Diabetes induced by Coxsackie virus: initiation by bystander damage and not molecular mimicry

Increased immune cell infiltration of the exocrine pancreas: a possible contribution to the pathogenesis of type 1 diabetes

Type 1 diabetes (T1D) results from a complex interplay between genetic susceptibility and environmental factors that have been implicated in the pathogenesis of disease both as triggers and potentiators of β-cell destruction. CD8 T cells are the main cell type found in human islets, and they have been shown in vitro to be capable of killing β-cells overexpressing MHC class I. In this study, we report that CD8 T cells infiltrate the exocrine pancreas of diabetic subjects in high numbers and not only endocrine areas. T1D subjects present significantly higher CD8 T cell density in the exocrine tissue without the presence of prominent insulitis. Even T1D donors without remaining insulin-containing islets and long disease duration show elevated levels of CD8 T cells in the exocrine compartment. In addition, higher numbers of CD4(+) and CD11c(+) cells were found in the exocrine tissue. Preliminary data in type 2 diabetic (T2D) subjects indicate that overall, there might be a spontaneous inflammatory infiltration of the exocrine tissue, common to both T1D and T2D subjects. Our study provides the first information on the precise tissue distribution of CD8 T cells in pancreata from T1D, T2D, autoantibody-positive, and healthy control subjects.

Bacterial peptides are intensively present throughout the human proteome

Forty bacterial proteomes-20 pathogens and 20 non-pathogens-were examined for amino acid sequence similarity to the human proteome. All bacterial proteomes, independent of their pathogenicity, share hundreds of nonamer sequences with the human proteome. This overlap is very widespread, with one third of human proteins sharing at least one nonapeptide with one of these bacteria. On the whole, the bacteria-versus-human nonamer overlap is numerically defined by 47,610 total perfect matches disseminated through 10,701 human proteins. These findings open new perspectives on the immune relationship between bacteria and host, and might help our understanding of fundamental phenomena such as self-nonself discrimination and tolerance versus auto-reactivity.

Death waits for no man--does it wait for a virus? How enteroviruses induce and control cell death

Enteroviruses (EVs) are the most common human viral pathogens. They cause a variety of pathologies, including myocarditis and meningoencephalopathies, and have been linked to the onset of type I diabetes. These pathologies result from the death of cells in the myocardium, central nervous system, and pancreas, respectively. Understanding the role of EVs in inducing cell death is crucial to understanding the etiologies of these diverse pathologies. EVs both induce and delay host cell death, and their exquisite control of this balance is crucial for their success as human viral pathogens. Thus, EVs are tightly involved with cell death signaling pathways and interact with host cell signaling at multiple points. Here, we review the literature detailing the mechanisms of EV-induced cell death. We discuss the mechanisms by which EVs induce cell death, the signaling pathways involved in these pathways, and the strategies by which EVs antagonize cell death pathways. We also discuss the role of cell death in both the resulting pathology in the host and in the facilitation of viral spread.

The impact of juvenile coxsackievirus infection on cardiac progenitor cells and postnatal heart development

Coxsackievirus B (CVB) is an enterovirus that most commonly causes a self-limited febrile illness in infants, but cases of severe infection can manifest in acute myocarditis. Chronic consequences of mild CVB infection are unknown, though there is an epidemiologic association between early subclinical infections and late heart failure, raising the possibility of subtle damage leading to late-onset dysfunction, or chronic ongoing injury due to inflammatory reactions during latent infection. Here we describe a mouse model of juvenile infection with a subclinical dose of coxsackievirus B3 (CVB3) which showed no evident symptoms, either immediately following infection or in adult mice. However following physiological or pharmacologically-induced cardiac stress, juvenile-infected adult mice underwent cardiac hypertrophy and dilation indicative of progression to heart failure. Evaluation of the vasculature in the hearts of adult mice subjected to cardiac stress showed a compensatory increase in CD31⁺ blood vessel formation, although this effect was suppressed in juvenile-infected mice. Moreover, CVB3 efficiently infected juvenile c-kit⁺ cells, and cardiac progenitor cell numbers were reduced in the hearts of juvenile-infected adult mice. These results suggest that the exhausted cardiac progenitor cell pool following juvenile CVB3 infection may impair the heart's ability to increase capillary density to adapt to increased load.

