Type I interferons protect mice against enterovirus 71 infection

Cordycepin Inhibits Enterovirus A71 Replication and Protects Host Cell from Virus-Induced Cytotoxicity through Adenosine Action Pathway

Enterovirus A71 (EV-A71) infection typically causes mild illnesses, such as hand-foot-and-mouth disease (HFMD), but occasionally leads to severe or fatal neurological complications in infants and young children. Currently, there is no specific antiviral treatment available for EV-A71 infection. Thus, the development of an effective anti-EV-A71 drug is required urgently. Cordycepin, a major bioactive compound found in Cordyceps fungus, has been reported to possess antiviral activity. However, its specific activity against EV-A71 is unknown. In this study, the potency and role of cordycepin treatment on EV-A71 infection were investigated. Results demonstrated that cordycepin treatment significantly reduced the viral load and viral ribonucleic acid (RNA) level in EV-A71-infected Vero cells. In addition, EV-A71-mediated cytotoxicity was significantly inhibited in the presence of cordycepin in a dose-dependent manner. The protective effect can also be extended to Caco-2 intestinal cells, as evidenced by the higher median tissue culture infectious dose (TCID50) values in the cordycepin-treated groups. Furthermore, cordycepin inhibited EV-A71 replication by acting on the adenosine pathway at the post-infection stage. Taken together, our findings reveal that cordycepin could be a potential antiviral candidate for the treatment of EV-A71 infection.

Advances in anti-EV-A71 drug development research

BACKGROUND

Enterovirus A71 (EV-A71) is capable of causing hand, foot and mouth disease (HFMD), which may lead to neurological sequelae and even death. As EV-A71 is resistant to environmental changes and mutates easily, there is still a lack of effective treatments or globally available vaccines.

AIM OF REVIEW

For more than 50 years since the HFMD epidemic, related drug research has been conducted. Progress in this area can promote the further application of existing potential drugs and develop more efficient and safe antiviral drugs, and provide useful reference for protecting the younger generation and maintaining public health security.

KEY SCIENTIFIC CONCEPTS OF REVIEW

At present, researchers have identified hundreds of EV-A71 inhibitors based on screening repurposed drugs, targeted structural design, and rational modification of previously effective drugs as the main development strategies. This review systematically introduces the current potential drugs to inhibit EV-A71 infection, including viral inhibitors targeting key sites such as the viral capsid, RNA-dependent RNA polymerase (RdRp), 2C protein, internal ribosome entry site (IRES), 3C proteinase (3Cpro), and 2A proteinase (2Apro), starting from each stage of the viral life cycle. Meanwhile, the progress of host-targeting antiviral drugs and their development are summarized in terms of regulating host immunity, inhibiting autophagy or apoptosis, and regulating the cellular redox environment. In addition, the current clinical methods for the prevention and treatment of HFMD are summarized and discussed with the aim of providing support and recommendations for the treatment of enterovirus infections including EV-A71.

Recent Advances in Enterovirus A71 Infection and Antiviral Agents

Enterovirus A71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease (HFMD) that majorly affects children. Most of the time, HFMD is a mild disease but can progress to severe complications, such as meningitis, brain stem encephalitis, acute flaccid paralysis, and even death. HFMD caused by EV-A71 has emerged as an acutely infectious disease of highly pathogenic potential in the Asia-Pacific region. In this review, we introduced the properties and life cycle of EV-A71, and the pathogenesis and the pathophysiology of EV-A71 infection, including tissue tropism and host range of virus infection, the diseases caused by the virus, as well as the genes and host cell immune mechanisms of major diseases caused by enterovirus 71 (EV-A71) infection, such as encephalitis and neurologic pulmonary edema. At the same time, clinicopathologic characteristics of EV-A71 infection were introduced. There is currently no specific medication for EV-A71 infection, highlighting the urgency and significance of developing suitable anti-EV-A71 agents. This overview also summarizes the targets of existing anti-EV-A71 agents, including virus entry, translation, polyprotein processing, replication, assembly and release; interferons; interleukins; the mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase B signaling pathways; the oxidative stress pathway; the ubiquitin-proteasome system; and so on. Furthermore, it overviews the effects of natural products, monoclonal antibodies, and RNA interference against EV-A71. It also discusses issues limiting the research of antiviral drugs. This review is a systematic and comprehensive summary of the mechanism and pathological characteristics of EV-A71 infection, the latest progress of existing anti-EV-A71 agents. It would provide better understanding and guidance for the research and application of EV-A71 infection and antiviral inhibitors.

