[Expression of Type-Ι Interferon Production Pathway-Related Genes Induced by Infection Due to Enterovirus 71 or Coxsackievirus A16 in Normal Human Airway Epithelial Cells]

Hand, foot, and mouth disease(HFMD)is caused by mainly enterovirus 71(EV-A71)and coxsackievirus A16(CV-A16),and is a serious healthcare problem worldwide.EV-A71 infection is thought to progress readily to serious complications whereas CV-A16 infection, in general, results in mild symptoms and presents repeatedly. However, the underlying mechanisms leading to these differences are not known. We compared changes in expression of type-I interferon(IFN-I)-related genes in normal human bronchial epithelial(16HBE) cells. Gene-expression levels of TLR3,MAVS,MDA5,MyD88,IRF7,IFNαand IFNβwere elevated significantly after EVA71 infection.MDA5expression was increased markedly, and that of TLR3 and IRF3was decreased obviously after CV-A16 infection, but that of MAVS,MyD88,IFNαand IFNβdid not show significant differences. Viral copy number and viral titers suggested that CV-A16 replicates more efficiently than EV-A71 in 16HBE.These results suggest that IFN-I production pathway-related genes in response to infection by EV-A71 and CV-A16 have notable discrepancies. Such information could shine a light on the different manifestations caused by EV-A71 and CV-A16,and the mechanism of repeat infection by CV-A16.

[Genetic Characteristics of the VP1 Region of the Coxsackie A16 Virus from Jiangsu Province, China, in 2015]

The aim of this study was to analyze the genetic characteristics of the VP1 gene of coxsackievirus A16(CA16)strains isolated from Jiangsu Province, China, in 2015.The VP1 regions of 20CA16 virus strains from Jiangsu Province in 2015 were amplified, and the amplification products were sequenced. Mega 6.0and DNA Star software were applied to build the phylogenetic tree and analyze the homogeneity of nucleotides and amino acids. The sequence homologies of the nucleotides and amino acids of the VP1 gene were 88.2%~100.0%and 98.0%~100.0%among 20CA16 isolates, respectively. Comparison with the sequence of the prototype strain A-G10 showed 75.3%~77.4% homologies in nucleotide sequence and90.6%~92.3%in amino-acid sequences, respectively. Comparison with the sequence of the representative strain B1 showed 88.3%~98.4% homologies in nucleotide sequence and 96.3%~100.0%in amino-acid sequence, respectively. Comparison with the sequence of the representative strain B2 showed 88.4%~90.8% homologies in nucleotide sequence and 96.6%~100.0%in amino-acid sequence, respectively. Twenty CA16 isolates were subgenotype B1.One isolate was subgenotype B1a, whereas the remainder of isolates was subgenotype B1b among 20 CA16 isolates. A subgenotype B1b transmission chain was also noted. The CA16 strains isolated from Jiangsu Province in 2015 belonged to subgenotype B1.There were two evolutionary branches, whereby B1 a and B1bwere co-circulating and evolving together. The epidemic strain was subgenotype B1b.

[The Epidemiology and Etiology Characteristics of Hand-foot-mouth Disease in Chongqing, China,2014～2015]

In this study, the epidemiology of Hand-foot-mouth disease(HFMD)composition of enterovirus (EV) pathogen and VP1 coding gene of Enterovirus A71(EV-A71)were analyzed in Chongqing from 2014 to 2015,to provide a scientific basis for strategies of prevention and control of HFMD in Chongqing. It is reported that there were a total of 100,176 cases of HFMD, of which 284 cases of severe,37 cases of death in Chongqing.39counties(autonomous counties)of Chongqing have reported cases, and the urbans reported incidence rate(298.83/100,000)was significantly higher than the suburbs(103.37/100,000),children 3and under 3years old accounted for 83.21%%,and 5and under 5years old accounted for 95.64%of reported cases, the big peak of epidemics of HFMD was from April to July and the small peak took shape from October to November. Severe cases(96.83%)and deaths(100%)were concentrated in the age group of 5years old and below. The severe cases were mainly in the three districts, WanZhou District, Liangping County and FuLing District, accounting for 74.65% of reported cases, and death cases were widely distributed, scattered in 17 counties.7503nucleic acid of clinical specimens of HFMD were detected, suggested that EV-A71,CV-A16,non-EV-A71/CV-A16 of other EV accounted for 23.54%,33.21%,43.25% respectively,Non-EV-A71/ CV-A16 of other EV became the dominant pathogen of HFMD in Chongqing, but EV-A71 was still the dominant pathogen in severe and death cases. The results showed that 54 strains belonged to C4a and one strain belonged to B5 in the analyses of the VP1 sequences of 55 strains during2014-2015 in Chongqing. This study provides important epidemiological and etiological data for HFMD prevention and control strategies and reduction of severe and death caused by EV-A71 in Chongqing.

