Antigenic sites of coxsackievirus A9

T-Cell Receptor Sequences Identify Combined Coxsackievirus-Streptococci Infections as Triggers for Autoimmune Myocarditis and Coxsackievirus-Clostridia Infections for Type 1 Diabetes

Recent research suggests that T-cell receptor (TCR) sequences expanded during human immunodeficiency virus and SARS-CoV-2 infections unexpectedly mimic these viruses. The hypothesis tested here is that TCR sequences expanded in patients with type 1 diabetes mellitus (T1DM) and autoimmune myocarditis (AM) mimic the infectious triggers of these diseases. Indeed, TCR sequences mimicking coxsackieviruses, which are implicated as triggers of both diseases, are statistically significantly increased in both T1DM and AM patients. However, TCRs mimicking Clostridia antigens are significantly expanded in T1DM, whereas TCRs mimicking Streptococcal antigens are expanded in AM. Notably, Clostridia antigens mimic T1DM autoantigens, such as insulin and glutamic acid decarboxylase, whereas Streptococcal antigens mimic cardiac autoantigens, such as myosin and laminins. Thus, T1DM may be triggered by combined infections of coxsackieviruses with Clostridia bacteria, while AM may be triggered by coxsackieviruses with Streptococci. These TCR results are consistent with both epidemiological and clinical data and recent experimental studies of cross-reactivities of coxsackievirus, Clostridial, and Streptococcal antibodies with T1DM and AM antigens. These data provide the basis for developing novel animal models of AM and T1DM and may provide a generalizable method for revealing the etiologies of other autoimmune diseases. Theories to explain these results are explored.

Enterovirus D68 molecular and cellular biology and pathogenesis

In recent years, enterovirus D68 (EV-D68) has advanced from a rarely detected respiratory virus to a widespread pathogen responsible for increasing rates of severe respiratory illness and acute flaccid myelitis (AFM) in children worldwide. In this review, we discuss the accumulating data on the molecular features of EV-D68 and place these into the context of enterovirus biology in general. We highlight similarities and differences with other enteroviruses and genetic divergence from own historical prototype strains of EV-D68. These include changes in capsid antigens, host cell receptor usage, and viral RNA metabolism collectively leading to increased virulence. Furthermore, we discuss the impact of EV-D68 infection on the biology of its host cells, and how these changes are hypothesized to contribute to motor neuron toxicity in AFM. We highlight areas in need of further research, including the identification of its primary receptor and an understanding of the pathogenic cascade leading to motor neuron injury in AFM. Finally, we discuss the epidemiology of the EV-D68 and potential therapeutic approaches.

Genetic characterization of a novel recombinant echovirus 30 strain causing a regional epidemic of aseptic meningitis in Hokkaido, Japan, 2017

A regional epidemic of aseptic meningitis caused by echovirus 30 (E30) occurred in Hokkaido, Japan, during the period of August-December 2017. To investigate their phylogenetic relationship to other human enteroviruses, we determined the complete genomic nucleotide sequences of isolates from this outbreak. Phylogenetic analysis of the viral capsid protein 1 gene showed that the strains were most closely related to E30 strains detected in Germany, France, and Russia in 2013. In contrast, the region encoding the viral protease and the RNA-dependent RNA polymerase had a close phylogenetic relationship to non-E30 enteroviruses detected in the United Kingdom and Switzerland in 2015-2017, suggesting that a recombination event had occurred.

Evolutionary and Functional Diversity of the 5' Untranslated Region of Enterovirus D68: Increased Activity of the Internal Ribosome Entry Site of Viral Strains during the 2010s

The 5′ untranslated region (UTR) of the RNA genomes of enteroviruses possesses an internal ribosome entry site (IRES) that directs translation of the mRNA by binding to ribosomes. Infection with enterovirus D68 causes respiratory symptoms and is sometimes associated with neurological disorders. The number of reports of the viral infection and neurological disorders has increased in 2010s, although the reason behind this phenomenon remains unelucidated. In this study, we investigated the evolutionary and functional diversity of the 5′ UTR of recently circulating strains of the virus. Genomic sequences of 374 viral strains were acquired and subjected to phylogenetic analysis. The IRES activity of the viruses was measured using a luciferase reporter assay. We found a highly conserved sequence in the 5′ UTR and also identified the location of variable sites in the predicted RNA secondary structure. IRES activities differed among the strains in some cell lines, including neuronal and respiratory cells, and were especially high in strains of a major lineage from the recent surge. The effect of mutations in the 5′ UTR should be studied further in the future for better understanding of viral pathogenesis.

Human Parechovirus: an Increasingly Recognized Cause of Sepsis-Like Illness in Young Infants

Human parechovirus (HPeV) is increasingly being recognized as a potentially severe viral infection in neonates and young infants. HPeV belongs to the family Picornaviridae and is currently divided into 19 genotypes. HPeV-1 is the most prevalent genotype and most commonly causes gastrointestinal and respiratory disease. HPeV-3 is clinically the most important genotype due to its association with severe disease in younger infants, which may partly be explained by its distinct virological properties. In young infants, the typical clinical presentation includes fever, severe irritability, and rash, often leading to descriptions of "hot, red, angry babies." Infants with severe central nervous system (CNS) infections are at an increased risk of long-term sequelae. Considering the importance of HPeV as a cause of severe viral infections in young infants, we recommend that molecular diagnostic techniques for early detection be included in the standard practice for the investigation of sepsis-like illnesses and CNS infections in this age group.

Photodynamic inactivation of bacteriophage MS2: The A-protein is the target of virus inactivation

Singlet oxygen mediated oxidation has been shown to be responsible for photodynamic inactivation (PDI) of viruses in solution with photosensitisers such as 5, 10, 15, 20-tetrakis (1-methyl-4-pyridinio) porphyrin tetra p-toluenesulfonate (TMPyP). The capsids of non-enveloped viruses, such as bacteriophage MS2, are possible targets for viral inactivation by singlet oxygen oxidation. Within the capsid (predominantly composed of coat protein), the A-protein acts as the host recognition and attachment protein. The A-protein has two domains; an α-helix domain and a β-sheet domain. The α-helix domain is attached to the viral RNA genome inside the capsid while the β-sheet domain, which is on the surface of the capsid, is believed to be the site for attachment to the host bacteria pilus during infection. In this study, 4 sequence-specific antibodies were raised against 4 sites on the A-protein. Changes induced by the oxidation of singlet oxygen were compared to the rate of PDI of the virus. Using these antibodies, our results suggest that the rate of PDI is relative to loss of antigenicity of two sites on the A-protein. Our data further showed that PDI caused aggregation of MS2 particles and crosslinking of MS2 coat protein. However, these inter- and intra-capsid changes did not correlate to the rate of PDI we observed in MS2. Possible modes of action are discussed as a means to gaining insight to the targets and mechanisms of PDI of viruses.