A mouse model and pathogenesis study for CVA19 first isolated from hand, foot, and mouth disease

ABSTRACTCoxsackievirus A19 (CVA19) is a member of Enterovirus (EV) C group in the Picornaviridae family. Recently, we reported a case of CVA19-infected hand, foot, and mouth disease (HFMD) for the first time. However, the current body of knowledge on the CVA19 infection, particularly the pathogenesis of encephalomyelitis and diarrhoea is still very limited, due to the lack of suitable animal models. Here, we successfully established a CVA19 mouse model via oral route based on 7-day-old ICR mice. Our results found the virus strain could directly infect the neurons, astrocytes of brain, and motor neurons of spinal cord causing neurological complications, such as acute flaccid paralysis. Importantly, viruses isolated from the spinal cords of infected mice caused severe illness in suckling mice, fulfilling Koch's postulates to some extent. CVA19 infection led to diarrhoea with typical pathological features of shortened intestinal villi, increased number of secretory cells and apoptotic intestinal cells, and inflammatory cell infiltration. Much higher concentrations of serum cytokines and more peripheral blood inflammatory cells in CVA19-infected mice indicated a systematic inflammatory response induced by CVA19 infection. Finally, we found ribavirin and CVA19 VP1 monoclonal antibody could not prevent the disease progression, but higher concentrations of antisera and interferon alpha 2 (IFN-α2) could provide protective effects against CVA19. In conclusion, this study shows that a natural mouse-adapted CVA19 strain leads to diarrhoea and encephalomyelitis in a mouse model via oral infection, which provides a useful tool for studying CVA19 pathogenesis and evaluating the efficacy of vaccines and antivirals.

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.

Efficacy of an isoxazole-3-carboxamide analog of pleconaril in mouse models of Enterovirus-D68 and Coxsackie B5

Enteroviruses (EV) cause a number of life-threatening infectious diseases. EV-D68 is known to cause respiratory illness in children that can lead to acute flaccid myelitis. Coxsackievirus B5 (CVB5) is commonly associated with hand-foot-mouth disease. There is no antiviral treatment available for either. We have developed an isoxazole-3-carboxamide analog of pleconaril (11526092) which displayed potent inhibition of EV-D68 (IC50 58 nM) as well as other enteroviruses including the pleconaril-resistant Coxsackievirus B3-Woodruff (IC50 6-20 nM) and CVB5 (EC50 1 nM). Cryo-electron microscopy structures of EV-D68 in complex with 11526092 and pleconaril demonstrate destabilization of the EV-D68 MO strain VP1 loop, and a strain-dependent effect. A mouse respiratory model of EV-D68 infection, showed 3-log decreased viremia, favorable cytokine response, as well as statistically significant 1-log reduction in lung titer reduction at day 5 after treatment with 11526092. An acute flaccid myelitis neurological infection model did not show efficacy. 11526092 was tested in a mouse model of CVB5 infection and showed a 4-log TCID50 reduction in the pancreas. In summary, 11526092 represents a potent in vitro inhibitor of EV with in vivo efficacy in EV-D68 and CVB5 animal models suggesting it is worthy of further evaluation as a potential broad-spectrum antiviral therapeutic against EV.

Recent Developments of Gramine: Chemistry and Biological Activity

The natural alkaloid gramine has attracted significant attention in both academic and industrial circles because of its potential and diverse biological activities, including antiviral, antibacterial, antifungal, anti-inflammatory and antitumor activities; application in therapy for Alzheimer's disease; serotonin-receptor-related activity; insecticidal activity; and application as an algicide. In this review, we focus on the research advances that have been made for gramine-based molecules since their discovery, providing key information on their extraction and separation, chemical synthesis and diverse biological activities. Data regarding their mechanisms of action are also presented. This comprehensive and critical review will serve as a guide for developing more drug candidates based on gramine skeletons.

Ubiquitin-specific protease 24 promotes EV71 infection by restricting K63-linked polyubiquitination of TBK1

TANK-binding kinase 1 (TBK1) is an essential protein kinase for activation of interferon regulatory factor 3 (IRF3) and induction of the type I interferons (IFN-I). Although the biochemical regulation of TBK1 activation has been studied, little is known about how enterovirus 71 (EV71) employs the deubiquitinases (DUBs) to regulate TBK1 activation for viral immune evasion. Here, we found that EV71 infection upregulated the expression of ubiquitin-specific protease 24 (USP24). Further studies revealed that USP24 physically interacted with TBK1, and can reduce K63-linked polyubiquitination of TBK1. Knockdown of USP24 upregulated TBK1 K63-linked polyubiquitination, promoted the phosphorylation and nuclear translocation of IRF3, and in turn improved IFN-I production during EV71 infection. As a consequence, USP24 knockdown dramatically inhibited EV71 infection. This study revealed USP24 as a novel regulator of TBK1 activation, which promotes the understanding of immune evasion mechanisms of EV71 and could provide a potential strategy for treatment of EV71 infection.

