Enterovirus infections and enterovirus specific T-cell responses in infancy

Seroepidemiology of echovirus 30 in Korean children

BACKGROUND

Although aseptic meningitis associated with echovirus type 30 has emerged as a global public health concern, no data have been reported on Children's immune status against echovirus type 30. The current study aimed to investigate the seropositivity among Korean children for antibodies against echovirus 30.

METHODS

Two hundred and fifty residual serum samples were collected at St. Paul's Hospital. Individuals were categorized by age into four groups: group 1 (3 months-2 years), group 2 (3-6 years), group 3 (7-10 years) and group 4 (11-15 years). Neutralizing antibodies against echovirus 30 were measured.

RESULTS

Seroprotective neutralizing antibodies against echovirus 30 were detected in 129 (49%) individuals. Seropositivity rates were 23%, 48%, 55% and 73% in groups 1-4, respectively. For antibody titers, 1:256-1:512 was the highest neutralizing antibody titer range in group 2, while 1:1024-1:2048 in group 3 and 4. Among the seropositive individuals in group 3 and 4, 6% and 12% had neutralizing antibody titers of 1:2048, respectively.

CONCLUSIONS

The seropositivity rate increased significantly with age. The distribution of neutralizing antibody titers varied by age group, and higher ranges of neutralizing antibody titers were observed in higher age groups. These findings suggest high susceptibility to echovirus 30 infection in children younger than 2 years old. Echovirus 30 infection in childhood may have contributed to increased neutralizing antibody titers with age.

Seroprevalence of Enterovirus A71 and Coxsackievirus A16 in Healthy People in Shandong Province, China

Background

Hand, foot, and mouth disease has become very common in mainland of China in recent years, and enterovirus A71 and coxsackievirus A16 are its major etiologic factors. Here we investigated the seroprevalence of enterovirus A71 and coxsackievirus A16 based on a large group of healthy individuals in Shandong province, China.

Methods

A total of 1378 healthy individuals were tested for serum neutralizing antibodies against enterovirus A71 and coxsackievirus A16 using a micro neutralization test.

Results

The overall seroprevalence of enterovirus A71 neutralizing antibodies was 74.75%. It increased significantly from 48.84% in children aged 0–1 years old to 88.64% in those aged 20–29 years (p < 0.01) and decreased to 85.71% in adults > 40 years old with a significant gender-specific difference (p < 0.01). The overall coxsackievirus A16 antibody prevalence was 71.77%. It increased significantly from 39.53% in children aged 0–1 years to 80.68% in those aged 10–19 years (p < 0.01) and decreased to 75.63% in adults >40 years without a gender-specific difference. Nearly 50% of the children <1 year were susceptible to enterovirus A71 infection versus 40% to coxsackievirus A16 infection. Sample collection time and place also played a role in the enterovirus A71 and coxsackievirus A16 positive rates. The overall rates in January were significantly lower than those in April and August (p < 0.01); enterovirus A71 positive rates in Jinan city (capital city of Shandong province) were lower than those in Jining city and Zibo city (p < 0.05); and oxsackievirus A16 positive rates in Jining city were significantly higher than those in Jinan city and Zibo city (p < 0.01).

Conclusion

There were significant differences among age groups, locations, and time points in the seroprevalence rates of enterovirus A71 and coxsackievirus A16 neutralizing antibodies in healthy people in Shandong province.

Viruses in type 1 diabetes

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

Lower anti-echovirus antibody responses in children presenting to hospital with asthma exacerbations

BACKGROUND

Rhinoviruses from the Enterovirus genus cause frequent infections and induce remarkably high titres of anticapsid antigen antibodies in asthmatics, while the prevalence of neutralising antibodies to the gut-trophic echoviruses from the same genus is diminished.

OBJECTIVE

To assess the absolute and specific antibody titres to VP1 antigens of the gut-trophic enteroviruses, echovirus 30 and Sabin 1 poliovirus, in asthmatic and non-asthmatic children.

METHODS

Recombinant polypeptides representing the VP1 capsid antigens of echovirus 30 and Sabin poliovirus 1 were produced. Their ability to bind IgG1 antibodies from the plasma of asthmatic (n = 45) and non-asthmatic (n = 29) children were quantitated by immunoassays that incorporated immunoabsorptions to remove cross-reactivity.

