wreak havoc in the pancreas due to the beta cell expression of the as-yet-defined NKp46 ligand through interactions with the activating NKp46 receptor found on the surface of most NK cells. Blocking interactions between NKp46 and its ligand protects mice from STZ-induced diabetes, but differential expression non-diabetic and diabetic donor samples have not been tested. Additional studies have shown that peripheral blood NK cells from human T1D patients have altered phenotypes that reduce the lytic and functional ability of the NK cells. Investigations of humanT1D pancreas tissues have indicated that the presence of NK cells may be beneficial despite their infrequent detection. In non-obese diabetic (NOD) mice, we have noted that NK cells express high levels of the proinflammatory mediator 12/15-lipoxygenase (12/15-LO), and decreased levels of stimulatory receptors. Conversely, NK cells of 12/15-LO deficient NOD mice, which are protected from diabetes development, express significantly higher levels of stimulatory receptors. Furthermore, the human NK92 cell line expresses the ALOX12 protein [human 12-lipoxygenase (12-LO), related to mouse 12/15-LO] via Western blotting. Human 12-LO is upregulated in the pancreas of both T1D and T2D human donors with insulin-containing islets, showing a link between 12-LO expression and diabetes progression. Therefore, our hypothesis is that NK cells in those susceptible to developing T1D are unable to function properly during viral infections of pancreatic beta cells due to increased 12-LO expression and activation, which contributes to increased interferon-gamma production and an imbalance in activating and inhibitory NK cell receptors, and may contribute to downstream autoimmune T cell responses. The work presented here outlines evidence from our lab, as well as published literature, supporting our hypothesis, including novel data.

Detection and localization of viral infection in the pancreas of patients with type 1 diabetes using short fluorescently-labelled oligonucleotide probes

Enteroviruses, specifically of the Coxsackie B virus family, have been implicated in triggering islet autoimmunity and type 1 diabetes, but their presence in pancreata of patients with diabetes has not been fully confirmed.

To detect the presence of very low copies of the virus genome in tissue samples from T1D patients, we designed a panel of fluorescently labeled oligonucleotide probes, each of 17-22 nucleotides in length with a unique sequence to specifically bind to the enteroviral genome of the picornaviridae family.

With these probes enteroviral RNA was detected with high sensitivity and specificity in infected cells and tissues, including in FFPE pancreas sections from patients with T1D. Detection was not impeded by variations in sample processing and storage thereby overcoming the potential limitations of fragmented RNA. Co-staining of small RNA probes in parallel with classical immunstaining enabled virus detection in a cell-specific manner and more sensitively than by viral protein.

The innate immune receptor MDA5 limits rotavirus infection but promotes cell death and pancreatic inflammation

Melanoma differentiation-associated protein 5 (MDA5) mediates the innate immune response to viral infection. Polymorphisms in IFIH1, the gene coding for MDA5, correlate with the risk of developing type 1 diabetes (T1D). Here, we demonstrate that MDA5 is crucial for the immune response to enteric rotavirus infection, a proposed etiological agent for T1D. MDA5 variants encoded by minor IFIH1 alleles associated with lower T1D risk exhibit reduced activity against rotavirus infection. We find that MDA5 activity limits rotavirus infection not only through the induction of antiviral interferons and pro-inflammatory cytokines, but also by promoting cell death. Importantly, this MDA5-dependent antiviral response is specific to the pancreas of rotavirus-infected mice, similar to the autoimmunity associated with T1D. These findings imply that MDA5-induced cell death and inflammation in the pancreas facilitate progression to autoimmune destruction of pancreatic β-cells.

Type 1 diabetes and viral infections: What is the relationship?

Type 1 diabetes (T1D) is the most common chronic metabolic disorder in children. Epigenetic and environmental factors capable of altering the penetrance of major susceptibility genes or capable of increasing the penetrance of low-risk genes are currently thought to play a role in triggering autoimmunity and T1D development. This paper discusses the current knowledge of the role of viruses in T1D. Most studies that have evaluated the potential association between viral infections and T1D have indicated that it is highly likely that some of these infectious agents play a role in T1D development. However, most T1D cases are immune-mediated, and it is supposed that the initial viral infection is capable of creating, in genetically predisposed subjects, a particular condition in which chronic local inflammation occurs through the persistence of the infecting virus in pancreatic tissue and the activation of autoimmunity by means of molecular mimicry, bystander activation, or both. Theoretically, this knowledge could lead to possible prophylaxis and therapy for T1D. Further studies devoted to evaluating which infectious agents are linked to T1D and which immune mechanisms induce or protect against the disease are needed before adequate prophylactic and therapeutic measures can be developed.

Anti-coxsackievirus B4 (CV-B4) enhancing activity of serum associated with increased viral load and pathology in mice reinfected with CV-B4

In previous studies it was shown that inoculation of Swiss albino mice with CV-B4 E2 resulted in the production of serum IgG capable of enhancing the CV-B4 E2 infection of murine spleen cells cultures. To investigate whether such an enhancing activity of serum can play a role in vivo, we decided to study the CV-B4 E2 infection in mice exposed to successive inoculations of virus. In Swiss albino mice infected with CV-B4 E2 at the age of 21 days, anti-CV-B4 E2 neutralizing and enhancing activities of their serum peaked after 55 d. In contrast, mice inoculated at the age of 55 d expressed much lower activities. Despite the neutralizing activity of serum, CV-B4 E2 inoculated a second time to 55 day-old animals spread into the host. At the age of 72 and 89 d the levels of viral RNA and infectious particles were higher in organs of animals exposed to 2 successive infections compared with animals infected once at the age of 21 d or 55 d. In animals with 2 successive inoculations of CV-B4 E2 there was a relationship between the anti-CV-B4 E2 enhancing activity of serum and the level of viral RNA in organs and an enhancement of pathology was observed as displayed by histological analysis of pancreas and hyperglycaemia. Altogether our data strongly suggest that an anti-CV-B4 E2 enhancing activity in the host can play a role in the outcome of a secondary infection with this virus.