Coxsackievirus B (CVB) is a significant human pathogen, causing myocarditis, aseptic meningitis and encephalitis. The lasting consequences of juvenile CVB infection on the developing host have yet to be adequately inspected. Here, we show that CVB efficiently infected juvenile cardiac progenitor cells both in culture and the young heart. Furthermore, we describe a mouse model of juvenile infection with a subclinical dose of CVB which showed no symptoms of disease into adulthood. However following physiological or pharmacologically-induced cardiac stress, juvenile-infected mice underwent cardiac hypertrophy and dilation indicative of progression to heart failure. These results suggest that mild CVB infection in the young host may impair the ability of the heart to adapt to increased load leading to pathological remodeling later in adult life.

Narcolepsy as an autoimmune disease: the role of H1N1 infection and vaccination

Narcolepsy is a sleep disorder characterised by loss of hypothalamic hypocretin (orexin) neurons. The prevalence of narcolepsy is about 30 per 100 000 people, and typical age at onset is 12-16 years. Narcolepsy is strongly associated with the HLA-DQB1*06:02 genotype, and has been thought of as an immune-mediated disease. Other risk genes, such as T-cell-receptor α chain and purinergic receptor subtype 2Y11, are also implicated. Interest in narcolepsy has increased since the epidemiological observations that H1N1 infection and vaccination are potential triggering factors, and an increase in the incidence of narcolepsy after the pandemic AS03 adjuvanted H1N1 vaccination in 2010 from Sweden and Finland supports the immune-mediated pathogenesis. Epidemiological observations from studies in China also suggest a role for H1N1 virus infections as a trigger for narcolepsy. Although the pathological mechanisms are unknown, an H1N1 virus-derived antigen might be the trigger.

Developing a vaccine for Type 1 diabetes through targeting enteroviral infections

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

Apoptotic cell capture by DCs induces unexpectedly robust autologous CD4+ T-cell responses

Apoptotic cells represent an important source of self-antigens and their engulfment by dendritic cells (DCs) is usually considered to be related to tolerance induction. We report here an unexpectedly high level of human CD4(+) T-cell proliferation induced by autologous DCs loaded with autologous apoptotic cells, due to the activation of more than 10% of naive CD4(+) T cells. This proliferation is not due to an increase in the costimulatory capacity of DCs, but is dependent on apoptotic cell-associated material processed through an endo-lysosomal pathway and presented on DC MHC class II molecules. Autologous CD4(+) T cells stimulated with apoptotic cell-loaded DCs exhibit suppressive capacities. However, in the presence of bacterial lipopolysaccharide, apoptotic cell-loaded DCs induce the generation of IL-17-producing cells. Thus, apoptotic cell engulfment by DCs may lead to increased autologous responses, initially generating CD4(+) T cells with suppressive capacities able to differentiate into Th17 cells in the presence of a bacterial danger signal such as LPS.

Pathogen infection as a possible cause for autoimmune hepatitis

Autoimmune disorders afflicting the liver comprise the bona fide autoimmune diseases, primary biliary cirrhosis, primary sclerosing cholangitis, and autoimmune hepatitis as well as drug-induced autoimmune-like diseases, such as halothane hepatitis. Whereas drug-induced forms of acute or chronic hepatitis often have a clear triggering factor, the etiology of classical autoimmune liver diseases is only poorly understood. Besides a genetic component present in disease susceptible individuals, environmental triggering factors are likely to play a role in the initiation and/or propagation of the disease. In this article, we will review on current evidence obtained from epidemiological associations, case studies, and findings in animal models for pathogens, to be involved in the etiology of autoimmune liver disease with a special focus on autoimmune hepatitis.

Exploration of panviral proteome: high-throughput cloning and functional implications in virus-host interactions

Throughout the long history of virus-host co-evolution, viruses have developed delicate strategies to facilitate their invasion and replication of their genome, while silencing the host immune responses through various mechanisms. The systematic characterization of viral protein-host interactions would yield invaluable information in the understanding of viral invasion/evasion, diagnosis and therapeutic treatment of a viral infection, and mechanisms of host biology. With more than 2,000 viral genomes sequenced, only a small percent of them are well investigated. The access of these viral open reading frames (ORFs) in a flexible cloning format would greatly facilitate both in vitro and in vivo virus-host interaction studies. However, the overall progress of viral ORF cloning has been slow. To facilitate viral studies, we are releasing the initiation of our panviral proteome collection of 2,035 ORF clones from 830 viral genes in the Gateway® recombinational cloning system. Here, we demonstrate several uses of our viral collection including highly efficient production of viral proteins using human cell-free expression system in vitro, global identification of host targets for rubella virus using Nucleic Acid Programmable Protein Arrays (NAPPA) containing 10,000 unique human proteins, and detection of host serological responses using micro-fluidic multiplexed immunoassays. The studies presented here begin to elucidate host-viral protein interactions with our systemic utilization of viral ORFs, high-throughput cloning, and proteomic technologies. These valuable plasmid resources will be available to the research community to enable continued viral functional studies.

