Immunopathogenesis and Virus-Host Interactions of Enterovirus 71 in Patients with Hand, Foot and Mouth Disease

Effectiveness of Enterovirus 71 inactivated vaccines against hand, foot, and mouth disease: A test-negative case-control study

The Enterovirus A71 (EV-A71) vaccine was introduced in China in December 2015 as a preventive measure against hand, foot, and mouth disease (HFMD) caused by EV-A71. However, the effectiveness of the vaccine (VE) in real-world settings needs to be evaluated. We conducted a test-negative case-control study to assess the effectiveness of EV-A71 vaccines in preventing EV-A71-associated HFMD. Children aged 6-71 months with HFMD were enrolled as participants. The case group comprised those who tested positive for EV-A71, while the control group comprised those who tested negative for EV-A71. To estimate VE, a logistic regression model was employed, adjusting for potential confounders including age, gender, and clinical severity. In total, 3223 children aged 6 to 71 months were included in the study, with 162 in the case group and 3061 in the control group. The proportion of children who received EV-A71 vaccination was significantly lower in the case group compared to the control group (p < .001). The overall VEadj was estimated to be 90.8%. The VEadj estimates for partially and fully vaccinated children were 90.1% and 90.9%, respectively. Stratified by age group, the VEadj estimates were 88.7% for 6 to 35-month-olds and 95.5% for 36 to 71-month-olds. Regarding disease severity, the VEadj estimates were 86.3% for mild cases and 100% for severe cases. Sensitivity analysis showed minimal changes in the VE point estimates, with most changing by no more than 1% point. Our study demonstrates a high level of vaccine effectiveness against EV-A71-HFMD, especially in severe cases. Active promotion of EV-A71 vaccination is an effective strategy in preventing EV-A71 infections.

Immunogenicity and immunodominant linear B-cell epitopes of a new DNA-based tetravalent vaccine against four major enteroviruses causing hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD) poses a significant public health threat primarily caused by four major enteroviruses: enterovirus 71 (EV71), coxsackieviruses A16, A10, and A6. Broadly protective immune responses are essential for complete protection against these major enteroviruses. In this study, we designed a new tetravalent immunogen for HFMD, validated it in silico, in vivo evaluated the immunogenicity of the DNA-based tetravalent vaccine in mice, and identified immunogenic B-cell and T-cell epitopes. A new tetravalent immunogen, VP1me, was designed based on the chimeric protein and epitope-based vaccine principles. It contains a complete EV71 VP1 protein and six reported neutralizing B-cell epitopes derived from the four major enteroviruses causing HFMD. In silico validation using multiple immunoinformatic tools indicated good attributes of the VP1me immunogen suitable for vaccine development. The VP1me-based DNA vaccine efficiently induced both humoral and cellular immune responses in BALB/cAJcl mice. A combination of in silico prediction and immunoassays enabled the identification of immunogenic linear B-cell and CD8 T-cell epitopes within the VP1me immunogen. Immunodominant linear B-cell epitopes were identified in six regions of VP1me, with one epitope located at the N-terminus of the VP1 protein (aa 9-23) regarded as a novel epitope. Interestingly, some B-cell epitopes could also induce the CD8 T-cell response, suggesting their dual functions in immune stimulation. These results lay the groundwork for further development of VP1me as a new vaccine candidate.

Inferring B-cell derived T-cell receptor induced multi-epitope-based vaccine candidate against enterovirus 71: a reverse vaccinology approach

Purpose

Enterovirus 71, a pathogen that causes hand-foot and mouth disease (HFMD) is currently regarded as an increasing neurotropic virus in Asia and can cause severe complications in pediatric patients with blister-like sores or rashes on the hand, feet, and mouth. Notwithstanding the significant burden of the disease, no authorized vaccine is available. Previously identified attenuated and inactivated vaccines are worthless over time owing to changes in the viral genome.

Materials and Methods

A novel vaccine construct using B-cell derived T-cell epitopes from the virulent polyprotein found the induction of possible immune response. In order to boost the immune system, a beta-defensin 1 preproprotein adjuvant with EAAAK linker was added at the N-terminal end of the vaccine sequence.

Results

The immunogenicity of the designed, refined, and verified prospective three-dimensional-structure of the multi-epitope vaccine was found to be quite high, exhibiting non-allergenic and antigenic properties. The vaccine candidates bound to toll-like receptor 3 in a molecular docking analysis, and the efficacy of the potential vaccine to generate a strong immune response was assessed through in silico immunological simulation.

Conclusion

Computational analysis has shown that the proposed multi-epitope vaccine is possibly safe for use in humans and can elicit an immune response.

Modulation of plasmacytoid dendritic cell and CD4+ T cell differentiation accompanied by upregulation of the cholinergic anti-inflammatory pathway induced by enterovirus 71

Enterovirus 71 (EV71) is a neurotropic enterovirus associated with hand, foot, and mouth disease (HFMD) fatalities. In this study, we investigated the impact of EV71 on plasmacytoid dendritic cells (pDCs) and CD4+ T cells. The results showed that pDCs were promptly activated, secreting interferon (IFN)-α and inducing CD4+ T cell proliferation and differentiation during early EV71 infection. This initiated adaptive immune responses and promoted proinflammatory cytokine production by CD4+ T cells. Over time, viral nucleic acids and proteins were synthesized in pDCs and CD4+ T cells. Concurrently, the cholinergic anti-inflammatory pathway (CAP) was activated, exhibiting an anti-inflammatory role. With constant viral stimulation, pDCs and CD4+ T cells showed reduced differentiation and cytokine secretion. Defects in pDCs were identified as a key factor in CD4+ T cell tolerance. CAP had a more significant regulatory effect on CD4+ T cells than on pDCs and was capable of inhibiting inflammation in these cells.

Chinese parents' intention to vaccinate their 0-5-year-old children with the EV-71 vaccine against hand, foot, and mouth disease and willingness-to-pay

Background

This study aimed to determine the intention and willingness-to-pay (WTP) of Chinese parents/guardians to vaccinate their children with the EV-71 vaccine. Knowledge levels about hand, foot, and mouth disease (HFMD) and the EV-71 vaccine were also investigated.

Methods

A cross-sectional, self-administered online survey was conducted between November 2022 and March 2023. A stratified multi-stage random sampling method was used to recruit parents/guardians of children aged 0-5 years in southeastern China.

Results

A total of 3,626 complete responses were received. The mean knowledge score of HFMD was 9.99 (±4.23) out of a total of 14 points. The majority of the participants reported a somewhat willing intent (58.8%), followed by an extremely willing intent (28.9%). Participants who did not consider the EV-71 vaccine expensive (OR = 2.94, 95%CI 2.45-3.53) perceived that the EV-71 vaccine is effective (OR = 2.73, 95%CI 1.52-4.90), and a high knowledge level of HFMD (OR = 1.90, 95%CI 1.57-2.29) had the highest significant odds of having an extremely willing intent to vaccinate their children with the EV-71 vaccine. The median (interquartile range [IQR]) of WTP for the EV-71 vaccine was CNY¥200/USD$28 (IQR CNY¥100-400/USD$14-56). The highest marginal WTP for the vaccine was mainly influenced by the perceived high cost of the vaccine. Those participants who did not consider the EV-71 vaccine expensive had more than 10 times higher odds of vaccinating their children (OR = 10.86, 95%CI 8.49-13.88). Perceived susceptibility, perceived benefits, and perceived barriers were also significant influencing factors in the highest marginal WTP.

Conclusion

The findings demonstrate the importance of improving health promotion and reducing the barriers to EV-71 vaccination. Therefore, it is important to improve health promotion and reduce the barriers to EV-71 vaccination.

Enterovirus evolution reveals the mechanism of an RNA-targeted antiviral and determinants of viral replication

Selective pressures on viruses provide opportunities to establish target site specificity and mechanisms of antivirals. Enterovirus (EV)-A71 with resistant mutations in the stem loop (SL) II internal ribosome entry site (IRES) (SLIIresist) were selected at low doses of the antiviral dimethylamiloride (DMA)-135. The EV-A71 mutants were resistant to DMA-135 at concentrations that inhibit replication of wild-type virus. EV-A71 IRES structures harboring resistant mutations induced efficient expression of Luciferase messenger RNA in the presence of noncytotoxic doses of DMA-135. Nuclear magnetic resonance indicates that the mutations change the structure of SLII at the binding site of DMA-135 and at the surface recognized by the host protein AU-rich element/poly(U)-binding/degradation factor 1 (AUF1). Biophysical studies of complexes formed between AUF1, DMA-135, and either SLII or SLIIresist show that DMA-135 stabilizes a ternary complex with AUF1-SLII but not AUF1-SLIIresist. This work demonstrates how viral evolution elucidates the (DMA-135)-RNA binding site specificity in cells and provides insights into the viral pathways inhibited by the antiviral.