RESULTS

The IgG1 antibody titres and prevalence of antibody binding to echovirus 30 were significantly lower for asthmatic children compared to controls (P < 0.05) and inversely correlated with total IgE levels for the whole study population (r = -0.262; P < 0.05). There was no difference in the prevalence and titre between groups to the VP1 antigen of Sabin poliovirus. Anti-tetanus toxoid titres measured for comparison did not correlate with anti-echovirus or poliovirus, but correlated with anti-rhinovirus titres in controls but not asthmatics, where the titres were higher for the asthmatic group.

CONCLUSIONS AND CLINICAL RELEVANCE

The associations of lower antibody titres of asthmatic children to echovirus reported here and those of our previous findings of a heightened response to rhinovirus suggest a dichotomy where respiratory enterovirus infection/immunity increases the probability of developing asthma and enteric infections lower the risk. This provides further support for the concept of intestinal infection playing a key role in the development of allergic respiratory disease.

Characterization of the enterovirus 71 P1 polyprotein expressed in Pichia pastor as a candidate vaccine

Human enterovirus 71 (EV71) plays an important role in hand, foot, and mouth disease (HFMD), which recently caused the death of hundreds of children in the Asia-Pacific region. However, there are no specific treatments available for EV71 infections; thus, a safe and effective vaccine is needed urgently. In this study, we developed an effective and economical method for producing EV71 polyprotein (P1 protein) in Pichia pastoris. Furthermore, we evaluated the potential of P1 protein as a candidate vaccine against EV71 virus. The data revealed that P1 protein induced persistent high cross-neutralization antibodies for different EV71 subtypes, and elicited significant splenocyte proliferation. The high levels of interleukin-10(IL-10) and interferon-gamma (IFN-γ) showed that P1 protein induced Th1 and Th2 immune responses. Interestingly, vaccinating female mice with the P1 protein conferred cross-protection against different EV71 subtypes to their neonatal offspring.Compared with heat-inactivated EV71, the P1 protein elicited improved humoral and cellular immune responses and showed good cross-protection with different EV71 subtypes. Therefore, the EV71-P1 protein produced by P. pastoris is a promising candidate vaccine against EV71.

The compatibility of inactivated-Enterovirus 71 vaccination with Coxsackievirus A16 and Poliovirus immunizations in humans and animals

Enterovirus 71 (EV71) is the key pathogen for Hand, Foot, and Mouth Disease (HFMD) and can result in severe neurological complications and death among young children. Three inactivated-EV71 vaccines have gone through phase III clinical trials and have demonstrated good safety and efficacy. These vaccines will benefit young children under the threat of severe HFMD. However, the potential immunization-related compatibility for different enterovirus vaccines remains unclear, making it hard to include the EV71 vaccine in Expanded Program on Immunization (EPI). Here, we measured the neutralizing antibodies (NTAbs) against EV71, Coxsackievirus A16 (CA16) and Poliovirus from infants enrolled in those EV71 vaccine clinical trials. The results indicated that the levels of NTAb GMTs for EV71 increased significantly in all 3 vaccine groups (high, middle and low dosages, respectively) post-vaccination. Seroconversion ratios and Geometric mean fold increase were significantly higher in the vaccine groups (≥ 7/9 and 8.9 ～ 228.1) than in the placebo group (≤ 1/10 and 0.8 ～ 1.7, P < 0.05). But no similar NTAb response trends were found in CA16 and 3 types of Poliovirus. The decrease of 3 types of Poliovirus NTAb GMTs and an increase of CA16 GMTs post-EV71-vaccination were found in vaccine and placebo groups. Further animal study on CA16 and poliovirus vaccine co-immunization or pre-immunization with EV71 vaccine in mice indicated that there was no NTAb cross-activity between EV71 and CA16/Poliovirus. Our research showed that inactivated-EV71 vaccine has good specific-neutralizing capacity and can be included in EPI.

Characterization of the enterovirus 71 VP1 protein as a vaccine candidate

Enterovirus 71 (EV71) is an important agent responsible for hand-foot-and-mouth disease (HFMD), which can cause severe neurological complications and death in children. However, there is no specific treatment for EV71 infection, and a safe and effective vaccine is needed urgently. In this study, an effective and economical method for the production of EV71-VP1 protein was developed, and the VP1 protein was evaluated in humoral and cellular immune responses as an EV71 vaccine. The results revealed that the VP1 protein induced high titers of cross-neutralizing antibodies for different EV71 subtypes, and elicited significant splenocyte proliferation. The high levels of IFN-r and IL-10 showed the VP1 protein induced a mixed Th1 and Th2 immune response. Vaccinated female mice could confer protection in their neonatal offspring. Compared with the inactivated EV71, the VP1 protein elicited similar humoral and cellular responses, but the engineered protein is safer, less expensive and can be produced more efficiently. Therefore, EV71-VP1 protein can induce effective immunologic protection against EV71 and is an ideal candidate against EV71 infection.