Mapping a Type-specific Epitope by Monoclonal Antibody against VP3 Protein of Duck Hepatitis A Type 1 Virus

Duck hepatitis A subtype 1 virus (DHAV-1) infection causes high mortality in ducklings, resulting in significant losses to duck industries. VP3 is a structural protein of DHAV-1. However, B-cell epitopes on VP3 have not been investigated. To stimulate VP3 antibody response, eukaryotic expression plasmid pCI-neo-VP3 was constructed and used as DNA immunogen to prepare mAbs. Western blot showed that 25.5 kDa VP3 could be detected by mAbs in duck embryo fibroblast (DEF) cells transfected with pCI-neo-VP3. Immunofluorescence assay showed that mAbs could specifically bind to DEF cells infected with DHAV-1. DAPI staining indicated that VP3 localizes to the cytoplasm and nucleus of DHAV-1 infected DEF. With neutralizing mAb 3B7, minimal epitope PSNI was mapped. Sequence alignment indicated that ²⁰⁵PSNI²⁰⁸ is highly conserved among DHAV-1, but different from those of DHAV-2 and DHAV-3. Epitope peptide reacted specifically with DHAV-1-positive duck sera by dot blotting, revealing PSNI is DHAV-1 type-specific epitope and the importance of these amino acids in antibody-epitope binding reactivity. These findings provided useful information for understanding the antigenicity of VP3 and might be valuable in the development of epitope-based vaccine or diagnostic kit for DHAV-1 infection and provide insights for understanding the pathogenesis of DHAV-1.

Serum Neutralization Assay for the Determination of Antibody Levels Against Non-Polio Enterovirus Strains in Central and Western Greece

Mutations and recombination events have been identified in enteroviruses. Point mutations accumulate with a frequency of 6.3 × 10(-4) per base pair per replication cycle affecting the fitness, the circulation, and the infectivity of enteroviral strains. In the present report, the serological status of the Central and Western Greek population (Larissa and Ioannina, respectively) in the 1-10-year, 11-20-year, 21-30-year, and 31-40-year age groups against six non-polio enterovirus strains, their respective echovirus prototypes, and Sabin 1, 2, and 3 vaccine strains was evaluated, through serum-neutralization assay. In the Western Greek population, antibody levels were detected only for clinical isolates of E30 serotype in all age groups, and for environmental isolate LR61G3 (E6 serotype) only in the 31-40 age group, whereas an immunity level was observed in the Central Greek population, against all strains, except for EIS6B (E3 serotype). Amino acid substitutions were encountered across the structural region of the capsid, between the prototypes and the respective isolates. These substitutions may alter the antigenicity of each strain and may explain the variations observed in the neutralization titers of the different strains. As a consequence, these substitutions severely affect antibody binding and increase the ability of the virus to escape the immune response. It is tempting to assume that changes in the antigenic properties observed in circulating echoviruses represent a selection of viral variants that are less prone to be neutralized by human antibodies. These facts argue for the need of immunological studies to the population to avoid epidemics due to the circulation of highly evolved derivatives.

Role of Heparan Sulfate in Cellular Infection of Integrin-Binding Coxsackievirus A9 and Human Parechovirus 1 Isolates

Heparan sulfate/heparin class of proteoglycans (HSPG) have been shown to function in cellular attachment and infection of numerous viruses including picornaviruses. Coxsackievirus A9 (CV-A9) and human parechovirus 1 (HPeV-1) are integrin-binding members in the family Picornaviridae. CV-A9 Griggs and HPeV-1 Harris (prototype) strains have been reported not to bind to heparin, but it was recently shown that some CV-A9 isolates interact with heparin in vitro via VP1 protein with a specific T132R/K mutation. We found that the infectivity of both CV-A9 Griggs and HPeV-1 Harris was reduced by sodium chlorate and heparinase suggestive of HSPG interactions. We analyzed the T132 site in fifty-four (54) CV-A9 clinical isolates and found that only one of them possessed T132/R mutation while the other nine (9) had T132K. We then treated CV-A9 Griggs and HPeV-1 Harris and eight CV-A9 and six HPeV-1 clinical isolates with heparin and protamine. Although infectivity of Griggs strain was slightly reduced (by 25%), heparin treatment did not affect the infectivity of the CV-A9 isolates that do not possess the T132R/K mutation, which is in line with the previous findings. Some of the HPeV-1 isolates were also affected by heparin treatment, which suggested that there may be a specific heparin binding site in HPeV-1. In contrast, protamine (a specific inhibitor of heparin) completely inhibited the infection of both prototypes and clinical CV-A9 and HPeV-1 isolates. We conclude that T132R/K mutation has a role in heparin binding of CV-A9, but we also show data, which suggest that there are other HSPG binding sites in CV-A9. In all, we suggest that HSPGs play a general role in both CV-A9 and HPeV-1 infections.

Genotypic Differences in Dengue Virus Neutralization Are Explained by a Single Amino Acid Mutation That Modulates Virus Breathing

Flaviviruses sample an ensemble of virion conformations resulting from the conformational flexibility of their structural proteins. To investigate how sequence variation among strains impacts virus breathing, we performed studies with the monoclonal antibody (MAb) E111, which binds an inaccessible domain III envelope (E) protein epitope of dengue virus serotype 1 (DENV1). Prior studies indicated that an observed ~200-fold difference in neutralization between the DENV1 strains Western Pacific-74 (West Pac-74) and 16007 could not be explained by differences in the affinity of MAb E111 for each strain. Through neutralization studies with wild-type and variant viruses carrying genes encoding reciprocal mutations at all 13 amino acid differences between the E proteins of West Pac-74 and 16007, we found that E111 neutralization susceptibility mapped solely to the presence of a lysine or arginine at E domain II residue 204, located distally from the E111 epitope. This same residue correlated with neutralization differences observed for MAbs specific for epitopes distinct from E111, suggesting that this amino acid dictates changes in the conformational ensembles sampled by the virus. Furthermore, an observed twofold difference in the stability of infectious West Pac-74 versus 16007 in solution also mapped to E residue 204. Our results demonstrate that neutralization susceptibility can be altered in an epitope-independent manner by natural strain variation that influences the structures sampled by DENV. That different conformational ensembles of flaviviruses may affect the landscape available for antibody binding, as well as virus stability, has important implications for functional studies of antibody potency, a critical aspect of vaccine development.

The global burden of dengue virus (DENV) is growing, with recent estimates of ~390 million human infections each year. Antibodies play a crucial role in protection from DENV infection, and vaccines that elicit a robust antibody response are being actively pursued. We report here the identification of a single amino acid residue in the envelope protein of DENV serotype 1 that results in global changes to virus structure and stability when it is changed. Our results indicate that naturally occurring variation at this particular site among virus strains impacts the ensemble of structures sampled by the virus, a process referred to as virus breathing. The finding that such limited and conservative sequence changes can modulate the landscape available for antibody binding has important implications for both vaccine development and the study of DENV-reactive antibodies.

Human Memory B Cells Producing Potent Cross-Neutralizing Antibodies against Human Parechovirus: Implications for Prevalence, Treatment, and Diagnosis

The family Picornaviridae is a large and diverse group of positive-sense RNA viruses, including human enteroviruses (EVs) and human parechoviruses (HPeVs). The human immune response against EVs and HPeVs is thought to be mainly humoral, and an insufficient neutralizing antibody (Ab) response during infection is a risk factor and can ultimately be life threatening. The accessibility of different antigenic sites and observed cross-reactivity make HPeVs a good target for development of therapeutic human monoclonal antibodies (MAbs). In this study, we generated two different human MAbs specific for HPeV by screening culture supernatants of Ab-producing human B cell cultures for direct neutralization of HPeV1. Both MAbs showed HPeV1-specific neutralization as well as neutralization of HPeV2. One antibody, AM18, cross-neutralized HPeV4, -5, and -6 and coxsackievirus A9 (CV-A9). VP1 capsid protein-specific assays confirmed that AM18 bound VP1 of HPeV1, -2, and -4 with high affinity (11.5 pM). In contrast, the HPeV1-specific MAb AM28, which neutralized HPeV1 even more efficiently than did AM18, showed no cross-reactivity with HPeV3 to -6 or other EVs and did not bind any of the capsid proteins, suggesting that AM28 is specific for a conformation-dependent, nonlinear epitope on the virus. The discovery of MAbs that are cross-reactive between HPeVs may help development of HPeV treatment options with antibodies and vaccine design based on epitopes recognized by these antibodies.