Antiviral Activity of Total Flavonoid Extracts from Selaginella moellendorffii Hieron against Coxsackie Virus B3 In Vitro and In Vivo

The antiviral activity of total flavonoid extracts from Selaginella moellendorffii Hieron and its main constituents amentoflavone were investigated against coxsackie virus B3 (CVB3). When added during or after viral infection, the extracts and amentoflavone prevented the cytopathic effect (CPE) of CVB3, as demonstrated in a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay, with a 50% inhibitory concentration (IC50) from 19 ± 1.6 to 41 ± 1.2 μg/mL and 25 ± 1.2 to 52 ± 0.8 μg/mL, respectively. KM mice were used as animal models to test the extracts' activity in vivo. Oral administration of the total flavonoid extracts at 300 mg/kg/day significantly reduced mean viral titers in the heart and kidneys as well as mortality after infection for 15 days. The experimental results demonstrate that in vitro and in vivo the model mice infected with CVB3 can be effectively treated by the total flavonoid extracts from Selaginella moellendorffii Hieron.

Beta-cell specific production of IL6 in conjunction with a mainly intracellular but not mainly surface viral protein causes diabetes

Inflammatory mechanisms play a key role in the pathogenesis of type 1 and type 2 diabetes. IL6, a pleiotropic cytokine with impact on immune and non-immune cell types, has been proposed to be involved in the events causing both forms of diabetes and to play a key role in experimental insulin-dependent diabetes development. The aim of this study was to investigate how beta-cell specific overexpression of IL-6 influences diabetes development. We developed two lines of rat insulin promoter (RIP)-lymphocytic choriomeningitis virus (LCMV) mice that also co-express IL6 in their beta-cells. Expression of the viral nucleoprotein (NP), which has a predominantly intracellular localization, together with IL6 led to hyperglycemia, which was associated with a loss of GLUT-2 expression in the pancreatic beta-cells and infiltration of CD11b(+) cells, but not T cells, in the pancreas. In contrast, overexpression of the LCMV glycoprotein (GP), which can localize to the surface, with IL-6 did not lead to spontaneous diabetes, but accelerated virus-induced diabetes by increasing autoantigen-specific CD8(+) T cell responses and reducing the regulatory T cell fraction, leading to increased pancreatic infiltration by CD4(+) and CD8(+) T cells as well as CD11b(+) and CD11c(+) cells. The production of IL-6 in beta-cells acts prodiabetic, underscoring the potential benefit of targeting IL6 in diabetes.

The good and the bad of neuroinflammation in multiple sclerosis

Multiple sclerosis (MS) is the most common inflammatory, demyelinating, neurodegenerative disorder of the central nervous system (CNS). It is widely considered a T-cell mediated autoimmune disease that develops in genetically susceptible individuals, possibly under the influence of certain environmental trigger factors. The invasion of autoreactive CD4+ T-cells into the CNS is thought to be a central step that initiates the disease. Several other cell types, including CD8+ T-cells, B-cells and phagocytes appear to be involved in causing inflammation and eventually neurodegeneration. But inflammation is not entirely deleterious in MS. Evidence has accumulated in the recent years that show the importance of regulatory immune mechanisms which restrain tissue damage and initiate regeneration. More insight into the beneficial aspects of neuroinflammation might allow us to develop new treatment strategies for this enigmatic disease.