Development of autoantibodies precedes clinical manifestations of autoimmune diseases: A comprehensive review

The etiology of autoimmune diseases is due to a combination of genetic predisposition and environmental factors that alter the expression of immune regulatory genes through various mechanisms including epigenetics. Both humoral and cellular elements of the adaptive immune system play a role in the pathogenesis of autoimmune diseases and the presence of autoantibodies have been detected in most but not all autoimmune diseases before the appearance of clinical symptoms. In some cases, the presence or levels of these autoantibodies portends not only the risk of developing a corresponding autoimmune disease, but occasionally the severity as well. This observation is intriguing because it suggests that we can, to some degree, predict who may or may not develop autoimmune diseases. However, the role of autoantibodies in the pathogenesis of autoimmune diseases, whether they actually affect disease progression or are merely an epiphenomenon is still not completely clear in many autoimmune diseases. Because of these gaps in our knowledge, the ability to accurately predict a future autoimmune disease can only be considered a relative risk factor. Importantly, it raises the critical question of defining other events that may drive a patient from a preclinical to a clinical phase of disease.

Germinal centre frequency is decreased in pancreatic lymph nodes from individuals with recent-onset type 1 diabetes

AIMS/HYPOTHESIS

Pancreatic lymph nodes (PLNs) are critical sites for the initial interaction between islet autoantigens and autoreactive lymphocytes, but the histology of PLNs in tissue from individuals with type 1 diabetes has not been analysed in detail. The aim of this study was to examine PLN tissue sections from healthy donors compared with those at risk of, or with recent-onset and longer-duration type 1 diabetes.

METHODS

Immunofluorescence staining was used to examine PLN sections from the following donor groups: non-diabetic (n=15), non-diabetic islet autoantibody-positive (n=5), recent-onset (≤1.5 years duration) type 1 diabetes (n=13), and longer-duration type 1 diabetes (n=15). Staining for CD3, CD20 and Ki67 was used to detect primary and secondary (germinal centre-containing) follicles and CD21 and CD35 to detect follicular dendritic cell networks.

RESULTS

The frequency of secondary follicles was lower in the recent-onset type 1 diabetes group compared with the non-diabetic control group. The presence of insulitis (as evidence of ongoing beta cell destruction) and diagnosis of type 1 diabetes at a younger age, however, did not appear to be associated with a lower frequency of secondary follicles. A higher proportion of primary B cell follicles were observed to lack follicular dendritic cell networks in the recent-onset type 1 diabetes group.

CONCLUSIONS/INTERPRETATION

Histological analysis of rare PLNs from individuals with type 1 diabetes suggests a previously unrecognised phenotype comprising decreased primary B cell follicle frequency and fewer follicular dendritic cell networks in recent-onset type 1 diabetes.

Bifidobacteria-derived lipoproteins inhibit infection with coxsackievirus B4 in vitro

The aim of the present study was to investigate the potential of bifidobacteria in protecting cells from coxsackievirus B4 (CV-B4) infection. Bifidobacterial screening identified two of five strains that protected human epithelial type 2 (HEp-2) cell viability when bifidobacteria were incubated with viral particles prior to inoculation. In contrast, no effect was shown by incubating HEp-2 cells with bifidobacteria prior to CV-B4 inoculation. Cell wall lipoprotein aggregates (LpAs) secreted by the selected strains were assayed for their antiviral activity. The two LpAs exhibited antiviral activity when they were incubated with viral particles prior to inoculation of HEp-2 cells. Recombinant LpA-derived protein exhibited identical antiviral activity. To identify the peptide sequences interacting with the virus particles, LpA proteins were aligned with the peptide sequences of the north canyon rim and puff footprint onto coxsackievirus and adenovirus receptor (CAR). The in silico molecular docking study using CV-B3 as template showed low-energy binding, indicating a stable system for the selected peptides and consequently a likely binding interaction with CV-B. Bifidobacterium longum and Bifidobacterium breve peptides homologous to the viral north rim footprint onto CAR sequence formed hydrogen bonds with several viral residues in the north rim of the canyon, which were already predicted as interacting with CAR. In conclusion, proteins from bifidobacterial LpAs can inhibit infection with CV-B4, likely through binding to the capsid amino acids that interact with CAR.

Siglec-7 restores β-cell function and survival and reduces inflammation in pancreatic islets from patients with diabetes

Chronic inflammation plays a key role in both type 1 and type 2 diabetes. Cytokine and chemokine production within the islets in a diabetic milieu results in β-cell failure and diabetes progression. Identification of targets, which both prevent macrophage activation and infiltration into islets and restore β-cell functionality is essential for effective diabetes therapy. We report that certain Sialic-acid-binding immunoglobulin-like-lectins (siglecs) are expressed in human pancreatic islets in a cell-type specific manner. Siglec-7 was expressed on β-cells and down-regulated in type 1 and type 2 diabetes and in infiltrating activated immune cells. Over-expression of Siglec-7 in diabetic islets reduced cytokines, prevented β-cell dysfunction and apoptosis and reduced recruiting of migrating monocytes. Our data suggest that restoration of human Siglec-7 expression may be a novel therapeutic strategy targeted to both inhibition of immune activation and preservation of β-cell function and survival.

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.

In Vivo Persistence of Human Rhinoviruses in Immunosuppressed Patients

Several species of the genus Enterovirus cause persistent infections in humans. Human rhinovirus (HRV) infections are generally self-limiting but occasionally persistent infections have been described. This study aimed to identify persistent HRV infections and investigate the clinical and virologic characteristics of patients with persistent infections. From January 2012 to March 2015, 3714 respiratory specimens from 2608 patients were tested for respiratory viruses by using a multiplex reverse transcription–polymerase chain reaction. A retrospective study was performed. Patients with at least two specimens positive for HRV/enterovirus taken 45 days or longer apart were identified and the HRV/enteroviruses were typed. Patients with persistent infection were compared to patients with reinfection and patients with cleared infection. Phylogenetic analysis of the viral protein(VP)4/VP2 region was performed. 18 patients with persistent HRV/enterovirus infection were identified. Minimum median duration of persistence was 92 days (range 50–455 days). All but one patients with persistence were immunosuppressed. Immunosuppression and hematologic disorders were more frequent in patients with persistence (n = 18) than in patients with reinfection (n = 33) and with cleared infection (n = 25) (p = 0.003 and p = 0.001, respectively). In conclusion, this retrospective study identified HRV persistence in vivo which occurred mainly in immunosuppressed patients.