Murine models of neonatal susceptibility to a clinical strain of enterovirus A71

Enterovirus A71 (EV-A71) is neurotropic and one of the primary enteric pathogens responsible for severe central nervous system infection in infants and young children. Neonatal mice are ideal models for studying the pathogenesis of infection caused by EV-A71. In this study, we assessed the susceptibility of neonatal BALB/c, C57BL/6, ICR, Kunming, and NIH mice to a clinically isolated EV-A71 strain. One-day-old mice were challenged with a clinical isolate of EV-A71 via intraperitoneal injection, then observed for 13 days for mortality, body-weight changes, and limb paralysis. RT-qPCR was performed to quantify viral RNA in the brain, spinal cord, skeletal muscle, and lungs of BALB/c and C57BL/6 mice. The expression of murine scavenger receptor class B member 2 (mSCARB2) was measured by western blotting. Finally, lesions were assessed by histological examination. We found that neonatal BALB/c and C57BL/6 mice were both susceptible to EV-A71, leading to decreased survival rate, greater body weight loss, and prominent hind-limb paralysis. Tissue viral loads of C57BL/6J mice were markedly higher than those of BALB/c mice, indicating that EV-A71 replicated more efficiently in C57BL/6 mice. Increased expression of mSCARB2 was observed 5 days after infection in C57BL/6 mice, which coincided with the peak in EV-A71 replication. Histological examination indicated that infection caused obvious pathogenic lesions. In conclusion, C57BL/6 are most susceptible to infection caused by EV-A71 and can be used as a model for studying its pathogenesis and test therapeutic options.

Gasdermin E is required for induction of pyroptosis and severe disease during enterovirus 71 infection

Pyroptosis is an inflammatory form of programmed cell death that is executed by the gasdermin (GSDM)-N domain of GSDM family proteins, which form pores in the plasma membrane. Although pyroptosis acts as a host defense against invasive pathogen infection, its role in the pathogenesis of enterovirus 71 (EV71) infection is unclear. In the current study, we found that EV71 infection induces cleavage of GSDM E (GSDME) by using western blotting analysis, an essential step in the switch from caspase-3-mediated apoptosis to pyroptosis. We show that this cleavage is independent of the 3C and 2A proteases of EV71. However, caspase-3 activation is essential for this cleavage, as GSDME could not be cleaved in caspase-3-KO cells upon EV71 infection. Further analyses showed that EV71 infection induced pyroptosis in WT cells but not in caspase-3/GSDME double-KO cells. Importantly, GSDME is required to induce severe disease during EV71 infection, as GSDME deficiency in mice was shown to alleviate pathological symptoms. In conclusion, our results reveal that GSDME is important for the pathogenesis of EV71 via mediating initiation of pyroptosis.

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.

Isolation and Identification of Andrographis paniculata (Chuanxinlian) and Its Biologically Active Constituents Inhibited Enterovirus 71-Induced Cell Apoptosis

Aim:Andrographis paniculata (Burm. f.) Nees (also known as Chuanxinlian in Chinese) of Acanthaceae family is one of the Chinese herbs reputed to be effective in the treatment of inflammation, infection, cold, and fever. Enterovirus 71 (EV71) is one of the most important enteroviruses that cause hand, foot, and mouth disease (HFMD) accompanied with neurological complication.

Methods: To explore an anti-infective Chinese herb medicine, pure compounds isolated or synthesized analogues from A. paniculata (AP) ethyl acetate (EtOAc) extract are used to explore their anti-EV71-induced cytotoxicity. The antiviral activity was determined by cytopathic effect (CPE) reduction, and sub-G1 assays were used for measuring lysis and apoptosis of EV71-infected rhabdomyosarcoma (RD) cells. IFNγ-driven luciferase reporter assay was used to evaluate their potential roles in activation of immune responses.

Results: Our data showed that EV71-induced sub-G1 phase of RD cells was dose dependently increased. Highly apoptotic EV71-infected RD cells were reduced by AP extract treatment. Ergosterol peroxide (4) has the most anti-apoptotic effect among these seven compounds. In addition, 3,19-O-acetyl-14-deoxy-11,12-didehydroandrographolide (8) synthesized from acetylation of compound 7 showed significantly better antiviral activity and the lowest sub-G1 phase of 6%–18%. Further investigation of IFNγ-inducer activity of these compounds showed that compounds 3, 6, 10, 11, and 12 had significantly higher IFNγ luciferase activities, suggesting their potential to promote IFNγ expression and thus activate immune responses for antivirus function.

Conclusion: Our study demonstrated that bioactive compounds of AP and its derivatives either protecting EV71-infected RD cells from sub-G1 arrest or possessing IFNγ-inducer activity might be feasible for the development of anti-EV71 agents.

Characterization of Pathogenesis and Inflammatory Responses to Experimental Parechovirus Encephalitis

Human parechovirus type 3 (PeV-A3) infection has been recognized as an emerging etiologic factor causing severe nerve disease or sepsis in infants and young children. But the neuropathogenic mechanisms of PeV-A3 remain unknown. To understand the pathogenesis of PeV-A3 infection in the neuronal system, PeV-A3-mediated cytopathic effects were analyzed in human glioblastoma cells and neuroblastoma cells. PeV-A3 induced interferons and inflammatory cytokine expression in these neuronal cells. The pronounced cytopathic effects accompanied with activation of death signaling pathways of apoptosis, autophagy, and pyroptosis were detected. A new experimental disease model of parechovirus encephalitis was established. In the disease model, intracranial inoculation with PeV-A3 in C57BL/6 neonatal mice showed body weight loss, hindlimb paralysis, and approximately 20% mortality. PeV-A3 infection in the hippocampus and cortex regions of the neonatal mouse brain was revealed. Mechanistic assay supported the in vitro results, indicating detection of PeV-A3 replication, inflammatory cytokine expression, and death signaling transduction in mouse brain tissues. These in vitro and in vivo studies revealed that the activation of death signaling and inflammation responses is involved in PeV-A3-mediated neurological disorders. The present results might account for some of the PeV-A3-associated clinical manifestations.