[Genetic Characterization of Coxsackievirus A6 Strains Isolated in Ningxia Region, China, 2013～2015]

To study the genetic characteristics of coxsackievirus (CV)-A6 strains isolated from hand, food and mouth(HFMD)cases in Ningxia Province, China, in 2013~2015.A total of 998 specimens identified as non-EV71,non-CVA16 enteroviruses by real-time polymerase chain reaction were collected in 2013~2015and cultured using RD cells. The viral protein(VP)1gene of isolated strains was amplified by reverse transcription-polymerase chain reaction with degenerate primers and sequenced.Sequences were compared using the GenBank database by the BLAST algorithm to identify virus genotypes. All CV-A6 stains identified underwent homologous comparison and phylogenetic analyses. A total of 227 virus strains were isolated from 998 clinical specimens, and 61 stains were identified as CV-A6.Homologies of nucleotides and amino acids among Ningxia CV-A6 strains were 96.1%~99.8% and 98%~100%,respectively.The nucleotide homogeneity of Ningxia CV-A6 strains with Gudla strains, and the similarity of nucleotides and amino-acid sequences with VP1 of CV-A6 were 82.0%~83.5% and 93.8%~95.7%,respectively.CVA6 was the main pathogen of HFMD apart from EV71 and CV-A16 in Ningxia Province in 2013~2015.

A cluster of Enterovirus 71 subgenogroup C2 in a nursery school, Italy, 2014

During October 2014, enterovirus (EV) RNA was detected in the stools of four children attending the same class in a nursery school, and hospitalized with mild febrile and vomiting disease in Parma, Italy. Upon sequencing, the viruses were characterized as EV71 subgenogroup C2. Phylogenetic analysis of the four EV71 C2 viruses allowed the distinction of a diverging lineage within subgenogroup C2, containing the Italian EV71 C2 strains and viruses detected in France in 2013. The identification of an outbreak of EV71 C2 in Italy extended information on the geographic diffusion and clinical relevance of these viruses in Europe.

Comparative Genomic Analysis of Enterovirus 71 Revealed Six New Potential Neurovirulence-associated Sites

In the present study, the complete genomes of four common (4/EV71/Wenzhou/CHN/2014, 15/ EV71/Wenzhou/CHN/2014, 116/EV71/Wenzhou/ CHN/2014, and 120/EV71/Wenzhou/CHN/2014) and two virulent (11/EV71/Wenzhou/CHN/2014 and 109/EV71/Wenzhou/CHN/2014) enterovirus 71 (EV71) isolates were sequenced and described. They are 7405 bp in length and belong to EV71 sub-genotype C4 (C4a cluster). Nucleotide sequence alignment revealed six nucleotide variations (GP151→TP151, GP199→AP199, GP261→TP261, AP328→CP328, GP422→AP422, and GP437→TP437) in the two virulent isolates within the 5'UTR of the IRES element. RNA secondary structure predictions of IRES and FCE indicated that the common isolates shared similar structures, which were different from those of the virulent isolates. Moreover, the GP114→CP114 and GP151→TP151 mutations in the virulent isolates contributed to the formation of the unique RNA secondary structures in SL II. Furthermore, nucleotide/amino acid sequence alignments of 82 EV71 isolates indicated that six sites (TP488 and CP577 in the 5'UTR; AsnP57 in 2A; IleP56 in 3C; CP10 and AP47 in the 3'UTR) are potentially associated with the neurovirulence of EV71. Finally, the 3D structures of 2A were analogous, whereas the structures of VP1 and 3C were variable.