Circulating Zonulin Correlates with Density of Enteroviruses and Tolerogenic Dendritic Cells in the Small Bowel Mucosa of Celiac Disease Patients

BACKGROUND

Impaired intestinal integrity, including increased permeability of the small bowel mucosa, has been shown in patients with celiac disease (CD) as well as with type 1 diabetes (T1D). Zonulin (ZO, pre-haptoglobin), a tight junction regulator, plays a particular role in the regulation of intestinal barrier function and in the pathogenesis of the above-mentioned diseases.

AIM

To investigate whether enteroviruses (EVs) and immunoregulatory cells are associated with intestinal permeability in patients with CD alone and with coexistent T1D.

MATERIALS AND METHODS

Altogether 80 patients (mean age 10.68 ± 6.69 years) who had undergone small bowel biopsy were studied. Forty patients with functional dyspepsia and normal small bowel mucosa formed the control group. The circulating ZO level in sera was evaluated using ELISA. The densities of EV, FOXP3+ regulatory T cells (Tregs), indoleamine 2,3-dioxygenase (IDO+) dendritic cells (DCs) and glutamic acid dexarboxylase (GAD)65+ cells in small bowel mucosa were investigated by immunohistochemistry. The expression analysis of FOXP3, tight junction protein 1 (TJP1), gap junction (GJA1), IDO and CD103 genes was evaluated by real-time PCR.

RESULTS

The ZO level was higher in CD patients compared to subjects with a normal small bowel mucosa, particularly in those with Marsh IIIc atrophy (p = 0.01), and correlated with the density of EV (r = 0.63; p = 0.0003) and IDO+ DCs (r = 0.58; p = 0.01) in the small bowel mucosa. The density of GAD65+ epithelial cells was correlated with the density of EV (r = 0.59; p = 0.03) and IDO+ DCs (r = 0.78; p = 0.004) in CD patients. The relative expression of FOXP3 mRNA in the small bowel mucosa tissue was significantly higher in patients with CD, compared to subjects with a normal mucosa, and correlated with the density of EV (r = 0.62; p = 0.017) as well as with the relative expression of IDO mRNA (r = 0.54; p = 0.019).

CONCLUSIONS

The CD is associated with elevation of the circulating ZO level, the value of which correlates with the density of EV in CD patients with severe atrophic changes in the small bowel mucosa, particularly in cases of concomitant T1D. The CD is also characterized by the close relationship of the density of GAD65+ epithelial cells with the EV, ZO level and IDO+ DCs.

Insulitis in human diabetes: a histological evaluation of donor pancreases

AIMS/HYPOTHESIS

According to the consensus criteria developed for type 1 diabetes, an individual can be diagnosed with insulitis when ≥ 15 CD45⁺ cells are found within the parenchyma or in the islet-exocrine interface in ≥ 3 islets. The aim of this study was to determine the frequency of individuals with type 2 diabetes fulfilling these criteria with reference to non-diabetic and type 1 diabetic individuals.

METHODS

Insulitis was determined by examining CD45⁺ cells in the pancreases of 50, 13 and 44 organ donors with type 2 diabetes, type 1 diabetes and no diabetes, respectively. CD3⁺ cells (T cells) infiltrating the islets were evaluated in insulitic donors. In insulitic donors with type 2 diabetes, the pancreases were characterised according to the presence of CD68 (macrophages), myeloperoxidase (MPO; neutrophils), CD3, CD20 (B cells) and HLA class I hyperstained islets. In all type 2 diabetic donors, potential correlations of insulitis with dynamic glucose-stimulated insulin secretion in vitro or age, BMI, HbA_1c or autoantibody positivity were examined.

RESULTS

Overall, 28% of the type 2 diabetic donors fulfilled the consensus criteria for insulitis developed for type 1 diabetes. Of the type 1 diabetic donors, 31% fulfilled the criteria. None of the non-diabetic donors met the criteria. Only type 1 diabetic donors had ≥ 15 CD3⁺ cells in ≥ 3 islets. Type 2 diabetic donors with insulitis also had a substantial number of CD45⁺ cells in the exocrine parenchyma. Macrophages constituted the largest fraction of CD45⁺ cells, followed by neutrophils and T cells. Of type 2 diabetic pancreases with insulitis, 36% contained islets that hyperstained for HLA class I. Isolated islets from type 2 diabetic donors secreted less insulin than controls, although with preserved dynamics. Insulitis in the type 2 diabetic donors did not correlate with glucose-stimulated insulin secretion, the presence of autoantibodies, BMI or HbA_1c.

CONCLUSIONS/INTERPRETATION

The current definition of insulitis cannot be used to distinguish pancreases retrieved from individuals with type 1 diabetes from those with type 2 diabetes. On the basis of our findings, we propose a revised definition of insulitis, with a positive diagnosis when ≥ 15 CD3⁺ cells, not CD45⁺ cells, are found in ≥ 3 islets.

Echovirus 6 Infects Human Exocrine and Endocrine Pancreatic Cells and Induces Pro-Inflammatory Innate Immune Response

Human enteroviruses (HEV), especially coxsackievirus serotype B (CVB) and echovirus (E), have been associated with diseases of both the exocrine and endocrine pancreas, but so far evidence on HEV infection in human pancreas has been reported only in islets and ductal cells. This study aimed to investigate the capability of echovirus strains to infect human exocrine and endocrine pancreatic cells. Infection of explanted human islets and exocrine cells with seven field strains of E6 caused cytopathic effect, virus titer increase and production of HEV protein VP1 in both cell types. Virus particles were found in islets and acinar cells infected with E6. No cytopathic effect or infectious progeny production was observed in exocrine cells exposed to the beta cell-tropic strains of E16 and E30. Endocrine cells responded to E6, E16 and E30 by upregulating the transcription of interferon-induced with helicase C domain 1 (IF1H1), 2′-5′-oligoadenylate synthetase 1 (OAS1), interferon-β (IFN-β), chemokine (C–X–C motif) ligand 10 (CXCL10) and chemokine (C–C motif) ligand 5 (CCL5). Echovirus 6, but not E16 or E30, led to increased transcription of these genes in exocrine cells. These data demonstrate for the first time that human exocrine cells represent a target for E6 infection and suggest that certain HEV serotypes can replicate in human pancreatic exocrine cells, while the pancreatic endocrine cells are permissive to a wider range of HEV.