The current landscape of the antimicrobial peptide melittin and its therapeutic potential

Melittin, a main component of bee venom, is a cationic amphiphilic peptide with a linear α-helix structure. It has been reported that melittin can exert pharmacological effects, such as antitumor, antiviral and anti-inflammatory effects in vitro and in vivo. In particular, melittin may be beneficial for the treatment of diseases for which no specific clinical therapeutic agents exist. Melittin can effectively enhance the therapeutic properties of some first-line drugs. Elucidating the mechanism underlying melittin-mediated biological function can provide valuable insights for the application of melittin in disease intervention. However, in melittin, the positively charged amino acids enables it to directly punching holes in cell membranes. The hemolysis in red cells and the cytotoxicity triggered by melittin limit its applications. Melittin-based nanomodification, immuno-conjugation, structural regulation and gene technology strategies have been demonstrated to enhance the specificity, reduce the cytotoxicity and limit the off-target cytolysis of melittin, which suggests the potential of melittin to be used clinically. This article summarizes research progress on antiviral, antitumor and anti-inflammatory properties of melittin, and discusses the strategies of melittin-modification for its future potential clinical applications in preventing drug resistance, enhancing the selectivity to target cells and alleviating cytotoxic effects to normal cells.

Extracorporeal life support and continuous renal replacement therapy in a patient with Enterovirus A71 associated cardiopulmonary failure: A case report

RATIONALE

Hand-foot-mouth disease (HFMD) caused by Enterovirus A71, complicated by cardiopulmonary failure, is associated with a high mortality rate despite intensive treatment. To date, there is a paucity of clinical management data, regarding the use of extracorporeal life support (VA-ECMO) for Enterovirus-A71 associated cardiopulmonary failure reported.

PATIENT CONCERNS

The patient in this study presented with severe HFMD complicated by cardiopulmonary failure, polymorphic ventricular tachycardia, and cardiac arrest.

DIAGNOSES

Clinical presentations, laboratory data, and polymerase chain reaction (PCR) results from rectal swabs were used to confirm the diagnosis of severe HFMD caused by Enterovirus A71.

INTERVENTIONS

The patient was managed with chest compression and an automatic external defibrillator, mechanical ventilation, intravenous immunoglobulin (IVIG), continuous renal replacement therapy (CRRT) and inotrope (milrinone). The patient did not respond to these interventions and subsequently required further management with VA-ECMO.

OUTCOMES

The patient achieved a favorable outcomes.

LESSONS

Our study highlights that extracorporeal membrane oxygenation and CRRT can enhance the survival outcomes of patients with severe HFMD with cardiopulmonary failure complications. Furthermore, we propose specific indications for the initiation of VA-ECMO.

Monitoring hand foot and mouth disease using long-term wastewater surveillance in Japan: Quantitative PCR assay development and application

Hand, foot, and mouth disease (HFMD) is a highly contagious disease that primarily affects children under five years of age. It is mainly caused by serotypes of Enterovirus A (EVA): EVA71, Coxsackievirus A types 6 (CVA6), 10 (CVA10), and 16 (CVA16). Despite being highly prevalent in Japan and other countries in the Asia-Pacific region, few studies have investigated HFMD pathogens in wastewater. The present study aimed to develop a highly sensitive and broadly reactive quantitative polymerase chain reaction (qPCR) assay of dominant serotype CVA6, to revise previously developed CVA6, CVA10, and CVA16 assays, and to test these assays in wastewater samples from Yamanashi Prefecture, Japan. The new-CVA6 qPCR assay was developed with maximal nucleotide percent identity among CVA6 isolates from Japan. The new-CVA6 and revised assays were highly sensitive and had the ability to quantify respective positive controls at levels as low as 1 copy/μL. Among the 53 grab influent samples collected between March 2022 and March 2023, EVA71, CVA10, and CVA16 RNA were not detected in any samples, whereas the new-CVA6 assay could detect CVA6 RNA in 38 % (20/53) of samples. CVA6 RNA was detected at a significantly higher concentration in the summer season (3.3 ± 0.8 log10 copies/L; 79 % (11/14)) than in autumn (2.7 ± 0.6 log10 copies/L; 69 % (9/13)). The seasonal trend of CVA6 RNA detection in wastewater aligned with the trend of HFMD case reports in the catchment of the wastewater treatment plant. This is the first study to report the detection and seasonal trends of the EVA serotypes associated with HFMD in wastewater samples in Japan. It provides evidence that wastewater-based epidemiology is applicable even for diseases that are prevalent only in specific population groups.

Ubiquitin E3 ligase SPOP is a host negative regulator of enterovirus 71-encoded 2A protease

IMPORTANCE

EV71 poses a significant health threat to children aged 5 and below. The process of EV71 infection and replication is predominantly influenced by ubiquitination modifications. Our previous findings indicate that EV71 prompts the activation of host deubiquitinating enzymes, thereby impeding the host interferon signaling pathway as a means of evading the immune response. Nevertheless, the precise mechanisms by which the host employs ubiquitination modifications to hinder EV71 infection remain unclear. The present study demonstrated that the nonstructural protein 2Apro, which is encoded by EV71, exhibits ubiquitination and degradation mediated by the host E3 ubiquitin ligase SPOP. In addition, it is the first report, to our knowledge, that SPOP is involved in the host antiviral response.

Molecular evolutionary dynamics of enterovirus A71, coxsackievirus A16 and coxsackievirus A6 causing hand, foot and mouth disease in Thailand, 2000-2022

Hand, foot and mouth disease (HFMD) is a public health threat worldwide, particularly in the Asia-Pacific region. Enterovirus A71 (EV-A71), coxsackievirus A16 (CVA16), and CVA6 are the major pathogens causing HFMD outbreaks in several countries, including Thailand. We retrieved 385 VP1 nucleotide sequences, comprising 228 EV-A71, 33 CVA16, and 124 CVA6, deposited in the databases between 2000 and 2022 for molecular evolutionary characterization using Bayesian phylogeny. All EV-A71 identified belonged to genotype B, subgenotypes B4, and B5, and to genotype C, subgenotypes C1, C2, C4a, C4b, and C5. The analyzes demonstrated these viruses' co-circulation and subgenotypic changes throughout the past two decades. The CVA16 was grouped in genotype B1, predominantly subgenotype B1a, and the CVA6 was grouped in subgenotype D3, clades 1-4. The tMRCA of EV-A71 genotypes B and C, CVA16 B1, and CVA6 D3 dated 1993.79, 1982.62, 1995.86, and 2007.31, respectively, suggesting that the viruses were likely introduced and cryptically circulated in Thailand before the HFMD cases were recognized. We demonstrated these viruses' fluctuation and cyclical pattern throughout the two decades of observation. This study provided insight into evolutionary dynamics concerning molecular epidemiology and supported the selection of current genotype-matched vaccines, vaccine development, and implementation.

Research progress on pathogenic and therapeutic mechanisms of Enterovirus A71

In recent years, enterovirus A71 (EV-A71) infection has become a major global public health problem, especially for infants and young children. The results of epidemiological research show that EV-A71 infection can cause acute hand, foot, and mouth disease (HFMD) and complications of the nervous system in severe cases, including aseptic pediatric meningoencephalitis, acute flaccid paralysis, and even death. Many studies have demonstrated that EV-A71 infection may trigger a variety of intercellular and intracellular signaling pathways, which are interconnected to form a network that leads to the innate immune response, immune escape, inflammation, and apoptosis in the host. This article aims to provide an overview of the possible mechanisms underlying infection, signaling pathway activation, the immune response, immune evasion, apoptosis, and the inflammatory response caused by EV-A71 infection and an overview of potential therapeutic strategies against EV-A71 infection to better understand the pathogenesis of EV-A71 and to aid in the development of antiviral drugs and vaccines.

miR-342-5p targets CTNNBIP1 to promote enterovirus 71 replication

OBJECTIVE

The aim of this research was to explore the role of miR-342-5p in EV71 replication.

METHODS

Peritoneal injection of EV71 (107 TCID50/mL) at 50, 100, and 150 μL was conducted to infect 12-day-old suckling mice (n = 10 per group), and clinical scores and survival rates were recorded during a 6-day trial duration and followed by transcriptome sequencing of collected spinal cord tissues. The differential miRNAs and target genes of the infected and uninfected EV71 mice were analyzed. The miR-342 and CTNNBIP1 binding sites were detected using a dual luciferase reporter assay. Cell viability was detected by CCK-8. RT-qPCR, Western blot, immunofluorescence, and immunohistochemistry assays were conducted to detect VP1 protein levels.

RESULTS

Transcriptome sequencing analyses know that the Wnt pathway played a role in EV71 infection, and the CTNNBIP1 gene in this pathway was the target gene of miR-342-5p. Whether in HMC3 cells or in the spinal cord tissue from the suckling mice, high levels of miR-342-5p markedly promoted EV71 VP1 mRNA and protein expression, elevated TNF-α, IL-6, and IL-10 levels, and inhibited IFN-β levels. In addition, highly expressed miR-342-5p destroyed neuronal structure in spinal cord tissues and reduced the number of glial cells. Highly expressed CTNNBIP1 blocked the promotion of miR-342-5p in EV71 replication, and inhibited TNF-α, IL-6, and IL-10 levels, whereas elevated IFN-β levels. This mechanism is that miR-342-5p can target the CTNNBIP1 3' UTR region, inhibit its expression and reduce its binding to CTNNB1, thus enhancing the interaction between CTNNB1 and TCF4 and activating the Wnt pathway-mediated type I interferon response.