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.

Modeling the complete kinetics of coxsackievirus B3 reveals human determinants of host-cell feedback

Complete kinetic models are pervasive in chemistry but lacking in biological systems. We encoded the complete kinetics of infection for coxsackievirus B3 (CVB3), a compact and fast-acting RNA virus. The model consists of separable, detailed modules describing viral binding-delivery, translation-replication, and encapsidation. Specific module activities are dampened by the type I interferon response to viral double-stranded RNAs (dsRNAs), which is itself disrupted by viral proteinases. The experimentally validated kinetics uncovered that cleavability of the dsRNA transducer mitochondrial antiviral signaling protein (MAVS) becomes a stronger determinant of viral outcomes when cells receive supplemental interferon after infection. Cleavability is naturally altered in humans by a common MAVS polymorphism, which removes a proteinase-targeted site but paradoxically elevates CVB3 infectivity. These observations are reconciled with a simple nonlinear model of MAVS regulation. Modeling complete kinetics is an attainable goal for small, rapidly infecting viruses and perhaps viral pathogens more broadly. A record of this paper's transparent peer review process is included in the Supplemental information.

Recent advances in the understanding of enterovirus A71 infection: a focus on neuropathogenesis

Introduction: Hand, foot, and mouth disease caused by enterovirus A71 (EV-A71) is more frequently associated with neurological complications and deaths compared to other enteroviruses.Areas covered: The authors discuss current understanding of the neuropathogenesis of EV-A71 based on various clinical, human, and animal model studies. The authors discuss the important advancements in virus entry, virus dissemination, and neuroinvasion. The authors highlight the role of host immune system, host genetic factors, viral quasispecies, and heparan sulfate in EV-A71 neuropathogenesis.Expert opinion: Comparison of EV-A71 with EV-D68 and PV shows similarity in primary target sites and dissemination to the central nervous system. More research is needed to understand cellular tropisms, persistence of EV-A71, and other possible invasion routes. EV-A71 infection has varied clinical manifestations which may be attributed to multiple receptors usage. Future development of antivirals and vaccines should target neurotropic enteroviruses. Repurposing drug and immunomodulators used in combination could reduce the severity of EV-A71 infection. Only a few drugs have been tested in clinical trials, and in the absence of antiviral and vaccines (except China), active virus surveillance, good hand hygiene, and physical distancing should be advocated. A better understanding of EV-A71 neuropathogenesis is critical for antiviral and multivalent vaccines development.

Enterovirus 71 induces autophagy in mice via mTOR inhibition and ERK pathway activation

AIMS

Enterovirus 71 (EV71) is one of the main viruses that cause hand-foot-mouth disease; however, its pathogenic mechanism remains unclear. This study characterized the relationship between EV71 infection and autophagy in vivo and explored the molecular mechanism underlying EV71-induced autophagy.

MATERIALS AND METHODS

A mouse model of EV71 infection was prepared by intraperitoneally injecting one-day-old BALB/c suckling mice with 30 μL/g of EV71 virus stock solution for 3 days. The behavior, fur condition, weight, and mice mortality were monitored, and disease scores were calculated. The pathological damage to the brain, lung, and muscle tissues after the viral infection was assessed by hematoxylin and eosin staining. Western blot and immunofluorescence analyses were used to detect the expression levels of viral protein 1, Beclin-1, microtubule-associated protein light chain 3B, mammalian target of rapamycin (mTOR), phosphorylated (p)-mTOR, extracellular signal-regulated protein kinase (ERK) 1/2, and p-ERK.

KEY FINDINGS

EV71 infection can trigger autophagy in the brains, lungs, and muscles of infected mice. The autophagy response triggered by EV71 is achieved by the simultaneous mTOR inhibition and the ERK pathway activation. Blocking the mTOR pathway may aggravate autophagy, whereas ERK inhibition alleviates autophagy but cannot completely prevent it.

SIGNIFICANCE

EV71 infection can induce autophagy in mice, involving mTOR and ERK signaling pathways. These two signaling pathways are independent and do not interfere with each other.