Molecular epidemiology of human enterovirus 71 at the origin of an epidemic of fatal hand, foot and mouth disease cases in Cambodia

Human enterovirus 71 (EV-A71) causes hand, foot and mouth disease (HFMD). EV-A71 circulates in many countries and has caused large epidemics, especially in the Asia-Pacific region, since 1997. In April 2012, an undiagnosed fatal disease with neurological involvement and respiratory distress occurred in young children admitted to the Kantha Bopha Children's Hospital in Phnom Penh, Cambodia. Most died within a day of hospital admission, causing public panic and international concern. In this study, we describe the enterovirus (EV) genotypes that were isolated during the outbreak in 2012 and the following year. From June 2012 to November 2013, 312 specimens were collected from hospitalized and ambulatory patients and tested by generic EV and specific EV-A71 reverse transcription PCR. EV-A71 was detected in 208 clinical specimens while other EVs were found in 32 patients. The VP1 gene and/or the complete genome were generated. Our phylogenetic sequencing analysis demonstrated that 80 EV-A71 strains belonged to the C4a subgenotype and 3 EV-A71 strains belonged to the B5 genotype. Furthermore, some lineages of EV-A71 were found to have appeared in Cambodia following separate introductions from neighboring countries. Nineteen EV A (CV-A6 and CV-A16), 9 EV B (EV-B83, CV-B3, CV-B2, CV-A9, E-31, E-2 and EV-B80) and 4 EV C (EV-C116, EV-C96, CV-A20 and Vaccine-related PV-3) strains were also detected. We found no molecular markers of disease severity. We report here that EV-A71 genotype C4 was the main etiological agent of a large outbreak of HFMD and particularly of severe forms associated with central nervous system infections. The role played by other EVs in the epidemic could not be clearly established.

Seroepidemiology of Human Enterovirus 71 Infection among Children, Cambodia

Enterovirus 71 is reported to have emerged in Cambodia in 2012; at least 54 children with severe encephalitis died during that outbreak. We used serum samples collected during 2000–2011 to show that the virus had been widespread in the country for at least a decade before the 2012 outbreak.

Different Antibody Response against the Coxsackievirus A16 VP1 Capsid Protein: Specific or Non-Specific

Coxsackievirus A16 (CA16) is one of the major causative agents of hand, foot, and mouth disease worldwide. The non-neutralizing antibody response that targets CA16 VP1 remains poorly elucidated. In the present study, antibody responses against CA16 VP1 in Shanghai blood donors and Shanxi individuals were analyzed by ELISA and inhibitory ELISA using five CA16 VP1 antigens: VP1_1-297, VP1_41-297, VP1_1-60, VP1_45-58 and VP1_61-297. The correlation coefficients for most of the reactions against each of the five antigens and the inhibition of the anti-CA16 VP1 antibody response produced by the various antigens were higher in Shanghai blood donors compared to those in Shanxi individuals. VP1_1-297 and VP1_41-297 strongly inhibited the anti-CA16 VP1 response in serum samples from both populations, while VP1_45-58 and VP1_61-297 intermediately and weakly inhibited the anti-CA16 VP1 response, respectively, in only Shanghai group. A specific type of inhibition (anti-CA16 VP1 was completely inhibited by both VP1_1-60 and VP1_41-297) characterized by high neutralizing antibody titers was identified and accounted for 71.4% of the strongly reactive samples from the Shanghai group. These results indicate that the Shanghai blood donors exhibited a consistent and specific antibody response, while the Shanxi individuals showed an inconsistent and non-specific antibody response. These findings may improve the understanding of host humoral immunity against CA16 and help to identify an effective approach for seroepidemiological surveillance and specific diagnosis of CA16 infection based on normal and competitive ELISA.