CONCLUSION

In nerve cells and tissues, the overexpression of miR-342-5p promoted the replication of EV71 and attenuated the innate immune response to antiviral disease via Wnt/CTNNB1 signaling pathway.

Detection of Enteroviruses and SARS-CoV-2 in Tunisian Wastewater

Monitoring the circulation of enteric viruses in environmental wastewater is a valuable tool for preventing the emergence of waterborne and food-borne diseases in humans. The detection of viruses was performed in five Tunisian wastewater treatment plants, three located in the Grand Tunis City (WWTP 1, WWTP 2, WWTP 3) and two in the Sahel of Tunisia (WWTP 4, WWTP 4), known as very developed and crowded zones, to assess the effectiveness of three biological wastewater treatment procedures namely natural oxidizing lagoons, rotating biodisks procedure, activated sludge procedure, and one tertiary sewage treatment using UV-C254 reactor for this enteric viruses' removal. Thus, 242 sewage samples were collected between June 2019 and May 2020 from different lines of wastewater treatment procedures implemented in the five wastewater treatment plants investigated. SARS-CoV-2 was analyzed using real-time multiplex reverse-transcription polymerase chain reaction (multiplex real-time RT-PCR) and enteroviruses using reverse-transcription polymerase chain reaction (RT-PCR). The enteroviruses detection showed 93% and 73% respective high frequencies only in the two WWTPs of the Grand Tunis (WWTP 1 and WWTP 2). SARS-CoV-2 was detected in 58% of the all wastewater samples collected from the five studied WWTPs with a respective dominance of N gene (47%), S gene (42%), RdRp gene (42%) and at last E gene (20%). These enteroviruses and SARS-CoV-2 detection were revealed in all steps of the wastewater treatment procedures, so poor virological quality is found at the exit of each biological and tertiary step of treatment investigated. For the first time in Tunisia, these results highlighted the enterovirus and SARS-CoV-2 detection with high rates, and the ineffectiveness of the biological and UV-C254 treatment implemented to remove these viruses. The preliminary results of SARS-CoV-2 circulation in Tunisian wastewater confirmed the wide positivity rate underlined by other works worldwide and allowed showing a move towards integrating wastewater as a way for this virus to spread in different areas and environments. So, this last result about SARS-CoV-2 circulation allowed us to caution about the strong probability of diffusion of this hazardous virus through water and sewage; despite its enveloped character and nature, as a labile and sensitive virus in these environments. Thus, establishing a national surveillance strategy is needed to improve the sanitary quality of treated wastewater and prevent public health problems related to these viruses in treated wastewater.

The upregulation of peripheral blood polyamine metabolites spermidine and spermine in children with hand, foot, mouth disease is related to enterovirus 71 capsid protein VP1, but not VP4

BACKGROUND

Hand, foot, and mouth disease (HFMD) is a common viral childhood illness caused most commonly by enterovirus 71 (EV71) and coxsackievirus A16. The pathogenesis of EV71 has been extensively studied, and the regulation of the host immune response is suspected to aggravate the serious complications induced by EV71. Our previous research showed that EV71 infection significantly increased the release of circulating interleukin (IL)-6, IL-10, IL-13, and IL-27. Notably, these cytokines are related to the EV71 infection risk and clinical stage. Polyamines are compounds that are ubiquitous in mammalian cells and play a key role in various cellular processes. Several studies have shown that targeting polyamine metabolic pathways can reduce infections caused by viruses. However, the significance of polyamine metabolism in EV71 infection remains largely unknown.

METHODS

Serum samples from 82 children with HFMD and 70 healthy volunteers (HVs) were collected to determine the polyamine metabolites spermidine (SPD) and spermine (SPM), and IL-6 levels. In addition, peripheral blood mononuclear cells (PBMCs) were treated with EV71 viral protein 1 (VP1) and EV71 VP4, and the cells and supernatant were then collected to analyze the expression of polyamine metabolism-related enzymes by western blot. The data were analyzed using GraphPad Prism 7.0 software (USA).

RESULTS

The serum polyamine metabolites SPD and SPM were elevated in the HFMD patients, especially in the EV71-infected children. Further, a positive correlation was found between serum SPD and IL-6 levels in the EV71-infected children. We also found that the upregulation of peripheral blood polyamine metabolites in the EV71-infected HFMD children was related to EV71 capsid protein VP1, but not VP4. VP1 may promote the expression of polyamine metabolism-related enzymes and promote the production of polyamine metabolites, thereby upregulating the SPD/nuclear factor kappa B/IL-6 signaling pathway. However, VP4 has the opposite effect in this process.

CONCLUSIONS

Our results suggest that EV71 capsid protein may regulate the polyamine metabolic pathways of infected cells in a variety of ways. This study provides insights into the mechanism of EV71 infection and polyamine metabolism and has good reference value for the development of EV71 vaccine.

Cell membrane-bound toll-like receptor-1/2/4/6 monomers and -2 heterodimer inhibit enterovirus 71 replication by activating the antiviral innate response

Host immune activation is critical for enterovirus 71 (EV71) clearance and immunopathogenesis. However, the mechanism of innate immune activation, especially of cell membrane-bound toll-like receptors (TLRs), against EV71 remains unknown. We previously demonstrated that TLR2 and its heterodimer inhibit EV71 replication. In this study, we systematically investigated the effects of TLR1/2/4/6 monomers and TLR2 heterodimer (TLR2/TLR1, TLR2/TLR6, and TLR2/TLR4) on EV71 replication and innate immune activation. We found that the overexpression of human- or mouse-derived TLR1/2/4/6 monomers and TLR2 heterodimer significantly inhibited EV71 replication and induced the production of interleukin (IL)-8 via activation of the phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinase (MAPK) pathways. Furthermore,human-mouse chimeric TLR2 heterodimer inhibited EV71 replication and activated innate immunity. Dominant-negative TIR-less (DN)-TLR1/2/4/6 did not exert any inhibitory effects, whereas DN-TLR2 heterodimer inhibited EV71 replication. Prokaryotic expression of purified recombinant EV71 capsid proteins (VP1, VP2, VP3, and VP4) or overexpression of EV71 capsid proteins induced the production of IL-6 and IL-8 via activation of the PI3K/AKT and MAPK pathways. Notably, two types of EV71 capsid proteins served as pathogen-associated molecular patterns for TLR monomers (TLR2 and TLR4) and TLR2 heterodimer (TLR2/TLR1, TLR2/TLR6, and TLR2/TLR4) and activated innate immunity. Collectively, our results revealed that membrane TLRs inhibited EV71 replication via activation of the antiviral innate response, providing insights into the EV71 innate immune activation mechanism.

Recent advances in anti-coxsackievirus A16 viral drug research

Hand, foot and mouth disease, a childhood disorder caused by enteroviruses, is intermittently endemic in the Asia-Pacific region and endangers the lives of many infants and young children. Coxsackievirus A16 (CV-A16) is one of the major pathogens causing hand, foot, and mouth disease on occasion, resulting in catastrophic neurological sequelae and patient death. Currently, no clinical interventions are available that completely block the CV-A16 infection. Therefore, research on anti-CV-A16 treatment continues to be a significant focus of interest. This report provides a detailed background on and an introduction to CV-A16; a description of the viral gene and protein structures and a summary of the current advances in pharmaceutical targets, drug research and other related areas.

Hand-Foot-and-Mouth Disease-Associated Enterovirus and the Development of Multivalent HFMD Vaccines

Hand-foot-and-mouth disease (HFMD) is an infectious disease of children caused by more than 20 types of enteroviruses, with most cases recovering spontaneously within approximately one week. Severe HFMD in individual children develops rapidly, leading to death, and is associated with other complications such as viral myocarditis and type I diabetes mellitus. The approval and marketing of three inactivated EV-A71 vaccines in China in 2016 have provided a powerful tool to curb the HFMD epidemic but are limited in cross-protecting against other HFMD-associated enteroviruses. This review focuses on the epidemiological analysis of HFMD-associated enteroviruses since the inactivated EV-A71 vaccine has been marketed, collates the progress in the development of multivalent enteroviruses vaccines in different technical routes reported in recent studies, and discusses issues that need to be investigated for safe and effective HFMD multivalent vaccines.

Epidemiology of hand, foot, and mouth disease and the genetic characteristics of Coxsackievirus A16 in Taiyuan, Shanxi, China from 2010 to 2021

Hand, foot, and mouth disease (HFMD) is a common childhood infectious disease caused by human enteroviruses (EV). This study aimed to describe the epidemiological features of HFMD and the genetic characteristics of Coxsackievirus A16 (CVA16) in Taiyuan, Shanxi, China, from 2010 to 2021. Descriptive epidemiological methods were used to analyze the time and population distribution of HFMD and the genetic characteristics of CVA16. Except being affected by the COVID-19 epidemic in 2020, HFMD epidemics were sporadic from January to March each year, and began to increase in April, with a major epidemic peak from May to August, which declined in September, followed by a secondary peak from October to December. The prevalence of EV infection was the highest in children aged one to five years (84.42%), whereas its incidence was very low in children under one year of age (5.48%). Enterovirus nucleic acid was detected by real-time reverse transcription polymerase chain reaction in 6641 clinical specimens collected from patients with HFMD from 2010 to 2021, and 4236 EV-positive specimens were detected, including 988 enterovirus A71 (EV-A71), 1488 CVA16, and 1760 other enteroviruses. CVA16 remains prevalent and has co-circulated with other EVs in Taiyuan from 2010 to 2021. A phylogenetic tree constructed based on the VP1 region showed that all CVA16 strains belonged to two different clades of the B1 genotype, B1a and B1b. They showed a nucleotide similarity of 86.5-100%, and an amino acid similarity of 96.9-100%. Overall, these findings add to the global genetic resources of CVA16, demonstrate the epidemiological characteristics of HFMD as well as the genetic features of CVA16 in Taiyuan City during 2010-2021, and provide supporting evidence for the prevention and control of HFMD.