IMPORTANCE

HPeV infections are widespread among young children and adults, causing a broad range of disease. Infections can be severe and life threatening, while no antiviral treatment is available. Given that the absence of neutralizing Abs is a risk factor for severe disease in infants, treatment of picornavirus infections with MAbs would be a therapeutic option. To study antibody neutralization of HPeV in more detail, we generated two different HPeV1-specific human MAbs. Both MAbs show HPeV1-specific neutralization and cross-neutralized HPeV2. One MAb also cross-neutralized other HPeVs. Surprisingly, this MAb also neutralized CV-A9. These MAbs provide a unique tool for further research and for the diagnosis (antigen detection) and possible treatment of HPeV infections.

Identification of a conserved B-cell epitope on duck hepatitis A type 1 virus VP1 protein

Background

The VP1 protein of duck hepatitis A virus (DHAV) is a major structural protein that induces neutralizing antibodies in ducks; however, B-cell epitopes on the VP1 protein of duck hepatitis A genotype 1 virus (DHAV-1) have not been characterized.

Methods and Results

To characterize B-cell epitopes on VP1, we used the monoclonal antibody (mAb) 2D10 against Escherichia coli-expressed VP1 of DHAV-1. In vitro, mAb 2D10 neutralized DHAV-1 virus. By using an array of overlapping 12-mer peptides, we found that mAb 2D10 recognized phages displaying peptides with the consensus motif LPAPTS. Sequence alignment showed that the epitope ¹⁷³LPAPTS¹⁷⁸ is highly conserved among the DHAV-1 genotypes. Moreover, the six amino acid peptide LPAPTS was proven to be the minimal unit of the epitope with maximal binding activity to mAb 2D10. DHAV-1–positive duck serum reacted with the epitope in dot blotting assay, revealing the importance of the six amino acids of the epitope for antibody-epitope binding. Competitive inhibition assays of mAb 2D10 binding to synthetic LPAPTS peptides and truncated VP1 protein fragments, detected by Western blotting, also verify that LPAPTS was the VP1 epitope.

Conclusions and Significance

We identified LPAPTS as a VP1-specific linear B-cell epitope recognized by the neutralizing mAb 2D10. Our findings have potential applications in the development of diagnostic techniques and epitope-based marker vaccines against DHAV-1.

Molecular evolution of VP3, VP1, 3C(pro) and 3D(pol) coding regions in coxsackievirus group A type 24 variant isolates from acute hemorrhagic conjunctivitis in 2011 in Okinawa, Japan

A large acute hemorrhagic conjunctivitis (AHC) outbreak occurred in 2011 in Okinawa Prefecture in Japan. Ten strains of coxsackievirus group A type 24 variant (CA24v) were isolated from patients with AHC and full sequence analysis of the VP3, VP1, 3C(pro) and 3D(pol) coding regions performed. To assess time-scale evolution, phylogenetic analysis was performed using the Bayesian Markov chain Monte Carlo method. In addition, similarity plots were constructed and pairwise distance (p-distance) and positive pressure analyses performed. A phylogenetic tree based on the VP1 coding region showed that the present strains belong to genotype 4 (G4). In addition, the present strains could have divided in about 2010 from the same lineages detected in other countries such as China, India and Australia. The mean rates of molecular evolution of four coding regions were estimated at about 6.15 to 7.86 × 10(-3) substitutions/site/year. Similarity plot analyses suggested that nucleotide similarities between the present strains and a prototype strain (EH24/70 strain) were 0.77-0.94. The p-distance of the present strains was relatively short (<0.01). Only one positive selected site (L25H) was identified in the VP1 protein. These findings suggest that the present CA24v strains causing AHC are genetically related to other AHC strains with rapid evolution and emerged in around 2010.

Innate and adaptive immune responses against picornaviruses and their counteractions: An overview

Picornaviruses, small positive-stranded RNA viruses, cause a wide range of diseases which is based on their differential tissue and cell type tropisms. This diversity is reflected by the immune responses, both innate and adaptive, induced after infection, and the subsequent interactions of the viruses with the immune system. The defense mechanisms of the host and the countermeasures of the virus significantly contribute to the pathogenesis of the infections. Important human pathogens are poliovirus, coxsackievirus, human rhinovirus and hepatitis A virus. These viruses are the best-studied members of the family, and in this review we want to present the major aspects of the reciprocal effects between the immune system and these viruses.

Structure of the Fab-labeled "breathing" state of native poliovirus

At 37°C, the structure of poliovirus is dynamic, and internal polypeptides VP4 and N terminus of VP1 (residues 1 to 53) externalize reversibly. An Fab fragment of a monospecific antibody, which binds to residues 39 to 55 of VP1, was utilized to locate the N termini of VP1 in native (160S) particles in this "breathing" state. Fab and virus were mixed and imaged via cryogenic electron microscopy. The resulting reconstruction showed the capsid expands similarly to the irreversibly altered cell entry intermediate (135S) particle, but the N terminus of VP1 is located near the 2-fold axes, instead of the "propeller tip" as in 135S particles.

Characterization and specificity of the linear epitope of the enterovirus 71 VP2 protein

Background

Enterovirus 71 (EV71) has emerged as a major causative agent of hand, foot and mouth disease in the Asia-Pacific region over the last decade. Hand, foot and mouth disease can be caused by different etiological agents from the enterovirus family, mainly EV71 and coxsackieviruses, which are genetically closely related. Nevertheless, infection with EV71 may occasionally lead to high fever, neurologic complications and the emergence of a rapidly fatal syndrome of pulmonary edema associated with brainstem encephalitis. The rapid progression and high mortality of severe EV71 infection has highlighted the need for EV71-specific diagnostic and therapeutic tools. Monoclonal antibodies are urgently needed to specifically detect EV71 antigens from patient specimens early in the infection process. Furthermore, the elucidation of viral epitopes will contribute to the development of targeted therapeutics and vaccines.

Results

We have identified the monoclonal antibody 7C7 from a screen of hybridoma cells derived from mice immunized with the EV71-B5 strain. The linear epitope of 7C7 was mapped to amino acids 142-146 (EDSHP) of the VP2 capsid protein and was characterized in detail. Mutational analysis of the epitope showed that the aspartic acid to asparagine mutation of the EV71 subgenogroup A (BrCr strain) did not interfere with antibody recognition. In contrast, the serine to threonine mutation at position 144 of VP2, present in recently emerged EV71-C4 China strains, abolished antigenicity. Mice injected with this virus strain did not produce any antibodies against the VP2 protein. Immunofluorescence and Western blotting confirmed that 7C7 specifically recognized EV71 subgenogroups and did not cross-react to Coxsackieviruses 4, 6, 10, and 16. 7C7 was successfully used as a detection antibody in an antigen-capture ELISA assay.

Conclusions

Detailed mapping showed that the VP2 protein of Enterovirus 71 contains a single, linear, non-neutralizing epitope, spanning amino acids 142-146 which are located in the VP2 protein's E-F loop. The S/T(144) mutation in this epitope confers a loss of VP2 antigenicity to some newly emerged EV71-C4 strains from China. The corresponding monoclonal antibody 7C7 was used successfully in an AC-ELISA and did not cross-react to coxsackieviruses 4, 6, 10, and 16 in immunofluorescence assay and Western blots. 7C7 is the first monoclonal antibody described, that can differentiate Coxsackievirus 16 from Enterovirus 71.

