Modulation of innate immunity in human pancreatic islets infected with enterovirus in vitro

Charting Peptide Shared Sequences Between 'Diabetes-Viruses' and Human Pancreatic Proteins, Their Structural and Autoimmune Implications

Diabetes mellitus (DM) is a metabolic syndrome characterized by hyperglycaemia, polydipsia, polyuria, and weight loss, among others. The pathophysiology for the disorders is complex and results in pancreatic abnormal function. Viruses have also been implicated in the metabolic syndrome. This study charted peptides to investigate and predict the autoimmune potential of shared sequences between 8 viral species proteins (which we termed 'diabetes-viruses') and the human pancreatic proteins. The structure and immunological relevance of shared sequences between viruses reported in DM onset and human pancreatic proteins were analysed. At nonapeptide mapping between human pancreatic protein and 'diabetic-viruses', reveal 1064 shared sequences distributed among 454 humans and 4288 viral protein sequences. The viral results showed herpesviruses, enterovirus (EV), human endogenous retrovirus, influenza A viruses, rotavirus, and rubivirus sequences are hosted by the human pancreatic protein. The most common shared nonapeptide was AAAAAAAAA, present in 30 human nonredundant sequences. Among the viral species, the shared sequence NSLEVLFQG occurred in 18 nonredundant EVs protein, while occurring merely in 1 human protein, whereas LGLDIEIAT occurred in 8 influenza A viruses overlapping to 1 human protein and KDELSEARE occurred in 2 rotaviruses. The prediction of the location of the shared sequences in the protein structures, showed most of the shared sequences are exposed and located either on the surface or cleft relative to the entire protein structure. Besides, the peptides in the viral protein shareome were predicted computationally for binding to MHC molecules. Here analyses showed that the entire 1064 shared sequences predicted 203 to be either HLA-A or B supertype-restricted epitopes. Fifty-one of the putative epitopes matched reported HLA ligands/T-cell epitopes majorly coming from EV B supertype representative allele restrictions. These data, shared sequences, and epitope charts provide important insight into the role of viruses on the onset of DM and its implications.

Functional Impact of Risk Gene Variants on the Autoimmune Responses in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease that develops in the interplay between genetic and environmental factors. A majority of individuals who develop T1D have a HLA make up, that accounts for 50% of the genetic risk of disease. Besides these HLA haplotypes and the insulin region that importantly contribute to the heritable component, genome-wide association studies have identified many polymorphisms in over 60 non-HLA gene regions that also contribute to T1D susceptibility.

Combining the risk genes in a score (T1D-GRS), significantly improved the prediction of disease progression in autoantibody positive individuals. Many of these minor-risk SNPs are associated with immune genes but how they influence the gene and protein expression and whether they cause functional changes on a cellular level remains a subject of investigation. A positive correlation between the genetic risk and the intensity of the peripheral autoimmune response was demonstrated both for HLA and non-HLA genetic risk variants. We also observed epigenetic and genetic modulation of several of these T1D susceptibility genes in dendritic cells (DCs) treated with vitamin D3 and dexamethasone to acquire tolerogenic properties as compared to immune activating DCs (mDC) illustrating the interaction between genes and environment that collectively determines risk for T1D. A notion that targeting such genes for therapeutic modulation could be compatible with correction of the impaired immune response, inspired us to review the current knowledge on the immune-related minor risk genes, their expression and function in immune cells, and how they may contribute to activation of autoreactive T cells, Treg function or β-cell apoptosis, thus contributing to development of the autoimmune disease.

Advances in Knowledge of Candidate Genes Acting at the Beta-Cell Level in the Pathogenesis of T1DM

T1DM (type 1 diabetes mellitus), which results from the irreversible elimination of beta-cells mediated by autoreactive T cells, is defined as an autoimmune disease. It is widely accepted that T1DM is caused by a combination of genetic and environmental factors, but the precise underlying molecular mechanisms are still unknown. To date, more than 50 genetic risk regions contributing to the pathogenesis of T1DM have been identified by GWAS (genome-wide association studies). Notably, more than 60% of the identified candidate genes are expressed in islets and beta-cells, which makes it plausible that these genes act at the beta-cell level and play a key role in the pathogenesis of T1DM. In this review, we focus on the current status of candidate genes that act at the beta-cell level by regulating the innate immune response and antiviral activity, affecting susceptibility to proapoptotic stimuli and influencing the pancreatic beta-cell phenotype.

