Enterovirus RNA is found in peripheral blood mononuclear cells in a majority of type 1 diabetic children at onset

Pathogenesis of type 1 diabetes mellitus: interplay between enterovirus and host

Enteroviruses are believed to contribute to the pathogenesis of type 1 diabetes mellitus (T1DM). In this Review, the interplay between infection with enteroviruses, the immune system and host genes is discussed. Data from retrospective and prospective epidemiological studies strongly suggest the involvement of enteroviruses, such as coxsackievirus B, in the development of T1DM. Enteroviral RNA and/or proteins can be detected in tissues of patients with T1DM. Isolation of coxsackievirus B4 from the pancreas of patients with T1DM or the presence of enteroviral components in their islets strengthens the hypothesis of a relationship between the virus and the disease. Enteroviruses can play a part in the early phase of T1DM through the infection of beta cells and the activation of innate immunity and inflammation. In contrast with its antiviral role, virus-induced interferon alpha can be deleterious, acting as an initiator of the autoimmunity directed against beta cells. Enteroviruses, through persistent and/or successive infections, can interact with the adaptive immune system. Host genes, such as IFIH1, that influence susceptibility to T1DM are associated with antiviral activities. An increased activity of the IFIH1 protein may promote the development of T1DM. An improved knowledge of the pathogenic mechanisms of enterovirus infections should help to uncover preventive strategies for T1DM.

Enteroviruses in the pathogenesis of type 1 diabetes

The question if enteroviruses could cause beta-cell damage and type 1 diabetes has become more and more relevant when recent studies have provided new evidence supporting this scenario. One important observation is the recent discovery of IFIH1 as a risk gene for type 1 diabetes. This gene is an innate immune system receptor for enteroviruses offering one possible mechanism for the diabetogenic effect of enteroviruses. This is further emphasized by the observations suggesting that the innate immune system is activated in the pancreatic islets of type 1 diabetic patients and that the innate immune system is important for the defense against the virus and for the regulation of adaptive immune system. Important progress has also been gained in studies analyzing pancreas tissue for possible presence of enteroviruses. Several studies have found enteroviruses in the pancreatic islets of type 1 diabetic patients using various methods. The virus seems to be located in the islets while exocrine pancreas is mostly uninfected. One recent study found the virus in the intestinal mucosa in the majority of diabetic patients. Enteroviruses can also infect cultured human pancreatic islets causing either rapid cell destruction or a persistent-like noncytolytic infection. Combined with all previous, epidemiological findings indicating the risk effect of enteroviruses in cross-sectional and prospective studies, these observations fit to a scenario where certain diabetogenic enterovirus variants establish persistent infection in gut mucosa and in the pancreatic islets. This in turn could lead to a local inflammation and the breakdown of tolerance in genetically susceptible individuals. This is also supported by mouse experiments showing that enteroviruses can establish prolonged infection in the pancreas and intestine, and some virus strains cause beta-cell damage and diabetes. In conclusion, recent studies have strengthened the hypothesis that enteroviruses play a role in the pathogenesis of type 1 diabetes. These findings open also new opportunities to explore the underlying mechanism and get closer to causal relationship.

Detection of enterovirus RNA in peripheral blood mononuclear cells of type 1 diabetic patients beyond the stage of acute infection

Previous studies have shown that enteroviral RNA can be detected in blood at the onset of type 1 diabetes (T1D). The infection may play a role in triggering T1D and genetic host factors may contribute to this process. We investigated (1) whether enterovirus is present at the onset of T1D in peripheral blood mononuclear cells (PBMC), plasma, throat, or stool, and (2) whether enteroviral presence is linked with HLA-DR type and/or polymorphisms in melanoma differentiation-associated gene 5 (MDA5) and 2'-5' oligoadenylate synthetase 1 (OAS1), factors of antiviral immunity. To this end, PBMC, plasma, throat, and stool samples from 10 T1D patients and 20 unrelated controls were tested for the presence of enteroviruses (RT-PCR), for HLA-DR type, and polymorphisms in MDA5 and OAS1. Enterovirus RNA was detected in PBMC of 4/10 T1D patients, but none of 20 controls. Plasma was positive in 2/10 T1D patients and none of 20 controls, suggesting that enteroviruses found at the onset of T1D are mainly present in PBMC. All throat samples from positive T1D patients were virus-negative and only 1 fecal sample was positive. The negative results for all throat and most stool samples argues against acute infection. Enterovirus presence was linked with HLA-DR4, but not with polymorphisms in MDA5 or OAS1.

MDA5 and MAVS mediate type I interferon responses to coxsackie B virus

Coxsackie B viruses (CVB) are enteroviruses that have been associated with a variety of human diseases, including myocarditis. In the present study, we found that MDA5 and its adaptor molecule MAVS are critical for type I interferon responses to CVB, since the absence of either MAVS or MDA5 leads to deficient type I interferon production and early mortality in mice infected with CVB. Pancreatic and hepatic necrosis were observed on histopathological examination of MAVS and MDA5 knockout mice infected with CVB. Inflammatory cytokine production in response to systemic CVB infection was independent of MAVS. Surprisingly, virus titers were not elevated in MAVS-deficient mice, despite significant reductions in type I interferon levels. These data highlight the importance of type I interferon in host defense and provide insight on the mechanisms of innate immune responses following coxsackievirus infection.

Infection with viruses from several families triggers autoimmune diabetes in LEW*1WR1 rats: prevention of diabetes by maternal immunization

OBJECTIVE

The contribution of antecedent viral infection to the development of type 1 diabetes in humans is controversial. Using a newer rat model of the disease, we sought to 1) identify viruses capable of modulating diabetes penetrance, 2) identify conditions that increase or decrease the diabetogenicity of infection, and 3) determine whether maternal immunization would prevent diabetes.

RESEARCH DESIGN AND METHODS

About 2% of LEW*1WR1 rats develop spontaneous autoimmune diabetes, but disease penetrance is much higher if weanling rats are exposed to environmental perturbants including Kilham rat virus (KRV). We compared KRV with other viruses for diabetogenic activity.

RESULTS

Both KRV and rat cytomegalovirus (RCMV) induced diabetes in up to 60% of LEW*1WR1 rats, whereas H-1, vaccinia, and Coxsackie B4 viruses did not. Simultaneous inoculation of KRV and RCMV induced diabetes in 100% of animals. Pretreatment of rats with an activator of innate immunity increased the diabetogenicity of KRV but not RCMV and was associated with a moderate rate of diabetes after Coxsackie B4 and vaccinia virus infection. Inoculation of LEW*1WR1 dams with both KRV and RCMV prior to pregnancy protected weanling progeny from virus-induced diabetes in a virus-specific manner.