Peculiar antibody reactivity to human connexin 37 and its microbial mimics in patients with Crohn's disease

BACKGROUND/AIMS

We found that pooled Crohn's disease (CD) sera strongly react with a human gap-junction connexin 37 (Cx37) peptide and tested for anti-Cx37 antibody reactivity in sera from CD patients and controls. We also investigated whether peptide-recognition is due to Cx37/microbial molecular mimicry.

METHODS

The PSI-BLAST program was used for Cx37(121-135)/microbial alignment. Reactivity to biotinylated human Cx37(121-135) and its microbial mimics was determined by ELISA using sera from 44 CD, 30 ulcerative colitis and 28 healthy individuals.

RESULTS

Anti-Cx37(121-135) reactivity (1/200 dilution) was present in 30/44 (68%) CD cases and persisted at 1/1000 dilution. Database search shows that Cx37(121-135) contains the -ALTAV- motif which is cross-recognized by diabetes-specific phogrin and enteroviral immunity. Testing of 9 Cx37(121-135)-microbial mimics revealed 57-68% reactivity against human enterovirus C, Lactococcus lactis, coxsackie virus A24 and B4. Anti-Cx37(121-135) was inhibited by itself or the microbial mimics. No reactivity was found against the poliovirus, rubella, and Mycobacterium tuberculosis mimics, or the beta cell phogrin autoantigen. Microbial/Cx37 reactivity was not able to differentiate CD patients from UC or healthy controls, in terms of overall prevalence and antibody titres, but microbial mimics were unable to inhibit reactivity to human Cx37 in the majority of the controls.

CONCLUSIONS

Sera from CD patients react with connexin 37 and cross-react with specific Cx37-mimicking enteroviral peptides. Microbial/self reactivity can be seen in UC and healthy controls. The lack of responses to other Cx37(121-135) microbial mimics and the inability of the reactive microbes to inhibit reactivity to self is intriguing and warrants further investigation.

Development of polyclonal antisera to clone enterovirus 71 cellular receptor

PURPOSE

Enterovirus 71 (ENV71) is a member of Picornaviridae family and was shown to be of public health concern in the Far East because of the notorious outbreaks it caused, with novel clinical features in the affected patients. In this study we assessed the use of virus capsid protein VP1 in viral receptor research.

MATERIAL AND METHODS

The capsid protein (VP1) was cloned, expressed in a prokaryotic system, and purified for immunisation of rabbits. The immunisation was carried out according to the UK Home Office regulations. The polyclonal antisera were collected and tested for reactivity against recombinant and native VP1 of ENV71.

RESULTS

Both antisera were reactive against native and partially/fully denatured viral particles.

CONCLUSION

The antisera are functional in receptor studies.

Widespread circulation of echovirus type 13 demonstrated by increased seroprevalence in Toyama, Japan, between 2000 and 2003

To confirm the magnitude of an echovirus type 13 (E13) outbreak in 2002 and to evaluate whether genetic and antigenic changes in E13 influenced the occurrence of the outbreak, we measured titers of neutralizing (NT) antibody against the Toyama, 2002-240-SF, and prototype Del Carmen E13 strains among inhabitants of Toyama before and after 2002. The rate of positivity for NT antibodies against both 2002-240-SF and Del Carmen in 2003 made a remarkable upturn in children 0 to 14 years old, compared to that in 2000. Titers of NT antibody against strain 2002-240-SF of inhabitants were slightly higher than those against Del Carmen, whereas anti-E13 rabbit serum raised against either strain Del Carmen or 2002-240-SF showed almost the same titer of NT antibody against both strains. These data indicate that the antigenic properties of the strains may be slightly different. Differences in amino acids between strains 2002-240-SF and Del Carmen in the VP4, VP2, VP3, and VP1 regions may affect both antigenic and receptor binding properties, even though they do not seem to be significant enough to escape widespread immunity. One of the factors of the outbreak was thought to be the increase in susceptibility in the young generation.

Internalization of coxsackievirus A9 is mediated by {beta}2-microglobulin, dynamin, and Arf6 but not by caveolin-1 or clathrin

Coxsackievirus A9 (CAV9) is a member of the human enterovirus B species within the Enterovirus genus of the family Picornaviridae. It has been shown to utilize alphaV integrins, particularly alphaVbeta6, as its receptors. The endocytic pathway by which CAV9 enters human cells after the initial attachment to the cell surface has so far been unknown. Here, we present a systematic study concerning the internalization mechanism of CAV9 to A549 human lung carcinoma cells. The small interfering RNA (siRNA) silencing of integrin beta6 subunit inhibited virus proliferation, confirming that alphaVbeta6 mediates the CAV9 infection. However, siRNAs against integrin-linked signaling molecules, such as Src, Fyn, RhoA, phosphatidylinositol 3-kinase, and Akt1, did not reduce CAV9 proliferation, suggesting that the internalization of the virus does not involve integrin-linked signaling events. CAV9 endocytosis was independent of clathrin or caveolin-1 but was restrained by dynasore, an inhibitor of dynamin. The RNA interference silencing of beta2-microglobulin efficiently inhibited virus infection and caused CAV9 to accumulate on the cell surface. Furthermore, CAV9 infection was found to depend on Arf6 as both silencing of this molecule by siRNA and the expression of a dominant negative construct resulted in decreased virus infection. In conclusion, the internalization of CAV9 to A549 cells follows an endocytic pathway that is dependent on integrin alphaVbeta6, beta2-microglobulin, dynamin, and Arf6 but independent of clathrin and caveolin-1.

Antibodies to the buried N terminus of rhinovirus VP4 exhibit cross-serotypic neutralization

Development of a vaccine for the common cold has been thwarted by the fact that there are more than 100 serotypes of human rhinovirus (HRV). We previously demonstrated that the HRV14 capsid is dynamic and transiently displays the buried N termini of viral protein 1 (VP1) and VP4. Here, further evidence for this "breathing" phenomenon is presented, using antibodies to several peptides representing the N terminus of VP4. The antibodies form stable complexes with intact HRV14 virions and neutralize infectivity. Since this region of VP4 is highly conserved among all of the rhinoviruses, antiviral activity by these anti-VP4 antibodies is cross-serotypic. The antibodies inhibit HRV16 infectivity in a temperature- and time-dependent manner consistent with the breathing behavior. Monoclonal and polyclonal antibodies raised against the 30-residue peptide do not react with peptides shorter than 24 residues, suggesting that these peptides are adopting three-dimensional conformations that are highly dependent upon the length of the peptide. Furthermore, there is evidence that the N termini of VP4 are interacting with each other upon extrusion from the capsid. A Ser5Cys mutation in VP4 yields an infectious virus that forms cysteine cross-links in VP4 when the virus is incubated at room temperature but not at 4 degrees C. The fact that all of the VP4s are involved in this cross-linking process strongly suggests that VP4 forms specific oligomers upon extrusion. Together these results suggest that it may be possible to develop a pan-serotypic peptide vaccine to HRV, but its design will likely require details about the oligomeric structure of the exposed termini.