Demyelination in multiple sclerosis

This review, focused on demyelination in multiple sclerosis, is divided in two parts. The first part addresses the many and not exclusive mechanisms leading to demyelination in the central nervous system. Although the hypothesis that a primary oligodendrocyte or myelin injury induces a secondary immune response in the central nervous system is still a matter of debate, most recent advances underline the influence of a primary immune response against myelin antigen(s), with a diversity of potential targets. Whereas multiple sclerosis was long considered as a T cell-mediated disease, the role of B lymphocytes is now increasingly recognized, and the influence of antibodies on tissue damage actively investigated. The second part of the review describes the axonal consequences of demyelination. Segmental demyelination results in conduction block or slowing of conduction through adaptative responses, notably related to modifications in the distribution of voltage gated sodium channels along the denuded axon. If demyelination persists, these changes, as well as the loss of trophic and metabolic support, will lead to irreversible axonal damage and loss. In this respect, favouring early myelin repair, during a window of time when axonal damage is still reversible, might pave the way for neuroprotection.

Effects of Tacrolimus (FK506) on Encephalomyocarditic Virus-Induced Diabetes in Mice

The effects of tacrolimus on insulin-dependent diabetes mellitus (IDDM) induced by the D-variant of encephalomyocarditis virus (D-EMCV) have been investigated. Male BALB/c mice were treated with tacrolimus before viral inoculation, and then were inoculated with 10 plaque forming units (PFU) of DEMCV. The mice continued to be treated with tacrolimus until the animals were sacrificed. D-EMCV-infected mice, which were treated with saline as controls, showed abnormal glucose tolerance test (GTT) values, whereas all infected mice with tacrolimus pretreatment were normal on 7 days-post inoculation (DPI). Histological observations revealed that non-treated tacrolimus D-EMCV-infected mice and which developed diabetes showed severe insulitis in their islets of Langerhans. On the other hand, D-EMCV-infected mice treated with tacrolimus were normal. In D-EMCV-infected mice, viruses in the pancreata were detected at the same level regardless of treatment with tacrolimus or saline. Expressions of TNF-alpha and IFN-gamma mRNA in spleens of tacrolimus-treated D-EMCV-infected mice were lower than that of non-treated tacrolimus DEMCV-infected mice on 7 DPI. The results suggest that tacrolimus suppresses expressions of TNF-alpha and IFN-gamma mRNAs to prevent the onset of D-EMCV-induced IDDM.

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

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

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.

APECED: A Paradigm of Complex Interactions between Genetic Background and Susceptibility Factors

Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare autosomal recessive disease, caused by mutations of a single gene named Autoimmune regulator gene (AIRE) which results in a failure of T-cell tolerance. Central tolerance takes place within the thymus and represents the mechanism by which potentially auto-reactive T-cells are eliminated through the negative selection process. The expression of tissue-specific antigens (TSAs) by medullary thymic epithelial cells (mTECs) in the thymus is a key process in the central tolerance and is driven by the protein encoded by AIRE gene, the transcription factor autoimmune regulator (AIRE). A failure in this process caused by AIRE mutations is thought to be responsible of the systemic autoimmune reactions of APECED. APECED is characterized by several autoimmune endocrine and non-endocrine manifestations and the phenotype is often complex. Although APECED is the paradigm of a monogenic autoimmune disorder, it is characterized by a wide variability of the clinical expression even between siblings with the same genotype, thus implying that additional mechanisms, other than the failure of Aire function, are involved in the pathogenesis of the disease. Unraveling open issues of the molecular basis of APECED, will help improve diagnosis, management, and therapeutical strategies of this complex disease.

Infectious triggers in type 1 diabetes: is there a case for epitope mimicry?

Environmental factors are the main contributors to type 1 diabetes (T1D) pathogenesis, yet they remain unidentified. Enteroviruses are proposed candidate triggers due to temporal correlations between infection and T1D autoimmunity and to detection of viral proteins in diseased islets. However, such correlations are not universal and may be relatively uncommon. Furthermore, evidence of a cause-effect relationship is lacking, as infection of non-obese diabetic mice with Coxsackie enteroviruses can either trigger or blunt disease. The proposed mechanisms are either non-antigen-specific (i.e. β-cell destruction and release of sequestered antigens, islet inflammation) or antigen-specific (i.e. epitope mimicry, by which immune responses to enteroviruses may be diverted against homologous β-cell antigens). The case for the latter mechanisms is even less stringent, as there is little evidence of promiscuous antigen recognition at the single T-cell level. Other infectious agents may thus be implicated. Demonstration of their role will require fulfilling the Koch's postulates, namely isolation of the agent preferentially in T1D patients, including before disease onset; and T1D induction when the agent is inoculated into mice. The same is needed for cross-reactive T cells to support epitope mimicry mechanisms. Generation of alternative (humanized) mouse models that could be challenged with candidate microbes is needed.