CONCLUSIONS

Exposure to viruses can affect the penetrance of autoimmune diabetes in genetically susceptible animals. The diabetogenicity of infection is virus specific and is modified by immunomodulation prior to inoculation. Maternal immunization protects weanlings from virus-induced diabetes, suggesting that modification of immune responses to infection could provide a means of preventing islet autoimmunity.

Murine pancreatic beta TC3 cells show greater 2', 5'-oligoadenylate synthetase (2'5'AS) antiviral enzyme activity and apoptosis following IFN-alpha or poly(I:C) treatment than pancreatic alpha TC3 cells

Type 1 diabetes is caused by autoimmune destruction of pancreatic beta cells, possibly virus initiated. Virus infection induces alpha-interferon (IFN-α), leading to upregulation of genes encoding double-stranded (ds) RNA-dependent antiviral enzymes 2′, 5′-oligoadenylate synthetase (2′5′AS) and PKR (p68). To investigate whether beta cell specificity could be due to antiviral differences between beta and alpha cells, we treated beta and alpha TC3 cell lines with IFN-α and/or poly(I:C) (a synthetic dsRNA). Results showed that, following IFN-α stimulation, increases in 2′5′AS levels and activities were significantly higher in beta than alpha cells (P < .001), whereas increases in PKR level and activity were comparable in the two cell types. Poly(I:C) stimulated 2′5′AS activity in beta but not alpha cells, and co-transfection IFN-α plus poly(I:C) induced apoptosis in beta but not alpha cells. These findings suggest that the elevated 2′5′AS response of pancreatic beta cells could render them particularly vulnerable to damage and/or apoptosis during virus infection.

Coxsackievirus B4 and type 1 diabetes pathogenesis: contribution of animal models

The role of enteroviruses, in particular type B coxsackieviruses (CV-B), in type 1 diabetes (T1D) pathogenesis is supported by epidemiological, clinical and experimental observations.The investigation of T1D pathogenesis benefits from the contribution of animal models called spontaneously diabetic. Among these animals the non-obese diabetic (NOD) mouse and the bio-breeding diabetes-prone (BBDP) rat present a genetic susceptibility manifested by the expression of an autoimmune diabetes similar to the pathology observed in human beings. Other models whose genetic predisposition is less known are of considerable contribution as well. Numerous major observations relative to several aspects of T1D pathogenesis in the context of CV-B infections, such as susceptibility, diabetogenicity, pancreatotropism, mechanisms of beta cells destruction and others, have been deduced thanks to investigations with animal models. Despite their limits, these models are necessary in improving our knowledge of the role of enteroviruses, like CV-B4, in the pathogenesis of T1D, and the recent advances ensuing from their contribution may have important therapeutic and preventive spin-offs.

Antiviral effect of nicotinamide on enterovirus-infected human islets in vitro: effect on virus replication and chemokine secretion

Type 1 diabetes is a chronic disease characterized by the selective destruction of insulin-producing cells in the pancreas. Enterovirus (EV) is the prime candidate to initiate this destruction and several inflammatory chemokines are induced by EV infection. Nicotinamide has been shown to protect isolated human islets, and to modulate chemokine expression. The aim of this study was to evaluate the effect of nicotinamide on EV replication and EV-induced chemokine secretion and cytolysis of human islets. Two EV strains were used to infect human islets in vitro, one lytic (Adrian) isolated from a child at onset of type 1 diabetes, and one non-lytic (VD2921). Secretion of the chemokines IP-10 and MCP-1, viral replication, and virus-induced cytopathic effect (CPE), were measured at different time points post-infection. Addition of nicotinamide to the culture medium reduced viral replication and virus-induced islet destruction/CPE, significantly. Both EV strains increased secretion of IP-10 and MCP-1, when measured days 2-3, and days 5-7 post infection, compared to mock-infected control islets. IP-10 was not produced by uninfected isolated islets, whereas a basal secretion of MCP-1 was detected. Interestingly, addition of nicotinamide blocked completely (Adrian), or reduced significantly (VD2921), the virus-induced secretion of IP-10. Secretion of MCP-1 was also reduced in the presence of nicotinamide, from infected and uninfected islets. The reported antiviral effects of nicotinamide could have implications for the treatment/prevention of virus- and immune-mediated disease. Also, this study highlights a possible mechanism of virus-induced type 1 diabetes through the induction of MCP-1 and IP-10 in pancreatic islets.

Viral RNA kinetics is associated with changes in trace elements in target organs of Coxsackie virus B3 infection

Trace elements are pivotal for the host defense, as well as potentially important for viral replication and virulence. Studies of sequential changes in viral replication in target organs of infection are sparse and a possible association with changes in specific trace elements is unknown. In this study Balb/c mice were infected with Coxsackie virus B3 (CVB3). Results indicated that sequential changes in viral replication (RT-PCR) were related to changes in trace element (arsenic, copper, iron, selenium and zinc) concentrations (as determined by ICP-MS) on days 3, 5 and 7 of the infection in serum, heart, lung, liver, pancreas, kidney, spleen, intestine and brain. After an initial viral peak on day 3, viral load drastically decreased in all organs, i.e. by >99% (serum), 97% (lung), 98% (liver), 60% (pancreas), 95% (kidney) and 93% (spleen), except in the heart, intestine and brain in which viral load increased after day 3. Selenium decreased in all organs except the heart while arsenic decreased in all organs except the kidney, spleen and brain. Moreover, selenium was negatively correlated to viral load in serum, liver, pancreas and intestine. To conclude, these findings give evidence that trace elements are directly involved in the replication of CVB3.

Maternal enterovirus infection during pregnancy as a risk factor in offspring diagnosed with type 1 diabetes between 15 and 30 years of age

Maternal enterovirus infections during pregnancy may increase the risk of offspring developing type 1 diabetes during childhood. The aim of this study was to investigate whether gestational enterovirus infections increase the offspring's risk of type 1 diabetes later in life. Serum samples from 30 mothers without diabetes whose offspring developed type 1 diabetes between 15 and 25 years of age were analyzed for enterovirus-specific immunoglobulin M (IgM) antibodies and enterovirus genome (RNA), and compared to a control group. Among the index mothers, 9/30 (30%) were enterovirus IgM-positive, and none was positive for enterovirus RNA. In the control group, 14/90 (16%) were enterovirus IgM-positive, and 4/90 (4%) were positive for enterovirus RNA (n.s.). Boys of enterovirus IgM-positive mothers had approximately 5 times greater risk of developing diabetes (OR 4.63; 95% CI 1.22–17.6), as compared to boys of IgM-negative mothers (P < .025). These results suggest that gestational enterovirus infections may be related to the risk of offspring developing type 1 diabetes in adolescence and young adulthood.