The spot technique: synthesis and screening of peptide macroarrays on cellulose membranes

Peptide arrays are a widely used tool for drug development. For peptide-based drug design it is necessary to screen a large number of peptides. However, there are often difficulties with this approach. Most common peptide synthesis techniques are able to simultaneously synthesize only up to a few hundred single peptides. Spot synthesis is a positionally addressable, multiple synthesis technique offering the possibility of synthesizing and screening up to 10,000 peptides or peptide mixtures on cellulose or other membrane surfaces. In this chapter we present the basic procedures and screening methods related to spot synthesis and outline protocols for easy-to-use detection methods on these peptide arrays.

An enterovirus strain isolated from diabetic child belongs to a genetic subcluster of echovirus 11, but is also neutralised with monotypic antisera to coxsackievirus A9

An enterovirus strain (designated D207) isolated from a Slovakian diabetic child and originally serotyped as coxsackievirus A9 (CAV-9) was found to cause rapid cytolysis coinciding with severe functional damage of the surviving cells in primary cultures of human pancreatic islets. This finding prompted us to clone the isolate for full-length genome sequencing and molecular characterization as the prototype strain of CAV-9 is known to cause only minimal damage to insulin-producing β-cells. Based on capsid-coding sequence comparisons, the isolate turned out to be echovirus 11 (E-11). Phylogenetic analyses demonstrated that E-11/D207 was closely related to a specific subgroup B of E-11 strains known to cause uveitis. To study further antigenic properties of isolate E-11/D207 and uveitis-causing E-11 strains, neutralization experiments were carried out with CAV-9- and E-11-specific antisera. Unlike the prototype strains, the isolate E-11/D207 and uveitis-causing E-11 strains were well neutralized with both CAV-9- and E-11-specific antisera. Attempts to identify recombination of the capsid coding sequences as a reason for double-reactivity using the Simplot analysis failed to reveal major transferred motifs. However, peptide scanning technique was able to identify antigenic regions of capsid proteins of E-11/D207 as well as regions cross-reacting with an antiserum raised to CAV-9. Thus, double specificity of E-11/D207 seems to be a real characteristic shared by the phylogenetically closely related virus strains in the genetic subgroup B of E-11.

Basic rationale, current methods and future directions for molecular typing of human enterovirus

Enterovirus is a genus of the Picornaviridae family including more than 80 serotypes belonging to four species designed Human enterovirus A to D. The antigens of the structural proteins support the subdivision of enteroviruses into multiple serotypes. Comparative phylogeny based on molecular typing methods has been of great help to classify former and new types of enterovirus, and to investigate the diversity of enteroviruses and the evolutionary mechanisms involved in their diversity. By now, molecular typing methods of enterovirus rely mainly on the sequencing of an amplicon targeting a variable part of the region coding for the capsid proteins (VP1 and, alternatively, VP2 or VP4), either from a strain recovered by cell culture or, more recently, by direct amplification of a clinical or environmental specimen. In the future, microarrays are thought to play a major role in enterovirus typing and in the analysis of the determinants of virulence that support the puzzling diversity of the pathological conditions associated with human infection by these viruses.

Molecular characterization of a new serotype of duck hepatitis virus

Duck hepatitis strains 90D and 04G were determined to be antigenically unrelated to type 1 duck hepatitis virus (DHV-1) by in vitro cross-neutralization assay. The genome sequences of 90D and 04G revealed that both strains of the new serotype DHV (N-DHV) possessed a typical picornavirus genome organization apart from the unique possession of three in-tandem 2A genes present in DHV-1. The 2A1, 2A2, and 2A3 proteins represented an aphthovirus-like 2A protein, AIG1-like protein, and human parechovirus-like 2A protein, respectively. The N-DHV genome displayed unique features, compared to the DHV-1 genome. The 366 nt 3'UTR of N-DHV, the largest determined thus far among picornaviruses, was 52 nt longer than DHV-1. The pairwise percent identity of the nucleic acid and amino acid sequences at 1D region of N-DHV and DHV-1 were only 69.1-69.7 and 70.1-70.5%, respectively. Finally, phylogenetic and evolutionary analysis of N-DHV revealed that the N-DHV and DHV-1 belong to two different clusters of a novel genus in the Picornaviridae family.

Phylogenetic Analysis of Echovirus 11 in the 3′ End of the VP1

OBJECTIVE

Echovirus 11 is one of the most frequently isolated enterovirus serotypes, causing a wide range of clinical diseases. We studied the genetic diversity in the 3' end of the VP1 gene of strains from different geographical origin in the world.

METHODS

The sequences in the 3' end of the VP1 of 11 Tunisian isolates were determined and aligned with the published sequences to establish a phylogenetic profile.

RESULTS

The grouping of the sequences was similar to what was previously reported by analyzing the whole VP1 gene with 4 genogroups, designated A-D, and 5 lineages in genogroup D. All Tunisian strains belonged to genogroup D, together with other sequences mainly from the USA and Europe. Contrary to the sequences from the USA isolated during the last 3 decades, which mostly belonged to the D4 lineage, those from Tunisia belonged to different lineages within genogroup D according to their isolation date: isolates from the early 1990s belonged to D3, those of the mid 1990s to D4 and the most recent ones to D5.

CONCLUSION

Our findings further widen the interest of partial sequencing in the VP1 to study the molecular epidemiology of echovirus 11 and indicate that the genetic evolution of circulating strains may differ from one country to another according to the region's epidemiological specificities.

Analysis of the genetic and the corresponding antigenic variability of the VP1 3' end of ECHO virus type 11 and ECHO virus type 30

The enteroviruses (EV), RNA viruses belonging to the Picornaviridae family, have a high genetic variability due to the absence of the efficient proofreading and post replicative repair activities associated with the RNA polymerase. In the present work, we studied the genetic and the antigenic variability of ECHO virus types 11 (E11) and 30 (E30), which are the most isolated echoviruses serotypes in clinical and environmental samples. We established on the 3' end of the VP1 gene, consensus sequences of E11 and E30 by alignment of 67 E11 and 247 E30 published sequences in GenBank. Our results of sequences comparison showed that the majority of the mutational sites are situated on the third nucleotide of the codon. These mutations were without consequence on the antigenic sequences of the VP1 protein. Thus, E11 and E30 have a high genetic variability (1/3 of the nucleotides are variable), but a relative antigenic conservation. The analysis of the intertypic antigenic variability between E11 and E30 was obtained by the alignment of the corresponding amino acids sequences relative to the N-terminal part of the VP1 protein. Two discriminating parts were highlighted, probably representing antigenic sites for neutralisation antibodies.

RGD motifs on the surface of baculovirus enhance transduction of human lung carcinoma cells

Baculovirus vectors have been shown to enter a variety of mammalian cell lines and gene transfer with wild-type baculovirus (WT) has been demonstrated both in vitro and in vivo. Different protein motifs have been displayed on the viral surface to serve as ligands for cell-specific receptor molecules. We have generated recombinant baculovirus vectors displaying an RGD-motif, recognized by alphaV integrin, on the viral surface. The RGD motifs within the C-terminus of coxsackie virus A9 and human parechovirus 1 VP1 proteins were fused to the N-terminus of the major envelope glycoprotein, gp64, of Autographa californica multiple nucleopolyhedrovirus. The recombinant RGD-presenting viruses bound more efficiently to the surface of human lung carcinoma cells (A549), known to contain alphaV integrins, as compared to WT baculovirus. In addition, the binding pattern of the RGD-displaying baculovirus showed extensive clustering. This most likely represents clustering of the integrin molecules on the cell surface, induced by binding of the RGD-displaying baculovirus. Finally, the transduction efficiency of an RGD-representing virus increased by almost three-fold as monitored by light emission measurements. In conclusion, these results suggest that the RGD-motif is functional on the surface of baculovirus and thereby these tropism-modified viruses bind more efficiently as well as enhance the transduction efficiency of human cancer cells expressing alphaV integrins.