Dominant CD4-dependent RNA-dependent RNA polymerase-specific T-cell responses in children acutely infected with human enterovirus 71 and healthy adult controls

Human enterovirus 71 (EV71) is one of the major causes of hand, foot and mouth disease (HFMD), which leads to significant mortality in infected children. A prophylactic vaccine is urgently needed. However, little is known about the protective T-cell immunity in individuals infected with the EV71 virus. In this study, we performed a comprehensive ex vivo interferon-γ ELISPOT analysis in 31 children infected with EV71 as well as in 40 healthy adult controls of the CD4(+) and CD8(+) T-cell responses to overlapping peptides spanning the VP1 structural protein and RNA-dependent RNA polymerase (RdRp) non-structural protein. EV71-specific CD4 T-cell responses were detected in most of the acute patients and were mostly CD4-dependent RdRp-specific responses. CD8-dependent VP1 and RdRp-specific responses were also detected in a small proportion of recently infected children. There was no significant association between the strength of the T-cell responses and disease severity observed during the acute EV71 infection phase. Interestingly, an RdRp-specific, but no VP1-specific, CD4-dependent T-cell response was detected in 30% of the adult controls, and no T-cell responses were detected in healthy children. In addition, 24 individual peptides containing potential T-cell epitope regions were identified. The data suggest that CD4-dependent RdRp-specific T-cell responses may play an important role in protective immunity, and the epitopes identified in this study should provide valuable information for future therapeutic and prophylactic vaccine design as well as basic research.

Does oral polio vaccine at birth affect the size of the thymus? Observations within a randomized trial

BACKGROUND

There is increasing evidence that vaccines have an effect on general mortality which goes beyond specific disease protection. Oral polio vaccine (OPV) is widely used in low-income countries, but in observational studies in Guinea-Bissau we observed that not receiving OPV at birth was associated with reduced overall male infant mortality and enhanced immune response to BCG vaccine. We therefore initiated a randomized trial to test the overall effect of OPV at birth (OPV0).

OBJECTIVE

A small thymic gland is a predictor of mortality in high-mortality settings. Within the trial we aimed to test whether no-OPV0 was associated with increased thymic size.

METHODS

In 511 normal birth weight infants who were randomized to receive or not receive OPV0, thymic index and thymus/weight index were measured before randomization and after 2 weeks (N=49), 4 weeks (N=308) or 6 weeks (N=27). The association between OPV0 and the log transformed thymic size indicators were analyzed in ANCOVA models with thymic size at follow-up as the outcome and adjusting for thymic size at enrollment and age at follow-up. Estimates were reported as geometric mean ratios (GMR) with 95% confidence intervals, comparing no-OPV0 to OPV0.

RESULTS

No-OPV0 was not associated with thymic index after 2 weeks (GMR: 1.14 (0.99-1.30)), after 4 weeks (GMR: 0.98 (0.93-1.05)) or after 6 weeks (GMR: 1.00 (0.81-1.23)). However, no-OPV0 was associated with increased thymus/weight index after 2 weeks (GMR: 1.22 (1.06-1.40)), but the effect was not seen after 4 weeks (GMR: 0.97 (0.92-1.03)) and 6 weeks (GMR: 0.99 (0.82-1.19)). There were no strong sex-differences.

DISCUSSION

Overall there was no effect on thymic size of OPV0 when administered with BCG. The results could indicate that if an effect occurs, it is only within the first weeks after vaccination.

Seroepidemiology of human enterovirus71 and coxsackievirusA16 in Jiangsu province, China

Background

The major etiology of hand, foot and mouth disease (HFMD) is infection with human enterovirus A (HEV-A). Among subtypes of HEV-A, coxsackievirusA16 (CoxA16) and enterovirus 71 (EV71) are major causes for recurrent HFMD among infants and children in Jiangsu Province, mainland China. Here, we analyzed maternal antibodies between prenatal women and their neonates, to determine age-specific seroprevalence of human EV71 and CoxA16 infections in infants and children aged 0 to 15 years. The results may facilitate the development of immunization against HFMD.

Methods

This study used cross-section of 40 pairs of pregnant women and neonates and 800 subjects aged 1 month to 15 years old. Micro-dose cytopathogenic effects measured neutralizing antibodies against EV71 and CoxA16. Chi-square test compared seroprevalence rates between age groups and McNemar test, paired-Samples t-test and independent-samples t-test analyzed differences of geometric mean titers.