Cathelicidin antimicrobial peptides suppress EV71 infection via regulating antiviral response and inhibiting viral binding

Cathelicidin antimicrobial peptides (human LL-37 and mouse CRAMP) are mainly virucidal to enveloped virus. However, the effects and relative mechanisms of LL-37 and CRAMP on non-enveloped virus are elusive. We herein found that CRAMP expression was significantly up-regulated post non-enveloped Enterovirus 71 (EV71) infection in different tissues of newborn ICR mice, while EV71 replication gradually declined post CRAMP up-regulation, indicating the antiviral potential of cathelicidin against EV71. In vitro antiviral assay showed that LL-37 and CRAMP markedly reduced cytopathic effects (CPE), intracellular viral RNA copy numbers, viral VP1 protein levels, and extracellular virons in U251 cells post EV71 infection, indicating that LL-37 and CRAMP significantly inhibited EV71 replication. Mechanism of action assay showed that LL-37 and CRAMP were not virucidal to EV71, but markedly regulated antiviral immune response in U251 cells. Co-incubation of LL-37 or CRAMP with U251 cells markedly increased the basal interferon-β (IFN-β) expression and interferon regulatory transcription factor 3 (IRF3) phosphorylation, modestly enhanced IFN-β production and IRF3 phosphorylation upon EV71 infection, and significantly reduced interleukin-6 (IL-6) production and p38 mitogen-activated protein kinase (MAPK) activation post EV71 infection. Additionally, LL-37 and CRAMP directly inhibited viral binding to U251 cells. Collectively, LL-37 and CRAMP markedly inhibited EV71 replication via regulating antiviral response and inhibiting viral binding, providing potent candidates for peptide drug development against EV71 infection.

The TLR3/IRF1/Type III IFN Axis Facilitates Antiviral Responses against Enterovirus Infections in the Intestine

Enteroviruses infect gastrointestinal epithelium cells, cause multiple human diseases, and present public health risks worldwide. However, the mechanisms underlying host immune responses in intestinal mucosa against the early enterovirus infections remain elusive. Here, we showed that human enteroviruses including enterovirus 71 (EV71), coxsackievirus B3 (CVB3), and poliovirus 1 (PV1) predominantly induce type III interferons (IFN-λ1 and IFN-λ2/3), rather than type I interferons (IFN-α and IFN-β), in cultured human normal and cancerous intestine epithelial cells (IECs), mouse intestine tissues, and human clinical intestine specimens. Mechanistic studies demonstrated that IFN-λ production is induced upon enterovirus infection through the Toll-like receptor 3/interferon regulatory factor 1 (TLR3/IRF1) signaling pathway in IECs. In turn, the supplementation of IFN-λ subsequently induces intrinsically antiviral responses against enterovirus replication. Notably, intraperitoneal injection in neonatal C57BL/6J mice with mouse recombinant IFN-λ2 protein represses EV71 replication and protects mice from viral lethal effects. Altogether, these results revealed a distinct mechanism by which the host elicited immune responses against enterovirus infections in intestine through activating the TLR3/IRF1/type III IFN axis. The new findings would provide an antiviral strategy for the prevention and treatment of enterovirus infections and associated diseases.IMPORTANCE Enterovirus infections are significant sources of human diseases and public health risks worldwide, but little is known about the mechanism of innate immune response in host intestine epithelial surface during the viral replication. We reported the epithelial immune response in cultured human normal and cancerous cells (IECs), mouse tissues, and human clinical intestine specimens following infection with enterovirus 71. The results mechanistically revealed type III interferons (IFN-λ1 and IFN-λ2/3), rather than type I interferons (IFN-α and IFN-β), as the dominant production through TLR3/IRF1 signaling upon multiple human enterovirus infection, including enterovirus 71 (EV71), coxsackievirus B3 (CVB3), and poliovirus 1 (PV1). IFN-λ subsequently induced antiviral activity against enterovirus replication in vitro and in vivo. These studies uncovered the role of the novel process of type III IFN production involved in the TLR3/IRF1 pathway in host intestine upon enterovirus infection, which highlighted a regulatory manner of antiviral defense in intestine during enterovirus infection.

The Function and Mechanism of Enterovirus 71 (EV71) 3C Protease

Enterovirus 71 (EV71) is the main pathogen of the hand, foot, and mouth disease. It was firstly isolated from sputum specimens of infants with central nervous system diseases in California in 1969, and has been repeatedly reported in various parts of the world, especially in the Asia-Pacific region. EV71 3C protein is a 183 amino acid cysteine protease that can cleave most structural and non-structural proteins of EV71. Based on the analysis and understanding of EV71 3C protease, it is helpful to study and treat diseases caused by EV71 virus infection. The EV71 3C protease promotes virus replication by cleaving EV71 synthesis or host proteins. Moreover, EV71 3C protease inhibits the innate immune system and causes apoptosis. At present, in order to deal with the damage caused by the EV71, it is urgent to develop antiviral drugs targeting 3C protease. This review will focus on the structure, function, and mechanism of EV71 3C protease.

A real-time polymerase chain reaction-based approach for qualitative estimation of viral RNA in organ tissues of coxsackievirus A-16-infected neonatal mice

Hand, foot and mouth disease (HFMD) is a paediatric disease associated with enteroviruses (EVs). Among EVs, coxsackievirus A-16 (CVA-16) strain is currently in circulation and causing outbreaks in India. Neonatal mice (Institute of Cancer Research) strains were infected with CVA-16 strain isolated from HFMD patients to conduct pathological and molecular studies. Infected organs were harvested as per time points. A real-time polymerase chain reaction was used for qualitative estimation of viral RNA in organ tissues of infected mice. Skeletal muscle, brain tissue and cardiac tissues were the major target sites of CVA-16 tropism. The first-ever study was conducted on CVA-16 strains using the current approach in India.