A whole cell immunization-derived monoclonal antibody that protects cells from coxsackievirus A9 infection binds to both cell surface and virions

Coxsackievirus A9 (CAV-9) infects human rhabdomyosarcoma (RD) cells using an unidentified RGD-independent receptor. Monoclonal antibodies were prepared by immunizing mice with intact RD cells and by selecting cells from the cytopathic effect of CAV-9 for protection. Here we describe a monoclonal antibody that binds to host cell plasma membrane and protects cells from virus infection. In addition, binding of the virus to cell monolayers was more efficient in the presence of the antibody, suggesting that the antibody is also capable of recognizing virus particles. Immunoprecipitation and electron microscopy studies with highly purified virus preparations verified binding of the monoclonal antibody to the virus particles. The antibody also recognized coxsackievirus A21 and all three serotypes of poliovirus, but without affecting their infectivity. The amino acid sequence of CAV-9 recognized by the monoclonal antibody was identified by peptide mapping and by producing escape mutants in the presence of the antibody.

Molecular comparison of echovirus 11 strains circulating in Europe during an epidemic of multisystem hemorrhagic disease of infants indicates that evolution generally occurs by recombination

We compared echovirus 11 (E11) strains implicated in a severe epidemic in Hungary in 1989 with the prototype E11 strain Gregory and with other E11 strains, most of which were isolated over the same period in Europe (Finland, The Netherlands, Romania, Russia) from sporadic cases or from environmental water. Partial sequencing indicated that the Hungarian strains were closely related to each other and to most European strains. They were particularly closely related to one Romanian strain associated with a sporadic case of hemiparesis and several Finnish strains isolated from environmental water. Sequencing of the complete genomes of one Hungarian strain, the Romanian strain, and one Finnish strain revealed differences of only a few nucleotides in the 5' half of the genome, including the 5' nontranslated region (5'-NTR) and the capsid coding region. However, significant differences were observed in the nucleotide sequences of the 3' half of the genome (nonstructural viral protein region and 3'-NTR), indicating that these strains evolved recently and independently by genetic recombination with other unknown E11 or enterovirus strains.

Pathogenesis of coxsackievirus A9 in mice: role of the viral arginine-glycine-aspartic acid motif

Coxsackievirus A9 (CAV9) contains an arginine-glycine-aspartic acid (RGD) motif which participates in cell entry. Mutants with alterations in the RGD-containing region were utilized to explore the importance of the tripeptide in the pathogenesis of CAV9 in mice. Using in situ hybridization, the parental CAV9 strain was observed to infect skeletal muscle (intercostal, platysma, lingual and thigh muscles) of newborn mice, whereas the RGD-less mutants were detectable only in platysma and lingual muscles. In addition, newborn mice infected with the mutants survived longer than CAV9-infected mice. In adult mice, the parental strain of CAV9, but not the mutants, achieved moderately high titres in the pancreas. These results suggest that the RGD motif has a significant role in the pathogenesis of CAV9 in mice but also that RGD-independent entry routes can be utilized in the infection of murine tissue.

Antigenic sites of coxsackie A9 virus inducing neutralizing monoclonal antibodies protective in mice

A panel of murine IgG monoclonal antibodies (MAbs) was produced against coxsackievirus A9 (CAV9). Fifty-nine MAbs reactive in ELISA with purified CAV9 were identified. Eighteen of them could efficiently inhibit infection by CAV9 but not coxsackieviruses B. Neutralization-resistant CAV9 variants to four different MAbs were isolated and tested for resistance to neutralization by other MAbs of the panel. Three groups of reactivity including 10, 7, and 1 MAbs were thus identified. Sequencing of neutralization-escape virus mutants showed that neutralization by one MAb group was affected by change of VP3 amino acids 62 or 69. For the second group of reactivity, mutations included amino acids 154 or 165 of VP2. The only MAb of the third group selected for a change at residue 70 of VP2. Protection studies in a newborn mouse model of myositis suggested that either epitopes in VP2 or in VP3 mediate protection from CAV9 infection in vivo.

Diagnostic potential of parechovirus capsid proteins

To study humoral and cellular immunity against human parechovirus type 1 (HPEV1), the viral capsid proteins VP0, VP1, and VP3 were expressed and purified as glutathione S-transferase (GST)-tagged recombinant proteins. The fusion proteins were used to raise antisera in rabbits. VP0 and VP1 antisera specifically detected HPEV1-infected cells in culture by immunoperoxidase staining and immunofluorescence. Furthermore, antisera against the VP0 and VP1 proteins had neutralizing effects against HPEV1 infection. When the HPEV1 antibody titers of 20 adults and 55 children were determined by a microneutralization test, the prevalence of HPEV1 antibodies in the adult population was 96%, while 50% of children were seropositive. Selected sera were used to evaluate HPEV1 fusion proteins as antigens in an enzyme immunoassay. The VP3 capsid protein appeared to be suitable for the purpose, with specificity of 100% and sensitivity of 96% compared to the neutralization test. Furthermore, T-cell responses to the purified HPEV1 and HPEV1 capsid fusion proteins were studied in 20 adults. Sixty percent of the subjects had T-cell proliferation responses to purified HPEV1, and 90% of the subjects also had positive T-cell responses to at least one of the GST capsid proteins.

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.

Enterovirus infection may induce humoral immune response reacting with islet cell autoantigens in humans

Molecular mimicry is one of the mechanisms by which enterovirus infections have been postulated to have a role in the pathogenesis of type 1 diabetes. Immunogenic epitopes in enterovirus capsid protein VP1 and procapsid protein VP0 have sequence similarities with diabetes-associated epitopes in tyrosine phosphatase IA-2/IAR and heat shock protein 60. In the present study, documented enterovirus infection was shown to induce humoral responses, that in 7% and 1% of patients cross-reacted with the known diabetes-associated epitopes in tyrosine phosphatase IAR and heat shock protein 60, respectively. In contrast, none of the children vaccinated against poliomyelitis had antibodies to the diabetes-associated epitope of tyrosine phosphatases IA-2/IAR. The antibody response studied in serum samples from six patients with coxsackievirus A9 infection was mainly targeted to capsid protein VP1. Coxsackievirus A9 infection induced antibodies cross-reacted with one epitope in heat shock protein 60, but not with epitopes derived from other autoantigens. Most diabetic children had high levels of antibodies to both coxsackievirus and poliovirus derived VP1 peptides but the pattern of reactivity did not differ from that seen in healthy children. The reactivity of linear epitopes derived from autoantigens was low in general and associated with the presence of multiple autoantibodies in the patients. Some linear auto-epitopes derived from tyrosine phosphatase IA-2, glutamic acid decarboxylase 65, preproinsulin, and heat shock protein 60 were recognized by sera from diabetic patients, but not by sera from healthy children. In conclusion, enteroviruses may induce immune responses that react with islet cell autoantigens, which is a concern when a putative inactivated enterovirus vaccine is considered.