Results

A strong correlation between titers of neutralizing antibody against EV71 and CoxA16 in prenatal women and neonates was observed (r_EV71 = 0.67, r_CoxA16 = 0.56, respectively, p < 0.05). Seroprevalence rates of anti-EV71 antibody gradually decreased with age between 0 to 6 months old, remained low between 7 to 11 months (5.0–10.0%), and increased between 1 and 4 years (22.5–87.5%). Age-specific seroprevalence rates of anti-EV71 antibody stabilized in >80% of children between 5 to 15 years of age. However, seroprevalence rates of anti-CoxA16 antibody were very low (0.0–13.0%) between 0 to 6 months of age, gradually increased between 7 months to 4 years (15.0–70.0%), and stabilized at 54.0% (108/200) between 5 to 15 years. Seroprevalence rates against EV71 and CoxA16 were low under 1 year (0.0–10.0%), and showed an age dependent increase with high seroprevalence (52.5–62.5%) between 4 and10 years of age.

Conclusions

Concomitant infection of EV71 and CoxA16 was common in Jiangsu Province. Therefore, development of bivalent vaccine against both EV71 and CoxA16 is critical. The optimal schedule for vaccination may be 4 to11 months of age.

Viral interference induced by live attenuated virus vaccine (OPV) can prevent otitis media

Background

The goal of this study was to evaluate whether a live attenuated poliovirus vaccine (OPV) has clinically relevant interfering effect with non-polio infections causing otitis media in young children.

Methods

Open trial in which the intervention group (64 children) received OPV at the age of 2, 3, 6 and 12 months. The control group (250 children) received IPV (inactivated polio vaccine) at the age of 6 and 12 months. Clinical symptoms were recorded by a questionnaire at the age of 3, 6, 12, 18 and 24 months.

Results

Otitis media episodes were less frequent in the OPV than in the control group. A significant difference was seen at the age of 6–18 months (IRR = 0.76 [95% CI 0.59–0.94], P = 0.011) and was particularly clear among children, who attended daycare (IRR 0.37 [95% CI 0.19–0.71], P = 0.003).

Conclusions

OPV provides some protection against otitis media. This effect may be mediated by viral interference with non-polio viruses.

A systematic approach to virus-virus interactions

A virus–virus interaction is a measurable difference in the course of infection of one virus as a result of a concurrent or prior infection by a different species or strain of virus. Many such interactions have been discovered by chance, yet they have rarely been studied systematically. Increasing evidence suggests that virus–virus interactions are common and may be critical to understanding viral pathogenesis in natural hosts. In this review we propose a system for classifying virus–virus interactions by organizing them into three main categories: (1) direct interactions of viral genes or gene products, (2) indirect interactions that result from alterations in the host environment, and (3) immunological interactions. We have so far identified 15 subtypes of interaction and assigned each to one of these categories. It is anticipated that this framework will provide for a more systematic approach to investigating virus–virus interactions, both at the cellular and organismal levels.

Hand, foot and mouth disease: seroprevalence of Coxsackie A16 and Enterovirus 71 in Germany

Coxsackie A16 (CA16) and Enterovirus 71 (EV71) are members of the picornaviridae family and are associated with hand, foot and mouth disease (HFMD), in rare cases also to acute neurological diseases. HFMD outbreaks have been reported from many parts of the world, especially Southeast Asia. The objective of the study was to analyze CA16 and EV71 seroepidemiologically in the population of Frankfurt/M., Germany. A total of 696 individuals (349 males and 347 females, divided into seven different age groups, 1-4, 5-9, 10-14, 15-19, 20-39, 40-59 and >60 years) were tested for serum antibodies against CA16 and EV71 by the use of a microneutralization test. Sera were collected at the Frankfurt university hospital from patients suffering from other diseases between March and September 2006. CA16 and EV71 infections were observed to be widely present in the population. The age-adjusted seroprevalence for individuals >or=1 year was found to be 62.9% for CA16 and 42.8% for EV71 without a gender-specific significant difference. Only 12.0 and 27.0% of the children aged 1-4 had antibodies to EV71 and CA16, respectively - indicating that 88 and 73% of the children in this age group were susceptible to the infection. A total of 213 individuals (30.6%) was seropositive for both viruses, 303 (43.5%) showed neutralizing antibodies (NtAb) to at least one of the two viruses. A total of 180 individuals (25.9%) revealed no antibodies. High CA16 and EV71 antibody titers were found especially in the age group of the 10- to 14-year-olds, without gender-specific difference. The seroprevalence study demonstrates a common spread of CA16 and EV71 in Germany, but a relatively high susceptibility of the younger population to CA16 and EV71. Obviously, the manifestation rate, i.e., distinct disease of these infections is low.

