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

Coxsackievirus group B3 regulates ASS1-mediated metabolic reprogramming and promotes macrophage inflammatory polarization in viral myocarditis

Coxsackievirus group B3 (CVB3) belongs to the genus Enteroviruses of the family Picornaviridae and is the main pathogen underlying viral myocarditis (VMC). No specific therapeutic is available for this condition. Argininosuccinate synthase 1 (ASS1) is a key enzyme in the urea cycle that converts citrulline and aspartic acid to argininosuccinate. Here, we found that CVB3 and its capsid protein VP2 inhibit the autophagic degradation of ASS1 and that CVB3 consumes citrulline to upregulate ASS1, triggers urea cycle metabolic reprogramming, and then activates macrophages to develop pro-inflammatory polarization, thereby promoting the occurrence and development of VMC. Conversely, citrulline supplementation to prevent depletion can downregulate ASS1, rescue macrophage polarization, and alleviate the pathogenicity of VMC. These findings provide a new perspective on the occurrence and development of VMC, revealing ASS1 as a potential new target for treating this disease.

IMPORTANCE

Viral myocarditis (VMC) is a common and potentially life-threatening myocardial inflammatory disease, most commonly caused by CVB3 infection. So far, the pathogenesis of VMC caused by CVB3 is mainly focused on two aspects: one is the direct myocardial injury caused by a large number of viral replication in the early stage of infection, and the other is the local immune cell infiltration and inflammatory damage of the myocardium in the adaptive immune response stage. There are few studies on the early innate immunity of CVB3 infection in myocardial tissue, but the appearance of macrophages in the early stage of CVB3 infection suggests that they can play a regulatory role as early innate immune response cells in myocardial tissue. Here, we discovered a possible new mechanism of VMC caused by CVB3, revealed new drug targets for anti-CVB3, and discovered the therapeutic potential of citrulline for VMC.

Beyond bNAbs: Uses, Risks, and Opportunities for Therapeutic Application of Non-Neutralising Antibodies in Viral Infection

The vast majority of antibodies generated against a virus will be non-neutralising. However, this does not denote an absence of protective capacity. Yet, within the field, there is typically a large focus on antibodies capable of directly blocking infection (neutralising antibodies, NAbs) of either specific viral strains or multiple viral strains (broadly-neutralising antibodies, bNAbs). More recently, a focus on non-neutralising antibodies (nNAbs), or neutralisation-independent effects of NAbs, has emerged. These can have additive effects on protection or, in some cases, be a major correlate of protection. As their name suggests, nNAbs do not directly neutralise infection but instead, through their Fc domains, may mediate interaction with other immune effectors to induce clearance of viral particles or virally infected cells. nNAbs may also interrupt viral replication within infected cells. Developing technologies of antibody modification and functionalisation may lead to innovative biologics that harness the activities of nNAbs for antiviral prophylaxis and therapeutics. In this review, we discuss specific examples of nNAb actions in viral infections where they have known importance. We also discuss the potential detrimental effects of such responses. Finally, we explore new technologies for nNAb functionalisation to increase efficacy or introduce favourable characteristics for their therapeutic applications.

Antibody-dependent enhancement and neutralization against CVB4 investigated in vitro and in silico through an agent-based model

The infection with coxsackievirus B4 (CVB4) can be enhanced in vitro by antibodies directed against the viral capsid protein VP4. In peripheral blood mononuclear cells, antibody-dependent enhancement (ADE) of CVB4 infection leads to the production of interferon alpha (IFN-α). To investigate ADE of CVB4-induced production of IFN-α, an agent-based model was constructed with enhancing and neutralizing antibodies. The model recapitulates viral neutralization and ADE in silico. The enhancing and neutralizing activities of serum samples were evaluated in vitro to confront the model predictions with experimental results. Increasing the incubation time of CVB4 with serum samples improves virus neutralization in silico as well as in vitro. It also results in ADE at lower antibody numbers in silico, which is confirmed in vitro with IFN-α production at lower serum concentrations. Furthermore, incubation of CVB4 with serum at a low temperature does not induce IFN-α production in vitro. Thus, taken together our results suggest that enhancing antibodies bind cryptic epitopes, more accessible with longer incubation time and at higher temperature due to changes in capsid conformation, consistent with previous results indicating that enhancing antibodies are anti-VP4 antibodies.