Persistence of Coxsackievirus B4 in pancreatic ductal-like cells results in cellular and viral changes

INTRODUCTION

Although known as cytolytic viruses, group B coxackieviruses (CVB) are able to establish a persistent infection in vitro and in vivo. Viral persistence has been reported as a key mechanism in the pathogenesis of CVB-associated chronic diseases such as type 1 diabetes (T1D). The impact of CVB4 persistence on human pancreas ductal-like cells was investigated.

METHODS

A persistent CVB4 infection was established in ductal-like cells. PDX-1 expression, resistance to CVB4-induced lysis and CAR expression were evaluated. The profile of cellular microRNAs (miRNAs) was investigated through miRNA-sequencing. Viral phenotypic changes were examined, and genomic modifications were assessed by sequencing of the viral genome.

RESULTS

The CVB4 persistence in ductal-like cells was productive, with continuous release of infectious particles. Persistently infected cells displayed a resistance to CVB4-induced lysis upon superinfection and expression of PDX-1 and CAR was decreased. These changes were maintained even after virus clearance. The patterns of cellular miRNA expression in mock-infected and in CVB4-persistently infected ductal-like cells were clearly different. The persistent infection-derived virus (PIDV) was still able to induce cytopathic effect but its plaques were smaller than the parental virus. Several mutations appeared in various PIDV genome regions, but amino acid substitutions did not affect the predicted site of interaction with CAR.

CONCLUSION

Cellular and viral changes occur during persistent infection of human pancreas ductal-like cells with CVB4. The persistence of cellular changes even after virus clearance supports the hypothesis of a long-lasting impact of persistent CVB infection on the cells.

The Folate Cycle As a Cause of Natural Killer Cell Dysfunction and Viral Etiology in Type 1 Diabetes

The folate pathway is critical to proper cellular function and metabolism. It is responsible for multiple functions, including energy (ATP) production, methylation reactions for DNA and protein synthesis and the production of immunomodulatory molecules, inosine and adenosine. These play an important role in immune signaling and cytotoxicity. Herein, we hypothesize that defects in the folate pathway in genetically susceptible individuals could lead to immune dysfunction, permissive environments for chronic cyclical latent/lytic viral infection, and, ultimately, the development of unchecked autoimmune responses to infected tissue, in this case islet beta cells. In the context of type 1 diabetes (T1D), there has been a recent increase in newly diagnosed cases of T1D in the past 20 years that has exceeded previous epidemiological predictions with yet unidentified factor(s). This speaks to a potential environmental trigger that adversely affects immune responses. Most research into the immune dysfunction of T1D has focused on downstream adaptive responses of T and B cells neglecting the role of the upstream innate players such as natural killer (NK) cells. Constantly, surveilling the blood and tissues for pathogens, NK cells remove threats through direct cytotoxic responses and recruitment of adaptive responses using cytokines, such as IL-1β and IFN-γ. One long-standing hypothesis suggests viral infection as a potential trigger for the autoimmune response in T1D. Recent data suggest multiple viruses as potential causal agents. Intertwined with this is an observed reduced NK cell enumeration, cytotoxicity, and cytokine signaling in T1D patients. Many of the viruses implicated in T1D are chronic latent/lysogenic infections with demonstrated capacity to reduce NK cell response and number through mechanisms that resemble those of pregnancy tolerance. Defects in the folate pathway in T1D patients could result in decreased immune response to viral infection or viral reactivation. Dampened NK responses to infections result in improper signaling, improper antigen presentation, and amplified CD8⁺ lymphocyte proliferation and cytotoxicity, a hallmark of beta cell infiltrates in patients with T1D onset. This would suggest a critical role for NK cells in T1D development linked to viral infection and the importance of the folate pathway in maintaining proper NK response.

An IFIH1 gene polymorphism associated with risk for autoimmunity regulates canonical antiviral defence pathways in Coxsackievirus infected human pancreatic islets

The IFIH1 gene encodes the pattern recognition receptor MDA5. A common polymorphism in IFIH1 (rs1990760, A946T) confers increased risk for autoimmune disease, including type 1-diabetes (T1D). Coxsackievirus infections are linked to T1D and cause beta-cell damage in vitro. Here we demonstrate that the rs1990760 polymorphism regulates the interferon (IFN) signature expressed by human pancreatic islets following Coxsackievirus infection. A strong IFN signature was associated with high expression of IFNλ1 and IFNλ2, linking rs1990760 to the expression of type III IFNs. In the high-responding genotype, IRF-1 expression correlated with that of type III IFN, suggesting a positive-feedback on type III IFN transcription. In summary, our study uncovers an influence of rs1990760 on the canonical effector function of MDA5 in response to an acute infection of primary human parenchymal cells with a clinically relevant virus linked to human T1D. It also highlights a previously unrecognized connection between the rs1990760 polymorphism and the expression level of type III IFNs.

MicroRNAs in Type 1 Diabetes: Complex Interregulation of the Immune System, β Cell Function and Viral Infections

Since the discovery of the first mammalian microRNA (miRNA) more than two decades ago, a plethora of miRNAs has been identified in humans, now amounting to more than 2500. Essential for post-transcriptional regulation of gene networks integral for developmental pathways and immune response, it is not surprising that dysregulation of miRNAs is often associated with the aetiology of complex diseases including cancer, diabetes and autoimmune disorders. Despite massive expansion of small RNA studies and extensive investigation in diverse disease contexts, the role of miRNAs in type 1 diabetes has only recently been explored. Key studies using human islets have recently implicated virus-induced miRNA dysregulation as a pivotal mechanism of β cell destruction, while the interplay between miRNAs, the immune system and β cell survival has been illustrated in studies using animal and cellular models of disease. The role of specific miRNAs as major players in immune system homeostasis highlights their exciting potential as therapeutics and prognostic biomarkers of type 1 diabetes.