Immunity to avirulent enterovirus 71 and coxsackie A16 virus protects against enterovirus 71 infection in mice

In this study, we sought to determine whether intratypic and intertypic cross-reactivity protected against enterovirus 71 (EV71) infection in a murine infection model. We demonstrate that active immunization of 1-day-old mice with avirulent EV71 strain or coxsackie A16 virus (CA16) by the oral route developed anti-EV71 antibodies with neutralizing activity (1:16 and 1:2, respectively). Splenocytes from both EV71- and CA16-immunized mice proliferated upon EV71 or CA16, but not coxsackie B3 virus (CB3), antigen stimulation. Immunized mice became more resistant to virulent EV71 strain challenge than nonimmunized mice. There was an increase in the percentage of activated splenic T cells and B cells in the immunized mice 2 days after EV71 challenge. The CA16 immune serum reacted with EV71 antigens in an enzyme-linked immunosorbent assay and neutralized EV71 but not CB3 or poliovirus at a titer of 1:4. Passive immunization with the CA16 immune serum reduced the clinical score, diminished the organ viral load, and increased the survival rate of mice upon EV71 challenge. CB3 neither shared in vitro cross-reactivity with EV71 nor provided in vivo protection after both active and passive immunization. These results illustrated that live vaccine is feasible for EV71 and that intertypic cross-reactivity of enteroviruses may provide a way to determine the prevalence of EV71.

Human parechovirus 1 infections in young children--no association with type 1 diabetes

The epidemiology, transmission and clinical symptoms of human parechoviruses [HPeV, classified earlier as enteroviruses; echovirus 22 (HPeV1) and echovirus 23 (HPeV2)] remain poorly characterized. Enteroviruses and one parechovirus species, the Ljungan virus, have been associated with type 1 diabetes in humans and rodents. The occurrence of human parechovirus 1 (HPeV1) infections in young children and their possible association with type 1 diabetes was evaluated. The prospective birth cohort study comprised 221 Finnish children carrying genetic type 1 diabetes susceptibility and who were observed from birth. Thirty-four children developed multiple diabetes-associated autoantibodies, and 18 children progressed to clinical type 1 diabetes during the follow-up. HPeV1 infections were diagnosed by measuring neutralizing antibodies from the follow-up sera taken every 3-12 months. In addition, viral RNA was analysed by RT-PCR from stool samples taken every month from six of the participants. HPeV1 infections were found to occur early in childhood. The median age of infection was 18 months and 20% of the children had had an infection by the age of 1 year. The number of infections started to increase from the age of 6 months and most children had their first infection by 36 months. Nearly all (99%) mothers were HPeV1 antibody positive. No difference was found in infection frequency between boys and girls, nor between prediabetic, diabetic and control subjects. Most infections (87%) occurred during autumn, winter and spring.

Immunisation of premature infants

Premature infants are at increased risk of vaccine preventable infections, but audits have shown that their vaccinations are often delayed. Early protection is desirable. While the evidence base for immunisation of preterm infants is limited, the available data support early immunisation without correction for gestational age. For a number of antigens the antibody response to initial doses may be lower than that of term infants, but protective concentrations are often achieved and memory successfully induced. A 2-3-4 month schedule may be preferable for immunisation of preterm infants in order to achieve protection as early as possible, but an additional dose may be required to achieve persistence of protection. This update focuses on the use of routine childhood vaccines in premature infants.

Enteral virus infections in early childhood and an enhanced type 1 diabetes-associated antibody response to dietary insulin

Enteral virus infections may trigger the development of beta-cell-specific autoimmunity by interacting with the gut-associated lymphoid system. We analyzed the effect of three different virus infections on immunization to dietary insulin in children carrying increased genetic risk for type 1 diabetes. Forty-six of 238 children developed multiple diabetes-associated autoantibodies and 31 clinical diabetes (median follow-up time 75 months). Insulin-binding antibodies were measured with EIA method (median follow-up time 24 months). Antibodies to enteroviruses, rotavirus and adenovirus were measured with EIA in samples drawn at birth and the ages of 3 and 6 months. Nineteen enterovirus, 14 rotavirus and 8 adenovirus infections were diagnosed. At the ages of 6, 12, and 18 months, the concentrations of insulin-binding antibodies were higher in children with postnatal entero-, rota- and/or adenovirus infections than in children without these infections. Children who subsequently developed ICA or IA-2 antibodies or clinical type 1 diabetes had higher concentrations of insulin-binding antibodies than children who remained autoantibody negative. Our data suggest that enteral virus infections can enhance immune response to insulin, induced primarily by bovine insulin in cow's milk. An enhanced antibody response to dietary insulin preceded the development of beta-cell specific autoimmunity and type 1 diabetes.