Enterovirus A71 DNA-Launched Infectious Clone as a Robust Reverse Genetic Tool

Enterovirus A71 (EV-A71) causes major outbreaks of hand, foot and mouth disease, and is occasionally associated with neurological complications and death in children. Reverse genetics is widely used in the field of virology for functional study of viral genes. For EV-A71, such tools are limited to clones that are transcriptionally controlled by T7/SP6 bacteriophage promoter. This is often time-consuming and expensive. Here, we describe the development of infectious plasmid DNA-based EV-A71 clones, for which EV-A71 genome expression is under transcriptional control by the CMV-intermediate early promoter and SV40 transcriptional-termination signal. Transfection of this EV-A71 infectious DNA produces good virus yield similar to in vitro-transcribed EV-A71 infectious RNA, 6.4 and 5.8 log₁₀PFU/ml, respectively. Infectious plasmid with enhanced green fluorescence protein and Nano luciferase reporter genes also produced good virus titers, with 4.3 and 5.0 log₁₀ PFU/ml, respectively. Another infectious plasmid with both CMV and T7 promoters was also developed for easy manipulation of in vitro transcription or direct plasmid transfection. Transfection with either dual-promoter infectious plasmid DNA or infectious RNA derived from this dual-promoter clone produced infectious viral particles. Incorporation of hepatitis delta virus ribozyme, which yields precise 3’ ends of the DNA-launched EV-A71 genomic transcripts, increased infectious viral production. In contrast, the incorporation of hammerhead ribozyme in the DNA-launched EV-A71 resulted in lower virus yield, but improved the virus titers for T7 promoter-derived infectious RNA. This study describes rapid and robust reverse genetic tools for EV-A71.

The Current Status of the Disease Caused by Enterovirus 71 Infections: Epidemiology, Pathogenesis, Molecular Epidemiology, and Vaccine Development

Enterovirus 71 (EV71) infections have a major public health impact in the Asia-Pacific region. We reviewed the epidemiology, pathogenesis, and molecular epidemiology of EV71 infection as well as EV71 vaccine development. Previous studies were found using the search terms "enterovirus 71" and "epidemiology" or "pathogenesis" or "molecular epidemiology" or "vaccine" in Medline and PubMed. Articles that were not published in the English language, manuscripts without an abstract, and opinion articles were excluded from the review. The reported epidemiology of cases caused by EV71 infection varied from country to country; seasonal variations in incidence were observed. Most cases of EV71 infection that resulted in hospitalization for complications occurred in children less than five years old. The brainstem was the most likely major target of EV71 infection. The emergence of the EV71 epidemic in the Asia-Pacific region has been associated with the circulation of different genetic lineages (genotypes B3, B4, C1, C2, and C4) that appear to be undergoing rapid evolutionary changes. The relationship between the gene structure of the EV71 virus and the factors that ensure its survival, circulation, and evasion of immunity is still unknown. EV71 infection has emerged as an important global public health problem. Vaccine development, including the development of inactivated whole-virus live attenuated, subviral particles, and DNA vaccines, has been progressing.

[The Complete Sequence Analysis of 18 Strains of Coxsackievirus A6 in Guangdong Province of China]

In this study, we examined the complete genome of coxsackievirus A6 (CVA6) from hand, foot, and mouth disease in Guangdong Province from 2013,and explored the genetic similarities and differences in epidemic and non-epidemic stains of CVA6.Eighteen strains of CVA6 were included in complete genome sequencing, and the sequences were subject to phylogenetic analysis,sequence alignment analysis and genetic recombination analysis using the software DNASTAR6.0,MEGA5.2and SimPlot3.5.1.The results showed that the complete genome of 18 Guangdong CVA6strains ranged from 7390bp to 7392bp.No insertions or deletions were detected in the coding region. There were several insertions and deletions in 5′UTR and 3′UTR.Phylogenetic analysis indicated that the nucleotide and amino acid sequence identity between the 18 complete genomes were 90.5%-99.6% and 97.5%-99.9%,respectively.The strains isolated in2013 could be further divided into two clusters, III and IV, while the strains isolated in 2011 were only present in the IV cluster. Genetic recombination analysis revealed that the Guangdong representative strain of CVA6,GD870/2013,had gene recombination in the P2 and P3regions,while the GD839/2013 strain did not show obvious genetic recombination. Genome-wide analysis of CVA6 revealed that there are two possible transmitted chains, III and IV, in epidemic strains from Guangdong Province in 2013.The transmitted chain Ⅲ originated from the strain with genetic recombination in the P2 and P3regions,whichwas completely different from the chain IV. Transmission of chain IV of CVA6 was only observed in the nonepidemic 2011 strain.