Recent progress and advances towards developing enterovirus 71 vaccines for effective protection against human hand, foot and mouth disease (HFMD)

The main pathogen causing severe and neurotrophic hand, foot and mouth disease (HFMD) is enterovirus A71 (EV71). EV71 infection is among the major cause of serious public health burden and economic loss especially in the Asia-pacific region. Yet, no specific anti-viral treatment against this life-threatening infection is currently available. Thus, the best way to control EV71 infection is by vaccination with an effective and safe vaccine. Several strategies are being employed to develop vaccines against EV71. These include conventional and modern recombinant vaccine strategies. Conventional vaccines such as inactivated EV71 vaccines are the most studied and advanced vaccines against HFMD. Recombinant HFMD vaccines developed based on the recombinant DNA technology have been employed but are mostly at early or late preclinical development stage. In this article, we discuss the recent progress and advances in modern recombinant strategies of EV71 vaccine development including subunit, VLP, epitope-based, DNA, and vector-based vaccines, as well as conventional approaches, focusing on their various prospects, advantages and disadvantages.

The CXCL10/CXCR3 Axis Promotes Disease Pathogenesis in Mice upon CVA2 Infection

Coxsackievirus A2 (CVA2) is an emerging pathogen that results in hand-foot-and-mouth disease (HFMD) outbreaks. Systemic inflammatory response and central nervous system inflammation are the main pathological features of fatal HFMD. However, the immunopathogenesis of CVA2 infection is poorly understood. We first detected the transcriptional levels of 81 inflammation-related genes in neonatal mice with CVA2 infection. Remarkably, CVA2 induced higher expression of chemokine (C-X-C motif) ligand 10 (CXCL10) in multiple organs and tissues. CXCL10 acts through its cognate receptor chemokine (C-X-C motif) receptor 3 (CXCR3) and regulates immune responses. CXCL10/CXCR3 activation contributes to the pathogenesis of many inflammatory diseases. Next, we found CXCL10 and CXCR3 expression to be significantly elevated in the organs and tissues from CVA2-infected mice at 5 days postinfection (dpi) using immunohistochemistry (IHC). To further explore the role of CXCL10/CXCR3 in CVA2 pathogenesis, an anti-CXCR3 neutralizing antibody (αCXCR3) or IgG isotype control antibody was used to treat CVA2-infected mice on the same day as infection and every 24 h until 5 dpi. Our results showed that αCXCR3 therapy relieved the clinical manifestations and pathological damage and improved the survival rate of CVA2-infected mice. Additionally, αCXCR3 treatment reduced viral loads and reversed the proinflammatory cytokine (interleukin 6 [IL-6], tumor necrosis factor alpha [TNF-α], and IL-1β) expression, apoptosis, and inflammatory cell infiltration induced by CVA2. Collectively, our study presents evidence for the involvement of the CXCL10/CXCR3 axis in CVA2 pathogenesis. The activation of CXCL10/CXCR3 contributes to CVA2 pathogenesis by inducing apoptosis, proinflammatory cytokine expression, and inflammatory cell infiltration, which can be reversed by αCXCR3 therapy. This study provides new insight into the pathogenesis of HFMD, which has an important guiding significance for the treatment of HFMD. IMPORTANCE Systemic inflammatory response and central nervous system inflammation are the main pathological features of fatal HFMD cases. We detected the expression of 81 inflammation-related genes and found higher expression of CXCL10 in CVA2-infected mice. Next, we confirmed CXCL10/CXCR3 activation using immunohistochemistry and found that anti-CXCR3 neutralizing antibody (αCXCR3) therapy could relieve the clinical manifestations and pathological damage and improve the survival rate of CVA2-infected mice. Additionally, αCXCR3 treatment reduced viral loads and reversed the proinflammatory cytokine (IL-6, TNF-α, and IL-1β) expression, apoptosis, and inflammatory cell infiltration induced by CVA2. Collectively, our study presents the first evidence for the involvement of the CXCL10/CXCR3 axis in CVA2 pathogenesis. The activation of CXCL10/CXCR3 contributes to CVA2 pathogenesis via inducing apoptosis, proinflammatory cytokine expression, and inflammatory cell infiltration, which can be reversed by αCXCR3 therapy. This study provides new insight into the pathogenesis of HFMD, which has an important guiding significance for the treatment of HFMD.

Pharmacological perturbation of CXCL1 signaling alleviates neuropathogenesis in a model of HEVA71 infection

Hand, foot and mouth disease (HFMD) caused by Human Enterovirus A71 (HEVA71) infection is typically a benign infection. However, in minority of cases, children can develop severe neuropathology that culminate in fatality. Approximately 36.9% of HEVA71-related hospitalizations develop neurological complications, of which 10.5% are fatal. Yet, the mechanism by which HEVA71 induces these neurological deficits remain unclear. Here, we show that HEVA71-infected astrocytes release CXCL1 which supports viral replication in neurons by activating the CXCR2 receptor-associated ERK1/2 signaling pathway. Elevated CXCL1 levels correlates with disease severity in a HEVA71-infected mice model. In humans infected with HEVA71, high CXCL1 levels are only present in patients presenting neurological complications. CXCL1 release is specifically triggered by VP4 synthesis in HEVA71-infected astrocytes, which then acts via its receptor CXCR2 to enhance viral replication in neurons. Perturbing CXCL1 signaling or VP4 myristylation strongly attenuates viral replication. Treatment with AZD5069, a CXCL1-specific competitor, improves survival and lessens disease severity in infected animals. Collectively, these results highlight the CXCL1-CXCR2 signaling pathway as a potential target against HFMD neuropathogenesis.

A Novel Attenuated Enterovirus A71 Mutant with VP1-V238A,K244R Exhibits Reduced Efficiency of Cell Entry/Exit and Augmented Binding Affinity to Sulfated Glycans

Enterovirus A71 (EV-A71) is one of the major etiological agents of hand, foot, and mouth disease (HFMD), and infection occasionally leads to fatal neurological complications in children. However, only inactivated whole-virus vaccines against EV-A71 are commercially available in Mainland China. Furthermore, the mechanisms underlying the infectivity and pathogenesis of EV-A71 remain to be better understood. By adaptation of an EV-A71 B5 strain in monkey Vero cells in the presence of brilliant black BN (E151), an anti-EV-A71 agent, a double mutant with VP1-V238A,K244R emerged whose infection was enhanced by E151. The growth of the reverse genetics (RG) mutant RG/B5-VP1-V238A,K244R (RG/B5-AR) was promoted by E151 in Vero cells but inhibited in other human and murine cells, while its parental wild type, RG/B5-wt, was strongly prevented by E151 from infection in all tested cells. In the absence of E151, RG/B5-AR exhibited defective cell entry/exit, resulting in reduced viral transmission and growth in vitro. It had augmented binding affinity to sulfated glycans, cells, and tissue/organs, which probably functioned as decoys to restrict viral dissemination and infection. RG/B5-AR was also attenuated, with a 355 times higher 50% lethal dose (LD₅₀) and a shorter timing of virus clearance than those of RG/B5-wt in suckling AG129 mice. However, it remained highly immunogenic in adult AG129 mice and protected their suckling mice from lethal EV-A71 challenges through maternal neutralizing antibodies. Overall, discovery of the attenuated mutant RG/B5-AR contributes to better understanding of virulence determinants of EV-A71 and to further development of novel vaccines against EV-A71.

IMPORTANCE Enterovirus A71 (EV-A71) is highly contagious in children and has been responsible for thousands of deaths in Asia-Pacific region since the 1990s. Unfortunately, the virulence determinants and pathogenesis of EV-A71 are not fully clear. We discovered that a novel EV-A71 mutant, VP1-V238A,K244R, showed growth attenuation with reduced efficiency of cell entry/exit. In the Vero cell line, which has been approved for manufacturing EV-A71 vaccines, the growth defects of the mutant were compensated by a food dye, brilliant black BN. The mutant also showed augmented binding affinity to sulfated glycans and other cellular components, which probably restricted viral infection and dissemination. Therefore, it was virulence attenuated in a mouse model but still retained its immunogenicity. Our findings suggest the mutant as a promising vaccine candidate against EV-A71 infection.