Role of coxsackievirus B4 in the pathogenesis of type 1 diabetes

Environmental factors, especially viruses, are thought to play an important role in the initiation or acceleration of the pathogenesis of type 1 diabetes (T1D). Data from retrospective and prospective epidemiological studies strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), may be associated with the development of T1D. It has also been shown that enterovirus infections are significantly more prevalent in at-risk individuals such as the siblings of diabetic patients, when they develop anti-beta-cell autoantibodies or T1D, and in recently diagnosed diabetic patients, compared with control subjects. The isolation of CV-B4 from the pancreas of diabetic patients supports the hypothesis of a relationship between the virus and the disease. Furthermore, studies performed in vitro and in vivo in animal models have increased our knowledge of the role of CV-B4 in T1D by helping to clarify the pathogenic mechanisms of the infection that can lead to beta-cell destruction, including direct virus-induced beta-cell lysis, molecular mimicry, 'bystander activation' and viral persistence. The role of enteroviruses as the sole agents in T1D, and a causal link between these agents and T1D, have not yet been established, although arguments that support such a role for these viruses in the pathogenesis of the disease cannot be ignored.

Complete nucleotide sequence of a coxsackievirus B4 strain that establishes infection in ICR mice pancreas and induces glucose intolerance

Some coxsackievirus B serotypes are potentially diabetogenic. Previous studies revealed that the virulence and the tissue damage varied with the genetics of the virus strain as well as with the genetics of the mice. A single amino acid variation can alter virulence and tropism in both murine and in vitro models. However, the genetic determinants of this phenomenon have not been determined. In this study, infections with a laboratory strain of coxsackievirus B4 resulted in a diabetes-like syndrome in ICR mice, characterized by chronic pancreatic inflammation together with dysregulation in glucose metabolism, loss of pancreatic acinar tissue and persistent infection in islets. To characterize the genetic determinants involved in the mouse pancreas adaptation, the laboratory strain of coxsackievirus B4 was cloned for molecular characterization. Comparing the whole genome sequence of this virus strain with the other coxsackievirus B4 strains revealed some differences. Altogether 15 nucleotides were changed, resulting in 10 amino acid substitutions, which might be responsible for the pathogenic phenotype of this strain in mice.

A part of the VP4 capsid protein exhibited by coxsackievirus B4 E2 is the target of antibodies contained in plasma from patients with type 1 diabetes

The capsid protein VP4 was identified previously as the target of antibodies contained in plasma enhancing the coxscakievirus B4 (CV-B4) E2-induced production of IFN-alpha by peripheral blood mononuclear cells (PBMCs). The sequence of VP4 recognized by these antibodies was investigated. This sequence was identified as amino acids 11 to 30 by using synthetic overlapping peptides spanning VP4(CV-B4 E2) in competition experiments for antibodies enhancing the CV(B4 E2) induced production of IFN-alpha by PBMCs. This amino acid sequence was the major target of anti-VP4 antibodies according to enzyme-linked immunosorbent assays (ELISA). There was a positive correlation between the levels of anti-VP4 and anti-VP4(11-30) peptide antibodies detected by ELISA. The levels and the prevalences of these antibodies were significantly higher in patients with type 1 diabetes than in healthy controls. The proportions and the levels of those antibodies in patients were independent of HLA-DR alleles, age, or presence of ketosis in blood and were not associated with newly or previously diagnosed disease. The VP4(CV-B4 E2) amino acid sequence was submitted to the Swiss-model in project mode to visualize the possible shape of the sequence of VP4 corresponding to amino acids 11-30 which appeared to be constituted principally by an non-structured loop. In conclusion, the sequence of VP4 corresponding to amino acids 11-30, or a part of it plays a role in the plasma-dependent enhancement of CV-B4 E2-induced production of IFN-alpha by PBMCs, suggesting that at 37 degrees C the virus exhibits that region of VP4 to antibodies.

Occurrence of enterovirus RNA in serum of children with newly diagnosed type 1 diabetes and islet cell autoantibody-positive subjects in a population with a low incidence of type 1 diabetes

BACKGROUND

The penetrance of type 1 diabetes mellitus (T1DM) in a genetically susceptible population is largely determined by environmental influences amongst which the human enteroviruses are prominent putative factors.

AIM/HYPOTHESIS

The aim of this study was to determine the occurrence of enterovirus RNA in serum of children with type 1 diabetes at onset and ICA-positive subjects in a population with low incidence of type 1 diabetes and high circulation of enteroviruses.

SUBJECTS AND METHODS

Serum samples were collected from children with newly diagnosed type 1 diabetes (n = 34); islet autoantibody-positive (n = 32) and -negative (n = 31) first-degree relatives of type 1 diabetic patients; and control subjects (n = 194). Enteroviral RNA was assessed using a highly sensitive reverse transcriptase-polymerase chain reaction method.

RESULTS

The frequency of positive signals corresponding to enteroviral sequence amplifications were higher in newly diagnosed T1DM children (9/34, 26.5%) and islet autoantibody-positive first-degree relatives (5/32, 15.6%) than in their corresponding matched controls (2/68, 2.9%, p = 0.0007 and 0/64, 0.0%, p = 0.0033, respectively). The presence of enteroviral RNA appeared to be associated with severe diabetic ketoacidosis at onset (pH < 7.1, p = 0.0328) and high ICA titres ( > or = 20 JDF units, p < 0.05).

CONCLUSIONS

Despite there is a high circulation of enteroviruses and a low type 1 diabetes incidence in the Cuban population, the presence of enteroviral RNA is associated with type 1 diabetes and beta-cell autoimmunity and is similar to European countries in which this scenario is reversed.