The Expanding Role of Natural Killer Cells in Type 1 Diabetes and Immunotherapy

Treatments for autoimmune diseases including type 1 diabetes (T1D) are aimed at resetting the immune system, especially its adaptive arm. The innate immune system is often ignored in the design of novel immune-based therapies. There is increasing evidence for multiple natural killer (NK) subpopulations, but their role is poorly understood in autoimmunity and likely is contributing to the controversial role reported for NKs. In this review, we will summarize NK subsets and their roles in tolerance, autoimmune diabetes, and immunotherapy.

A new monoclonal antibody (Cox mAB 31A2) detects VP1 protein of coxsackievirus B3 with high sensitivity and specificity

Human enteroviruses, e.g. coxsackieviruses, induce a variety of severe acute and chronic forms of disease, including myocarditis, meningitis and diabetes mellitus type 1. To visualize enterovirus infection with a diagnostic intent, many studies have applied a commercially available antibody (anti-CVB5 VP1, clone 5-D8/1, Dako, Hamburg, Germany) that identifies VP1 of different enteroviral serotypes. Many antibodies, however, have been found to bind non-specifically to proteins of cardiomyocytes and in the interstitial space, resulting in non-specific staining in immunohistochemistry. In this paper we show that the anti-CVB5 VP1 antibody, recognizing VP1 of coxsackieviruses and widely used in diagnostics and research, shows strong cross-reactivity with cellular proteins in the heart (and pancreas) of humans and mice, which calls for a more specific antibody to be used for diagnostic purposes. We observed by Western blot analyses of lysates from human heart tissue samples and HeLa cells two cross-reactive bands when using clone 5-D8/1. Peptide mass fingerprinting (MALDI-TOF) identified these proteins as creatine kinase (B-type) and tubulin, confirming that this mAb detects cellular proteins in addition to viral VP1. In order to overcome the problems of false positive VP1 staining we generated a new highly specific and sensitive monoclonal antibody (Cox mAB 31A2) that recognizes VP1 from CVB3. The new antibody was characterized and was found to function well in immunohistochemistry, immunofluorescence staining, Western blotting, ELISA and FACS analyses.

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.

Viruses in type 1 diabetes

Environmental factors play an important role in the pathogenesis of type 1 diabetes and can determine if a genetically susceptible individual develops the disease. Increasing evidence suggest that among other exogenous agents certain virus infections can contribute to the beta-cell damaging process. Possible viral etiology of type 1 diabetes has been explored extensively but the final proof for causality is still lacking. Currently, the group of enteroviruses (EVs) is considered as the strongest candidate. These viruses have been found in the pancreas of type 1 diabetic patients, and epidemiological studies have shown more EV infections in diabetic patients than in controls. Prospective studies, such as the Type 1 Diabetes Prediction and Prevention (DIPP) study in Finland, are of fundamental importance in the evaluation viral effects as they can cover all stages of the beta-cell damaging process, including those preceding the initiation of the process. DIPP study has carried out the most comprehensive virological analyses ever done in prospective cohorts. This article summarizes the findings from these analyses and discuss them in the context of the existing other knowledge and the prospects for intervention studies with EV vaccines or antiviral drugs.

Environmental risk factors for type 1 diabetes

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

Viral infections in type 1 diabetes mellitus--why the β cells?

Type 1 diabetes mellitus (T1DM) is caused by progressive autoimmune-mediated loss of pancreatic β-cell mass via apoptosis. The onset of T1DM depends on environmental factors that interact with predisposing genes to induce an autoimmune assault against β cells. Epidemiological, clinical and pathology studies in humans support viral infection--particularly by enteroviruses (for example, coxsackievirus)--as an environmental trigger for the development of T1DM. Many candidate genes for T1DM, such as MDA5, PTPN2 and TYK2, regulate antiviral responses in both β cells and the immune system. Cellular permissiveness to viral infection is modulated by innate antiviral responses that vary among different tissues or cell types. Some data indicate that pancreatic islet α cells trigger a more efficient antiviral response to infection with diabetogenic viruses than do β cells, and so are able to eradicate viral infections without undergoing apoptosis. This difference could account for the varying ability of islet-cell subtypes to clear viral infections and explain why chronically infected pancreatic β cells, but not α cells, are targeted by an autoimmune response and killed during the development of T1DM. These issues and attempts to target viral infection as a preventive therapy for T1DM are discussed in the present Review.

Innate inflammation in type 1 diabetes

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

Enterovirus infection of human islets of Langerhans affects β-cell function resulting in disintegrated islets, decreased glucose stimulated insulin secretion and loss of Golgi structure

AIMS/HYPOTHESIS

In type 1 diabetes (T1D), most insulin-producing β cells are destroyed, but the trigger is unknown. One of the possible triggers is a virus infection and the aim of this study was to test if enterovirus infection affects glucose stimulated insulin secretion and the effect of virus replication on cellular macromolecules and organelles involved in insulin secretion.

METHODS

Isolated human islets were infected with different strains of coxsackievirus B (CVB) virus and the glucose-stimulated insulin release (GSIS) was measured in a dynamic perifusion system. Classical morphological electron microscopy, large-scale electron microscopy, so-called nanotomy, and immunohistochemistry were used to study to what extent virus-infected β cells contained insulin, and real-time PCR was used to analyze virus induced changes of islet specific genes.

RESULTS

In islets infected with CVB, GSIS was reduced in correlation with the degree of virus-induced islet disintegration. The expression of the gene encoding insulin was decreased in infected islets, whereas the expression of glucagon was not affected. Also, in islets that were somewhat disintegrated, there were uninfected β cells. Ultrastructural analysis revealed that virus particles and virus replication complexes were only present in β cells. There was a significant number of insulin granules remaining in the virus-infected β cells, despite decreased expression of insulin mRNA. In addition, no typical Golgi apparatus was detected in these cells. Exposure of islets to synthetic dsRNA potentiated glucose-stimulated insulin secretion.

CONCLUSIONS/INTERPRETATION

Glucose-stimulated insulin secretion; organelles involved in insulin secretion and gene expression were all affected by CVB replication in β cells.