Enterovirus A71 Induces Neurological Diseases and Dynamic Variants in Oral Infection of Human SCARB2-Transgenic Weaned Mice

Enterovirus A71 (EV-A71) and many members of the Picornaviridae family are neurotropic pathogens of global concern. These viruses are primarily transmitted through the fecal-oral route, and thus suitable animal models of oral infection are needed to investigate viral pathogenesis. An animal model of oral infection was developed using transgenic mice expressing human SCARB2 (hSCARB2 Tg), murine-adapted EV-A71/MP4 virus, and EV-A71/MP4 virus with an engineered nanoluciferase gene that allows imaging of viral replication and spread in infected mice. Next-generation sequencing of EV-A71 genomes in the tissues and organs of infected mice was also performed. Oral inoculation of EV-A71/MP4 or nanoluciferase-carrying MP4 virus stably induced neurological symptoms and death in infected 21-day-old weaned mice. In vivo bioluminescence imaging of infected mice and tissue immunostaining of viral antigens indicated that orally inoculated virus can spread to the central nervous system (CNS) and other tissues. Next-generating sequencing further identified diverse mutations in viral genomes that can potentially contribute to viral pathogenesis. This study presents an EV-A71 oral infection murine model that efficiently infects weaned mice and allows tracking of viral spread, features that can facilitate research into viral pathogenesis and neuroinvasion via the natural route of infection. IMPORTANCE Enterovirus A71 (EV-A71), a positive-strand RNA virus of the Picornaviridae, poses a persistent global public health problem. EV-A71 is primarily transmitted through the fecal-oral route, and thus suitable animal models of oral infection are needed to investigate viral pathogenesis. We present an animal model of EV-A71 infection that enables the natural route of oral infection in weaned and nonimmunocompromised 21-day-old hSCARB2 transgenic mice. Our results demonstrate that severe disease and death could be stably induced, and viral invasion of the CNS could be replicated in this model, similar to severe real-world EV-A71 infections. We also developed a nanoluciferase-containing EV-A71 virus that can be used with this animal model to track viral spread after oral infection in real time. Such a model offers several advantages over existing animal models and can facilitate future research into viral spread, tissue tropism, and viral pathogenesis, all pressing issues that remain unaddressed for EV-A71 infections.

Viral determinants that drive Enterovirus-A71 fitness and virulence

Hand, Foot and Mouth Disease (HFMD) is usually a self-limiting, mild childhood disease that is caused mainly by Coxsackie virus A16 (CVA16) and Enterovirus A71 (EV-A71), both members of the Picornaviridae family. However, recurring HFMD outbreaks and epidemics due to EV-A71 infection in the Western Pacific region, and the propensity of EV-A71 strains to cause severe neurological complications have made this neurotropic virus a serious public health concern in afflicted countries. High mutation rate leading to viral quasispecies combined with frequent intra- and inter-typic recombination events amongst co-circulating EV-A71 strains have contributed to the great diversity and fast evolution of EV-A71 genomes, making impossible any accurate prediction of the next epidemic strain. Comparative genome sequence analyses and mutagenesis approaches have led to the identification of a number of viral determinants involved in EV-A71 fitness and virulence. These viral determinants include amino acid residues located in the structural proteins of the virus, affecting attachment to the host cell surface, receptor binding, and uncoating events. Critical residues in non-structural proteins have also been identified, including 2C, 3A, 3C proteases and the RNA-dependent RNA polymerase. Finally, mutations altering key secondary structures in the 5’ untranslated region were also found to influence EV-A71 fitness and virulence. While our current understanding of EV-A71 pathogenesis remains fragmented, these studies may help in the rational design of effective treatments and broadly protective vaccine candidates.

Muscle Tissue Damage and Recovery After EV71 Infection Correspond to Dynamic Macrophage Phenotypes

Enterovirus 71 (EV71) is a positive single-stranded RNA virus from the enterovirus genus of the Picornaviridae family. Most young children infected with EV71 develop mild symptoms of hand, foot and mouth disease, but some develop severe symptoms with neurological involvement. Limb paralysis from EV71 infection is presumed to arise mainly from dysfunction of motor neurons in the spinal cord. However, EV71 also targets and damages skeletal muscle, which may also contribute to the debilitating symptoms. In this study, we have delineated the impacts of EV71 infection on skeletal muscle using a mouse model. Mouse pups infected with EV71 developed limb paralysis, starting at day 3 post-infection and peaking at day 5-7 post-infection. At later times, mice recovered gradually but not completely. Notably, severe disease was associated with high levels of myositis accompanied by muscle calcification and persistent motor end plate abnormalities. Interestingly, macrophages exhibited a dynamic change in phenotype, with inflammatory macrophages (CD45⁺CD11b⁺Ly6C^hi) appearing in the early stage of infection and anti-inflammatory/restorative macrophages (CD45⁺CD11b⁺Ly6C^low/-) appearing in the late stage. The presence of inflammatory macrophages was associated with severe inflammation, while the restorative macrophages were associated with recovery. Altogether, we have demonstrated that EV71 infection causes myositis, muscle calcification and structural defects in motor end plates. Subsequent muscle regeneration is associated with a dynamic change in macrophage phenotype.

Comprehensive analysis of the circRNA expression profile and circRNA-miRNA-mRNA network in the pathogenesis of EV-A71 infection

Enterovirus A71 (EV-A71) is an important emerging virus posing a threat to children under five years old. Circular RNAs (circRNAs), a novel class of endogenous RNAs, have been recognized to play important roles in the onset and development of viral diseases. However, it has not been determined which specific circRNAs are involved in the pathological mechanisms of EV-A71 infection. In this study, RNA-sequencing (RNA-seq) was conducted to characterize differentially expressed circRNAs during the process of EV-A71 infection. Overall, 8726, 10405 and 4710 circRNAs were detected in the control, EV-A71-12 h and EV-A71-24 h groups, respectively, of which 1851 and 951 circRNAs were differentially expressed in the EV-A71-12 h and EV-A71-24 h groups versus the control group. The overlapping circRNAs in the EV-A71-infected groups were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, which further demonstrated that the host genes of these circRNAs were principally implicated in activities associated with the progression of viral infection, such as immune system process, Wnt signaling pathway, etc. Additionally, qRT-PCR detection showed that six selected circRNAs were identical to the sequencing data. To excavate the key circRNAs in EV-A71 infection, we comprehensively evaluated and integrated the relationship of circRNA/miRNA/mRNA, and eventually screened 2 key circRNA regulatory axes, namely hsa_circ_0017115/hsa-miR-150-5p/EGR1 and hsa_circ_0005060/hsa-miR-4685-5p/MMP2. In summary, our findings not only provide the first comprehensive expression and functional profile of circRNAs in response to EV-A71 infection, but also offer a novel direction to elucidate the molecular mechanism underlying viral pathogenesis and the cellular immune response in host-EV-A71 interactions.

SAMHD1 Inhibits Multiple Enteroviruses by Interfering with the Interaction between VP1 and VP2 Proteins

Sterile alpha motif and histidine-aspartic acid domain-containing protein 1 (SAMHD1) possesses multiple biological activities such as virus restriction, innate immunity regulation, and autoimmunity. Our previous study demonstrated that SAMHD1 potently inhibits the replication of enterovirus 71 (EV71). In this study, we observed that SAMHD1 also restricts multiple enteroviruses (EVs), including coxsackievirus A16 (CA16) and enterovirus D68 (EVD68), but not coxsackievirus A6 (CA6). Mechanistically, SAMHD1 competitively interacted with the same domain in VP1 that binds to VP2 of EV71 and EVD68, thereby interfering with the interaction between VP1 and VP2 , and therefore viral assembly. Moreover, we showed that the SAMHD1 T592A mutant maintained the EV71 inhibitory effect by attenuating the interaction between VP1 and VP2, whereas the T592D mutant failed to. We also demonstrated that SAMHD1 could not inhibit CA6 because a different binding site is required for the SAMHD1 and VP1 interaction. Our findings reveal the mechanism of SAMHD1 inhibition of multiple EVs, and this could potentially be important for developing drugs against a broad range of EVs. IMPORTANCE Enterovirus causes a wide variety of diseases, such as hand, foot, and mouth disease (HFMD), which is a severe public problem threatening children under 5 years. Therefore, identifying essential genes which restrict EV infection and exploring the underlying mechanisms are necessary to develop an effective strategy to inhibit EV infection. In this study, we report that host restrictive factor SAMHD1 has broad-spectrum antiviral activity against EV71, CA16, and EVD68 independent of its well-known deoxynucleoside triphosphate triphosphohydrolase (dNTPase) or RNase activity. Mechanistically, SAMHD1 restricts EVs by competitively interacting with the same domain in VP1 that binds to VP2 of EVs, thereby interfering with the interaction between VP1 and VP2, and therefore viral assembly. In contrast, we also demonstrated that SAMHD1 could not inhibit CA6 because a different binding site is required for the SAMHD1 and CA6 VP1 interaction. Our study reveals a novel mechanism for the SAMHD1 anti-EV replication activity.