[Identification of the Transcriptional Activity Domain of EV71 3D(pol)]

Enterovirus 71（EV71）is one of the major pathogens of hand, foot and mouth disease (HFMD). The EV71 genome encodes an RNA-dependent RNA polymerase（RdRp）,3D(pol),which is critical for genome transcription and translation. However, how the 3D(pol) interacts with the host remains unclear. Yeast two-hybrid systems provide an effective approach for detecting protein-protein interactions. In this report, we inserted the DNA sequence of 3D(pol) into the pGBKT7 vector as the bait plasmid for the yeast two-hybrid experiment and transformed the plasmid into the yeast AH109 strain. We detected the expression,cytotoxicity and self-activity of 3D(pol).The 3D(pol) expressed well without affecting cell growth but exhibited strong transcriptional activation in yeast cells. We further constructed a series of pGBKT7-3D(pol) deletion mutants and identified the shortest transcriptional activation domain（1-94aa）using a self-activation assay. The results provide a molecular basis for screening the host proteins that interact with 3D(pol) using the yeast two hybrid system.

A new animal model containing human SCARB2 and lacking stat-1 is highly susceptible to EV71

Enterovirus 71 (EV71) is a major threat to children worldwide. Children infected with EV71 could develop subclinical infection and hand-foot-and -mouth disease (HFMD). In severe cases, patients could develop encephalitis, paralysis, pulmonary edema, and death. A more user-friendly and robust animal model is essential to investigating EV71 pathogenesis. Here, we established a hybrid (hSCARB2(+/+)/stat-1(-/-)) mouse strain from crossbreeding SCARB2 transgenic and stat-1 KO mice, and compared the susceptibilities to EV71 infection and pathogenesis between parental and hybrid mice. Virus-encoded VP1 protein can be detected in the streaking nerve fibers in brain and spinal cord. This hybrid mouse strain at 2-week-old age can still be infected with different genotypes of EV71 at 1000-fold lower titer via an ip route. Infected hybrid mice developed earlier onset of CNS disease, paralysis, and death at a higher incidence. These advantages of this novel model meet the urgent need from the scientific community in basic and preclinical research in therapeutics and pathogenesis.

[Preparation of monoclonal antibodies against enterovirus type 71 with an epitope-incorporated adenovirus type 3 vector]

Objective To develop the monoclonal antibodies (mAbs) against enterovirus type 71 (EV71). Methods Two neutralization epitopes, SP70 and SP55, from EV71 were cloned into the hexon gene of adenovirus type 3 to generate a recombinant adenovirus type 3 (R1R2A3) presenting SP70 and SP55 antigens. BALB/c mice were immunized with the R1R2A3. The mAbs were developed with hybridoma technology and were analyzed with microneutralizing assay, indirect ELISA, Western blotting and direct immunofluorescence assay (DFA). Results The study obtained four hybridoma cell clones, 2C4, D2C9, I2G2 and I12C3. ELISA showed that the titer of D2C9 against EV71 was 1:8 000 000 and the titers of 2C4, I2G2, and I12C3 all were 1:500 000. ELISA and Western blotting demonstrated that all mAbs could specifically recognize the VP1 of EV71. In addition, D2C9 recognized the SP70 epitope, and 2C4, I12C3 and I2G2 all recognized the SP55 epitope. DFA revealed that all mAbs could react with EV71, but not with Coxsackie virus A16 (CoxA16). Conclusion Four mAbs against EV71 have been developed successfully, and all of them could react with EV71 rather than CoxA16.