Multiple subtypes of coxsackievirus group B can cause congenital heart disease

BACKGROUND

Different serotypes of coxsackievirus B (CVB), which is the most common cause of viral myocarditis, target cardiomyocytes through Coxsackie and Adenovirus Receptor and Decay-Accelerating Factor. Both receptors are expressed in the fetal heart. We hypothesized that infection with different serotypes of CVB during early pregnancy plays a role in pathogenesis of congenital heart defect (CHD).

METHODS

In this study, we use a murine model to infect with CVB1, CVB4, and combination of CVB3 + CVB4 during a critical period in gestation. We examined offspring of pregnant mice for fetal death and heart defects following viral infection.

RESULT

Fetuses from uninfected control dams showed normal heart development, while maternal CVB infection precipitates CHD: majorly ventricular septal defects (VSD) and non-compaction of ventricular myocardium (NC), with some infrequent cases of double outlet right ventricle, left ventricle wall rupture, right ventricle hypertrophy, and thickened/dysplastic semilunar valves. Infection of pregnant dams with CVB1 leads to 44% VSD and 41.2% NC cases, while with CVB4 leads to 31.7% VSD and 13.3% NC cases. Co-infection with CVB3 + CVB4 increases fetal pathology to 51.3% VSD and 41% NC cases. Infection can also result in fetal death, with higher incidences with CVB3 + CVB4 with 46.2% cases, compared to 33.3% by CVB1 and 21.7% by CVB4. Male fetuses were more susceptible to all phenotypes.

CONCLUSION

Our report shows that prenatal CVB infections can lead to pathogenesis of certain heart defects in mouse model, particularly exacerbated with co-infections. This data confirms a link between prenatal CVB infection and CHD development and highlights it is not unique to just one serotype of CVB.

Persistent coxsackievirus B infection and pathogenesis of type 1 diabetes mellitus

Enteroviruses are believed to trigger or accelerate islet autoimmunity in genetically susceptible individuals, thereby resulting in loss of functional insulin-producing β-cells and type 1 diabetes mellitus (T1DM). Although enteroviruses are primarily involved in acute and lytic infections in vitro and in vivo, they can also establish a persistent infection. Prospective epidemiological studies have strongly associated the persistence of enteroviruses, especially coxsackievirus B (CVB), with the appearance of islet autoantibodies and an increased risk of T1DM. CVB can persist in pancreatic ductal and β-cells, which leads to structural or functional alterations of these cells, and to a chronic inflammatory response that promotes recruitment and activation of pre-existing autoreactive T cells and β-cell autoimmune destruction. CVB persistence in other sites, such as the intestine, blood cells and thymus, has been described; these sites could serve as a reservoir for infection or reinfection of the pancreas, and this persistence could have a role in the disturbance of tolerance to β-cells. This Review addresses the involvement of persistent enterovirus infection in triggering islet autoimmunity and T1DM, as well as current strategies to control enterovirus infections for preventing or reducing the risk of T1DM onset.

Effect of Coxsackievirus B4 Infection on the Thymus: Elucidating Its Role in the Pathogenesis of Type 1 Diabetes

The thymus gland is a primary lymphoid organ for T-cell development. Various viral infections can result in disturbance of thymic functions. Medullary thymic epithelial cells (mTECs) are important for the negative selection of self-reactive T-cells to ensure central tolerance. Insulin-like growth factor 2 (IGF2) is the dominant self-peptide of the insulin family expressed in mTECs and plays a crucial role in the intra-thymic programing of central tolerance to insulin-secreting islet β-cells. Coxsackievirus B4 (CVB4) can infect and persist in the thymus of humans and mice, thus hampering the T-cell maturation and differentiation process. The modulation of IGF2 expression and protein synthesis during a CVB4 infection has been observed in vitro and in vivo in mouse models. The effect of CVB4 infections on human and mouse fetal thymus has been studied in vitro. Moreover, following the inoculation of CVB4 in pregnant mice, the thymic function in the fetus and offspring was disturbed. A defect in the intra-thymic expression of self-peptides by mTECs may be triggered by CVB4. The effects of viral infections, especially CVB4 infection, on thymic cells and functions and their possible role in the pathogenesis of type 1 diabetes (T1D) are presented.