Neonatal coxsackie B virus infection-a treatable disease?

Ten neonates with coxsackie B viral infection presented over a 3-month period. Clinical features included meningoencephalitis, thrombocytopenia, disseminated intravascular coagulopathy, cardiomyopathy, and hepatitis. Eight infants had multiorgan disease, four with severe myocardial dysfunction, of whom two died. All of the infants with severe disease developed symptoms within 7 days of age. In infants presenting within 10 days of birth, in all cases there were symptoms compatible with maternal infection prior to delivery. Severity was associated with perinatal transmission. Enteroviral polymerase chain reaction of CSF, urine, stool or throat swab was positive in nine of the ten babies. Seven of the infants were treated with a 7-day course of the new anti-picornaviral drug pleconaril (5 mg/kg 3 times daily).

CONCLUSION

These cases highlight the importance of not missing coxsackie B viral infection in the differential diagnosis of the septic neonate, especially as there is now a potential treatment.

Induction of T Lymphocytes Specific for Bovine Viral Diarrhea Virus in Calves with Maternal Antibody

Passive antibody to bovine viral diarrhea virus (BVDV) acquired through colostrum intake may interfere with the development of a protective immune response by calves to this virus. The objective of this study was to determine if calves, with a high level of maternal antibody to bovine viral diarrhea virus (BVDV), develop CD4(+), CD8(+), or gammadelta T lymphocyte responses to BVDV in the absence of a measurable humoral immune response. Colostrum or milk replacer fed calves were challenged with virulent BVDV at 2-5 weeks of age and/or after maternal antibody had waned. Calves exposed to BVDV while passive antibody levels were high did not mount a measurable humoral immune response to BVDV. However, compared to nonexposed animals, these animals had CD4(+), CD8(+), and gammadelta T lymphocytes that were activated by BVDV after exposure to in vitro BVDV. The production of IFNgamma by lymphocytes after in vitro BVDV exposure was also much greater in lymphocytes from calves exposed to BVDV in the presence of maternal antibody compared to the nonexposed calves. These data indicate that calves exposed to BVDV while maternal antibody levels are high can develop antigen specific CD4(+), CD8(+), and gammadelta T lymphocytes in the absence of an active antibody response. A manuscript presented separately demonstrates that the calves with T lymphocytes specific for BVDV in this study were also protected from virulent BVDV genotype 2 challenge after maternal antibody became undetectable.

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.

Enterovirus infections as a risk factor for type I diabetes: virus analyses in a dietary intervention trial

This study evaluated the possible role of enterovirus infections in the pathogenesis of type I (insulin-dependent) diabetes in a prospective dietary intervention trial. Children participated in the second pilot of the Trial to Reduce IDDM in Genetically at Risk (TRIGR) project. They were randomized into two groups receiving either a casein hydrolysed formula (Nutramigen) or a regular formula, whenever breast milk was not available over the first 6-8 months of life. Altogether 19 children who turned positive for autoantibodies associated with type I diabetes by 2 years of age and 84 matched control children were analysed for enterovirus antibodies and enterovirus RNA in serum. Enterovirus infections were common during the first 2 years of life and more frequent among boys than girls (P = 0.02). Autoantibody-positive children had more enterovirus infections than autoantibody-negative children before the appearance of autoantibodies (0.83 versus 0.29 infection per child, P = 0.01). The average levels of IgG antibodies to echovirus antigen were also higher in autoantibody-positive than in autoantibody-negative children (P = 0.0009). No difference was found in the frequency of enterovirus infections between children receiving the casein hydrolysed formula or regular formula. These results suggest that enterovirus infections are associated with the induction of beta-cell autoimmunity in young children with increased genetic susceptibility to type I diabetes.

High levels of adenovirus DNA in serum correlate with fatal outcome of adenovirus infection in children after allogeneic stem-cell transplantation

An increase in the incidence of adenovirus (AdV) infection leading to death among children who have undergone allogeneic stem-cell transplantation has made it necessary to find new ways to monitor AdV infection. In this retrospective study, levels of AdV DNA in serum samples obtained from 36 transplant recipients with stool cultures positive for AdV were measured by polymerase chain reaction (PCR) semiquantitatively by analyzing serial dilutions of the DNA template. Six (86%) of 7 children who died of AdV infection, compared with only 2 (7%) of 29 other patients, had high serum levels of AdV DNA (detectable by PCR at a > or =100-fold dilution of the DNA template; P<.0001). High serum levels of AdV DNA were reached a mean of 18 days before death (range, 6-29 days). Quantification of adenoviral DNA in serum may prove to be a valuable tool to diagnose and monitor AdV infection and disease in immunocompromised children.