Recent enterovirus infection in type 1 diabetes: evidence with a novel IgM method

Enterovirus (EV) infection has been associated with Type 1 (T1D) diabetes and on a few occasions virus could be isolated at onset of the disease. Using two such isolates as antigens in a quantitative PCR enhanced immunoassay (T1D-EV-QPIA) we have measured IgM antibodies against such potentially diabetogenic viruses in serum from 33 newly diagnosed T1D children, 24 siblings, and 27 healthy children. Sera were also analysed with regard to autoantibodies against GAD65, the cytokine TNF-alpha and the chemokine IP-10. EV-RNA detection was performed on peripheral blood mononuclear cells (PBMC). IgM antibodies against this "new" EV antigen were more frequent in serum from T1D children than in serum from siblings and/or controls (P < 0.001). EV-RNA was detected more frequently in PBMC from T1D children than in healthy control children (P < 0.001) and also compared to the siblings (P < 0.003). The cytokine TNF-alpha was less frequently detected in serum from the T1D children compared with serum from siblings and/controls (P < 0.001). A positive correlation was found between the results obtained with the T1D-EV-QPIA and the EV-PCR (P < 0.001). These findings are in line with earlier findings of an increased frequency of enteroviral infections in newly diagnosed T1D patients. In addition, we found that T1D children at onset of the disease had lower frequencies of the chemokine TNF-alpha in their serum than age- and sex-matched controls had, suggesting an impaired immune response.

Prolonged viral RNA detection in blood and lymphoid tissues from coxsackievirus B4 E2 orally-inoculated Swiss mice

The spreading of viral RNA within Swiss Albino mice orally inoculated with coxsackievirus B4 E2 strain (CVB4 E2) was studied by using RT-PCR and semi-nested-RT-PCR methods. Viral RNA was detected in various organs: pancreas, heart, small intestine, spleen, thymus, and blood at various postinfectious (p.i.) times ranging from 8 hr to 150 days. Our results show that (i) outbred mice can be infected with CVB4 E2 following an oral inoculation, which results in systemic spreading of viral RNA, (ii) CVB4 E2 infection can be associated with a prolonged detection of viral RNA in spleen, thymus and blood, up to 70 days p.i. and further in other organ tissues.

An RNA extraction protocol for shellfish-borne viruses

The GPTT virus RNA extraction method, originally developed for extraction of human norovirus and hepatitis A virus RNAs from contaminated shellfish, was evaluated for extraction of RNA from Aichi virus strain A846/88 (AiV), coxsackievirus strains A9 (CAV9) and B5 (CBV5), murine norovirus (strain MNV-1), and the norovirus surrogate, feline calicivirus (FCV) strain KCD, for the purpose of RT-PCR detection within seeded oyster (Crassostrea virginica) extracts. The RT-PCR equivalent sensitivities observed within seeded oysters as compared to virus stocks were 0.68, 6.8, 26, 5.6, and 14.5 RT-PCR(50) units when assaying 10% of total RNA extracted from seeded oyster extracts for CAV9, CBV5, AiV, FCV, and MNV-1, respectively. For oysters exposed to virus-contaminated seawater, the detection equivalent sensitivities observed were 680, 68, 2600, 560, and 14.5 RT-PCR(50) for CAV9, CBV5, AiV and FCV, and MNV-1, respectively. These results indicate that the GPTT method can be used as a general viral RNA extraction method for multiple picornaviruses and caliciviruses that could potentially contaminate shellfish.

Coxsackie B4 virus infection of beta cells and natural killer cell insulitis in recent-onset type 1 diabetic patients

Type 1 diabetes is characterized by T cell-mediated autoimmune destruction of pancreatic beta cells. Several studies have suggested an association between Coxsackie enterovirus seroconversion and onset of disease. However, a direct link between beta cell viral infection and islet inflammation has not been established. We analyzed pancreatic tissue from six type 1 diabetic and 26 control organ donors. Immunohistochemical, electron microscopy, whole-genome ex vivo nucleotide sequencing, cell culture, and immunological studies demonstrated Coxsackie B4 enterovirus in specimens from three of the six diabetic patients. Infection was specific of beta cells, which showed nondestructive islet inflammation mediated mainly by natural killer cells. Islets from enterovirus-positive samples displayed reduced insulin secretion in response to glucose and other secretagogues. In addition, virus extracted from positive islets was able to infect beta cells from human islets of nondiabetic donors, causing viral inclusions and signs of pyknosis. None of the control organ donors showed signs of viral infection. These studies provide direct evidence that enterovirus can infect beta cells in patients with type 1 diabetes and that infection is associated with inflammation and functional impairment.

Echovirus infection causes rapid loss-of-function and cell death in human dendritic cells

Coxsackie B viruses (CVB) and Echoviruses (EV) form a single species; Human enterovirus B (HeV-B), within the genus Enterovirus. Although HeV-B infections are usually mild or asymptomatic, they can cause serious acute illnesses. In addition, HeV-B infections have been associated with chronic immune disorders, such as type 1 diabetes mellitus and chronic myocarditis/dilated cardiomyopathy. It has therefore been suggested that these viruses may trigger an autoimmune process. Here, we demonstrate that human dendritic cells (DCs), which play an essential role in orchestration of the immune response, are productively infected by EV, but not CVB strains, in vitro. Infection does not result in DC activation or the induction of antiviral immune responses. Instead, EV infection rapidly impedes Toll-like receptor-mediated production of cytokines and upregulation of maturation markers, and ultimately causes loss of DC viability. These results describe for the first time the effect of EV on the function and viability of human DCs and suggest that infection of DCs in vivo can impede regulation of immune responses.

Role of the capsid protein VP4 in the plasma-dependent enhancement of the Coxsackievirus B4E2-infection of human peripheral blood cells

It has been previously shown that antibodies contained in human plasma directed towards the Coxsackievirus B4 (CVB4)E2 capsid protein VP4 can enhance the CVB4E2-induced production of IFN-alpha by peripheral blood mononuclear cells (PBMC). The aim of this study was to produce a VP4 fusion protein to investigate the role of the internal capsid protein VP4 and anti-VP4 antibodies in the plasma-dependent enhancement of CVB4E2 infection of PBMC. A fusion protein MBPVP4 containing the VP4 insert of CVB4E2 and a control fusion protein MBP-beta-gal-alpha, were produced in Escherichia coli K12 TB1. The CVB4E2 infection of PBMC was quantified by using a real time PCR method amplifying CVB4E2-negative strand RNA. IFN-alpha concentrations in culture supernatants were assayed by DELFIA. MBPVP4 but not MBP-beta-gal-alpha, preincubated with plasma inhibited the plasma-dependent enhancement of CVB4E2-induced production of IFN-alpha by PBMC. Human plasma samples, antibodies contained in plasma eluted from MBPVP4-coated plates, but not from MBP-beta-gal-alpha-coated plates, incubated with CVB4E2 enhanced the infection of PBMC and the production of IFN-alpha by infected cells. Together our results show that VP4 and anti-VP4 antibodies play a role in the plasma-dependent enhancement of CVB4E2 infection of PBMC.