Genetic Adaptation of Coxsackievirus B1 during Persistent Infection in Pancreatic Cells

Coxsackie B (CVB) viruses have been associated with type 1 diabetes. We have recently observed that CVB1 was linked to the initiation of the autoimmune process leading to type 1 diabetes in Finnish children. Viral persistency in the pancreas is currently considered as one possible mechanism. In the current study persistent infection was established in pancreatic ductal and beta cell lines (PANC-1 and 1.1B4) using four different CVB1 strains, including the prototype strain and three clinical isolates. We sequenced 5′ untranslated region (UTR) and regions coding for structural and non-structural proteins and the second single open reading frame (ORF) protein of all persisting CVB1 strains using next generation sequencing to identify mutations that are common for all of these strains. One mutation, K257R in VP1, was found from all persisting CVB1 strains. The mutations were mainly accumulated in viral structural proteins, especially at BC, DE, EF loops and C-terminus of viral capsid protein 1 (VP1), the puff region of VP2, the knob region of VP3 and infection-enhancing epitope of VP4. This showed that the capsid region of the viruses sustains various changes during persistency some of which could be hallmark(s) of persistency.

Enhancing and neutralizing anti-coxsackievirus activities in serum samples from patients prior to development of type 1 diabetes

BACKGROUND

Studies in prospective cohorts have suggested that enterovirus infections are associated with the appearance of islet autoantibodies that precede later appearance of type 1 diabetes (T1D). It was shown that in addition to an antibody-mediated anti-coxsackievirus (CV)-B neutralizing activity of serum from patients with T1D, there was also enhancing anti-CV-B activity in vitro. In this study, the patterns of enhancing and neutralizing anti-CV activities were analysed from consecutive serum samples collected from children who were followed from birth until they developed T1D in the Finnish Type 1 Diabetes Prediction and Prevention (DIPP) study and compared to those in non-diabetic control children.

METHODS

The titres of serum neutralizing activity were analysed against those CVs which were detected in the stools in these children (CV-B3, CV-B5 or CV-A4) using plaque assay. The enhancing activity of these serum samples was analysed by measuring interferon-alpha (INF-α) production in cultures of peripheral blood mononuclear cells (PBMC) inoculated with a mixture of these viruses and diluted serum.

RESULTS

A sustained anti-CV enhancing activity was observed in consecutive serum samples in patients with T1D. The pattern of responses differed between children who developed T1D and control children. In patients, the anti-CV enhancing activity was predominant or even exclusive over the neutralizing activity, whereas in controls the enhancing and neutralising activities were more balanced or the neutralizing activity was largely predominant.

CONCLUSIONS

Evaluating the anti-enterovirus neutralizing and enhancing activity of serum samples can be useful to investigate further the relationship between enteroviruses and the development of T1D.

Coxsackievirus-B4 Infection Can Induce the Expression of Human Endogenous Retrovirus W in Primary Cells