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

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

Virus infections in type 1 diabetes

The precise etiology of type 1 diabetes (T1D) is still unknown, but viruses have long been suggested as a potential environmental trigger for the disease. However, despite decades of research, the body of evidence supporting a relationship between viral infections and initiation or acceleration of islet autoimmunity remains largely circumstantial. The most robust association with viruses and T1D involves enterovirus species, of which some strains have the ability to induce or accelerate disease in animal models. Several hypotheses have been formulated to mechanistically explain how viruses may affect islet autoimmunity and β-cell decay. The recent observation that certain viral infections, when encountered at the right time and infectious dose, can prevent autoimmune diabetes illustrates that potential relationships may be more complex than previously thought. Here, we provide a concise summary of data obtained in mouse models and humans, and identify future avenues toward a better characterization of the association between viruses and T1D.

Autoimmune thyroid disorders

Purpose of Review. Studies have been published in the field of autoimmune thyroid diseases since January 2005. The review is organized into areas of etiology, autoimmune features, autoantibodies, mechanism of thyroid cell injury, B-cell responses, and T-cell responses. Also it reviews the diagnosis and the relationship between autoimmune thyroid disease, neoplasm, and kidney disorders. Recent Findings. Autoimmune thyroid diseases have been reported in people living in different parts of the world including North America, Europe, Baalkans, Asia, Middle East, South America, and Africa though the reported figures do not fully reflect the number of people infected per year. Cases are unrecognized due to inaccurate diagnosis and hence are treated as other diseases. However, the most recent studies have shown that the human autoimmune thyroid diseases (AITDs) affect up to 5% of the general population and are seen mostly in women between 30 and 50 years. Summary. Autoimmune thyroid disease is the result of a complex interaction between genetic and environmental factors. Overall, this review has expanded our understanding of the mechanism involved in pathogenesis of AITD and the relationship between autoimmune thyroid disease, neoplasm, and kidney disease. It has opened new lines of investigations that will ultimately result in a better clinical practice.

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

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

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.

The role of environmental factors in the pathogenesis of non-organ-specific autoimmune diseases

The immune system must be able to discriminate between self and non-self. However, mechanisms of doing so sometimes fail, causing the activation and clonal expansion of autoreactive lymphocytes and the development of autoimmune conditions. Although some autoimmune diseases have heritable components, these components are not sufficient to develop an autoimmune condition. A variety of environmental factors have been described as possible triggers of autoimmune diseases, including drugs, infectious agents, smoking, vaccination and adjuvants. The aim of this chapter is to review the most common environmental factors associated with autoimmune diseases.

Previous maternal infection protects offspring from enterovirus infection and prevents experimental diabetes development in mice

AIMS/HYPOTHESIS

Enterovirus (e.g. Coxsackie B virus serotypes [CVBs]) infections may be associated with development of type 1 diabetes. Studies conducted in several European countries have, however, shown an inverse correlation between the incidence of type 1 diabetes and the prevalence of enterovirus infections. These findings could in part be explained by an extension of the poliovirus hypothesis, suggesting that the absence of maternally transferred antibodies protecting offspring from early infection increases the risk for diabetes development. Experimental evidence supporting this hypothesis in type 1 diabetes is, however, lacking. As maternally transferred protection from infection is a crucial component of the extended poliovirus hypothesis, we here tested the hypothesis that previously infected females transfer protection against infection and diabetes to offspring.

METHODS

The induction of CVB-specific maternal antibodies and transfer of protection from virus infection, replication and development of virus-induced diabetes to offspring was assessed using NOD and Socs1-transgenic NOD mice.

RESULTS

Infected mice produced neutralising antibodies to CVB. Offspring from infected females were positive for neutralising antibodies and were strongly protected from both infection and experimental diabetes.

CONCLUSIONS/INTERPRETATION

Our study shows that maternally transferred antibodies protect offspring from enterovirus infection and virus-induced diabetes. This suggests that the absence of maternally provided protection increases the risk for severe outcomes after an enterovirus infection in offspring. Moreover, our findings may have implications for the design of prospective studies aimed at investigating the possible role of enterovirus infections in the aetiology of human type 1 diabetes.