Sex differences underlying pancreatic islet biology and its dysfunction

Background

The sex of an individual affects glucose homeostasis and the pathophysiology, incidence, and prevalence of diabetes as well as the response to therapy.

Scope of the review

This review focuses on clinical and experimental sex differences in islet cell biology and dysfunction during development and in adulthood in human and animal models. We discuss sex differences in β-cell and α-cell function, heterogeneity, and dysfunction. We cover sex differences in communication between gonads and islets and islet-cell immune interactions. Finally, we discuss sex differences in β-cell programming by nutrition and other environmental factors during pregnancy.

Major conclusions

Important sex differences exist in islet cell function and susceptibility to failure. These differences represent sex-related biological factors that can be harnessed for gender-based prevention of and therapy for diabetes.

Pyroptosis induced by enterovirus 71 and coxsackievirus B3 infection affects viral replication and host response

Enterovirus 71 (EV71) is the primary causative pathogen of hand, foot, and mouth disease (HFMD), affecting children with severe neurological complications. Pyroptosis is a programmed cell death characterized by cell lysis and inflammatory response. Although proinflammatory response has been implicated to play important roles in EV71-caused diseases, the involvement of pyroptosis in the pathogenesis of EV71 is poorly defined. We show that EV71 infection induced caspase-1 activation. Responding to the activation of caspase-1, the expression and secretion of both IL-1β and IL-18 were increased in EV71-infected cells. The treatment of caspase-1 inhibitor markedly improved the systemic response of the EV71-infected mice. Importantly, caspase-1 inhibitor suppressed EV71 replication in mouse brains. Similarly, pyroptosis was activated by the infection of coxsackievirus B3 (CVB3), an important member of the Enterovirus genus. Caspase-1 activation and the increased expression of IL-18 and NLRP3 were demonstrated in HeLa cells infected with CVB3. Caspase-1 inhibitor also alleviated the overall conditions of virus-infected mice with markedly decreased replication of CVB3 and reduced expression of caspase-1. These results indicate that pyroptosis is involved in the pathogenesis of both EV71 and CVB3 infections, and the treatment of caspase-1 inhibitor is beneficial to the host response during enterovirus infection.

Type 1 Diabetes Candidate Genes Linked to Pancreatic Islet Cell Inflammation and Beta-Cell Apoptosis

Type 1 diabetes (T1D) is a chronic immune-mediated disease resulting from the selective destruction of the insulin-producing pancreatic islet β-cells. Susceptibility to the disease is the result of complex interactions between environmental and genetic risk factors. Genome-wide association studies (GWAS) have identified more than 50 genetic regions that affect the risk of developing T1D. Most of these susceptibility loci, however, harbor several genes, and the causal variant(s) and gene(s) for most of the loci remain to be established. A significant part of the genes located in the T1D susceptibility loci are expressed in human islets and β cells and mounting evidence suggests that some of these genes modulate the β-cell response to the immune system and viral infection and regulate apoptotic β-cell death. Here, we discuss the current status of T1D susceptibility loci and candidate genes with focus on pancreatic islet cell inflammation and β-cell apoptosis.

Expression of Interferon-Stimulated Genes in Insulitic Pancreatic Islets of Patients Recently Diagnosed With Type 1 Diabetes