Prefusion rearrangements resulting in fusion Peptide exposure in Semliki forest virus

Semliki Forest virus (SFV), like many enveloped viruses, takes advantage of the low pH in the endosome to convert into a fusion-competent configuration and complete infection by fusion with the endosomal membrane. Unlike influenza virus, carrying an N-terminal fusion peptide, SFV represents a less-well understood fusion principle involving an endosequence fusion peptide. To explore the series of events leading to a fusogenic configuration of the SFV, we exposed the virus to successive acidification, mimicking endosomal conditions, and followed structural rearrangements at probed sensor surfaces. Thus revealed, the initial phase involves a transient appearance of a non-linear neutralizing antibody epitope in the fusion protein, E1. Concurrent with the disappearance of this epitope, a set of masked sequences in proteins E1 and E2 became exposed. When pH reached 6.0-5.9 the virion transformed into a configuration of enlarged diameter with the fusion peptide optimally exposed. Simultaneously, a partly hidden sequence close to the receptor binding site in E2 became fully uncovered. At this presumably fusogenic stage, maximally 80 fusion peptide-identifying antibody Fab fragments could be bound per virion, i.e. one ligand per three copies of the fusion protein. The phenomena observed are discussed in terms of alphavirus structure and reported functional domains.

Mapping of linear epitopes on the capsid proteins of swine vesicular disease virus using monoclonal antibodies

The antigenic linear map of swine vesicular disease virus (SVDV) has been studied using a repertoire of monoclonal antibodies (mAbs) raised against a recombinant SVDV polyprotein, P1. Peptide-scanning analyses, cross-reactivity studies with homologous and heterologous viruses and predicted location on a computer-generated three-dimensional model of the capsid proteins have allowed the identification of five main linear sites. Two sites, the N terminus of VP3 and amino acids 51-60 on VP1, correspond to internal areas, conserved not only between SVDV isolates but also in the related enterovirus coxsackievirus B5. In contrast, three other regions, amino acids 142-161 of VP2, 61-70 of VP3 and the C terminus of VP1, are exposed on the external face of the capsid and subjected to antigenic variation, even among different SVDV isolates. Further minor sites that were antigenically conserved were identified on VP4. In contrast with conformational sites described previously, none of the linear epitopes identified in this work is involved in neutralization of virus infectivity and post-infection swine sera did not inhibit the binding of mAbs with the relevant epitopes. Both of these observations suggest that linear epitopes are poorly immunogenic in pigs. The characterization of linear sites has contributed to a better understanding of the antigenic structure of SVDV and mAbs used to this purpose may provide a useful tool for the improvement of diagnostic methods, such as antigen detection systems, and analyses of the antigenic profile of SVDV isolates.

Characterization of the T-cell response to coxsackievirus B4: evidence that effector memory cells predominate in patients with type 1 diabetes

Most of the evidence linking enterovirus (EV) infection with the development and/or acceleration of type 1 diabetes is indirect. Few studies have examined T-cell responses to these viruses, and therefore the nature of the viral targets and the immune cells involved in antiviral responses remain unclear. In the present study, we examined the characteristics of the T-cell response to the EV Coxsackievirus B4 (CVB4) in patients with type 1 diabetes and healthy control subjects. We find that CVB4-specific T-cells preferentially target the envelope proteins VP1, VP2, and VP3, and that the response to these and other CVB4 proteins differs markedly in type 1 diabetic patients compared with nondiabetic control subjects. The frequency of T-cell proliferative responses against VP2 was significantly reduced in type 1 diabetic patients compared with control subjects, especially in patients tested near to diagnosis (P < 0.001). In contrast, median levels of gamma-interferon (IFN-gamma) production by T-cells in response to the CVB4 antigens tested were generally high in new-onset type 1 diabetic patients, who produced significantly higher levels in response to VP3 compared with healthy subjects (P < 0.05) and patients with long-standing disease (P < 0.05). New-onset type 1 diabetic patients also had higher levels in response to P2C compared with healthy subjects (P < 0.005) and to VP2 compared with patients with long-standing disease (P < 0.05). These results suggest that the quality of the immune response to CVB4 antigens differs significantly between type 1 diabetic patients and control subjects, with a predominance of primed effector (IFN-gamma-producing) memory cells near to disease diagnosis. The data are consistent with the notion that the diagnosis of type 1 diabetes is associated with recent or persistent exposure to EV antigens.

Enterovirus infection can induce immune responses that cross-react with beta-cell autoantigen tyrosine phosphatase IA-2/IAR

Insulin-dependent (type 1) diabetes is characterized by progressive destruction of insulin-producing beta cells probably by autoreactive T lymphocytes. Viral infections, especially those caused by coxsackieviruses, are postulated to play a role in the pathogenesis of the disease in humans. One mechanism by which viral infections could initiate or accelerate diabetogenic processes is "molecular mimicry," induction of antiviral immune responses cross-reacting with epitopes in the beta-cell autoantigens. Tyrosine phosphatases (IA-2, IAR) represent a major target autoantigen in type 1 diabetes. Both humoral and cellular immune responses are directed to the carboxy-terminal (C-terminal) part of the protein. This region has a 5-amino acid sequence identity, followed by five amino acid similarity with the conservative motif in the VP1-protein of enteroviruses (PALTAVETGA/HT), which is a highly immunogenic B- and T-cell epitope in enterovirus infection-induced immune responses. This observation prompted us to investigate potential humoral cross-reactions between immune responses induced by tyrosine phosphatases and enteroviruses. The reactivities of various peptide- and virus-induced rabbit antisera clearly demonstrated that cross-reactions do exist, and in both directions. Using epitope mapping, we were able to show that several diabetes-linked epitopes in IA-2 were also recognized by CBV-4-induced antisera. Immunization of female NOD-mice with formalin-inactivated purified strain of coxsackievirus B4 (CBV-4-E2) induced an immune response that recognized the IA-2/IAR diabetogenic peptide. The results obtained with human paired sera, collected during enterovirus infection, indicated that enterovirus infection in humans may also occasionally induce a humoral response that cross-reacts with IA-2/IAR.

Entry of human parechovirus 1

Human parechovirus 1 (HPEV-1) is a prototype member of parechoviruses, a recently established picornavirus genus. Although there is preliminary evidence that HPEV-1 recognizes alpha(V) integrins as cellular receptors, our understanding of early events during HPEV-1 infection is still very limited. The aim of this study was to clarify the entry mechanisms of HPEV-1, including the attachment of the virus onto the host cell surface and subsequent internalization. In blocking experiments with monoclonal antibodies against different receptor candidates, antibodies against alpha(V) and beta(3) integrin subunits, in particular in combination, appeared to be the most efficient ones in preventing the HPEV-1 infection. To find out whether HPEV-1 uses clathrin-coated vesicles or other routes for the entry into the host cell, we carried out double-labeling experiments of virus-infected cells with anti-HPEV-1 antibodies and antibodies against known markers of the clathrin and the caveolin routes. At the early phase of infection (5 min postinfection [p.i.]) HPEV-1 colocalized with EEA1 (early endosomes), and later, after 30 min p.i., it colocalized with mannose-6-phosphate receptor (late endosomes), whereas no colocalization with caveolin-1 was observed. The data indicate that HPEV-1 utilizes the clathrin-dependent endocytic pathway for entry into the host cells. Interestingly, endocytosed HPEV-1 capsid proteins were observed in the endoplasmic reticulum and cis-Golgi network 30 to 60 min p.i. Depolymerization of microtubules with nocodazole inhibited translocation of the virus to the late endosomes but did not block HPEV-1 replication, suggesting that the RNA genome may be released early during the entry process.