Enterovirus A71 Oncolysis of Malignant Gliomas

Malignant gliomas, the most lethal type of primary brain tumor, continue to be a major therapeutic challenge. Here, we found that enterovirus A71 (EV-A71) can be developed as a novel oncolytic agent against malignant gliomas. EV-A71 preferentially infected and killed malignant glioma cells relative to normal glial cells. The virus receptor human scavenger receptor class B, member 2 (SCARB2), and phorbol-12-myristate-13-acetate-induced protein 1 (PMAIP1)-mediated cell death were involved in EV-A71-induced oncolysis. In mice with implanted subcutaneous gliomas, intraneoplastic inoculation of EV-A71 caused significant tumor growth inhibition. Furthermore, in mice bearing intracranial orthotopic gliomas, intraneoplastic inoculation of EV-A71 substantially prolonged survival. By insertion of brain-specific microRNA-124 (miR124) response elements into the viral genome, we improved the tumor specificity of EV-A71 oncolytic therapy by reducing its neurotoxicity while maintaining its replication potential and oncolytic capacity in gliomas. Our study reveals that EV-A71 is a potent oncolytic agent against malignant gliomas and may have a role in treating this tumor in the clinical setting.

Interplays between Enterovirus A71 and the innate immune system

Enterovirus A71 (EV-A71) is a growing threat to public health, particularly in the Asia-Pacific region. EV-A71 infection is most prevalent in infants and children and causes a wide spectrum of clinical complications, including hand-foot-and-mouth disease (HFMD), pulmonary and neurological disorders. The pathogenesis of EV-A71 infection is poorly understood at present. It is likely that viral factors and host immunity, and their interplay, affect the pathogenesis and outcome of EV-A71 infection. The mammalian innate immune system forms the first layer of defense against viral infections and triggers activation of adaptive immunity leading to full protection. In this review, we discuss recent advances in our understanding of the interaction between EV-A71 and the innate immune system. We discuss the role of pattern-recognition receptors (PRRs), including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs), and inflammasomes, in the detection of EV-A71 infection and induction of antiviral immunity. As a counteraction, EV-A71 viral proteins target multiple innate immune pathways to facilitate viral replication in host cells. These novel insights at the virus-host interphase may support the future development of vaccines and therapeutics against EV-A71 infection.

Insights into innate and adaptive immune responses in vaccine development against EV-A71

Enterovirus A71 (EV-A71) is one of the major causative agents of hand, foot and mouth disease (HFMD) in the world, infecting mostly infants and young children (<5 years of age) in Asia. Approximately 2 million cases of HFMD were reported in China each year, of which approximately 45-50% were due to EV-A71. Most of the HFMD infections caused by EV-A71 usually result in mild symptoms with rashes and ulcers in the mouth. However, virulent strains of EV-A71 can infect the central nervous system and cause severe neurologic diseases, leading to reduced cognitive ability, acute flaccid paralysis and death. The lack of understanding of cellular immunity for long-term protection from the HFMD disease represents a major obstacle for vaccine development. In particular, the role of innate and T cell immunity during HFMD infection remains unclear and there is evidence suggesting the importance of CD4⁺ and CD8⁺ T cells for protective immunity. Currently, no US FDA-approved vaccine is available for EV-A71. Although the inactivated vaccines produced in China are highly effective (vaccine efficacy >95%), they lack the cellular immunity required for long-term protection. In this review, we discuss the findings that support the protective roles of innate and T cell immunity against EV-A71 infection, which will provide the knowledge needed for the urgent development of efficacious vaccines that will confer long-term protection.

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.

Dendritic cells and regulatory T cells expressing CCR4 provide resistance to coxsackievirus B5-induced pancreatitis

Type B coxsackieviruses (CVB) are enteroviruses responsible for a common infectious myocarditis and pancreatitis. DCs and regulatory T cells (Tregs) are key players in controlling virus replication and regulating the immune response and tissue damage, respectively. However, the mechanisms underlying cellular migration to target tissues remain unclear. In the present study, we found that CVB5 infection induced CCL17 production and controlled the migration of CCR4⁺ DCs and CCR4⁺ Tregs to the pancreatic lymph nodes (pLN). CVB5 infection of CCR4^-/- mice reduced the migration of the CD8α⁺ DC subset and reduced DC activation and production of IFN-β and IL-12. Consequently, CCR4^-/- mice presented decreased IFN-γ-producing CD4⁺ and CD8⁺ T cells, an increased viral load and more severe pancreatitis. In addition, CCR4^-/- mice had impaired Treg accumulation in pLN as well as increased T lymphocyte activation. Adoptive transfer of CCR4⁺ Tregs but not CCR4^- Tregs was able to regulate T lymphocyte activation upon CVB5 infection. The present data reveal a previously unknown role for CCR4 in coordinating immune cell migration to CVB-infected tissues and in controlling subsequent pancreatitis. These new insights may contribute to the design of future therapies for acute and chronic infection of non-polio enteroviruses.