MicroRNAs miR-18a and miR-452 regulate the replication of enterovirus 71 by targeting the gene encoding VP3

MicroRNAs (miRNAs) are crucial in the process of host-pathogen interaction. In this study, we established a screening system for miRNAs of target genes to detect the effect of miRNAs on Enterovirus 71 (EV71) replication in rhabdomyosarcoma (RD) cells. A 3'-untranslated region (UTR) dual-luciferase assay was performed to confirm putative miRNA targets in EV71 genome. Firstly, 13 fragments of EV71 genome were inserted into the vector pMIR, and luciferase activities were analyzed to identify the putative miRNAs of target genes. The expression of the reporter protein was significantly downregulated in cells transfected with the vector containing gene VP3. Then we screened for miRNAs that might target to VP3 through online analysis software. In addition, Western blot, real-time PCR, virus titration, and morphological changes were considered to examine the effects of miRNAs on virus replication. The results suggested that miR-18a and miR-452 repress the reproduction of EV71 virus by binding to VP3. Moreover, EV71 infection also affected the expression of endogenous miR-18a and miR-452. In addition, no significant cytotoxic effects were observed. The results from this study suggest that the intracellular miRNAs may play vital roles in the host-virus interaction.

TLR7 Is Critical for Anti-Viral Humoral Immunity to EV71 Infection in the Spinal Cord

Enterovirus 71 (EV71) is a positive single-stranded RNA (ssRNA) virus from the enterovirus genus of Picornaviridae family and causes diseases ranged from the mild disease of hand, foot and mouth disease (HFMD) to the severe disease of neurological involvement in young children. TLR7 is an intracellular pattern recognition receptor (PRR) recognizing viral ssRNA. In this study, we investigated the role of TLR7 in EV71 infection in mouse pups (10-12 days old) and found that wild-type (WT) and TLR7 knock-out (TLR7KO) mice infected with EV71 showed similar limb paralysis at the onset and peak of the disease, comparable loss of motor neurons, and similar levels of antiviral molecules in the spinal cord. These results suggest that TLR7 is not the absolute PRR for EV71 in the spinal cord. Interestingly, TLR7KO mice infected with EV71 exhibited significantly delayed recovery from limb paralysis compared with WT mice. TLR7KO mice infected with EV71 showed significantly decreased levels of IgM and IgG2, important antibodies for antiviral humoral immunity. Furthermore, TLR7KO mice infected with EV71 showed a decrease of germinal center B cells in the spleen compared with WT mice. Altogether, our study suggests that TLR7 plays a critical role in anti-viral humoral immunity rather than in being a PRR in the spinal cord during EV71 infection in young mice.

Novel Naturally Occurring Mutations of Enterovirus 71 Associated With Disease Severity

Infection with the re-emerging enterovirus 71 (EV-A71) is associated with a wide range of disease severity, including herpangina, encephalitis, and cardiopulmonary failure. At present, there is no FDA-approved therapeutics for EV-A71. Early diagnosis for the high-risk children is the key to successful patient care. We examined viral genome sequences at the 5′ untranslated region (UTR) and the capsid protein VP1 from 36 mild and 27 severe cases. We identified five EV-A71 mutations associated with severe diseases, including (1) the 5′ UTR mutations C580U, A707G, C709U; (2) a VP1 alanine-to-threonine mutation at position 280 (280T), and (3) a VP1 glutamic acid-to-(non-glutamic acid) at position 145 [145(non-E)]. SCARB2 is a known entry receptor for EV-A71. Based on a recent cryoEM structure of the EV-A71-SCARB2 binding complex, VP1-280T is near the binding interface between the VP1-VP2 complex and its entry receptor SCARB2. A de novo created hydrogen bonding between the mutant VP1-280T and the VP2-139T, could help strengthen a web-like interaction structure of the VP1-VP2 complex. A stabilized loop turn of VP2, once in contact with SCARB2, can enhance interaction with the host SCARB2 receptor for viral entry. Our findings here could facilitate early detection of severe cases infected with EV-A71 in clinical medicine. In addition, it opens up the opportunity of functional studies via infectious cDNA cloning, site-directed mutagenesis, and animal models in the future.

Sulfonated azo dyes enhance the genome release of enterovirus A71 VP1-98K variants by preventing the virions from being trapped by sulfated glycosaminoglycans at acidic pH

Enterovirus A71 (EV-A71) is a causative agent of hand, foot and mouth disease and occasionally causes death in children. Its infectivity and pathogenesis, however, remain to be better understood. Three sulfonated azo dyes, including acid red 88 (Ar88), were identified to enhance the infectivity of EV-A71, especially isolates with VP1-98K, 145E (-KE), by mainly promoting viral genome release in vitro. Enzymatic removal of sulfated glycosaminoglycans (GAGs) or knockout of xylosyltransferase II (XT2) responsible for biosynthesis of sulfated GAGs weakened the Ar88 enhanced EV-A71 infection. Ar88 is proposed to prevent the -KE variants from being trapped by sulfated GAGs at acidic pH and to facilitate the viral interaction with uncoating factors for genome release in endosomes. The results suggest dual roles of sulfated GAGs as attachment factors and as decoys during host interaction of EV-A71 and caution that these artificial dyes in our environment can enhance viral infection.

Enterovirus 2C Protein Suppresses IKKα Phosphorylation by Recruiting IKKβ and IKKα into Viral Inclusion Bodies

The nuclear factor-kappa B (NF-κB) signaling network constitutes a first line of defense against the invading viruses. However, viruses also adopted multiple strategies to interfere with NF-κB activation. Enterovirus 71 (EV71), in the family Picornaviridae, has become the main pathogen responsible for hand, foot, and mouth disease. Recent studies have reported that the nonstructural protein 2C of EV71 inhibits TNF-α induced NF-κB activation by suppressing IKKβ phosphorylation. In our study, we found that 2C can form inclusion bodies (IBs) in infected and transfected cells. Furthermore, 2C was able to sequester IKKβ into IBs through direct interaction with IKKβ. Although 2C did not directly interact with IKKα, viral protein 2C was able to sequester the IKKα into the IBs mediated by IKKβ. Our in vitro data further demonstrated that EV71 2C could suppress IKKα phosphorylation. These all together support a novel mechanism for EV71 to escape from NF-κB response, in which the phosphorylation of IKKα was suppressed by being recruited into viral IBs in the presence of 2C and IKKβ.

Human Antibodies to VP4 Inhibit Replication of Enteroviruses Across Subgenotypes and Serotypes, and Enhance Host Innate Immunity

Hand, foot, and mouth disease (HFMD) is a highly contagious disease that usually affects infants and young children (<5 years). HFMD outbreaks occur frequently in the Asia-Pacific region, and these outbreaks are associated with enormous healthcare and socioeconomic burden. There is currently no specific antiviral agent to treat HFMD and/or the severe complications that are frequently associated with the enterovirus of serotype EV71. Therefore, the development of a broadly effective and safe anti-enterovirus agent is an existential necessity. In this study, human single-chain antibodies (HuscFvs) specific to the EV71-internal capsid protein (VP4) were generated using phage display technology. VP4 specific-HuscFvs were linked to cell penetrating peptides to make them cell penetrable HuscFvs (transbodies), and readily accessible to the intracellular target. The transbodies, as well as the original HuscFvs that were tested, entered the enterovirus-infected cells, bound to intracellular VP4, and inhibited replication of EV71 across subgenotypes A, B, and C, and coxsackieviruses CVA16 and CVA6. The antibodies also enhanced the antiviral response of the virus-infected cells. Computerized simulation, indirect and competitive ELISAs, and experiments on cells infected with EV71 particles to which the VP4 and VP1-N-terminus were surface-exposed (i.e., A-particles that don’t require receptor binding for infection) indicated that the VP4 specific-antibodies inhibit virus replication by interfering with the VP4-N-terminus, which is important for membrane pore formation and virus genome release leading to less production of virus proteins, less infectious virions, and restoration of host innate immunity. The antibodies may inhibit polyprotein/intermediate protein processing and cause sterically strained configurations of the capsid pentamers, which impairs virus morphogenesis. These antibodies should be further investigated for application as a safe and broadly effective HFMD therapy.

A Mouse Model for Infection with Enterovirus A71 in Small Extracellular Vesicles

EV-A71 was supposed to infect the CNS through the neural pathway and the circulation of the blood in previous studies. Reverse axon transport had been confirmed as an important pathway for EV-A71 to infect the CNS; however, it is still unknown how EV-A71 infects the CNS through the circulation of the blood. Combined with the infectivity of sEVs secreted from EV-A71-infected cells and the characteristic that sEVs could cross the blood-brain barrier, we considered that sEVs may play a vital role in EV-A71 pathogenesis of the CNS.

Enterovirus A71 (EV-A71) is the major pathogen of hand, foot, and mouth disease (HFMD); in some severe cases, it could develop into central nervous system (CNS) disease such as aseptic meningitis, encephalitis, and neurogenic pulmonary edema in children under 5 years. The EV-A71 pathogenesis which is involved with the CNS is unclear due to the lack of a simple and reliable mouse model thus far. Most clinical EV-A71 isolates could not effectively infect the neonatal mouse, which used to be an EV-A71 infection model. The small extracellular vesicles (sEVs) released from clinical EV-A71 isolate-infected cells were infectious in cell lines and could cause a high viral replication in mice. Neonatal ICR mice were injected intraperitoneally with these infectious sEVs and showed more weight loss and higher mortality than those mice injected with the clinical EV-A71 isolate. By using these sEVs, we provided a simple and effective method by which we can generate a stable and valuable animal model for the studies of EV-A71 pathogenesis and therapy.