Effects on isolated human pancreatic islet cells after infection with strains of enterovirus isolated at clinical presentation of type 1 diabetes

Enterovirus (EV) infections have been associated with the pathogenesis of type 1 diabetes (T1D). They may cause beta-cell destruction either by cytolytic infection of the cells or indirectly by triggering the autoimmune response. Evidence for EV involvement have been presented in several studies, EV-IgM antibodies have been reported in T1D patients, EV-RNA has been found in the blood from T1D patients at onset, and EV have been isolated from newly diagnosed T1D. Our aim was to study infections with EV isolates from newly diagnosed T1D patients in human pancreatic islets in vitro. Two of them (T1 and T2) originated from a mother and her son diagnosed with T1D on the same day, the other two (A and E) were isolated from a pair of twins at the time of diagnosis of T1D in one of them. Isolated human pancreatic islets were infected and viral replication, viability and degree of cytolysis as well as insulin release in response to high glucose were measured. All four EV isolates replicated in the islet cells and virus particles and virus-induced vesicles were seen in the cytoplasm of the beta-cells. The isolates varied in their ability to induce cytolysis and to cause destruction of the islets and infection with two of the isolates (T1 and A) caused more pronounced destruction of the islets. Infection with the isolate from the healthy twin boy (E) was the least cytolytic. The ability to secrete insulin in response to high glucose was reduced in all infected islets as early as 3 days post infection, before any difference in viability was observed. To conclude, strains of EV isolated from T1D patients at clinical presentation of T1D revealed beta-cell tropism, and clearly affected the function of the beta-cell. In addition, the infection caused a clear increase in the number of dead cells.

Induction of the chemokine interferon-gamma-inducible protein-10 in human pancreatic islets during enterovirus infection

AIMS/HYPOTHESIS

Enterovirus infections have long been suspected to be environmental factors that may cause type 1 diabetes, but the pathways leading from infection to beta cell destruction are still unknown. We therefore examined whether enterovirus infection of human islets leads to upregulation of interferon-gamma-inducible protein (IP-10, now known as chemokine [C-X-C motif] ligand 10 [CXCL10]), a chemokine important for the induction of insulitis.

METHODS

Isolated human islets were infected with three different strains of Coxsackie B4 virus. IP-10 expression and secretion from the infected human islets were then measured using RT-PCR and ELISA at several time points.

RESULTS

IP-10 was clearly upregulated in and secreted from human islets during enterovirus infection. This was demonstrated with three different strains of Coxsackie B4 virus, two of which are lytic to islets and one which is non-lytic and can establish a persistent infection in human islets.

CONCLUSIONS/INTERPRETATION

We propose that enterovirus-induced upregulation of IP-10 during infection of the islets in vivo is the first step towards destructive insulitis. Our findings support the idea that enterovirus infection triggers immune-mediated beta cell destruction, and for the first time suggest a possible mechanism behind enterovirus-induced diabetes.

Environmental factors in the development of Type 1 diabetes

Environmental factors appear to play an important role in the pathogenesis of childhood-onset type 1 diabetes (T1D). The most important factors are thought to be infectious, dietary, perinatal, and psychosocial. Enteroviruses (especially Coxsackie B virus), breastfeeding, the early presence or lack of certain foods, birth weight, childhood over-nutrition, maternal islet autoimmunity, and negative stress events have been shown to be related to the prevalence of T1D. However, clear conclusions to date are limited because most studies lacked power to detect exposure/disease associations, were not prospective or long-term, did not start in infancy, had imprecise or infrequent exposure estimates, had confounding exposures, and failed to account for genetic susceptibility. In addition to the identification of specific antigenic triggers, several more general hypotheses, including the accelerator and hygiene hypotheses, are testable approaches worth pursuing.

Decreased in vitro type 1 immune response against coxsackie virus B4 in children with type 1 diabetes

Enteroviruses, particularly Coxsackie virus B4 (CVB4), are considered to be involved in the pathogenesis of type 1 diabetes. We wanted to compare the characteristics of T-cell immune response to CVB4 in children with type 1 diabetes and healthy children with and without HLA risk-associated haplotypes (HLA-DR3-DQ2 or HLA-DR4-DQ8) for type 1 diabetes. Peripheral blood mononuclear cells (PBMCs) were isolated and cultured with CVB4 and analyzed for cytokine and chemokine receptors by flow cytometry and for expression of transcription factors Tbet and GATA-3 by RT-PCR and Western blot. Culture supernatants were analyzed for secretion of gamma-interferon (IFN-gamma). In children with type 1 diabetes, a decreased percentage of T-cells expressed CCR2, CXCR6, interleukin (IL)-18R, and IL-12Rbeta2-chain after in vitro stimulation with CVB4 in comparison with healthy children with or without HLA risk genotype. Moreover, we found that children with type 1 diabetes had decreased IFN-gamma secretion and expression of Tbet, both on mRNA and protein level, in CVB4-stimulated PBMCs. Accordingly, children with type 1 diabetes show an impaired type 1 immune response against CVB4 compared with healthy children. This may lead to a delayed clearance of the virus and, at least partly, explain why children with type 1 diabetes may be more prone to CVB4 infections and related complications, such as beta-cell damage.

Longitudinal observation of enterovirus and adenovirus in stool samples from Norwegian infants with the highest genetic risk of type 1 diabetes

BACKGROUND

Enterovirus and adenovirus are common in infancy, causing mostly asymptomatic infections. However, even an asymptomatic infection may be associated with increased risk of development of certain chronic non-infectious diseases, as has been suggested for enterovirus and type 1 diabetes. Data on occurrence and course of the infections in infancy are therefore important for designing effective approaches towards study of the association.

OBJECTIVES

To estimate the frequency of enterovirus and adenovirus infections in Norwegian infants, to evaluate the duration of the infections, to investigate their association with symptoms, and to establish a robust procedure that will be used to study the association between these viruses and the development of auto-immunity leading to type 1 diabetes.

STUDY DESIGN

Parents of infants, recruited for a study on environmental triggers of type 1 diabetes, submitted monthly samples of infant faeces, as well as information on symptoms of infection. The samples were analysed for enterovirus and adenovirus using quantitative real-time PCR, and enterovirus-positive samples were sequenced.

RESULTS

Enteroviruses were found in 142/1,255 (11.3%), and adenoviruses in 138/1,255 (11.0%) of stool samples. Approximately half of the infants were exposed to these viruses at least once during the first year of observation (period 3-14 months of age). The presence of adenovirus was associated with fever and with symptoms of cold but not with diarrhoea and vomiting. The enterovirus positivity was not associated with any symptoms.