Pathological and molecular studies on Coxsackie virus A-16 isolated from hand, foot, and mouth disease cases in India: Approach using neonatal mouse model

The present study highlights pathogenesis and molecular aspects of Coxsackie virus A-16 (CVA-16) strains isolated from hand, foot, and mouth disease (HFMD) cases from India using a neonatal mice model. ICR mice were intraperitoneally inoculated with CVA-16/311 strain isolated from HFMD cases. Mice developed hind and forelimb paralysis on day 3 of post infection. Histopathological observations of hind limb muscles showed necrosis, dissolution of muscle fiber cells, infiltration of inflammatory cells, marked dilated ventricle, hemorrhages, and neuronal degeneration in the brain. Immunohistochemical studies revealed high expression of CVA-16/311-specific viral antigen in limb muscles, brain, heart from day 3 till day 7 of post-infection. VP1 gene-based reverse transcription polymerase chain reaction conducted in RNA samples of different tissue organs of infected mice followed by sequencing of the positive amplimers revealed presence of CVA-16/311-specific viral sequences. Phylogenetic analysis based on the VP1 gene showed the presence of B1c sub genotype of CVA-16/311 strain in targeted tissue organs. Sequence analysis revealed major genetic changes in heart, skeletal muscle tissues at the nucleotide and amino acid levels. Genetic changes occurred in organs of mice might predict some potential targets and might act as markers of virulence for neuronal tropism. Pathogenesis and molecular studies of CVA-16 strains isolated from HFMD cases using neonatal mice model was conducted for the first time from India.

Development of live attenuated Enterovirus 71 vaccine strains that confer protection against lethal challenge in mice

Besides causing mild hand, foot and mouth infections, Enterovirus A71 (EV-A71) is associated with neurological complications and fatality. With concerns about rising EV-A71 virulence, there is an urgency for more effective vaccines. The live attenuated vaccine (LAV) is a more valuable vaccine as it can elicit both humoral and cellular immune responses. A miRNA-based vaccine strain (pIY) carrying let-7a and miR-124a target genes in the EV-A71 genome which has a partial deletion in the 5′NTR (∆11 bp) and G64R mutation (3D^p°^l) was designed. The viral RNA copy number and viral titers of the pIY strain were significantly lower in SHSY-5Y cells that expressed both let-7a and miR-124a. Inhibition of the cognate miRNAs expressed in RD and SHSY-5Y cells demonstrated de-repression of viral mRNA translation. A previously constructed multiply mutated strain, MMS and the pIY vaccine strain were assessed in their ability to protect 4-week old mice from hind limb paralysis. The MMS showed higher amounts of IFN-γ ex vivo than the pIY vaccine strain. There was absence of EV-A71 antigen in the skeletal muscles and spinal cord micrographs of mice vaccinated with the MMS and pIY strains. The MMS and pIY strains are promising LAV candidates developed against severe EV-A71 infections.

Spiramycin and azithromycin, safe for administration to children, exert antiviral activity against enterovirus A71 in vitro and in vivo

Hand-foot-mouth disease (HFMD) is a common viral disease in young children, mainly caused by enterovirus A71 (EV-A71) and coxsackievirus A16 (CV-A16). Specific antiviral agents are not commercially available yet. Here we report that the macrolide antibiotics spiramycin (SPM) and azithromycin (AZM) possess antiviral activities against EV-A71 and CV-A16. SPM significantly reduced EV-A71 RNA and protein levels, most likely through interfering with viral RNA replication. The SPM-resistant EV-A71 variants showed similar resistance to AZM, indicating a similar anti-EV-A71 mechanism by which these two drugs exert their functions. The mutations of these variants were reproducibly mapped to VP1 and 2A, which were confirmed to confer resistance to SPM. Animal experiments showed that AZM possesses stronger anti-infection efficacy than SPM, greatly alleviated the disease symptoms and increased the survival rate in a mouse model severely infected with EV-A71. In all, our work suggests that AZM is a potential treatment option for EV-A71-induced HFMD, whose proved safety for infants and children makes it even more promising.

Viperin Inhibits Enterovirus A71 Replication by Interacting with Viral 2C Protein

Enterovirus A71 (EVA71) is a human enterovirus belonging to the Picornaviridae family and mostly causes hand-foot-and-mouth disease in infants. Viperin is an important interferon-stimulated gene with a broad antiviral activity against various viruses. However, the effect of viperin on human enteroviruses and the interaction mechanism between EVA71 and viperin remains elusive. Here, we confirmed the EVA71-induced expression of viperin in a mouse model and cell lines and showed that viperin upregulation by EVA71 infection occurred on both the mRNA and protein level. Viperin knockdown and overexpression in EVA71-infected cells indicated that this protein can markedly inhibit EVA71 infection. Interestingly, immunofluorescent confocal microscopy and co-immunoprecipitation assays indicated that viperin interacts and colocalizes with the EVA71 protein 2C in the endoplasmic reticulum. Furthermore, amino acids 50⁻60 in the N-terminal domain of viperin were the key residues responsible for viperin interaction with 2C. More importantly, the N-terminal domain of viperin was found responsible for inhibiting EVA71 replication. Our findings can potentially aid future research on the prevention and treatment of nervous system damage caused by EVA71 and may provide a potential target for antiviral therapy.