IMPORTANCE EV-A71 was supposed to infect the CNS through the neural pathway and the circulation of the blood in previous studies. Reverse axon transport had been confirmed as an important pathway for EV-A71 to infect the CNS; however, it is still unknown how EV-A71 infects the CNS through the circulation of the blood. Combined with the infectivity of sEVs secreted from EV-A71-infected cells and the characteristic that sEVs could cross the blood-brain barrier, we considered that sEVs may play a vital role in EV-A71 pathogenesis of the CNS.

Sequence analysis of the first B5 subgenogroup strain of enterovirus 71 isolated in Korea

Enterovirus A71 (EV71), the main etiological agent of handfoot- mouth disease (HFMD), circulates in many areas of the world and has caused large epidemics since 1997, especially in the Asia-Pacific region. In this study, we determined the full-genome sequence of CMC718, a newly isolated EV71 strain in Korea. The CMC718 genome was 7,415 nucleotides in length and was confirmed by whole-genome phylogenetic analysis to belong to the B5 genotype. In particular, CMC718 demonstrated maximum identity with strain M988 of the B5 genotype and numerous amino acid variants were detected in the 3D domain of the viral protein P3, which is consistent with the mutation pattern of a B5 strain isolated in 2012–2013. Comparison of the CMC718 sequence with other EV71 reference strains confirmed the relationship and genetic variation of CMC718. Our study was a full-genome sequence analysis of the first EV71 strain of the B5 genotype isolated in South Korea. This information will be a valuable reference for the development of methods for the detection of recombinant viruses, the tracking of infections, and the diagnosis of EV71.

Transcriptome sequencing analysis of SH-SY5Y cells infected with EV71 reveals the potential neuropathic mechanisms

Enterovirus A71 (EV71) remains the most common causative agent of hand, foot, and mouth disease (HFMD), and the neurological complications induced by EV71 are usually the leading cause of death in children with HFMD. However, the mechanism of nervous system changes caused by EV71 infection is still unclear. Therefore, in the current study, EV71 was inoculated into the human neuroblastoma cell line SH-SY5Y and subsequent transcriptome sequencing was used to examine the alterations of the transcriptome in infected SH-SY5Y cells. It is expected to determine the underlying mechanism of neurological diseases in response to EV71 infection. As a result, a total of 82,406,974, 112,410,808 and 87,780,371 clean reads were found in the control, EV71-12 h and EV71-24 h groups, respectively. Moreover, 160 and 745 differentially expressed genes were identified in the EV71-12 h and EV71-24 h groups, respectively, as compared to the control group. Next, to further explore the pathogenic mechanism triggered by EV71 infection, we mainly focused on the common differentially expressed genes at different time points of EV71 infection. And it was discovered that there were 95 common differentially expressed genes, which were used to conduct GO and pathway analysis. GO enrichment analysis demarcated related biological processes, molecular functions and cellular components, and KEGG pathway analysis enabled annotations of metabolic pathways and revealed interactions among the significantly enriched pathways. The results showed that the enriched GO term "Nervous system development" and enriched pathway "CCKR signaling map" might be important contributors to EV71-induced neuropathological mechanisms. In addition, we also screened 10 up- and down-regulated non-protein coding genes with significantly different expression in our transcriptome profiling, which suggested that these abnormally regulated non-protein-encoding genes might also play important roles in the pathogenesis of EV71 infection. Eventually, RT-qPCR technology was adopted to validate the transcriptome sequencing data and the experiment demonstrated that the RT-qPCR and transcriptome sequencing results were basically consistent. In summary, this is the first transcriptome analysis of SH-SY5Y cells in response to EV71 infection and provides valuable cues for further exploring the mechanism of nervous system changes caused by EV71 infection.

TREM-1 activation is a potential key regulator in driving severe pathogenesis of enterovirus A71 infection

Hand, foot and mouth disease (HFMD), caused by enterovirus A71 (EV-A71), presents mild to severe disease, and sometimes fatal neurological and respiratory manifestations. However, reasons for the severe pathogenesis remain undefined. To investigate this, infection and viral kinetics of EV-A71 isolates from clinical disease (mild, moderate and severe) from Sarawak, Malaysia, were characterised in human rhabdomyosarcoma (RD), neuroblastoma (SH-SY5Y) and peripheral blood mononuclear cells (PBMCs). High resolution transcriptomics was used to decipher EV-A71-host interactions in PBMCs. Ingenuity analyses revealed similar pathways triggered by all EV-A71 isolates, although the extent of activation varied. Importantly, several pathways were found to be specific to the severe isolate, including triggering receptor expressed on myeloid cells 1 (TREM-1) signalling. Depletion of TREM-1 in EV-A71-infected PBMCs with peptide LP17 resulted in decreased levels of pro-inflammatory genes for the moderate and severe isolates. Mechanistically, this is the first report describing the transcriptome profiles during EV-A71 infections in primary human cells, and the potential involvement of TREM-1 in the severe disease pathogenesis, thus providing new insights for future treatment targets.

An infectious clone of enterovirus 71(EV71) that is capable of infecting neonatal immune competent mice without adaptive mutations

Enterovirus 71 (EV71) is a major pathogen that causes hand, foot and mouth disease (HFMD), which is a life threatening disease in certain children. The pathogenesis of EV71-caused HFMD is poorly defined due to the lack of simple and robust animal models with severe phenotypes that recapitulate symptoms observed in humans. Here, we generated the infectious clone of a clinical isolate from a severe HFMD patient. Virus rescued from the cDNA clone was infectious in cell lines. When administrated intraperitoneally to neonatal ICR, BALB/c and C57 immune competent mice at a dosage of1.4 × 10⁴ pfu per mouse, the virus caused weight loss, paralysis and death in the infected mice after 4–5 days of infection. In the infected mice, detectable viral replication was detected in various tissues such as heart, liver, brain, lung, kidney, small intestine, leg skeletal muscle and medulla oblongata. The histology of the infected mice included massive myolysis, glomerular atrophy, villous blunting in small intestine, widened alveolar septum, diminished alveolar spaces and lymphocytes infiltration into the lung. By using the UV-inactivated virus as a control, we elucidated that the virus first amplified in the leg skeletal muscle tissue and the muscle tissue served as a primary viral replication site. In summary, we generated a stable EV71 infectious clone that is capable of infecting neonatal immune competent mice without adaptive mutations and provide a simple, valuable animal model for the studies of EV71pathogenesis and therapy.

Melittin: a venom-derived peptide with promising anti-viral properties

Despite tremendous advances in the development of anti-viral therapeutics, viral infections remain a chief culprit accounting for ongoing morbidity and mortality worldwide. Natural products, in particular animal venoms, embody a veritable cornucopia of exotic constituents, suggesting an immensurable source of anti-infective drugs. In this context, melittin, the principal constituent in the venom of the European honeybee Apis mellifera, has been demonstrated to exert anti-cancer, anti-inflammatory, anti-diabetic, anti-infective, and adjuvant properties. To our knowledge, there is no review appertaining to effects of melittin against viruses, prompting us to synopsize experimental investigations on its anti-viral activity throughout the past decades. Accumulating evidence indicates that melittin curbs infectivity of a diverse array of viruses including coxsackievirus, enterovirus, influenza A viruses, human immunodeficiency virus (HIV), herpes simplex virus (HSV), Junín virus (JV), respiratory syncytial virus (RSV), vesicular stomatitis virus (VSV), and tobacco mosaic virus (TMV). However, medication safety, different routes of administrations, and molecular mechanisms behind the anti-viral activity of melittin should be scrutinized in future studies.

Hypoxia and therapeutic treatment of EV-A71 with an immune modulator TLR7 agonist in a new immunocompetent mouse model

Background

Enterovirus 71 (EV71 or EV-A71) was first identified in California about half a century ago. In recent years, outbreaks of EV-A71 were prevalent worldwide, including Taiwan, Malaysia, Singapore, Japan, and China. Between 2008 and 2011, China alone reported 1894 deaths associated with EV-A71 infection. In mild cases, EV-A71 can cause herpangina and hand-foot-and-mouth disease (HFMD). However, in severe cases, it could cause neurological disorders, including meningitis and encephalitis. Cardiopulmonary failure is common among hospitalized children with EV-A71 infection. No effective FDA-approved therapeutics against EV-A71 are clinically available.

Methods

We report the establishment of an immunocompetent wild type strain 129 (wt-129) mouse model, which can be cross-species infected with human EV-A71 clinical isolates via an intraperitoneal route.

Results

One intriguing disease phenotype of this new model is the development of characteristic “White-Jade” patches in the muscle, which lost sporadically the normal pink color of uninfected muscle. Viral VP1 protein and massive leukocyte infiltration were detected in muscles with or without white-jades. We demonstrated further that hypoxia is a general phenomenon associated with white-jades in both immunocompetent and immunodeficient mouse models. Therefore, hypoxia appears to be a feature intrinsic to EV-A71 infection, irrespective of its host’s immunogenetic background. To date, no effective treatment for EV-A71 is available. Here, using this new wt-129 mouse model, we showed that timely treatment with compound R837 (a TLR7 immune modulator) via oral or intraperitoneal routes, rescued the hypoxia, limb paralysis, and death at a high therapeutic efficacy.