A primary insult to the pancreatic islets of Langerhans, leading to the activation of innate immunity, has been suggested as an important step in the inflammatory process in type 1 diabetes (T1D). The aim of this study was to examine whether interferon (IFN)-stimulated genes (ISGs) are overexpressed in human T1D islets affected with insulitis. By using laser capture microdissection and a quantitative PCR array, 23 of 84 examined ISGs were found to be overexpressed by at least fivefold in insulitic islets from living patients with recent-onset T1D, participating in the Diabetes Virus Detection (DiViD) study, compared with islets from organ donors without diabetes. Most of the overexpressed ISGs, including GBP1, TLR3, OAS1, EIF2AK2, HLA-E, IFI6, and STAT1, showed higher expression in the islet core compared with the peri-islet area containing the surrounding immune cells. In contrast, the T-cell attractant chemokine CXCL10 showed an almost 10-fold higher expression in the peri-islet area than in the islet, possibly partly explaining the localization of T cells mainly to this region. In conclusion, insulitic islets from recent-onset T1D subjects show overexpression of ISGs, with an expression pattern similar to that seen in islets infected with virus or exposed to IFN-γ/interleukin-1β or IFN-α.

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.

Genes affecting β-cell function in type 1 diabetes

Type 1 diabetes (T1D) is a multifactorial disease resulting from an immune-mediated destruction of the insulin-producing pancreatic β cells. Several environmental and genetic risk factors predispose to the disease. Genome-wide association studies (GWAS) have identified around 50 genetic regions that affect the risk of developing T1D, but the disease-causing variants and genes are still largely unknown. In this review, we discuss the current status of T1D susceptibility loci and candidate genes with focus on the β cell. At least 40 % of the genes in the T1D susceptibility loci are expressed in human islets and β cells, where they according to recent studies modulate the β-cell response to the immune system. As most of the risk variants map to noncoding regions of the genome, i.e., promoters, enhancers, intergenic regions, and noncoding genes, their possible involvement in T1D pathogenesis as gene regulators will also be addressed.

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.

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.

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

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

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.

Evaluation of the fidelity of immunolabelling obtained with clone 5D8/1, a monoclonal antibody directed against the enteroviral capsid protein, VP1, in human pancreas

AIMS/HYPOTHESIS

Enteroviral infection has been implicated in the development of islet autoimmunity in type 1 diabetes and enteroviral antigen expression has been detected by immunohistochemistry in the pancreatic beta cells of patients with recent-onset type 1 diabetes. However, the immunohistochemical evidence relies heavily on the use of a monoclonal antibody, clone 5D8/1, raised against an enteroviral capsid protein, VP1. Recent data suggest that the clone 5D8/1 may also recognise non-viral antigens; in particular, a component of the mitochondrial ATP synthase (ATP5B) and an isoform of creatine kinase (CKB). Therefore, we evaluated the fidelity of immunolabelling by clone 5D8/1 in the islets of patients with type 1 diabetes.

METHODS

Enteroviral VP1, CKB and ATP5B expression were analysed by western blotting, RT-PCR and immunocytochemistry in a range of cultured cell lines, isolated human islets and human tissue.

RESULTS

Clone 5D8/1 labelled CKB, but not ATP5B, on western blots performed under denaturing conditions. In cultured human cell lines, isolated human islets and pancreas sections from patients with type 1 diabetes, the immunolabelling of ATP5B, CKB and VP1 by 5D8/1 was readily distinguishable. Moreover, in a human tissue microarray displaying more than 80 different cells and tissues, only two (stomach and colon; both of which are potential sites of enterovirus infection) were immunopositive when stained with clone 5D8/1.

CONCLUSIONS/INTERPRETATION

When used under carefully optimised conditions, the immunolabelling pattern detected in sections of human pancreas with clone 5D8/1 did not reflect cross-reactivity with either ATP5B or CKB. Rather, 5D8/1 is likely to be representative of enteroviral antigen expression.

CXCR3, CXCL10 and type 1 diabetes

Type 1 diabetes (T1D) is due to antigen-specific assaults on the insulin producing pancreatic β-cells by diabetogenic T-helper (Th)1 cells. (C-X-C motif) ligand (CXCL)10, an interferon-γ inducible Th1 chemokine, and its receptor, (C-X-C motif) receptor (CXCR)3, have an important role in different autoimmune diseases. High circulating CXCL10 levels were detected in new onset T1D patients, in association with a Th1 autoimmune response. Furthermore β-cells produce CXCL10, under the influence of Th1 cytokines, that suppresses their proliferation. Viral β-cells infections induce cytokines and CXCL10 expression, inducing insulin-producing cell failure in T1D. CXCL10/CXCR3 system plays a critical role in the autoimmune process and in β-cells destruction in T1D. Blocking CXCL10 in new onset diabetes seems a possible approach for T1D treatment.