CONCLUSIONS

The prevalence of enterovirus and adenovirus in longitudinally obtained faecal samples from infants is sufficiently high to enable studies of their association with chronic diseases. The present protocol for evaluating exposure to these viruses is well suited for large-scale efforts aimed at assessing possible long-term consequences, particularly in relation to type 1 diabetes.

Viral protein VP4 is a target of human antibodies enhancing coxsackievirus B4- and B3-induced synthesis of alpha interferon

Coxsackievirus B4 (CVB4)-induced production of alpha interferon (IFN-alpha) by peripheral blood mononuclear cells (PBMC) is enhanced in vitro by nonneutralizing anti-CVB4 antibodies from healthy subjects and, to a higher extent, from patients with insulin-dependent diabetes mellitus. In this study, we focused on identification of the viral target of these antibodies in CVB systems. High levels of IFN-alpha were obtained in supernatants of PBMC incubated with CVB4E2 or CVB3 and plasma from healthy subjects and, to a higher extent, from patients. The VP4 capsid proteins dissociated by heating at 56 degrees C from CVB4E2 (VP4(CVB4)) and CVB3 (VP4(CVB3)) but not H antigen preincubated with plasma from healthy subjects or patients inhibited the plasma-dependent enhancement of CVB4E2- and CVB3-induced IFN-alpha synthesis. There was no cross-reaction between VP4(CVB4) and VP4(CVB3) in the inhibiting effect. IFN-alpha levels in culture supernatants showed dose-dependent correlation with anti-VP4 antibodies eluted from plasma specimens using VP4-coated plates. There were higher index values for anti-VP4 antibodies detected by enzyme-linked immunosorbent assay (ELISA) and higher proportions of positive detection in 40 patients than in 40 healthy subjects (80% versus 15% for anti-VP4(CVB4)). There was no relationship between the levels of anti-CVB neutralizing antibodies and the detection of anti-VP4 antibodies by ELISA. The CVB plasma-induced IFN-alpha levels obtained in PBMC cultures in the anti-VP4 antibody-positive groups were significantly higher than those obtained in the anti-VP4 antibody-negative groups regardless of the titers of anti-CVB neutralizing antibodies. These results show that VP4 is the target of antibodies involved in the plasma-dependent enhancement of CVB4E2- and CVB3-induced IFN-alpha synthesis by PBMC.

How robust is the evidence for viruses in the induction of type 1 diabetes?

Viruses associated with type 1 diabetes have eluded definition as causal, with the exception of rubella virus. False-negative results may have occurred due to the focus on subjects at symptomatic onset, who may be heterogeneous and differently affected by viruses. In addition, assays have not always been sufficiently sensitive to deal with transient infections, and pancreatic tissue is scarce. Longitudinal studies of at-risk subjects and more sensitive DNA techniques now reveal that at initiation of islet autoimmunity, enteroviruses have only a small role, but are more likely to be important at symptomatic onset. Rotaviruses remain associated with initiation of islet autoimmunity, and generate strong T cell responses in the young.

Phenotypic and genetic changes in coxsackievirus B5 following repeated passage in mouse pancreas in vivo

Common enterovirus infections appear to initiate or facilitate the pathogenetic processes leading to type 1 diabetes, and also sometimes precipitate the clinical disease. In experimental infection of mice, coxsackieviruses have shown to have a strong affinity for the exocrine tissue, while even in lethal cases, the islets remain unaffected. The virus strain most intensively studied in this respect is the diabetogenic variant E2 of coxsackievirus B4. In addition, it is known that all six serotypes of coxsackie B viruses can be made diabetogenic by repeated passages in either mouse pancreas in vivo or in cultured mouse beta-cells in vitro. However, the genetic determinants of the phenomenon have not been determined. In the present study, a laboratory strain of coxsackievirus B5 was passaged repeatedly in mouse pancreas in vivo. After 15 passages, the virus phenotype was clearly changed and infection of the variant resulted in a diabetes-like syndrome in mice characterized by chronic pancreatic inflammation together with dysregulation in glucose metabolism, loss of pancreatic acinar tissue, and mild insulitis. In order to characterize the genetic determinants involved in mouse pancreas adaptation, the passaged virus variant together with the parental virus strain was cloned for molecular characterization. The whole genome sequencing of both virus strains revealed only limited differences. Altogether, eight nucleotides were changed resulting in five amino acid substitutions, of which three were located in the capsid proteins.

Inflammatory gene expression in Coxsackievirus B-4-infected human islets of Langerhans

The event that triggers the autoimmune destruction of insulin-producing beta-cells in type 1 diabetes mellitus (T1DM) is still unknown. Enterovirus, especially Coxsackievirus, infections have long been associated with this disease. Cytokines and chemokines induced by an enterovirus infection may act to trigger the autoimmune reactions that produce T1DM. Gene expression was examined in isolated human islets infected with a Coxsackievirus-B4 (CBV-4) strain causing lytic infection (V89-4557) and in islets infected with a CBV-4 strain establishing persistent infection (VD2921). Microarray analysis indicated that infection with the CBV-4 strains resulted in specific induction of a number of inflammatory genes, including IL-1beta, IL-6, IL-8, MCP-1, and RANTES. Importantly, the inflammatory genes induced by the CBV-4 infections differed in the two strains, with more cytokines being induced by the non-lytic CBV-4 strain than by the lytic strain. These cytokines and chemokines have the potential to rapidly induce inflammatory reactions when expressed in vivo and could contribute to the autoimmune reactions associated with the development of T1DM.

dsRNA formed as an intermediate during Coxsackievirus infection does not induce NO production in a β-cell line with or without addition of IFN-γ

Virus infection is one environmental factor that has been implicated as a precipitating event initiating beta-cell damage during the development of type 1 diabetes. One aim of this study was to investigate how permissive an insulin-producing beta-cell line, RINm5F, is to enterovirus (EV) infections. A second aim was to study if the viral replicative intermediate, double-stranded RNA (dsRNA), together with IFN-gamma results in nitric oxide (NO) production. Monolayer cultures of RINm5F cells were not permissive to infection with seven different strains of EV. However, when the growth pattern of the beta-cell line changed and the cells started to grow as free-floating RIN cell clusters (RCC), all EV strains replicated. Immunostaining for the Coxsackie-adenovirus-receptor (CAR) detected the protein on the free-floating RIN cell clusters, but not on the RINm5F cells cultured as a monolayer of beta-cells. This shows that the CAR expression can change and/or the CAR protein can be redistributed on the cell surface as a consequence of altered growth pattern thus allowing viral replication in a previously non-permissive beta-cell line. As expected, NO production was significantly increased (p<0.05) by addition of synthetic dsRNA and IFN-gamma to the RCC. In contrast, the dsRNA formed during virus infection with a Coxsackievirus B4 strain (E2) with or without addition of IFN-gamma did not induce NO production in these cells. This indicates that synthetic dsRNA does not mimic a real viral infection in that respect, and suggests an NO-independent mechanism for virus-induced beta-cell damage.