Human Endogenous Retrovirus W Envelope (HERV-W ENV) mRNA or protein can be found in peripheral blood mononuclear cells (PBMCs) and exocrine pancreas of patients with type 1 diabetes (T1D). Further, previous observations have shown an association between enteroviral infection and development of T1D; specifically, coxsackievirus-B (CV-B) has been detected in the blood and pancreas of patients with T1D. Notably, viruses can activate HERV-W expression. Hence, we evaluated the effect of CV-B4 infection on HERV-W ENV mRNA expression. Primary human pancreatic ductal cells were obtained from five brain-dead donors. In the pancreatic cells of three donors, the HERV-W ENV mRNA level measured using RT-qPCR was upregulated upon CV-B4 infection. The HERV-W ENV protein was detected in the infected cells using the immunoblot assay. In human PBMCs inoculated with CV-B4 or when CV-B4 was incubated with an enhancing serum, the HERV-W ENV mRNA level was higher than the background RNA level. In monocyte-derived macrophages obtained from 5 of 13 donors, the HERV-W ENV mRNA level was higher in cultures inoculated with CV-B4 than in the control. Therefore, CV-B4 can upregulate or induce the transcription of a certain HERV-W ENV copy (or copies) in primary cell cultures, such as monocytes, macrophages, and pancreatic cells.

Serum-derived IgG from coxsackievirus A6-infected patients can enhance the infection of peripheral blood mononuclear cells with coxsackievirus A6

Coxsackievirus A6 (CV-A6) has recently emerged as an enterovirus causing Hand Foot and Mouth Disease with severe complications. The pathogenic mechanisms of CV-A6- associated Hand foot and Mouth disease are largely unknown. In this study, it was investigated whether serum and IgG from patients with CV-A6 infection can enhance the infection of PBMC with the virus. Serum samples were obtained from five children with CV-A6 infection confirmed by RT-PCR and seven controls. IgG was isolated from serum by using affinity chromatography columns. CV-A6 was incubated with serum or IgG from controls and patients then the mixtures were added to PBMC cultures. The levels of IFNα in supernatants were measured by ELISA, and the levels of intracellular viral RNA were measured by RT-qPCR. It has been observed that there is an anti-CV-A6 enhancing activity in serum and serum-derived immunoglobulin G of children with CV-A6 infection but not in those of uninfected controls. Whether this activity has implications in the pathogenesis of CV-A6 associated diseases should be investigated.

Structure, Immunogenicity, and Protective Mechanism of an Engineered Enterovirus 71-Like Particle Vaccine Mimicking 80S Empty Capsid

Enterovirus 71 (EV71) is the major causative agent of severe hand, foot, and mouth disease, which affects millions of young children in the Asia-Pacific region annually. In this study, we engineered a novel EV71 virus-like particle (VLP) that lacks VP4 (therefore designated VLP_ΔVP4) and investigated its structure, antigenicity, and vaccine potential. The cryo-electron microscopy (cryo-EM) structure of VLP_ΔVP4 was reconstructed to 3.71-Å resolution. Results from structural and biochemical analyses revealed that VLP_ΔVP4 resembles the end product of the viral uncoating process, the 80S empty capsid. VLP_ΔVP4 is able to elicit high-titer neutralizing antibodies and to fully protect mice against lethal viral challenge. Mechanistic studies showed that, at the cellular level, the anti-VLP_ΔVP4 sera exert neutralization effects at both pre- and postattachment stages by inhibiting both virus attachment and internalization, and at the molecular level, the antisera can block multiple interactions between EV71 and its key receptors. Our study gives a better understanding of EV71 capsid assembly and provides important information for the design and development of new-generation vaccines for EV71, and perhaps for other enteroviruses, as well.IMPORTANCE Enterovirus 71 (EV71) infection may lead to severe hand, foot, and mouth disease, with significant morbidity and mortality. Knowledge regarding EV71 particle assembly remains limited. Here, we report the generation and characterization of a novel EV71 virus-like particle that lacks the VP4 capsid subunit protein. This particle, termed VLP_ΔVP4, structurally mimics the 80S empty capsid, which is the end stage of EV71 uncoating. We further show that VLP_ΔVP4 exhibits desirable immunogenicity and protective efficacy in proof-of-concept studies. In addition, the inhibitory mechanisms of the VLP_ΔVP4-induced antibodies are unraveled at both the cellular and molecular levels. Our work provides the first evidence of picornaviral particle assembly in the complete absence of VP4 and identifies VLP_ΔVP4 as an improved EV71 vaccine candidate with desirable traits. These findings not only enhance our understanding of particle assembly and uncoating of picornaviruses, but also provide important information for structure-guided vaccine design for EV71 and other enteroviruses.