CD4+ T cells recognize diverse epitopes within GAD65: implications for repertoire development and diabetes monitoring

Type 1 diabetes is associated with T-cell responses to β-cell antigens such as GAD65. Single T-cell epitopes have been investigated for immune monitoring with some success, but multiple epitopes may be required to fully characterize responses in all subjects. We used a systematic approach to examine the diversity of the GAD65-specific T-cell repertoire in subjects with DRB1*04:01 haplotypes. Using class II tetramers, we observed responses to 15 GAD65 epitopes, including five novel epitopes. The majority were confirmed to be processed and presented. Upon stimulation with peptides, GAD-specific responses were equally broad in subjects with diabetes and healthy controls in the presence or absence of CD25(+) T cells, suggesting that a susceptible HLA is sufficient to generate a potentially autoreactive repertoire. Without depleting CD25(+) cells, GAD(113-132) and GAD(265-284) responses were significantly stronger in subjects with diabetes. Although nearly every individual responded to at least one GAD65 epitope, most were seen in less than half of the subjects tested, suggesting that multiple epitopes are recommended for immune monitoring.

Why is type 1 diabetes increasing?

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

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

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

Prevention or acceleration of type 1 diabetes by viruses

Type 1 diabetes is an autoimmune disease characterized by the destruction of insulin-producing pancreatic β-cells. Even though extensive scientific research has yielded important insights into the immune mechanisms involved in pancreatic β-cell destruction, little is known about the events that trigger the autoimmune process. Recent epidemiological and experimental data suggest that environmental factors are involved in this process. In this review, we discuss the role of viruses as an environmental factor on the development of type 1 diabetes, and the immune mechanisms by which they can trigger or protect against this pathology.

Viral infections and diabetes

Type 1 diabetes mellitus (T1DM) is a multi-factorial autoimmune disease determined by the interaction of genetic, environmental and immunologic factors. One of the environmental risk factors identified by a series of independent studies is represented by viral infection, with strong evidence showing that viruses can indeed infect pancreatic beta cells with consequent effects ranging from functional damage to cell death. In this chapter we review the data obtained both in man and in experimental animal models in support of the potential participation of viral infections to Type 1 diabetes pathogenesis, with a particular emphasis on virus-triggered islet inflammation, beta-cell dysfunction and autoimmunity.

Molecular anatomy and number of antigen specific CD8 T cells required to cause type 1 diabetes

We quantified CD8 T cells needed to cause type 1 diabetes and studied the anatomy of the CD8 T cell/beta (β) cell interaction at the immunologic synapse. We used a transgenic model, in situ tetramer staining to distinguish antigen specific CD8 T cells from total T cells infiltrating islets and a variety of viral mutants selected for functional deletion(s) of various CD8 T cell epitopes. Twenty percent of CD8 T cells in the spleen were specific for all immunodominant and subdominant viral glycoprotein (GP) epitopes. CTLs to the immunodominant LCMV GP33-41 epitope accounted for 63% of the total (12.5% of tetramers). In situ hybridization analysis demonstrated only 1 to 2% of total infiltrating CD8 T cells were specific for GP33 CD8 T cell epitope, yet diabetes occurred in 94% of mice. The immunologic synapse between GP33 CD8 CTL and β cell contained LFA-1 and perforin. Silencing both immunodominant epitopes (GP33, GP276–286) in the infecting virus led to a four-fold reduction in viral specific CD8 CTL responses, negligible lymphocyte infiltration into islets and absence of diabetes.

Insulin-dependent type 1 diabetes (T1D) is characterized by elevated blood sugar, lymphocytic infiltration into the islets of Langerhans and T cell destruction of beta (β) cells. β cells produce insulin whose function is to maintain and regulate glucose hemostasis. However, in vivo, the numbers of antigen specific T cells that migrate to the islets to cause T1D, the engagement of such T cells with β cells at the immunologic synapse and the molecules expressed at the synapse are not clear. Using a transgenic model of virus induced T1D, a panel of viruses with CD8 T cell epitope mutations and in situ tetramer hybridization, we note of the total CD8 T cells infiltrating the islets, only 1–2% are antigen specific recognizing the immunodominant virus CD8 T cell epitope expressed on β cells. Immunohistochemical analysis of the synapse found between antigen specific CD8 T cells and β cells displays attachment by LFA-1 and presence of perforin, the molecule indicative of lytic activity.