Antigenic properties of human parechovirus 1

Human parechoviruses 1 and 2 (HPEV1 and HPEV2, respectively), formerly known as echoviruses 22 and 23, have been assigned to a novel picornavirus genus on the basis of their distinct molecular and biological properties. To study the immunological characteristics of HPEV1 capsid proteins, antigenic analysis was carried out by a peptide scanning technique, which can be used to identify the immunogenic peptide sequences of a protein. Partially overlapping peptides, representing the capsid of HPEV1, were synthesized using a 12 aa window in a three residue shift and reactivity of rabbit and murine HPEV1 antisera against these peptides were tested. Using this method, an antigenic site in the VP0 polypeptide, recognized by both rabbit and murine antisera, was identified. The sequence of this region was conserved among HPEV1 clinical isolates obtained from Finland and the United States. Antiserum against this peptide region showed neutralizing activity against HPEV1 in cell culture. Because the C-terminal region of HPEV1 VP1 contains a functional RGD motif, the antigenicity of this region was also tested. By using the corresponding peptide antiserum, neutralization of HPEV1 was observed. Cross-neutralization between HPEV1 and coxsackievirus A9, an enterovirus with a similar RGD motif in VP1, was also detected.

Sequencing and characterization of A-2 plaque virus: A new member of the Picornaviridae family

A-2 plaque virus (A2 virus) was originally isolated from the icteric-phase sera of US servicemen with viral hepatitis in the 1960s, but apart from a preliminary characterization little is known about the agent. We have now successfully cloned and sequenced the complete viral genome. A2 viral RNA consists of 7312 nucleotides, excluding the 62 nucleotide poly(A) tract at the 3' end, with one large open reading frame. Although clearly a member of the Picornaviridae, there is low homology to the available sequences, suggesting it is only loosely related to the classic rhino/enterovirus genus. In addition, there was no reactivity with group specific monoclonal antibody blends against polioviruses, enteroviruses 70 and 71, coxsackievirus B, and echoviruses. Two tamarins were inoculated with A2 virus to study viral pathogenesis. Both animals that received A2 virus became transiently viremic 1 week after the infection, as determined by RT-PCR, and they developed an antibody response to A2 virus. However, no physical signs or biochemical abnormalities, including elevated liver transaminases, were observed. In addition, no liver samples from patients with fulminant hepatitis (n = 7) or controls (n = 7) were positive for A2 viral RNA nor was anti-A2 neutralizing antibody detected in sera from hepatitis patients (n = 14), healthy laboratory donors (n = 14), or US blood donors (n = 33); however, most sera contained antibodies reactive with A2 virus proteins. These results suggest that A2 virus is a new member of the Picornaviridae but that its pathogenicity in nonhuman primates and association with human disease still need to be determined.

Molecular epidemiology and evolution of coxsackievirus A9

Genetic relationships between 35 clinical isolates of coxsackievirus A9 (CAV9), collected during the last five decades from different geographical regions, were investigated by partial sequencing. Analysis of a 150 nucleotide sequence at the VP1/2A junction region identified 12 CAV9 genotypes. While most of the strains within each genotype showed geographical clustering, the analysis also provided evidence for long-range importation of virus strains. Phylogenetic analysis of a longer region around the VP1/2A junction (approximately 390 nucleotides) revealed that the designated genotypes actually represented phylogenetic lineages. The phylogenetic grouping pattern of the isolates in the analysis of the VP4/VP2 region was similar to that obtained in the VP1/2A region whereas analysis of the 3D region indicated a strikingly different grouping, which suggests that recombination events may occur in the region encoding the nonstructural proteins. Analysis of the deduced amino acid sequences of the VP1 polypeptide demonstrated that the RGD (arginine-glycine-aspartic acid) motif, implicated in the interaction of the virus with integrin, was fully conserved among the isolates.

Immune recognition of swine vesicular disease virus structural proteins: novel antigenic regions that are not exposed in the capsid

Swine vesicular disease virus (SVDV) is an enterovirus of the Picornaviridae family that belongs to the coxsackievirus B group. A number of antigenic sites have been identified in SVDV by analysis of neutralizing monoclonal antibody-resistant mutants and shown to be exposed on the surface of the capsid. In this paper we have identified seven new immunodominant antigenic regions in SVDV capsid proteins by a peptide scanning method, using a panel of sera from infected pigs. When these antigenic regions were located in the capsid by using a computer-generated three-dimensional model of the virion, one was readily exposed on the surface of the virus and the remaining sites were located facing the inner side of the capsid shell, at subunit contacts, or in the interior of the subunit structure.

Molecular epidemiology of coxsackievirus B4 and disclosure of the correct VP1/2A(pro) cleavage site: evidence for high genomic diversity and long-term endemicity of distinct genotypes

Genetic diversity among 107 coxsackievirus B4 field isolates has been studied. These isolates included clinical and environmental isolates originating from Finland, the Netherlands and France, and also from several other countries, including the USA. Three genomic regions were used for phylogenetic analyses: the VP1/2A junction, the entire VP1 and the VP4/VP2 region. Alignment of the deduced amino acid sequence in the VP1/2A junction revealed extensive sequence variation at the previously proposed cleavage site. MS analysis of proteolytic fragments from VP1 revealed that the exact cleavage site is situated between amino acid residues Thr-849 and Gly-850. At least seven distinct genetic lineages, or genotypes, had been circulating in Europe during the period 1959-1998. Two genotypes were endemic in the Netherlands during most of the investigated period. Genetically closely related strains could be found in different countries, and different genotypes co-circulated at the same time in a given country. Clustering patterns were identical in the three genomic intervals. In the VP4/VP2 region, the intraserotypic variation approached interserotype variation. Sequence comparisons of the entire VP1 gene gave a reliable genetic identification of enterovirus serotype. It is suggested that, for genotype classification of previously serotyped coxsackievirus B4 isolates, comparison of VP1/2A sequences is sufficient, but for more detailed investigation of genetic relationships, and for 'genetic serotyping', the entire VP1 gene should be used. The VP4/VP2 region is less reliable for genetic serotyping and genotyping, although the primers are able to amplify many different serotypes.

The crystal structure of coxsackievirus A9: new insights into the uncoating mechanisms of enteroviruses

BACKGROUND

Coxsackievirus A9 (CAV9), a human pathogen causing symptoms ranging from common colds to fatal infections of the central nervous system, is an icosahedral single-stranded RNA virus that belongs to the genus Enterovirus of the family Picornaviridae. One of the four capsid proteins, VP1, includes the arginine-glycine-aspartate (RGD) motif within its C-terminal extension. This region binds to integrin alpha v beta 3, the only receptor for CAV9 to be conclusively identified to date.

RESULTS

The crystal structure of CAV9 in complex with the antiviral compound WIN 51711 has been solved to 2.9 A resolution. The structures of the four capsid proteins, VP1 to VP4, resemble those of other picornaviruses. The antiviral compound is bound in the VP1 hydrophobic pocket, and it is possible that the pocket entrance contains a second WIN 51711 molecule. Continuous electron density for the VP1 N terminus provides a complete picture of the structure close to the fivefold axis. The VP1 C-terminal portion is on the outer surface of the virus and becomes disordered five-residues N-terminal to the RGD motif.

CONCLUSIONS

The RGD motif is exposed and flexible in common with other known integrin ligands. Although CAV9 resembles coxsackie B viruses (CBVs), several substitutions in the areas implicated in CBV receptor attachment suggest it may recognise a different receptor. The structure along the fivefold axis provides new information on the uncoating mechanism of enteroviruses. CAV9 might bind a larger natural pocket factor than other picornaviruses, an observation of particular relevance to the design of new antiviral compounds.