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

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

Naturally Occurring Fc-Dependent Antibody From HIV-Seronegative Individuals Promotes HIV-Induced IFN-α Production

A majority of adults without HIV infection and with a low risk of HIV-exposure have plasma IgG antibodies that enhance the rate and magnitude of HIV-induced interferon alpha (IFN-α) production. Fc-dependent IgG-HIV complexes induce IFN-α rapidly and in high titers in response to HIV concentrations that are too low to otherwise stimulate an effective IFN-α response. IFN-α promoting antibody (IPA) counters HIV-specific inhibition of IFN-α production, and compensates for the inherent delay in IFN-α production common to HIV infection and other viruses. Naturally occurring IPA has the potential to initiate a potent IFN-α response early in the course of HIV mucosal invasion in time to terminate infection prior to the creation of a pool of persistently infected cells. The current study adds IPA as a mediator of an Fc-dependent antiviral state capable of preventing HIV infection.

Immunoglobulin G-dependent enhancement of the infection with Coxsackievirus B4 in a murine system

It was demonstrated that specific IgG can enhance the infection with CV-B4, in vitro, in the human system. This enhancement could be involved in the pathophysiology of CV-B4 induced diseases. To investigate further the role of enhancing IgG in the infection with CV-B4 E2 in vivo, animal models are needed. Therefore, it was decided to assess whether inoculation of CV-B4 E2 to mice results in the appearance of IgG able to enhance the infection with this virus. Swiss albino mice were inoculated with CV-B4 E2 intraperitoneally. Serum samples were obtained from tail vein blood collected from day 0 to day 80 p.i. IgG were isolated by Protein G affinity chromatography. Seroneutralisation assays were carried out. In total murine spleen cells cultures inoculated with CV-B4 E2 mixed with various dilutions of serum or IgG samples, the enhancing activity was assayed through i) the antiviral activity titer of supernatants ii) the detection of intracellular viral RNA by RT-PCR iii) the level of infectious particles in supernatants. In most serum samples (76/105), neutralizing and enhancing activities were detected peaking between days 14 and 30 p.i and were higher in sera from mice inoculated with 2.10(6) TCID50 units than with lower doses. The enhancing activity was due to the IgG-enriched fraction of serum from CV-B4 E2 infected animals but not from control animals. These data show that IgG from immune mice can enhance the infection of splenocytes with CV-B4 E2 in vitro and open the way to explore whether such an enhancing activity can play a role in vivo.

Coxsackievirus B4 Can Infect Human Peripheral Blood-Derived Macrophages

Beyond acute infections, group B coxsackieviruses (CVB) are also reported to play a role in the development of chronic diseases, like type 1 diabetes. The viral pathogenesis mainly relies on the interplay between the viruses and innate immune response in genetically-susceptible individuals. We investigated the interaction between CVB4 and macrophages considered as major players in immune response. Monocyte-derived macrophages (MDM) generated with either M-CSF or GM-CSF were inoculated with CVB4, and infection, inflammation, viral replication and persistence were assessed. M-CSF-induced MDM, but not GM-CSF-induced MDM, can be infected by CVB4. In addition, enhancing serum was not needed to infect MDM in contrast with parental monocytes. The expression of viral receptor (CAR) mRNA was similar in both M-CSF and GM-CSF MDM. CVB4 induced high levels of pro-inflammatory cytokines (IL-6 and TNFα) in both MDM populations. CVB4 effectively replicated and persisted in M-CSF MDM, but IFNα was produced in the early phase of infection only. Our results demonstrate that CVB4 can replicate and persist in MDM. Further investigations are required to determine whether the interaction between the virus and MDM plays a role in the pathogenesis of CVB-induced chronic diseases.