Conclusions

In this new immunocompetent mouse 129 model, we observed an unexpected white-jade phenotype and its associated hypoxia. The successful treatment with TLR7 immune modulators via an oral route, provide us a new research direction for EV-A71 basic science and translational research. It remains an open issue whether R837 or its related compounds, will be a promising drug candidate in clinical trials in EV-A71 endemic or epidemic areas in the future.

Enterovirus-Associated Hand-Foot and Mouth Disease and Neurological Complications in Japan and the Rest of the World

Enteroviruses (EVs) are responsible for extremely large-scale, periodic epidemics in pediatric cohorts, particularly in East and Southeast Asia. Clinical presentation includes a diverse disease spectrum, including hand-foot and mouth disease (HFMD), aseptic meningitis, encephalitis, acute flaccid paralysis, and acute flaccid myelitis. HFMD is predominantly attributable to EV-A types, including the major pathogen EV-A71, and coxsackieviruses, particularly CV-A6, CV-A16, and CV-A10. There have been multiple EV-A71 outbreaks associated with a profound burden of neurological disease and fatal outcomes in Asia since the early 1980s. Efficacious vaccines against EV-A71 have been developed in China but widespread pediatric vaccination programs have not been introduced in other countries. Encephalitis, as a consequence of complications arising from HFMD infection, leads to damage to the thalamus and medulla oblongata. Studies in Vietnam suggest that myoclonus is a significant indicator of central nervous system (CNS) complications in EV-A71-associated HFMD cases. Rapid response in HFMD cases in children is imperative to prevent the progression to a CNS infection; however, prophylactic and therapeutic agents have not been well established internationally, therefore surveillance and functional studies including development of antivirals and multivalent vaccines is critically important to reduce disease burden in pediatric populations.

Enterovirus 71 targets the cardiopulmonary system in a robust oral infection mouse model

Severe infection with the re-emerging enterovirus 71 (EV71 or EV-A71) can cause cardiopulmonary failure. However, in patients' heart and lung, viral protein has not been detected. In mouse models, heart disease has not been reported. EV71-infected brainstem is generally believed to be responsible for the cardiopulmonary collapse. One major limitation in EV71 research is the lack of an efficient oral infection system using non-mouse-adapted clinical isolates. In a robust oral infection NOD/SCID mouse model, we detected EV71 protein at multiple organs, including heart and lung, in 100% of moribund mice with limb paralysis. Infiltrating leukocytes were always detected in heart and muscle, and VP1-positive M2 macrophages were abundant in the lung. Functional dissection on the pathogenesis mechanism revealed severe apoptosis, inflammatory cytokines, and abnormal electrocardiogram (EKG) in orally infected hearts. Therefore, cardiopulmonary disease could be one plausible cause of death in this mouse model. Inoculation of EV71 through an oral route resulted in viral infection in the intestine, viremia, and EV71 appeared to spread to peripheral tissues via blood circulation. Infectious virus was no longer detected in the blood on day 5 post-infection by the plaque formation assay. We demonstrated that both EV71 clinical isolate and cloned virus can target the cardiopulmonary system via a natural infection-like oral route.

[Atypical variant of hand-foot-mouth disease]

An atypical variant of hand-foot-mouth disease (HFMD) has sporadically been reported in recent years, with outbreaks in Europe, Asia, the USA and South America. A new lineage of Coxsackie virus A6 has been identified as the causative agent, a virus-type belonging to the group of enteroviruses. HFMD is transmitted through droplet infection or through faecal-oral transmission. The disease may begin with a prodromal stage and is often accompanied by fever and malaise. Typical skin findings include a papular and vesiculobullous exanthema that might be accompanied by confluent blisters (bullae), crusting, and ulceration. In contrast to "classic" HFMD, predilection sites include the dorsal aspects of the hands and feet, forearms, lower legs, neck and trunk. Oral lesions may be present, but are less often seen compared to "classic" HFMD. The course of the disease is self-limiting, with complete resolution usually within 7-14 days after disease onset. The treatment of atypical HFMD is usually symptomatic. A diagnosis of atypical HFMD might be challenging due to the polymorphous presentation of the disease. This review describes a rarely reported but more frequently diagnosed viral condition.

Neutrophil extracellular traps induced by VP1 contribute to pulmonary edema during EV71 infection

Pulmonary edema is a fatal complication of EV71-associated hand, foot, and mouth disease (HFMD). The pathogenesis of EV71-induced pulmonary edema remains largely unclear. In this study, we aimed to explore the roles of the capsid protein VP1 in the occurrence of EV71-induced pulmonary edema. The intranasal inoculation of recombinant VP1 protein caused lung inflammation with an elevation of inflammatory cytokines and neutrophils infiltration. Moreover, neutrophil extracellular traps (NETs) were observed in the lung parenchyma of the mice treated with VP1. VP1 directly induced the formation of NETs, which depended on PAD4. VP1 also damaged the lung barrier via the reduction of the tight junction protein occludin. Moreover, the EV71 attachment receptor vimentin was increased upon VP1 administration. In contrast, NETs decreased vimentin levels, suggesting a novel role for NETs in viral immune defense. These results evidenced a direct role of VP1 in EV71-induced pulmonary edema and demonstrated that NETs may be both harmful and beneficial in EV71 infection.

PLCβ2 negatively regulates the inflammatory response to virus infection by inhibiting phosphoinositide-mediated activation of TAK1

Excessive or uncontrolled release of proinflammatory cytokines caused by severe viral infections often results in host tissue injury or even death. Phospholipase C (PLC)s degrade phosphatidylinositol-4, 5-bisphosphate (PI(4,5)P2) lipids and regulate multiple cellular events. Here, we report that PLCβ2 inhibits the virus-induced expression of pro-inflammatory cytokines by interacting with and inhibiting transforming growth factor-β-activated kinase 1 (TAK1) activation. Mechanistically, PI(4,5)P2 lipids directly interact with TAK1 at W241 and N245, and promote its activation. Impairing of PI(4,5)P2's binding affinity or mutation of PIP2-binding sites on TAK1 abolish its activation and the subsequent production of pro-inflammatory cytokines. Moreover, PLCβ2-deficient mice exhibit increased expression of proinflammatory cytokines and a higher frequency of death in response to virus infection, while the PLCβ2 activator, m-3M3FBS, protects mice from severe Coxsackie virus A 16 (CVA16) infection. Thus, our findings suggest that PLCβ2 negatively regulates virus-induced pro-inflammatory responses by inhibiting phosphoinositide-mediated activation of TAK1.

Immunocompetent and Immunodeficient Mouse Models for Enterovirus 71 Pathogenesis and Therapy

Enterovirus 71 (EV71) is a global health threat. Children infected with EV71 could develop hand-foot-and-mouth disease (HFMD), encephalitis, paralysis, pulmonary edema, and death. At present, no effective treatment for EV71 is available. We reviewed here various mouse models for EV71 pathogenesis and therapy. Earlier studies relied on the use of mouse-adapted EV71 strains. To avoid artificial mutations arising de novo during the serial passages, recent studies used EV71 clinical isolates without adaptation. Several human receptors for EV71 were shown to facilitate viral entry in cell culture. However, in vivo infection with human SCARB2 receptor transgenic mice appeared to be more limited to certain strains and genotypes of EV71. Efficacy of oral infection in these transgenic models is extremely low. Intriguingly, despite the lack of human receptors, immunodeficient neonatal mouse models can still be infected with EV71 clinical isolates via oral or intraperitoneal routes. Crossbreeding between SCARB2 transgenic and stat1 knockout mice generated a more sensitive and user-friendly hybrid mouse model. Infected hybrid mice developed a higher incidence and earlier onset of CNS disease and death. Different pathogenesis profiles were observed in models deficient in various arms of innate or humoral immunity. These models are being actively used for antiviral research.

Manipulation of Non-canonical NF-κB Signaling by Non-oncogenic Viruses

Nuclear factor (NF)-κB is a major regulator of antiviral response. Viral pathogens exploit NF-κB activation pathways to avoid cellular mechanisms that eliminate the infection. Canonical (classical) NF-κB signaling, which regulates innate immune response, cell survival and inflammation, is often manipulated by viral pathogens that can counteract antiviral response. Oncogenic viruses can modulate not only canonical, but also non-canonical (alternative) NF-κB activation pathways. The non-canonical NF-κB signaling is responsible for adaptive immunity and plays a role in lymphoid organogenesis, B cell development, as well as bone metabolism. Thus, non-canonical NF-κB activation has been linked to lymphoid malignancies. However, some data strongly suggest that the non-canonical NF-κB activation pathway may also function in innate immunity and is modulated by certain non-oncogenic viruses. Collectively, these findings show the importance of studying the impact of different groups of viral pathogens on alternative NF-κB activation. This mini-review focuses on the influence of non-oncogenic viruses on the components of non-canonical NF-κB signaling.