Heterogeneity and Lobularity of Pancreatic Pathology in Type 1 Diabetes during the Prediabetic Phase

Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing beta cells are destroyed in the islets of Langerhans. One of its main pathological manifestations is the hyper-expression of Major Histocompatibility Complex I (MHC-I) by beta cells, which was first described over 3 decades ago yet its cause remains unknown. It might not only be a sign of beta cell dysfunction but could also render the cells susceptible to autoimmune destruction; for example, by islet-infiltrating CD8 T cells. In this report, we studied pancreas tissue from a 22-year-old non-diabetic male cadaveric organ donor who had been at high risk of developing T1D, in which autoantibodies against GAD and IA-2 were detected. Pancreas sections were analyzed for signs of inflammation. Multiple insulin-containing islets were identified, which hyper-expressed MHC-I. However, islet density and MHC-I expression exhibited a highly lobular and heterogeneous pattern even within the same section. In addition, many islets with high expression of MHC-I presented higher levels of CD8 T cell infiltration than normal islets. These results demonstrate the heterogeneity of human pathology that occurs early during the pre-diabetic, autoantibody positive phase, and should contribute to the understanding of human T1D.

Mechanisms of Beta Cell Dysfunction Associated With Viral Infection

Type 1 diabetes (T1D) results from genetic predisposition and environmental factors leading to the autoimmune destruction of pancreatic beta cells. Recently, a rapid increase in the incidence of childhood T1D has been observed worldwide; this is too fast to be explained by genetic factors alone, pointing to the spreading of environmental factors linked to the disease. Enteroviruses (EVs) are perhaps the most investigated environmental agents in relationship to the pathogenesis of T1D. While several studies point to the likelihood of such correlation, epidemiological evidence in its support is inconclusive or in some instances even against it. Hence, it is still unknown if and how EVs are involved in the development of T1D. Here we review recent findings concerning the biology of EV in beta cells and the potential implications of this knowledge for the understanding of beta cell dysfunction and autoimmune destruction in T1D.

Monocytes of Patients with Type 1 Diabetes Harbour Enterovirus RNA

BACKGROUND

Intracellular enterovirus (EV) RNA was detected in blood of patients with type 1 diabetes (T1D). The presence of EV RNA in subsets of peripheral blood mononuclear cells (PBMCs) of patients, and the in vitro infection of these cells with an EV, was investigated.

MATERIALS AND METHODS

Blood was collected from 42 patients with T1D, PBMCs were isolated and monocytes were purified. Interferon alpha (IFNα) mRNA and EV RNA were investigated using RT-PCR. Levels of IFNα in plasma were measured using an immunoassay. Cells were inoculated with Coxsackievirus B4 (CBV4) in vitro, and infection was assessed by indirect immunofluorescence (IFI).

RESULTS

Interferon alpha mRNA was detected in blood and in monocytes of 12 of 42 patients with T1D, but not in monocyte-depleted PBMCs of the same individuals. Significant plasma levels of IFNα (≥ 5 IU/mL) were found in six patients. EV RNA was detected in whole blood and in monocytes of seven patients and negative-strand EV RNA was found in monocytes of 6 of them. When monocytes of patients with IFNα and/or EV RNA in their blood were inoculated with CVB4, the proportion of cells stained by an anti-VP1 antibody was 8.8 ± 1%, whereas no VP1 was detected in the monocytes of IFNα, EV RNA negative patients. Nevertheless, when CBV4 was mixed with plasma, VP1 was detected in monocytes of all patients with T1D (staining ranging from 12 to 36%).

CONCLUSIONS

Our data indicate that monocytes of patients with T1D can harbor EV RNA and IFNα mRNA and can be infected with an EV in vitro.

The subcellular distribution of cyclin-D1 and cyclin-D3 within human islet cells varies according to the status of the pancreas donor

AIMS/HYPOTHESIS

In humans, the rate of beta cell proliferation declines rapidly during the postnatal period and remains low throughout adult life. Recent studies suggest that this may reflect the distribution of cell cycle regulators which, unusually, are located in the cytosolic compartment of beta cells in islets isolated from adults. In the present work, we examined whether the localisation of cyclin-D molecules is also cytosolic in the islet cells of pancreatic samples studied in situ.

METHODS

Immunohistochemical approaches were employed to examine the subcellular localisation of cyclin-D1, -D2 and -D3 in human pancreatic samples recovered either from heart-beating donors or post mortem. Immunofluorescence methods were used to reveal the cellular localisation of cyclin-D1 and -D3.

RESULTS

The distribution of cyclin-D2 was invariably cytosolic in islet cells, whereas the localisation of cyclin-D1 and -D3 varied according to the status of the donor. In pancreatic sections from heart-beating donors these molecules were primarily nuclear. By contrast, in samples collected post mortem, they were mainly cytosolic. Cyclin-D1 was detected only in beta cells whereas cyclin-D3 was detected in both alpha and beta cells. The proportion of donors who were immunopositive for cyclin-D1 declined from 71% in controls to 30% in those with type 1 diabetes. Cyclin-D3 was present in the islets of the majority of donors in both groups.

CONCLUSIONS/INTERPRETATION

The subcellular localisation of cyclin-D molecules varies according to the status of the donor. Both cyclin-D1 and -D3 can be found in the nuclei of human islet cells in situ.

Organ donor specimens: What can they tell us about type 1 diabetes?

Type 1 diabetes (T1D) is a chronic disease resulting from the destruction of pancreatic beta cells, due to a poorly understood combination of genetic, environmental, and immune factors. The JDRF Network for Pancreatic Organ donors with Diabetes (nPOD) program recovers transplantation quality pancreas from organ donors throughout the USA. In addition to recovery of donors with T1D, non-diabetic donors include those with islet autoantibodies. Donors with type 2 diabetes and other conditions are also recovered to aid investigations directed at the full spectrum of pathophysiological mechanisms affecting beta cells. One central processing laboratory conducts standardized procedures for sample processing, storage, and distribution, intended for current and future cutting edge investigations. Baseline histology characterizations are performed on the pancreatic samples, with images of the staining results provided though whole-slide digital scans. Uniquely, these high-grade biospecimens are provided without expense to investigators, working worldwide, seeking methods for disease prevention and reversal strategies. Collaborative working groups are highly encouraged, bringing together multiple investigators with different expertise to foster collaborations in several areas of critical need. This mini-review will provide some key histopathological findings emanating from the nPOD collection, including the heterogeneity of beta cell loss and islet inflammation (insulitis), beta cell mass, insulin-producing beta cells in chronic T1D, and pancreas weight reductions at disease onset. Analysis of variations in histopathology observed from these organ donors could provide for mechanistic differences related to etiological agents and serve an important function in terms of identifying the heterogeneity of T1D.