In vitro interaction between coxsackievirus B3 VP1 protein and human pleckstrin homology domain retinal protein (PHR1)

Coxsackievirus B3 (CVB3) infection causes central nervous system diseases including aseptic meningitis and encephalitis. To understand the mechanism of this virus, a yeast two-hybrid system was used to screen cellular proteins from a human heart cDNA library. The results revealed that the human Pleckstrin Homology Domain Retinal protein (PHR1), a PH domain-containing protein with low expression in the heart and high expression in the brain, interacts with CVB3 VP1, a major structural protein of CVB3. Yeast mating assays and in vitro coimmunoprecipitation verified the interaction between CVB3 VP1 and PHR1. An α-galactosidase assay indicated that of α-galactosidase activity was higher in positive clones than in controls suggesting a strong interaction. Furthermore, assay of deletion mutants defined the minimal region of PHR1 required for its interaction with VP1 as amino acids 95-172 and two regions of VP1 required for its interaction with PHR1 as amino acids 729-767 and 811-859. The results revealed multiple binding sites between PHR1 and CVB3 VP1 and suggested that the strong interaction between these two proteins might play an important role in central nervous system disease in the human brain.

Viruses contained in droplets applied on warmed surface are rapidly inactivated

Heat inactivation of viruses was reported, however, the thermal resistance of viruses in droplets has not been studied. The aim of this study was to evaluate the pattern of heat resistance of minute virus of mice (MVM), coxsackievirus B4 (CVB4), influenza A virus (H1N1), and herpes simplex virus type 1 (HSV1) contained in droplets. Four μL droplets containing viruses (> 10(4.5) TCID50) were applied onto warmed surface obtained by using a self-made heating device. Viral suspensions were exposed to temperatures ranging from 70 to 130°C for 0 to 90 min depending on the virus, and then the recovered viral preparations were tittered. Inactivation rates were calculated from curves that were analysed according to the first order kinetics model. Full inactivation was obtained for MVM in 90 min at 80°C and in 2 s at 130°C, for H1N1 in 14 s at 70°C and in 1 s at 110°C, for CVB4 and HSV-1 in 5 s and 7 s respectively at 70°C and in 1 s at 100°C. Clearly, MVM was more resistant than H1N1 that was more resistant than HSV-1 and CVB4, which was reflected by increasing inactivation rates. The impact of short time exposure to heat onto the infectivity of viruses contained in a small volume of suspension has been determined. For the first time, the inactivation of viral particles contained in drops exposed to temperatures higher than 100°C has been investigated. It appears that heating can have an unexpected faster virucidal effect than previously described.

Immunology in the clinic review series; focus on type 1 diabetes and viruses: role of antibodies enhancing the infection with Coxsackievirus-B in the pathogenesis of type 1 diabetes

Type 1 diabetes results from an interaction between genetic and environmental factors. Coxsackieviruses B (CV-B) are major environmental candidates, as suggested by epidemiological and experimental studies. The mechanisms leading to the disease involve interactions between the virus, host target tissue (pancreas) and the immune system. The infection of target cells with viruses can be prevented by antibodies. Conversely, the infection can be enhanced by antibodies. The antibody-dependent enhancement (ADE) of infection has been described with various viruses, especially Picornaviruses. In mice infected with CV-B3 this phenomenon resulted in an extended inflammatory reaction and myocarditis. In the human system non-neutralizing antibodies can increase the infection of monocytes with CV-B4 and stimulate the production of interferon (IFN)-α by these cells in vitro. CV-B4/immunoglobulin (Ig)G immune complexes interacted with a specific viral receptor [Coxsackievirus and adenovirus receptor (CAR)] and with IgG Fc fraction receptors (FcγRII and FcγRIII) at the surface of monocytes. The virus-antibody complexes are internalized (CAR) and receptors for the Fc of IgG (FcγRII and FcγRIII). Such antibodies have been detected in patients with type 1 diabetes and they could be responsible for the presence of enteroviral RNA and IFN-α in peripheral blood mononuclear cells (PBMC) of these individuals. The target of enhancing antibodies has been identified as the VP4 protein, which allowed the detection of these antibodies by enzyme-linked immunosorbent assay (ELISA). It cannot be excluded that antibodies enhancing the infection with CV-B may play a role in the pathogenesis of type 1 diabetes, induced or aggravated by these viruses. They can cause a viral escape from the immune response and may participate in the spreading of viruses to β cells. Whether enhancing antibodies raised against VP4 can play a role in iterative homologous and/or heterologous CV-B infections and in the persistence of viruses within the host deserves further study.