Immunity status against poliomyelitis in Germany: determination of cut-off values in International Units

BACKGROUND

To prevent importations of wild polioviruses into a polio free region a high level of population immunity must be kept. Standard methodology for determination of polio antibodies is a feature aimed at obtaining consistent results. An International Standard Serum for polio antibodies exists, but no protective level in International Units is defined.

METHODS

A representative study was carried out in order to determine the serological status against poliomyelitis in Germany (n = 2564, age 18-79 years). Furthermore, sera from persons aged less than 18 years were included (n = 881). Microneutralization test has been used for determination of antibody levels. Results have been expressed in International Units.

RESULTS

The results of this study indicate that the cut-off level for polio antibodies is 0.075 IU/ml for Polio 1, 0.180 IU/ml for Polio 2 and 0.080 IU/ml for Polio 3. Neutralizing antibodies against poliovirus type 1, 2 and 3 were detected in 96.2%, 96.8% and 89.6% of samples, respectively.

CONCLUSIONS

Overall, this seroprevalence indicates a very high level of immunity of the general population. It must be kept after the switch of immunization strategy from attenuated to inactivated vaccine in Germany.

Enterovirus infections and type 1 diabetes

Type 1 (insulin-dependent) diabetes is a typical organ-specific autoimmune disease where insulin-producing beta cells are destroyed by immune mediated mechanisms. The risk of the disease is modulated by genetic factors, mainly genes coding for human leukocyte antigens (HLA), but environmental factors are needed to trigger the process in genetically susceptible individuals. Possible viral triggers of the disease have been sought for years but their identification has been very difficult. Recently, considerable progress has been made by employing new research methods which have supported the idea that the group of enteroviruses may be particularly important in the pathogenesis. An association between enterovirus infections and type 1 diabetes was first reported 30 years ago and since then evaluated in several studies. Recent molecular studies have considerably strengthened this hypothesis by showing that enterovirus genome is present in the blood of diabetic patients. In addition, the first prospective studies have suggested that enterovirus infections may initiate the beta-cell damaging process several years before clinical diabetes is diagnosed. Ecological studies have also indicated similarities in the epidemiology of type 1 diabetes and poliomyelitis - a well-known enterovirus disease. Experimental models, like enterovirus-infected mice or in vitro-cultured beta cells, have provided important information about possible mechanisms, but still it is not known how beta cells are destroyed in human beings. The ongoing prospective studies will answer many open questions, and should the association still hold true, intervention trials will be needed to confirm causality. Even if enterovirus infections were not associated with all diabetes cases but rather with a subgroup of them, this would offer attractive possibilities to prevent the disease or part of it, for example, by an enterovirus vaccine.

No evidence of abnormal regulation of antibody response to coxsackievirus B4 antigen in prediabetic children

Enterovirus infections are a potential environmental trigger of the autoimmune process leading to clinical type 1 diabetes. It has been suggested that the risk of virus-induced beta-cell damage might be connected with a defect in humoral immune responsiveness to enteroviruses. In the present study we assessed whether such a defect in IgG responsiveness to coxsackievirus B4 antigen existed in young children who developed diabetes-associated autoantibodies during prospective observation from birth until the age of 18 months. IgG levels and maturation of antibody avidity were analysed in 21 children with autoantibodies and 41 control children who had experienced an equal number of enterovirus infections and were additionally matched for age, sex and HLA-DQB1 risk alleles for type 1 diabetes but had not produced diabetes-associated autoantibodies. IgG levels to coxsackievirus B4 were high in cord serum reflecting the presence of maternal antibodies. Mean IgG levels gradually decreased but began to increase after the age of 6 months, showing no significant difference between autoantibody positive and control children. The avidity of antibodies was strong in cord serum and decreased gradually during the first year of life when maternal antibodies disappeared. The avidity indices, which varied considerably from child to child, did not differ between the autoantibody-positive and -negative subjects. In conclusion, our data suggest that children affected by a beta-cell damaging autoimmune process show normal responses to coxsackievirus B4 antigens.