Coxsackievirus B4 infection of human fetal thymus cells

The infection of human fetal thymus organ cultures (FTOC) with coxsackievirus B4 E2 (CVB4 E2) was investigated. Both positive- and negative-strand viral RNA were detected by real-time quantitative reverse transcription-PCR (RT-PCR) in CVB4 E2-infected FTOC, which supported high yields of virus production (approximately 10(6) 50% tissue culture infective doses/ml), and in flow-sorted thymocyte populations for 7 days after inoculation. Cortical CD4+ CD8+ thymocytes were found to be the principal targets of infection. Inoculation of human FTOC with CVB4 E2 led to a marked and progressive depletion of immature thymocytes (CD4+ CD8+ cells) with no enhancement of Annexin V-positive cells. CVB4 E2 replication caused significant major histocompatibility complex (MHC) class I upregulation on these cells. MHC class I upregulation was correlated with positive- and negative-strand RNA quantitative detection and the release of infectious particles. In addition, chloroquine treatment of FTOC and single-thymocyte suspensions suggested that MHC class I upregulation on thymocytes was the result of direct infection rather than caused by production of soluble factors such as alpha interferon. Thus, CVB4 E2 can infect human fetal thymocytes, which subsequently results in quantitative and qualitative abnormalities of these cells.

Inactivation of selected picornaviruses by high hydrostatic pressure

The potential of high hydrostatic pressure processing (HPP) to inactivate Aichi virus (AiV), human parechovirus-1 (HPeV-1), and the coxsackievirus strains A9 and B5 was investigated. For coxsackievirus A9 (CAV9), a 5-min HPP treatment in minimum essential growth medium (MEM) supplemented with 10% fetal bovine sera (FBS) resulted in 3.4-, 6.5-, and 7.6-log(10) tissue culture infectious dose (50%) (TCID(50)) reductions at 400, 500, and 600megaPascals (MPa), respectively. For HPeV-1, a 5-min treatment in MEM with 10% FBS resulted in reductions of 1.3-, 4.3-, and 4.6-log(10) TCID(50) at 400, 500, and 600MPa, respectively; however, AiV and coxsackievirus B5 (CBV5) in MEM supplemented with 2 and 10% FBS, respectively, remained fully infectious after a 5-min treatment at 600MPa. These data establish that different picornaviruses have widely variable pressure inactivation thresholds in response to HPP.

Interferon alpha--a potential link in the pathogenesis of viral-induced type 1 diabetes and autoimmunity

The incidence of type 1 diabetes has been rapidly rising. Environmental factors such as viruses have been implicated as a possible agent accounting for this rise. Enteroviruses have recently been the focus in many research studies as a potential agent in the pathogenesis of type 1 diabetes. The mechanism of viral infection leading to beta cell destruction not only involves multiple pathways but also the cytokine-interferon alpha (IFN-alpha). Our hypothesis is that activation of toll receptors by double-stranded RNA or poly-IC (viral mimic) through induction of IFN-alpha may activate or accelerate immune-mediated beta cell destruction. Numerous clinical case reports have implicated that IFN-alpha therapy is associated with autoimmune diseases and that elevated serum IFN-alpha levels have been associated with type 1 diabetes. In multiple animal models, given specific genetic susceptibility, poly-IC can induce insulitis or diabetes. Therapeutic agents targeting IFN-alpha may potentially be beneficial in the prevention of type 1 diabetes and autoimmunity.

Coxsackie B virus serology and Type 1 diabetes mellitus: a systematic review of published case-control studies

BACKGROUND

Enteroviruses, in particular Coxsackie B4, have been implicated in the aetiology of Type 1 diabetes mellitus, but the epidemiological evidence has not been systematically evaluated.

METHODS

Systematic review of evidence from published controlled studies of the relationship between Coxsackie B virus serology and incident or prevalent Type 1 diabetes mellitus. Studies were identified through a Medline search (1966 to 2002), supplemented by references from identified papers and hand search of relevant journals. All studies (full papers, abstracts or letters) with data adequate for calculation of unadjusted odds ratios (with 95% confidence intervals) for Type 1 diabetes mellitus in relation to Coxsackie B virus serology were included.

RESULTS

The review included 26 case-control studies; no cohort study met the inclusion criteria. Odds ratios for Type 1 diabetes mellitus in serology-positive vs. serology-negative subjects ranged from 0.2 to 22.3. For Coxsackie B (any serotype) 7/13 studies had point estimates significantly greater than 1.0 (P < 0.05). For Coxsackie B3, Coxsackie B4 and Coxsackie B5-specific assays, 1/11, 6/17 and 1/11 studies, respectively, had point estimates significantly greater than 1.0. Summary odds ratios were not calculated because of doubts about the validity of individual study estimates, heterogeneity between studies, and the possibility of publication bias.

CONCLUSIONS

The results of these studies are inconsistent and do not provide convincing evidence for or against an association between Coxsackie B virus infection and Type 1 diabetes mellitus. Better designed studies using effective assays are needed to resolve this important issue.

Isolation of enterovirus strains from children with preclinical Type 1 diabetes

AIMS

To develop methods for isolation of enterovirus strains from subjects with preclinical Type 1 diabetes and evaluate if their presence in stools is associated with beta-cell damage.

METHODS

The study subjects were participants of the Finnish Type 1 Diabetes Prediction and Prevention Study (DIPP). The prospectively followed birth cohort comprised 12 children who turned positive for diabetes-associated autoantibodies during the follow-up (case children) and 53 controls matched for date of birth, sex and HLA-DQB1 alleles. Altogether, 878 stool samples were analysed for the presence of enterovirus RNA by RT-PCR followed by virus isolation and partial sequencing of viral genome. Enterovirus antibodies and RNA were simultaneously analysed from serum.

RESULTS

Eleven enterovirus infections were diagnosed in case children and 42 infections in control children by the presence of viral RNA in stools. The proportion of children who were repeatedly enterovirus RNA-positive stools was higher among case than control children (42% vs. 11% of children; P=0.02). Combined serum (antibody and RT-PCR) and stool analyses indicated at least one enterovirus infection in 83% of the case children before the appearance of autoantibodies, while only 42% of the control children had infection by the same age (P=0.006). Twelve enterovirus strains were isolated from case children and 38 strains from control children.