Group B coxsackieviruses and autoimmunity: focus on Type 1 diabetes

Group B coxsackieviruses (CVB) and/or their components have been found in the blood and pancreas of patients with Type 1 diabetes (T1D). CVB infections lead to the activation of the innate and adaptive immune systems, which can result in the induction or aggravation of autoimmune processes. Persistent and/or repeated infections of pancreas islet β cells with CVB and the resulting production of IFN-α and inflammatory mediators, combined with a predisposed genetic background, may induce bystander activation of autoimmune effector T cells and an autoreactive response to islet self-antigens through molecular mimicry. Moreover, the antibody-dependent enhancement of CVB infection of monocytes, as well as infection of the thymus can intervene in the pathogenesis of T1D. In contrast with the deleterious effect of CVB, it has been shown that these viruses can protect against the development of T1D under certain experimental conditions. The role of CVB in autoimmunity is complex, and therefore a better understanding of the inducer versus protective effects of these viruses in T1D will help to design new strategies to treat and prevent the disease.

Antibody dependent enhancement infection of enterovirus 71 in vitro and in vivo

BACKGROUND

Human enterovirus 71 (EV71) has emerged as a significant cause of acute encephalitis and deaths in young children. The clinical manifestations caused by EV71 varied from mild hand, foot and mouth disease to severe neurological complications and deaths, but its pathogenesis remains elusive. Antibody dependent enhancement (ADE) infection has been reported in various viruses and has been shown to contribute to disease severity.

RESULTS

In this study, the presence of sub-neutralizing antibody was demonstrated to enhance EV71 infection in THP-1 cells and increase the mortality of EV71 infection in a suckling mouse model. Further, a secondary infection model was established to characterize the correlation between ADE and disease severity, and primary asymptomatic EV71 infection was shown to increase the mortality of the secondary EV71 infection in suckling mice.

CONCLUSIONS

Together, these in vitro and in vivo experiments strongly supported the hypothesis of ADE infection of EV71. The present findings indicate ADE might contribute to the pathogenesis of severe EV71 infection, and raise practical issues of vaccine development and antibody-based therapy.

Antibody-dependent enhancement of coxsackievirus B3 infection of primary CD19+ B lymphocytes

Coxsackievirus B3 (CVB3) is associated with several different acute and chronic forms of human disease, including myocarditis, aseptic meningitis, and pancreatitis. Moreover, CVB3 also infects immune cells like CD19+ B lymphocytes, but the viral uptake mechanism into these cells is not well understood. Therefore, primary murine and human CD19+ B cells were isolated by magnetic-activated cell separation technology and analyzed for virus receptor expression, antibody-dependent enhancement of viral infection, and different cellular surface proteins, that might be involved in mechanisms of viral uptake. Western blot analysis of these cells revealed no significant expression of the coxsackievirus-adenovirus receptor CAR. But incubation of CVB3 with serum dilutions, which exhibited binding but not neutralizing characteristics, increased viral uptake and replication significantly in a dose-dependent manner. Viral entry was reduced when Fc portions of immunoglobulins were blocked by protein A treatment. Moreover, the classical complement system rather than Fc-gamma-receptor-mediated mechanisms could be involved in viral uptake. Taken together, these data suggest an antibody-dependent enhancement of CVB3 infection of primary murine and human CD19+ B cells.