[EV71 Infection and Innate Antiviral Innate Immunity]

Enterovirus 71 (EV71) is a major agent of hand, foot, and mouth disease in children under five years of age. In some cases,infection with EV71 can result in herpangina, pulmonary edema and/or brainstem encephalitis. In recent years, many advances have been made towards an understanding of EV71 pathogenesis. In this review, we summarize the cell types targeted by EV71,the activation of signaling pathways, the innate antiviral immune response and immune evasion by EV71 to better understand the immunopathogenesis of EV71 and to aid in the development of antiviral drugs.

Cooperative effect of the VP1 amino acids 98E, 145A and 169F in the productive infection of mouse cell lines by enterovirus 71 (BS strain)

Enterovirus 71 (EV71) is a neurotrophic virus that causes hand, foot and mouth disease (HFMD) and occasional neurological infection among children. It infects primate cells but not rodent cells, primarily due to the incompatibility between the virus and the expressed form of its receptor, scavenger receptor class B member 2 (SCARB2) protein, on rodent cells (mSCARB2). We previously generated adapted strains (EV71:TLLm and EV71:TLLmv) that were shown to productively infect primate and rodent cell lines and whose genomes exhibited a multitude of non-synonymous mutations compared with the EV71:BS parental virus. In this study, we aimed to identify mutations that are necessary for productive infection of murine cells by EV71:BS. Using reverse genetics and site-directed mutagenesis, we constructed EV71 infectious clones with specific mutations that generated amino acid substitutions in the capsid VP1 and VP2 proteins. We subsequently assessed the infection induced by clone-derived viruses (CDVs) in mouse embryonic fibroblast NIH/3T3 and murine neuroblastoma Neuro-2a cell lines. We found that the CDV:BS-VP1(K98E,E145A,L169F) with three substitutions in the VP1 protein-K98E, E145A and L169F-productively infected both mouse cell lines for at least three passages of the virus in murine cells. Moreover, the virus gained the ability to utilize the mSCARB2 protein to infect murine cell lines. These results demonstrate that the three VP1 residues cooperate to effectively interact with the mSCARB2 protein on murine cells and permit the virus to infect murine cells. Gain-of-function studies similar to the present work provide valuable insight into the mutational trajectory required for EV71 to infect new host cells previously non-susceptible to infection.

[Gene Characteristic Analysis for The VP1 Region of Coxsackievirus A6 Associated with HFMD in the Anyang Area of China during 2013]

This study aims to investigate the etiologic spectrum features of hand, foot and mouth disease(HFMD)and the VP1 region of coxsackievirus A6(CV-A6)in the Anyang area of China during 2013.A total of 479 HFMD fecal specimens were identified using real-time RT-PCR. The positive specimens of the different serotypes and the proportion of each serotype were calculated. A total of 10 positive of CV-A6 specimens were amplified and sequenced to obtain the profile of the VP1 region. Based on the data of the VP1 sequences from the Anyang strains and other referenced strains deposited in the NCBI database, the similarities of the nucleotide and amino-acid sequences for the VP1 region, as well as phylogenetic analyses were performed by the BIOEIDT 7.2and MEGA 5.1software packages. The results revealed that 429 positive specimens of enterovirus, including 90 positive specimens of CV-A6 were identified. The CV-A6 specimens accounted for 20.98%of the total positive specimens.CV-A6 had become the second preponderant pathogen of the HFMD in the Anyang area during 2013.It was the first record of an enterovirus serotype of which was neither CV-A16 nor EV-A71,had become one of the primary pathogens associated with HFMD in the region. A great diversity of the nucleotide and amino-acid sequences between 10 Anyang strains and a prototype strain (Gdula) was found. Compared with the Henan strain(HN421),four Anyang sequences with nucleotide and amino-acid sequences exhibited greater diversity than the other six Anyang sequences. The phylogenetic analysis showed that all of 49CV-A6 strains could be clustered into four branches. Branch D could be further clustered into two sub-branches;6 Anyang sequences belonged to sub-branch D1,and the other four belonged to sub-branch D2.