Differential cell autonomous responses determine the outcome of coxsackievirus infections in murine pancreatic α and β cells

Type 1 diabetes (T1D) is an autoimmune disease caused by loss of pancreatic β cells via apoptosis while neighboring α cells are preserved. Viral infections by coxsackieviruses (CVB) may contribute to trigger autoimmunity in T1D. Cellular permissiveness to viral infection is modulated by innate antiviral responses, which vary among different cell types. We presently describe that global gene expression is similar in cytokine-treated and virus-infected human islet cells, with up-regulation of gene networks involved in cell autonomous immune responses. Comparison between the responses of rat pancreatic α and β cells to infection by CVB5 and 4 indicate that α cells trigger a more efficient antiviral response than β cells, including higher basal and induced expression of STAT1-regulated genes, and are thus better able to clear viral infections than β cells. These differences may explain why pancreatic β cells, but not α cells, are targeted by an autoimmune response during T1D.

DOI:http://dx.doi.org/10.7554/eLife.06990.001

Type 1 diabetes is caused by a person's immune system attacking the cells in their pancreas that produce insulin. This eventually kills off so many of these cells—known as beta cells—that the pancreas is unable to make enough insulin. As a result, individuals with type 1 diabetes must inject insulin to help their bodies process sugars. One of the mysteries of type 1 diabetes is why the beta cells in the pancreas are killed by the immune system while neighboring alpha cells, which produce the hormone glucagon, are spared.

Scientists suspect a combination of genetic and environmental factors contributes to type 1 diabetes. Certain viruses, including one called Coxsackievirus, appear to trigger type 1 diabetes in susceptible individuals. Other factors may also make these individuals more likely to develop the disease. For example, they may ‘express’ genes that are thought to increase the risk of type 1 diabetes, many of which control how the immune system responds to viral infections. These genes may make susceptible individuals experience excessive inflammation, because inflammation is what ultimately kills off the beta cells.

Now, Marroqui, Lopes, dos Santos et al. provide evidence that suggests why the alpha cells are spared the immune onslaught in type 1 diabetes. In initial experiments, clusters of cells—known as islets—from the human pancreas were either exposed to small proteins that cause inflammation or infected with the Coxsakievirus. Both events caused a similar increase in the expression of particular immune response genes in the islets. This indicates that these islet cells are able to react to the virus and trigger a first line of defense, which will be further boosted when the immune system is subsequently called into action.

Islets contain both alpha and beta cells, and so further experiments on alpha and beta cells from rats investigated whether the two cell types respond differently when infected by the Coxsakievirus. The results revealed that alpha cells boost the expression of the genes needed to clear the virus to a greater extent than the beta cells, and so respond more efficiently to the virus. Therefore, an infection is more likely to establish itself in the beta cells and consequently trigger inflammation and the immune system's attack on the cells.

These observations explain one of the puzzling questions in the diabetes field and reinforce the possibility that a long-standing viral infection in beta cells—which seem to have a limited capacity to clear viral infections—may be one of the mechanisms leading to progressive beta cell destruction in type 1 diabetes. This knowledge will help in the search for ways to protect beta cells against both viral infections and the consequent immune assault.

DOI:http://dx.doi.org/10.7554/eLife.06990.002

Metabolic changes in type 2 diabetes are reflected in peripheral blood cells, revealing aberrant cytotoxicity, a viral signature, and hypoxia inducible factor activity

BACKGROUND

Metabolic syndrome (MetS) is characterized by central obesity, insulin resistance, dysglycemia, and a pro-atherogenic plasma lipid profile. MetS creates a high risk for development of type 2 diabetes (T2DM) and cardiovascular disease (CVD), presumably by altering inflammatory responses. Presently, it is unknown how the chronic metabolic disturbances in acute hyperglycemia, MetS and T2DM affect the immune activity of peripheral blood cells.

METHODS

We performed genome-wide expression analysis of peripheral blood cells obtained from patients with T2DM (n = 6) and age-, sex- , BMI- and blood pressure-matched obese individuals with MetS (n = 4) and lean healthy normoglycemic controls (n = 3), both under fasting conditions and after controlled induction of acute hyperglycemia during a 70 min hyperglycemic clamp. Differential gene expression during fasting conditions was confirmed by real-time PCR, for which we included additional age-, sex-, BMI-, and blood pressure-matched obese individuals with (n = 4) or without (n = 4) MetS.

RESULTS

Pathway and Gene ontology analysis applied to baseline expression profiles of peripheral blood cells from MetS and T2DM patients revealed metabolic changes, highly similar to a reoviral infection gene signature in T2DM patients. Transcription factor binding site analysis indicated that increased HIF-1α activity, a transcription factor induced by either hypoxia or oxidative stress, is responsible for this aberrant metabolic profile in peripheral blood cells from T2DM patients. Acute hyperglycemia in healthy controls resulted in reduced expression of cytotoxicity-related genes, representing NK- and CD8(+) cells. In obese controls, MetS and especially T2DM patients, baseline expression of genes involved in cytotoxicity was already low, compared to healthy controls and did not further decrease upon acute hyperglycemia.

CONCLUSIONS

The reduced activity of cytotoxic genes in T2DM is explained by chronic hyperglycemia, but its acute effects are restricted to healthy controls. Genome expression of circulating leukocytes from T2DM patients differs from MetS individuals by a specific reovirus signature. Our data thus suggest a role for suppressed anti-viral capacity in the etiology of diabetes.