High Risk First Degree Relatives of Type 1 Diabetics: An Association with Increases in CXCR3(+) T Memory Cells Reflecting an Enhanced Activity of Th1 Autoimmune Response

We analyzed the level of (a) CXCR3(+) (Th1) and CCR4(+) (Th2) T memory cells (b) interferon- γ inducible chemokine (IP-10)(Th1) and thymus and activation-regulated chemokine (TARC)(Th2), in 51 first degree relatives (FDRs) of type 1 diabetics (T1D) (17 high risk FDRs (GADA(+), IA-2(+)) and 34 low risk FDRs (GADA(-), IA-2(-))), 24 recent-onset T1D (R-T1D), and 18 healthy subjects. T memory subsets were analyzed by using four-color immunofluorescence staining and flowcytometry. IP-10 and TARC were determined by ELISA. High risk FDRs showed higher levels of CXCR3(+) and lower level of CCR4(+) T memory cells compared to low risk FDRs (64.98 ± 5.19 versus 42.13 ± 11.11; 29.46 ± 2.83 versus 41.90 ± 8.58%, resp., P < 0.001). Simultaneously, both IP-10 and TARC levels were increased in high risk versus low risk FDRs (160.12 ± 73.40 versus 105.39 ± 71.30; 438.83 ± 120.62 versus 312.04 ± 151.14 pg/mL, P < 0.05). Binary logistic regression analysis identified the level of CXCR3(+) T memory cells as predictors for high risk FDRs, together with high levels of IP-10. The results imply that, in FDRs, the risk for T1D might be strongly influenced by enhanced activity of Th1 and diminished activity of Th2 autoimmune response.

Expression of innate immunity genes and damage of primary human pancreatic islets by epidemic strains of Echovirus: implication for post-virus islet autoimmunity

Three large-scale Echovirus (E) epidemics (E4,E16,E30), each differently associated to the acute development of diabetes related autoantibodies, have been documented in Cuba. The prevalence of islet cell autoantibodies was moderate during the E4 epidemic but high in the E16 and E30 epidemic. The aim of this study was to evaluate the effect of epidemic strains of echovirus on beta-cell lysis, beta-cell function and innate immunity gene expression in primary human pancreatic islets. Human islets from non-diabetic donors (n = 7) were infected with the virus strains E4, E16 and E30, all isolated from patients with aseptic meningitis who seroconverted to islet cell antibody positivity. Viral replication, degree of cytolysis, insulin release in response to high glucose as well as mRNA expression of innate immunity genes (IFN-b, RANTES, RIG-I, MDA5, TLR3 and OAS) were measured. The strains of E16 and E30 did replicate well in all islets examined, resulting in marked cytotoxic effects. E4 did not cause any effects on cell lysis, however it was able to replicate in 2 out of 7 islet donors. Beta-cell function was hampered in all infected islets (P<0.05); however the effect of E16 and E30 on insulin secretion appeared to be higher than the strain of E4. TLR3 and IFN-beta mRNA expression increased significantly following infection with E16 and E30 (P<0.033 and P<0.039 respectively). In contrast, the expression of none of the innate immunity genes studied was altered in E4-infected islets. These findings suggest that the extent of the epidemic-associated islet autoimmunity may depend on the ability of the viral strains to damage islet cells and induce pro-inflammatory innate immune responses within the infected islets.