Neonatal and early life vaccinology

Preclinical and human vaccine studies indicate that, although neonatal immunisation does not generally lead to rapid and strong antibody responses, it may result in an efficient immunological priming, which can serve as an excellent basis for future responses. The apparent impairment of CD4 and CD8 T-cell function in early life seems to result from suboptimal antigen-presenting cells-T cell interactions, which can be overcome by use of specific adjuvants or delivery systems. Although persistence of maternal antibodies may limit infant antibody responses, induction of T-cell responses largely remain unaffected by these passively transferred antibodies. Thus, neonatal priming and early boosting with vaccine formulations optimised for sufficient early life immunogenicity and maximal safety profiles, could allow better control of the huge infectious disease burden in early life.

Vaccination in the neonatal period and early infancy

Immune maturation is responsible for a progressive increase in antibody responses that can be elicited during the first year of life, such that neonatal immunization may currently not be expected to induce strong antibody responses. In contrast, B and T cell priming can be induced very early in life, without interference of maternal immunity. Strong IL-5 and IL-13 responses in young mice, and limited IL-12 and IFN-gamma release capacity by early life APC and T cells both in young mice and infants, could contribute to the severity of infections with intracellular pathogens in early life. It calls for evaluation of novel delivery systems, adjuvants and/or prime-boost immunization strategies capable to meet the challenge of both strong neonatal immunogenicity and acceptable reactogenicity. The extent to which early life murine immunization models may be useful for preclinical evaluation of infant responses is outlined in this review.

Comparison of enterovirus-specific cellular immunity in two populations of young children vaccinated with inactivated or live poliovirus vaccines

Enterovirus-specific cellular immunity was studied in Estonian and in Finnish children at the age of 9 months. The aim was to evaluate the level of responsiveness in two neighbouring countries with different poliovirus immunization practices and striking differences in the incidence of insulin-dependent diabetes mellitus (IDDM), a disease in which early enterovirus infections are an aetiological risk factor. The Estonian children immunized with live attenuated polio vaccine had stronger T cell responses to coxsackievirus B4 and poliovirus type 1 when compared with Finnish children immunized with inactivated polio vaccine (median stimulation indices 10.4 and 6.3 in Estonian children and 1.9 and 2.9 in Finnish children, respectively; P < 0.05). Lymphocytes stimulated by poliovirus type 1 antigen expressed interferon-gamma (IFN-gamma) mRNAs, which strongly correlated with the level of proliferation responses. Lymphocytes of Estonian children had a tendency towards stronger expression of IFN-gamma upon poliovirus challenge when compared with Finnish children. The number of children who had experienced coxsackievirus B infections, as determined by the presence of neutralizing antibodies, did not differ between Estonian and Finnish children. The results show that Finnish children have weaker cellular immunity against enteroviruses at the age of 9 months compared with Estonian children at the same age. This is most probably due to the difference in polio vaccination schedules; in Estonia live poliovirus vaccine is used and given at earlier ages than the inactivated vaccines in Finland. This leads to stronger T cell immunity which cross-reacts with other enterovirus serotypes. This may explain the lower incidence of IDDM in Estonia by providing effective protection against diabetogenic enterovirus strains in Estonian children.

Enterovirus infections and insulin dependent diabetes mellitus--evidence for causality

BACKGROUND

Insulin-dependent diabetes mellitus (IDDM) has a long subclinical period characterised by gradually progressing autoimmune damage of insulin producing beta-cells. Clinical IDDM is manifested when 90% of beta-cells have been destroyed. Several studies have indicated that enterovirus infections, coxsackievirus B (CVB) infections especially, are frequent at the manifestation of clinical IDDM suggesting that they can precipitate the symptoms of IDDM in individuals who already have an advanced beta-cell damage. Recently, the first prospective studies have been published suggesting that enterovirus infections can also initiate the process several years before clinical IDDM. This implies that enterovirus infections may have a crucial role in the pathogenesis of human IDDM.

OBJECTIVE

The recent findings have brought up the question whether the time has come when a causal association between enterovirus infections and IDDM could finally be confirmed. This review focuses on this question summarising the current knowledge and the prospects of future research.

STUDY DESIGN

Review of the recent progress in studies evaluating the role of enterovirus infections in human IDDM.

CONCLUSIONS

The currently available information supports the assumption that the role of enterovirus infections may be more important than previously estimated. Enterovirus infections are obviously associated with increased risk of IDDM, but whether this association reflects causal relationship remains to be confirmed in future studies. Prospective birth-cohort studies will be among the most important ones giving important data on the etiologic fraction of enterovirus infections, the properties of diabetogenic virus variants and the mechanisms of beta-cell damage.