CONCLUSIONS

This protocol makes it possible to isolate a large number of enterovirus strains from prediabetic subjects. The findings suggest that enterovirus infections may be associated with the beta-cell damaging process.

Enterovirus infection in human pancreatic islet cells, islet tropism in vivo and receptor involvement in cultured islet beta cells

AIMS/HYPOTHESIS

It is thought that enterovirus infections cause beta-cell damage and contribute to the development of Type 1 diabetes by replicating in the pancreatic islets. We sought evidence for this through autopsy studies and by investigating known enterovirus receptors in cultured human islets.

METHODS

Autopsy pancreases from 12 newborn infants who died of fulminant coxsackievirus infections and from 65 Type 1 diabetic patients were studied for presence of enteroviral ribonucleic acid by in situ hybridisation. Forty non-diabetic control pancreases were included in the study. The expression and role of receptor candidates in cultured human islets were investigated with receptor-specific antibodies using immunocytochemistry and functional assays.

RESULTS

Enterovirus-positive islet cells were found in some of both autopsy specimen collections, but not in control pancreases. No infected cells were seen in exocrine tissue. The cell surface molecules, poliovirus receptor and integrin alphavbeta3, which act as enterovirus receptors in established cell lines, were expressed in beta cells. Antibodies to poliovirus receptor, human coxsackievirus and adenovirus receptor and integrin alphavbeta3 protected islets and beta cells from adverse effects of poliovirus, coxsackie B viruses, and several of the arginine-glycine-aspartic acid motifs containing enteroviruses and human parechovirus 1 respectively. No evidence was found for expression of the decay-accelerating factor which acts as a receptor for several islet-cell-replicating echoviruses in established cell lines.

CONCLUSIONS/INTERPRETATION

The results show a definite islet-cell tropism of enteroviruses in the human pancreas. Some enteroviruses seem to use previously identified cell surface molecules as receptors in beta cells, whereas the identity of receptors used by other enteroviruses remains unknown.

Can enteroviruses cause type 1 diabetes?

Enterovirus infections have long been considered as one possible environmental trigger of type 1 diabetes. These viruses have been detected from diabetic patients more often than from control subjects and they can infect beta cells in cell culture and induce diabetes in animal models. Furthermore, a same kind of seasonality has been observed in both the onset of clinical diabetes and subclinical beta cell autoimmunity (appearance of autoantibodies) as in enterovirus infections. Recently, considerable new evidence has cumulated from prospective studies indicating the risk effect of enterovirus infections long before clinical diabetes was diagnosed. In addition, several studies have reported enterovirus genome sequences in diabetic patients more often than in control subjects. Currently, the evidence for the role of enteroviruses is stronger than for most other environmental agents, but still the final proof is lacking. The ongoing studies aim to prove the risk effect in different populations and to identify the underlying mechanisms. This research field is becoming more and more important because it could open up possibilities to prevent type 1 diabetes by an enterovirus vaccine.

Enteroviruses and type 1 diabetes

The development of type 1 diabetes mellitus (T1DM) has been linked to exposure to environmental triggers, with Enteroviruses (EV) historically considered the prime suspects. Early serological studies suggested a link between EV infections and the development of T1DM and, though controversial, have been bolstered by more recent studies using more sensitive techniques such as direct detection of the EV genome by RT-PCR in peripheral blood. In this review, we consider the weight of evidence that EV can be considered a candidate trigger of T1DM, using three major criteria: (1) is EV infection associated with clinical T1DM, (2) can EV trigger the development of autoimmunity and (3) what would explain the putative association?

Coxsackievirus immunization delays onset of diabetes in non-obese diabetic mice

Enteroviruses may be involved in the pathogenesis of Type 1 diabetes through different mechanisms including triggering of autoimmunity. The effect of immunization with coxsackievirus B4-E2 on diabetes incidence was studied in the non-obese diabetic mice, an animal model for human autoimmune insulin-dependent diabetes mellitus. The immunization delayed the onset of diabetes in the mice, and the effect was mediated at least partially by virus immunization-activated splenocytes as demonstrated by adoptive transfer experiments. Immunization resulted in a strong humoral immune response against the immunizing virus, formalin-inactivated coxsackievirus B4-E2. Cell-mediated immune response to virus antigen was characterised by interferon gamma and interleukin 10 secretion. The immunization also resulted in increased antibody levels against several beta-cell autoantigens. By using epitope mapping we were able to show that in addition to reactivity with the known epitopes of viral proteins and tyrosine phosphatase IA-2 or heat shock protein 60, responses to some other regions of autoantigens were enhanced. In preproinsulin, the response was restricted against an antigenic region earlier identified as DR4-dependent epitope. This reactivity can not be explained by homologous amino acid sequences and it is possible that enterovirus immunization might change the autoantigen specific TH1/TH2 balance in non-obese diabetic mice. In conclusion, our results suggest that coxsackievirus immunization increased humoral immune response to beta cell autoantigens and this was associated with a less destructive pathology for spontaneous diabetes in non-obese diabetic mice.

A new look at viruses in type 1 diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells. Genetic factors are believed to be a major component for the development of T1D, but the concordance rate for the development of diabetes in identical twins is only about 40%, suggesting that nongenetic factors play an important role in the expression of the disease. Viruses are one environmental factor that is implicated in the pathogenesis of T1D. To date, 14 different viruses have been reported to be associated with the development of T1D in humans and animal models. Viruses may be involved in the pathogenesis of T1D in at least two distinct ways: by inducing beta cell-specific autoimmunity, with or without infection of the beta cells, [e.g. Kilham rat virus (KRV)] and by cytolytic infection and destruction of the beta cells (e.g. encephalomyocarditis virus in mice). With respect to virus-mediated autoimmunity, retrovirus, reovirus, KRV, bovine viral diarrhoea-mucosal disease virus, mumps virus, rubella virus, cytomegalovirus and Epstein-Barr virus (EBV) are discussed. With respect to the destruction of beta cells by cytolytic infection, encephalomyocarditis virus, mengovirus and Coxsackie B viruses are discussed. In addition, a review of transgenic animal models for virus-induced autoimmune diabetes is included, particularly with regard to lymphocytic choriomeningitis virus, influenza viral proteins and the Epstein-Barr viral receptor. Finally, the prevention of autoimmune diabetes by infection of viruses such as lymphocytic choriomeningitis virus is discussed.