[Proinflammatory Cytokine and Chemokine Production of Mouse Macrophages in Response to EV-A71 Infection]

To study the replication and antiviral innate immunity of EV-A71 in mouse macrophages, we selected the mouse macrophage RAW264.7cell line as a model. An absolute quantitative PCR detection method was constructed to detect the viral load of EV-A71 in RAW264.7cells.RT-qPCR detected the fold changes of the proinflammatory cytokine, chemokine, and pattern recognition receptors at different time points post-infection in RAW264.7cells infected with EV-A71 and UV-inactivated EV-A71.The results revealed that the viral load of EV-A71 in RAW264.7cells decreased as the time post-infection increased. Proinflammatory cytokines, including IL-1β,IL-6,TNF-α,and chemokines, including IP-10,MCP-1,and MIP-1αwere induced, and the mRNA expression levels of TLR2,TLR1,TLR6,MDA5,and RIG-I were up-regulated. These results indicate that EV-A71 could replicate in mouse macrophages at a lower level, and proinflammatory cytokine and chemokine responses were induced.

Establishment of an animal challenge model as a potency assay for an inactivated Enterovirus Type 71 vaccine

Enterovirus 71 (EV71) belongs to the Enterovirus genus of the Picornaviridae family, and its occurrence in Asia is associated with hand-foot-and-mouth disease (HFMD), leading to death in some cases, in young children. An effective EV71 vaccine is therefore urgently needed. In this study, we established a two-step EV71 vaccine potency model. Intraperitoneal injections in 2-day-old suckling mice were used to establish the LD50 of EV71 B4, B5, C2, C4, and C5 subgenotypes. Only C4 caused hind limb paralysis in mice (LD50: 2.62 ± 0.45). EV71 VP1 protein was identified in the brain tissues at histology. In the second phase of the model, 3-week-old female ICR mice received one primary and two boosting i.p. injections of formalin-inactivated EV71 B4 and C4 vaccine. Immunized serum was neutralized in vitro with EV71 C4 and applied to the murine challenge model. The C4 vaccine-immunized serum exhibited the highest protective titre (ED50 = 114.6), while the B4 immunized serum had the weakest protective titre (ED50 = 34.3). Additionally, human plasma and intravenous immunoglobulin displayed significant protection in the neutralization assay. Our results could facilitate candidate EV71 vaccine immunogenicity and efficacy evaluations, and may help establish reference EV71 antisera in the future.

Neurologic Manifestations of Enterovirus 71 Infection in Korea

Enterovirus 71 frequently involves the central nervous system and may present with a variety of neurologic manifestations. Here, we aimed to describe the clinical features, magnetic resonance imaging (MRI) findings, and cerebrospinal fluid (CSF) profiles of patients presenting with neurologic complications of enterovirus 71 infection. We retrospectively reviewed the records of 31 pediatric patients hospitalized with acute neurologic manifestations accompanied by confirmed enterovirus 71 infection at Ulsan University Hospital between 2010 and 2014. The patients' mean age was 2.9 ± 5.5 years (range, 18 days to 12 years), and 80.6% of patients were less than 4 years old. Based on their clinical features, the patients were classified into 4 clinical groups: brainstem encephalitis (n = 21), meningitis (n = 7), encephalitis (n = 2), and acute flaccid paralysis (n = 1). The common neurologic symptoms included myoclonus (58.1%), lethargy (54.8%), irritability (54.8%), vomiting (48.4%), ataxia (38.7%), and tremor (35.5%). Twenty-five patients underwent an MRI scan; of these, 14 (56.0%) revealed the characteristic increased T2 signal intensity in the posterior region of the brainstem and bilateral cerebellar dentate nuclei. Twenty-six of 30 patients (86.7%) showed CSF pleocytosis. Thirty patients (96.8%) recovered completely without any neurologic deficits; one patient (3.2%) died due to pulmonary hemorrhage and shock. In the present study, brainstem encephalitis was the most common neurologic manifestation of enterovirus 71 infection. The characteristic clinical symptoms such as myoclonus, ataxia, and tremor in conjunction with CSF pleocytosis and brainstem lesions on MR images are pathognomonic for diagnosis of neurologic involvement by enterovirus 71 infection.