The 'Hygiene hypothesis' and the sharp gradient in the incidence of autoimmune and allergic diseases between Russian Karelia and Finland

Autoimmune and allergic diseases have become a major health problem in the Western world during past decades. The hygiene hypothesis suggests that decreased microbial exposure in childhood leads to increasing prevalence of these diseases. This review summarizes epidemiological evidence and current immunological knowledge concerning the hygiene hypothesis. Recent results from Russian Karelia and Finland imply that environmental factors have greatly contributed to the increasing prevalence of immune-mediated disorders. Infections, or lack of them, may indeed be strongly involved in the development of both autoimmune and allergic diseases.

Molecular mimicry: Basis for autoimmunity

Structural similarity between a viral protein and a self-component can trigger an autoimmune response, which is the basis of molecular mimicry. Alternatively an invading virus can induce an inflammatory response which in turn can initiate an attack by hitherto dormant T cells on a specific self-antigen, a phenomenon which is referred to as Bystander Activation. Several viruses share amino acid sequences with target self-proteins. A widely studied viral interaction is the structural mimicry of a small portion of coxsackie virus to a specific region of the enzyme glutamic acid decarboxylase (GAD) which is expressed by the β cells of the islet of Langerhans in the pancreas leading to the destruction of insulin producing cells and the onset of Type I insulin dependent diabetes mellitus (IDDM). Knowledge of specific epitopes in GAD susceptible to autoimmune attack can permit devising therapeutic strategies for the prevention and suppression of IDDM.

Thymus and type 1 diabetes: an update

Type 1 diabetes (T1D) is a chronic disease resulting from the selective autoimmune destruction of pancreatic islet β cells. The absence and/or breakdown of immune self-tolerance to islet β cells is now recognized as the essential cause for the development of the diabetogenic autoimmune response. For a long time, a failure in peripheral tolerogenic mechanisms was regarded as the main source of an inappropriate immune process directed against insulin-secreting β cells. While defective peripheral self-tolerance still deserves to be further investigated, the demonstration that all members of the insulin gene family are transcribed in thymic epithelial cells (TECs) of different species under the control of the AutoImmune REgulator (AIRE) gene/protein has highlighted the importance of central self-tolerance to insulin-secreting islet β cells. Moreover, there is now evidence that a primary or acquired failure in thymus-dependent central self-tolerance to β cells plays a primary role in T1D pathogenesis. This novel knowledge is currently translated into the development of innovative tolerogenic/regulatory approaches designed to reprogram the specific immune self-tolerance to islet β cells.

Infection as a cause of type 1 diabetes?

PURPOSE OF REVIEW

It is the current opinion that pathogens, such as viruses, are contributing to the development of type 1 diabetes (T1D) in susceptible individuals. This opinion is based on epidemiological associations, direct isolation of pathogens from the islets of Langerhans, as well as a large amount of data from various experimental animal models. Human enteroviruses have dominated the literature associated with the etiology of T1D. However, virus infections have also been reported to protect from autoimmune disorders.

RECENT FINDINGS

Here we review the evidence for virus infections to be involved in the pathogenesis of T1D and discuss potential mechanisms of how such infections could accelerate the destruction of insulin-producing β-cells. In addition, we will review evidence from epidemiologic and experimental animal studies showing that virus infections could also have protective properties.

SUMMARY

Virus infections play an important role in the pathogenesis of T1D by inducing or accelerating the autodestructive process, but also by protecting from autoimmunity. Thus, multiple sequential infections might shape the autoreactive immune repertoire and the pathogenesis of T1D in a complex fashion.

Uric acid as a danger signal in gout and its comorbidities

Uric acid is a waste product of purine catabolism. This molecule comes to clinical attention when it nucleates to form crystals of monosodium urate (MSU) in joints or other tissues, and thereby causes the inflammatory disease of gout. Patients with gout frequently suffer from a number of comorbid conditions including hypertension, diabetes mellitus and cardiovascular disease. Why MSU crystals trigger inflammation and are associated with comorbidities of gout has been unclear, but recent studies provide new insights into these issues. Rather than simply being a waste product, uric acid could serve a pathophysiological role as a local alarm signal that alerts the immune system to cell injury and helps to trigger both innate and adaptive immune responses. The inflammatory component of these immune responses is caused when urate crystals trigger both inflammasome-dependent and independent pathways to generate the proinflammatory cytokine IL-1. The resulting bioactive IL-1 stimulates the inflammation of gout and might contribute to the development of other comorbidities. Surprisingly, the same mechanisms underlie the inflammatory response to a number of irritant particles, many of which also cause disease. These new insights help to explain the pathogenesis of gout and point to potential new therapeutic targets for this and other sterile inflammatory diseases.