Enteroviruses and type 1 diabetes: towards a better understanding of the relationship

Environmental factors, especially viruses, are involved in the initiation or the acceleration of type 1 diabetes (T1D) pathogenesis. Epidemiological data strongly suggest that enteroviruses, such as coxsackievirus B4 (CV-B4), can be associated with T1D. It has been demonstrated that enterovirus infections were significantly more prevalent in at risk individuals, such as siblings of diabetic patients, when they developed 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 strengthened the hypothesis of a relationship between the virus and the disease. Studies performed in vitro and in vivo in animal models helped to discover mechanisms of the infection of pancreas and other tissues, potentially able to play a role in the pathogenesis of T1D. Interestingly, it cannot be excluded that enteroviruses behave as half-devil half-angel since experimental studies suggest that, in certain conditions, these agents would be able to protect individuals against the disease. All of the plausible mechanisms by which enterovirus may be related to T1D will be reviewed here.

Virus infections and type 1 diabetes risk

Common intestinal infections caused by human enteroviruses (HEVs) are considered major environmental factors predisposing to type 1 diabetes (T1D). In spite of the active research of the field, the HEV-induced pathogenetic processes are poorly understood. Recently, after the first documented report on HEV infections in the pancreatic islets of deceased T1D patients, several groups became interested in the issue and studied valuable human material, the autopsy pancreases of diabetic and/or autoantibody-positive patients for HEV infections. In this review, the data on HEV infections in human pancreatic islets are discussed with special reference to the methods used. Likewise, mechanisms that could increase viral access to the pancreas are reviewed and discussed.

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.

Mechanisms and results of the antibody-dependent enhancement of viral infections and role in the pathogenesis of coxsackievirus B-induced diseases

The mechanisms of the antibody-dependent enhancement (ADE) of viral infection are presented, particularly within the Picornaviridae family. The ADE of infection has been described in both human and animal models, worsens viral infections and compromises vaccine safety. The ADE of coxsackievirus B infection can also be implied in the pathogenesis of diseases like chronic dilated cardiomyopathy or insulin-dependent type 1 diabetes.

A novel role for non-neutralizing antibodies against nucleoprotein in facilitating resistance to influenza virus

Current influenza vaccines elicit Abs to the hemagglutinin and neuraminidase envelope proteins. Due to antigenic drift, these vaccines must be reformulated annually to include the envelope proteins predicted to dominate in the following season. By contrast, vaccination with the conserved nucleoprotein (NP) elicits immunity against multiple serotypes (heterosubtypic immunity). NP vaccination is generally thought to convey protection primarily via CD8 effector mechanisms. However, significant titers of anti-NP Abs are also induced, yet the involvement of Abs in protection has largely been disregarded. To investigate how Ab responses might contribute to heterosubtypic immunity, we vaccinated C57BL/6 mice with soluble rNP. This approach induced high titers of NP-specific serum Ab, but only poorly detectable NP-specific T cell responses. Nevertheless, rNP immunization significantly reduced morbidity and viral titers after influenza challenge. Importantly, Ab-deficient mice were not protected by this vaccination strategy. Furthermore, rNP-immune serum could transfer protection to naive hosts in an Ab-dependent manner. Therefore, Ab to conserved, internal viral proteins, such as NP, provides an unexpected, yet important mechanism of protection against influenza. These results suggest that vaccines designed to elicit optimal heterosubtypic immunity to influenza should promote both Ab and T cell responses to conserved internal proteins.

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.

Antibody-mediated enhancement of the rate, magnitude, and responsiveness of vesicular stomatitis virus induced alpha interferon production

A majority of adults without evidence of exposure to vesicular stomatitis virus (VSV) have serum IgG antibodies that interact with pro-inflammatory TLR7 in the presence of VSV, and enhance several aspects of VSV-induced IFN-alpha production. Enhancing IgG antibody enables human PBMC to make IFN-alpha more rapidly and in higher titers in response to a broad range of VSV-concentrations that include those too low to independently stimulate IFN-alpha production. These antibody-mediated functions compensate for the inherent delay in virus-induced IFN-alpha production in vitro, and have the potential to improve the in vivo IFN-alpha response and effectively terminate infection before the occurrence of clinically apparent disease. The frequent presence of enhancing antibody in persons without predictable VSV exposure has implications for naturally occurring infections with this and other viruses, and for the use of viruses as vaccine vectors and oncolytic agents.

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.

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.