[Genetic Characteristics of Coxsackievirus Group A Type 4 Isolated from Patients with Acute Flaccid Paralysis in Shaanxi, China]

We analyzed the genetic characteristics of coxsackievirus A4 (CV-A4) based on the entire VP1 coding region. Samples were isolated from patients with acute flaccid paralysis (AFP) in Shaanxi, China from 2006 to 2010. We wished to ascertain the predominant genotype and the relationship between CV-A4 infection and AFP. Sixty-eight non-polio enteroviruses were inoculated onto RD cells (to increase the virus titer) and molecular typing was undertaken. The entire VP1 coding region was amplified. Percentage of CV-A4 was 10.3% (7/68). Analyses of genetic identify and creation of phylogenetic trees revealed that CV-A4 could be classified into A, B and C genotypes. Seven CV-A4 strains from Shaanxi and other CV-A4 strains from China formed an independent evolution lineage located in group 4 and belonged to the C2 sub-genotype. These data suggested that CV-A4 strains of sub-genotype C2 were the predominant genotypes in China. These strains co-evolved and co-circulated with those from other provinces in China, so continued monitoring of CV-A4 (by clinical and genetic surveillance) should be enhanced.

Pyruvate Carboxylase Activates the RIG-I-like Receptor-Mediated Antiviral Immune Response by Targeting the MAVS signalosome

When retinoic acid-inducible gene 1 protein (RIG-I)-like receptors sense viral dsRNA in the cytosol, RIG-I and melanoma differentiation-associated gene 5 (MDA5) are recruited to the mitochondria to interact with mitochondrial antiviral signaling protein (MAVS) and initiate antiviral immune responses. In this study, we demonstrate that the biotin-containing enzyme pyruvate carboxylase (PC) plays an essential role in the virus-triggered activation of nuclear factor kappa B (NF-κB) signaling mediated by MAVS. PC contributes to the enhanced production of type I interferons (IFNs) and pro-inflammatory cytokines, and PC knockdown inhibits the virus-triggered innate immune response. In addition, PC shows extensive antiviral activity against RNA viruses, including influenza A virus (IAV), human enterovirus 71 (EV71), and vesicular stomatitis virus (VSV). Furthermore, PC mediates antiviral action by targeting the MAVS signalosome and induces IFNs and pro-inflammatory cytokines by promoting phosphorylation of NF-κB inhibitor-α (IκBα) and the IκB kinase (IKK) complex, as well as NF-κB nuclear translocation, which leads to activation of interferon-stimulated genes (ISGs), including double-stranded RNA-dependent protein kinase (PKR) and myxovirus resistance protein 1 (Mx1). Our findings suggest that PC is an important player in host antiviral signaling.

siRNA Targeting the 2Apro Genomic Region Prevents Enterovirus 71 Replication In Vitro

Enterovirus 71 (EV71) is the most important etiological agent of hand, foot, and mouth disease (HFMD) in young children, which is associated with severe neurological complications and has caused significant mortalities in recent HFMD outbreaks in Asia. However, there is no effective antiviral therapy against EV71. In this study, RNA interference (RNAi) was used as an antiviral strategy to inhibit EV71 replication. Three small interfering RNAs (siRNAs) targeting the 2A^pro region of the EV71 genome were designed and synthesized. All the siRNAs were transfected individually into rhabdomyosarcoma (RD) cells, which were then infected with strain EV71-2006-52-9. The cytopathic effects (CPEs) in the infected RD cells, cell viability, viral titer, and viral RNA and protein expression were examined to evaluate the specific viral inhibition by the siRNAs. The results of cytopathogenicity and MTT tests indicated that the RD cells transfected with the three siRNAs showed slight CPEs and significantly high viability. The 50% tissue culture infective dose (TCID₅₀) values demonstrated that the viral titer of the groups treated with three siRNAs were lower than those of the control groups. qRT–PCR and western blotting revealed that the levels of viral RNA and protein in the RD cells treated with the three siRNAs were lower than those in the controls. When RD cells transfected with siRNAs were also infected with strain EV71-2008-43-16, the expression of the VP1 protein was significantly inhibited. The levels of interferon α (IFN-α) and IFN-β did not differ significantly in any group. These results suggest that siRNAs targeting the 2A^pro region of the EV71 genome exerted antiviral effects in vitro.