NKG2D blockade facilitates diabetes prevention by antigen-specific Tregs in a virus-induced model of diabetes

It is thought that viral infections might jeopardize regulatory T cell therapy in type 1 diabetes. Viral infections can lead to surface expression of ligands for the activating NKG2D receptor, such as retinoic acid early transcript 1 (Rae-1), whose expression on beta-cells recruits NKG2D(+) autoreactive CD8(+) T cells. Both in men and mice, autoreactive cytotoxic T cells express NKG2D. We showed that NKG2D expression increased on CD4(+) and CD8(+) T cells during virus-induced diabetes development in the rat insulin promotor (RIP) Lymphocytic Choriomeningitis Virus (LCMV) model. Combination treatment with anti-NKG2D and antigen-specific regulatory T cells (Treg), at doses inefficacious in mono-treatment, synergized to prevent diabetes in 75% of the virus-infected RIP-LCMV mice. Nevertheless, NKG2D blockade alone failed to reverse recent-onset diabetes in non-obese diabetic (NOD) mice, despite downregulation of NKG2D on NK cells in the blood and CD8(+) T cells in the spleen and pancreatic lymph nodes. Our data suggest that blocking the interaction of NKG2D with it ligands is insufficient to protect against diabetes when a strong inflammatory process actively drives NKG2D upregulation, but should be considered to help maintaining Treg functionality during ongoing pancreatic inflammation.

What is the key environmental trigger in type 1 diabetes--is it viruses, or wheat gluten, or both?

Prevention and treatment of type 1 diabetes is hampered by the fact that the key environmental trigger(s) of the disease is still unknown. Much of the data on this subject points to two possibilities, viruses and wheat gluten. Viruses appear to be involved as an etiological agent in some cases of type 1 diabetes, particularly in fulminant type 1 diabetes. Further analysis of the data suggests that viruses are not the sole trigger of type 1 diabetes in humans, and that wheat gluten may play a role in initiating the disease. Viruses may be the key environmental trigger in some cases of type 1 diabetes, and wheat gluten in others. Conceivably, some cases of type 1 diabetes might be caused by viruses and wheat gluten acting together as disease triggers.

Immunology in the clinic review series; focus on type 1 diabetes and viruses: the innate immune response to enteroviruses and its possible role in regulating type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease arising as a consequence of a misdirected T cell response to the pancreatic beta cell. In recent years, there has been a growing interest in the innate immune system as a regulator of disease development. Genome-wide association studies have identified diabetes-associated polymorphisms in genes encoding proteins with functions related to the innate immune response. Moreover, enteroviruses, known to activate a strong innate immune response, have been implicated in the disease pathogenesis. In this review, we discuss the innate immune response elicited by enteroviruses and how this response may regulate T1D development.

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

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

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

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

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

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

Immunomodulation of antigen presenting cells promotes natural regulatory T cells that prevent autoimmune diabetes in NOD mice

Progression towards type 1 diabetes (T1D) in susceptible patients is linked to a progressive decline in the capacity of regulatory T cells (Treg) to maintain tolerance. As such, therapies aimed at redressing the failing Treg compartment have been the subject of intense investigation. Treg dysfunction in T1D has recently been linked to a reduced capacity of antigen presenting cells (APCs) to maintain Treg function rather than Treg intrinsic defects. This suggests that therapies aimed simply at addressing the failing Treg compartment are unlikely to provide long-term protection. Here, we demonstrate that modulation of the inflammatory status of CD11b+CD11c− APCs favors the upregulation of protective Tregs in a mouse model of T1D. We further demonstrate that reduced expression of the costimulatory molecule CD40 plays a role in this increased immunoregulatory capacity. Strikingly, Treg upregulation resulted exclusively from an increase in natural Tregs rather than the peripheral conversion of conventional T cells. This suggests that modulation of CD11b+ CD11c− APCs inflammatory properties favors the establishment of natural Treg responses that, unlike adaptive Treg responses, are likely to maintain tolerance to a broad range of antigens. As such, modulation of this APC subset represents a potential therapeutic avenue to reestablish peripheral tolerance and protect from autoimmune diseases such as T1D.