Candidate genes expressed in human islets and their role in the pathogenesis of type 1 diabetes

In type 1 diabetes (T1D), the insulin-producing β cells are destroyed by an immune-mediated process leading to complete insulin deficiency. There is a strong genetic component in T1D. Genes located in the human leukocyte antigen (HLA) region are the most important genetic determinants of disease, but more than 40 additional loci are known to significantly affect T1D risk. Since most of the currently known genetic candidates have annotated immune cell functions, it is generally considered that most of the genetic susceptibility in T1D is caused by variation in genes affecting immune cell function. Recent studies, however, indicate that most T1D candidate genes are expressed in human islets suggesting that the functions of the genes are not restricted to immune cells, but also play roles in the islets and possibly the β cells. Several candidates change expression levels within the islets following exposure to proinflammatory cytokines highlighting that these genes may be involved in the response of β cells to immune attack. In this review, the compiling evidence that many of the candidate genes are expressed in islets and β cells will be presented. Further, we perform the first systematic human islet expression analysis of all genes located in 50 T1D-associated GWAS loci using a published RNA sequencing dataset. We find that 336 out of 857 genes are expressed in human islets and that many of these interact in protein networks. Finally, the potential pathogenetic roles of some candidate genes will be discussed.

Candidate genes for type 1 diabetes modulate pancreatic islet inflammation and β-cell apoptosis

Genome-wide association studies (GWAS) have identified more than 50 loci associated with genetic risk of type 1 diabetes (T1D). Several T1D candidate genes have been suggested or identified within these regions, but the molecular mechanisms by which they contribute to insulitis and β-cell destruction remain to be clarified. More than 60% of the T1D candidate genes are expressed in human pancreatic islets, suggesting that they contribute to T1D by regulating at least in part pathogenic mechanisms at the β-cell level. Recent studies by our group indicate that important genetically regulated pathways in β-cells include innate immunity and antiviral activity, involving RIG-like receptors (particularly MDA5) and regulators of type I IFNs (i.e. PTPN2 and USP18), and genes related to β-cell phenotype and susceptibility to pro-apoptotic stimuli (i.e. GLIS3). These observations reinforce the concept that the early pathogenesis of T1D is characterized by a dialogue between the immune system and pancreatic β-cells. This dialogue is probably influenced by polymorphisms in genes expressed at the β-cell and/or immune system level, leading to inadequate responses to environmental cues such as viral infections. Further studies are needed to clarify how these disease-associated variants affect pancreatic β-cell responses to inflammation and the subsequent triggering of autoimmune responses and progressive β-cell loss.

The case for virus-induced type 1 diabetes

PURPOSE OF REVIEW

Type 1 diabetes (T1D) results from the immune-mediated destruction of pancreatic insulin-producing cells because of the interaction among genetic susceptibility, the immune system and environmental factor(s). A possible role of viral infections in T1D pathogenesis has been hypothesized for some time; however, only in the most recent years, studies performed at the molecular and cellular level are starting to shed light on this issue.

RECENT FINDINGS

Studies in animal models and in man have shown that viruses can indeed infect pancreatic beta-cells, inducing islet inflammation and functional damage. In addition, recent in-situ investigations performed on pancreatic tissue samples have provided evidence that in addition to adaptive immune response, innate immunity is involved in T1D pathogenesis and the whole pancreas (not only its endocrine portion) is infiltrated by immune-mediated phenomena.

SUMMARY

The established role of inflammation in the insulitic process and the increasing evidence in support of the contribution of viral infections to a proinflammatory islet scenario are strongly suggestive that viruses may indeed contribute to beta-cell damage and dysfunction, thus setting the stage for the design of antiviral strategies (e.g. vaccines and antiviral drugs) aimed at protecting the beta-cells.

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.

Differential susceptibility and response of primary human myeloid BDCA1(+) dendritic cells to infection with different Enteroviruses