Type 1 diabetes: A predictable disease

Type 1 diabetes (T1D) is an autoimmune disease characterized by loss of insulin producing beta cells and reliance on exogenous insulin for survival. T1D is one of the most common chronic diseases in childhood and the incidence is increasing, especially in children less than 5 years of age. In individuals with a genetic predisposition, an unidentified trigger initiates an abnormal immune response and the development of islet autoantibodies directed against proteins in insulin producing beta cells. There are currently four biochemical islet autoantibodies measured in the serum directed against insulin, glutamic decarboxylase, islet antigen 2, and zinc transporter 8. Development of islet autoantibodies occurs before clinical diagnosis of T1D, making T1D a predictable disease in an individual with 2 or more autoantibodies. Screening for islet autoantibodies is still predominantly done through research studies, but efforts are underway to screen the general population. The benefits of screening for islet autoantibodies include decreasing the incidence of diabetic ketoacidosis that can be life threatening, initiating insulin therapy sooner in the disease process, and evaluating safe and specific therapies in large randomized clinical intervention trials to delay or prevent progression to diabetes onset.

Viral infection of engrafted human islets leads to diabetes

Type 1 diabetes (T1D) is characterized by the destruction of the insulin-producing β-cells of pancreatic islets. Genetic and environmental factors both contribute to T1D development. Viral infection with enteroviruses is a suspected trigger for T1D, but a causal role remains unproven and controversial. Studies in animals are problematic because of species-specific differences in host cell susceptibility and immune responses to candidate viral pathogens such as coxsackievirus B (CVB). In order to resolve the controversial role of viruses in human T1D, we developed a viral infection model in immunodeficient mice bearing human islet grafts. Hyperglycemia was induced in mice by specific ablation of native β-cells. Human islets, which are naturally susceptible to CVB infection, were transplanted to restore normoglycemia. Transplanted mice were infected with CVB4 and monitored for hyperglycemia. Forty-seven percent of CVB4-infected mice developed hyperglycemia. Human islet grafts from infected mice contained viral RNA, expressed viral protein, and had reduced insulin levels compared with grafts from uninfected mice. Human-specific gene expression profiles in grafts from infected mice revealed the induction of multiple interferon-stimulated genes. Thus, human islets can become severely dysfunctional with diminished insulin production after CVB infection of β-cells, resulting in diabetes.

Enterovirus-infected β-cells induce distinct response patterns in BDCA1+ and BDCA3+ human dendritic cells

Enteroviruses often cause mild disease, yet are also linked to development of autoimmune diabetes. Dendritic cells (DCs) shape both innate and adaptive immune responses, including anti-viral responses. How different human DC subsets shape anti-viral responses, whether they have complementary or overlapping functions and how this relates to autoimmune responses is largely unknown. We used enterovirus-infected β-cells and freshly isolated human myeloid DC (mDC) subsets as a model for autoimmune type 1 diabetes. Our data show that both the BDCA1⁺ and BDCA3⁺ mDC subsets engulf mock- as well as virus-infected β-cells, albeit BDCA1⁺ mDCs are more efficient. Uptake of enterovirus-infected, but not mock-infected cells, activated both DC subsets as indicated by the induction of co-stimulatory molecules and secretion of type I and type III interferons. Both subsets produced similar amounts of interferon-α, yet the BDCA3⁺ DC were superior in IFN-λ production. The BDCA1⁺ mDCs more strongly upregulated PD-L1, and were superior in IL-12 and IL-10 production as compared to the BDCA3⁺ DC. Despite lack of IL-12 production by the BDCA3+ DC, both BDCA1⁺ and BDCA3⁺ DCs activated T cells in allogeneic mixed lymphocyte reaction towards a Th1-type reactivity while suppressing Th2-associated cytokines.

A preclinical study on the efficacy and safety of a new vaccine against Coxsackievirus B1 reveals no risk for accelerated diabetes development in mouse models

AIMS/HYPOTHESIS

Enterovirus infections have been implicated in the aetiology of autoimmune type 1 diabetes. A vaccine could be used to test the causal relationship between enterovirus infections and diabetes development. However, the development of a vaccine against a virus suspected to induce an autoimmune disease is challenging, since the vaccine itself might trigger autoimmunity. Another challenge is to select the enterovirus serotypes to target with a vaccine. Here we aimed to evaluate the function and autoimmune safety of a novel non-adjuvanted prototype vaccine to Coxsackievirus serotype B1 (CVB1), a member of the enterovirus genus.

METHODS

A formalin-inactivated CVB1 vaccine was developed and tested for its immunogenicity and safety in BALB/c and NOD mice. Prediabetic NOD mice were vaccinated, infected with CVB1 or mock-treated to compare the effect on diabetes development.

RESULTS

Vaccinated mice produced high titres of CVB1-neutralising antibodies without signs of vaccine-related side effects. Vaccinated mice challenged with CVB1 had significantly reduced levels of replicating virus in their blood and the pancreas. Prediabetic NOD mice demonstrated an accelerated onset of diabetes upon CVB1 infection whereas no accelerated disease manifestation or increased production of insulin autoantibodies was observed in vaccinated mice.

CONCLUSIONS/INTERPRETATION

We conclude that the prototype vaccine is safe and confers protection from infection without accelerating diabetes development in mice. These results encourage the development of a multivalent enterovirus vaccine for human use, which could be used to determine whether enterovirus infections trigger beta cell autoimmunity and type 1 diabetes in humans.

Islet inflammation in human type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM) is caused by the selective deletion of pancreatic β-cells in response to an assault mounted within the pancreas by infiltrating immune cells. However, this apparently clear and focussed annunciation conceals a stark reality in which the cellular and molecular events leading to β-cell loss remain poorly understood in humans. This reflects the difficulty of studying these processes in living individuals and the fact that, using pathological specimens, islet inflammation has been analysed in fewer than 200 recent-onset cases of T1DM worldwide, over the past century. Nevertheless, insights have been gained and the composition of the islet infiltrate is being disclosed. This is shown to be primarily lymphocytic in nature, with populations of both CD8+ and CD4+ T cells displaying an autoreactivity against specific islet antigenic peptides. The T cells are often accompanied by influent CD20+ B cells, although new data imply that the proportions of these individual cell types vary and that patients fall into at least two distinct categories having either a hyper-immune (CD20Hi) or a pauci-immune (CD20Lo) phenotype. The overall rate of β-cell decline appears to correlate with these two phenotypes such that hyper-immune patients lose β-cells more quickly and tend to develop disease at an earlier age than those with the pauci-immune profile. In this article, we review the evidence which underpins our current understanding of the aetiology of T1DM and highlight both the established features as well as areas of on-going ambiguity and debate.

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

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