Coxsackie B viruses (CVBs) and echoviruses (EVs) form the Human Enterovirus-B (HEV-B) species within the family Picornaviridae. HEV-B infections are widespread and generally cause mild disease; however, severe infections occur and HEV-B are associated with various chronic diseases such as cardiomyopathy and type 1 diabetes. Dendritic cells (DCs) are the professional antigen-presenting cells of our immune system and initiate and control immune responses to invading pathogens, yet also maintain tolerance to self-antigens. We previously reported that EVs, but not CVBs, can productively infect in vitro generated monocyte-derived DCs. The interactions between HEV-B and human myeloid DCs (mDCs) freshly isolated from blood, however, remain unknown. Here, we studied the susceptibility and responses of BDCA1(+) mDC to HEV-B species and found that these mDC are susceptible to EV, but not CVB infection. Productive EV7 infection resulted in massive, rapid cell death without DC activation. Contrary, EV1 infection, which resulted in lower virus input at the same MOI, resulted in DC activation as observed by production of type I interferon-stimulated genes (ISGs), upregulation of co-stimulatory and co-inhibitory molecules (CD80, CD86, PDL1) and production of IL-6 and TNF-α, with a relative moderate decrease in cell viability. EV1-induced ISG expression depended on virus replication. CVB infection did not affect DC viability and resulted in poor induction of ISGs and CD80 induction in part of the donors. These data show for the first time the interaction between HEV-B species and BDCA1(+) mDCs isolated freshly from blood. Our data indicate that different HEV-B species can influence DC homeostasis in various ways, possibly contributing to HEV-B associated pathology.

Enterovirus-induced gene expression profile is critical for human pancreatic islet destruction

AIMS/HYPOTHESIS

Virally induced inflammatory responses, beta cell destruction and release of beta cell autoantigens may lead to autoimmune reactions culminating in type 1 diabetes. Therefore, viral capability to induce beta cell death and the nature of virus-induced immune responses are among key determinants of diabetogenic viruses. We hypothesised that enterovirus infection induces a specific gene expression pattern that results in islet destruction and that such a host response pattern is not shared among all enterovirus infections but varies between virus strains.

METHODS

The changes in global gene expression and secreted cytokine profiles induced by lytic or benign enterovirus infections were studied in primary human pancreatic islet using DNA microarrays and viral strains either isolated at the clinical onset of type 1 diabetes or capable of causing a diabetes-like condition in mice.

RESULTS

The expression of pro-inflammatory cytokine genes (IL-1-α, IL-1-β and TNF-α) that also mediate cytokine-induced beta cell dysfunction correlated with the lytic potential of a virus. Temporally increasing gene expression levels of double-stranded RNA recognition receptors, antiviral molecules, cytokines and chemokines were detected for all studied virus strains. Lytic coxsackievirus B5 (CBV-5)-DS infection also downregulated genes involved in glycolysis and insulin secretion.

CONCLUSIONS/INTERPRETATION

The results suggest a distinct, virus-strain-specific, gene expression pattern leading to pancreatic islet destruction and pro-inflammatory effects after enterovirus infection. However, neither viral replication nor cytotoxic cytokine production alone are sufficient to induce necrotic cell death. More likely the combined effect of these and possibly cellular energy depletion lie behind the enterovirus-induced necrosis of islets.

Cytokine and chemokine production by human pancreatic islets upon enterovirus infection

Enteroviruses of the human enterovirus B species (HEV-Bs) (e.g., coxsackie B viruses [CVBs] and echoviruses) have been implicated as environmental factors that trigger/accelerate type 1 diabetes, but the underlying mechanism remains elusive. The aim of this study was to gain insight into the cytokines and chemokines that are produced by human pancreatic islets upon infection with CVBs. To this end, we studied the response of human islets of Langerhans upon mock or CVB3 infection. Using quantitative PCR, we showed that upon CVB3 infection, transcription of interferon (IFN), IFN-stimulated genes, and inflammatory genes was induced. Analysis of secreted cytokines and chemokines by Luminex technology confirmed production and secretion of proinflammatory cytokines (e.g., interleukin [IL]-6 and tumor necrosis factor-α) as well as various chemotactic proteins, such as IFN-γ-induced protein 10, macrophage inflammatory protein (MIP)-1α, MIP-1β, and IL-8. Infection with other HEV-Bs induced similar responses, yet their extent depended on replication efficiency. Ultra violet-inactivated CVB3 did not induce any response, suggesting that virus replication is a prerequisite for antiviral responses. Our data represent the first comprehensive overview of inflammatory mediators that are secreted by human islets of Langerhans upon CVB infection and may shed light on the role of enteroviruses in type 1 diabetes pathogenesis.