Toll-Like Receptor 3 Is Involved in Detection of Enterovirus A71 Infection and Targeted by Viral 2A Protease

Enterovirus A71 (EV-A71) has emerged as a major pathogen causing hand, foot, and mouth disease, as well as neurological disorders. The host immune response affects the outcomes of EV-A71 infection, leading to either resolution or disease progression. However, the mechanisms of how the mammalian innate immune system detects EV-A71 infection to elicit antiviral immunity remain elusive. Here, we report that the Toll-like receptor 3 (TLR3) is a key viral RNA sensor for sensing EV-A71 infection to trigger antiviral immunity. Expression of TLR3 in HEK293 cells enabled the cells to sense EV-A71 infection, leading to type I, IFN-mediated antiviral immunity. Viral double-stranded RNA derived from EV-A71 infection was a key ligand for TLR3 detection. Silencing of TLR3 in mouse and human primary immune cells impaired the activation of IFN-β upon EV-A71 infection, thus reinforcing the importance of the TLR3 pathway in defending against EV-A71 infection. Our results further demonstrated that TLR3 was a target of EV-A71 infection. EV-A71 protease 2A was implicated in the downregulation of TLR3. Together, our results not only demonstrate the importance of the TLR3 pathway in response to EV-A71 infection, but also reveal the involvement of EV-A71 protease 2A in subverting TLR3-mediated antiviral defenses.

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.

Innate Immunity Evasion by Enteroviruses Linked to Epidemic Hand-Foot-Mouth Disease

Enterovirus (EV) infections are a major threat to global public health, and are responsible for mild respiratory illness, hand, foot, and mouth disease (HFMD), acute hemorrhagic conjunctivitis, aseptic meningitis, myocarditis, severe neonatal sepsis-like disease, and acute flaccid paralysis epidemic. Among them, HFMD is a common pediatric infectious disease caused by EVs of the family Picornaviridae including EV-A71, coxsackieviruses (CV)-A2, CV-A6, CV-A10, and CV-A16. Due to lack of vaccines and specific antiviral therapeutics, millions of children still suffer from HFMD. Innate immune system detects foreign invaders by means of a relatively limited number of sensors, such as pattern recognition receptors (PRRs) [e.g., retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), Toll-like receptors (TLRs), and NOD-like receptors (NLRs)] and even some secreted functional proteins. However, a range of research, highlighted in this review, suggest that EV-associated with HFMD have evolved different strategies to avoid detection by innate immunity via different proteases (e.g., 2A, 3C, 2C, and 3D). Ongoing efforts to better understand virus-host interactions that control innate immunity and then distill how that influences HFMD development promises to have real-world significance. In this review, we address this complex topic in nine sections including multiple proteins associated with PRR and type I interferon (IFN) signaling. Recognizing how EVs linked to HFMD evade host innate immune system, we also describe the interactions between them and, finally, suggest future directions to better inform drug development and public health.

Epidemiology and Immune Pathogenesis of Viral Sepsis

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Sepsis can be caused by a broad range of pathogens; however, bacterial infections represent the majority of sepsis cases. Up to 42% of sepsis presentations are culture negative, suggesting a non-bacterial cause. Despite this, diagnosis of viral sepsis remains very rare. Almost any virus can cause sepsis in vulnerable patients (e.g., neonates, infants, and other immunosuppressed groups). The prevalence of viral sepsis is not known, nor is there enough information to make an accurate estimate. The initial standard of care for all cases of sepsis, even those that are subsequently proven to be culture negative, is the immediate use of broad-spectrum antibiotics. In the absence of definite diagnostic criteria for viral sepsis, or at least to exclude bacterial sepsis, this inevitably leads to unnecessary antimicrobial use, with associated consequences for antimicrobial resistance, effects on the host microbiome and excess healthcare costs. It is important to understand non-bacterial causes of sepsis so that inappropriate treatment can be minimised, and appropriate treatments can be developed to improve outcomes. In this review, we summarise what is known about viral sepsis, its most common causes, and how the immune responses to severe viral infections can contribute to sepsis. We also discuss strategies to improve our understanding of viral sepsis, and ways we can integrate this new information into effective treatment.

Flt3 ligand treatment reduces enterovirus A71 lethality in mice with enhanced B cell responses

Enterovirus A71 (EV-A71) infection can induce encephalitis, which causes death or long-term neurological sequelae, especially in young children. Using a murine infection model, we searched for anti-EV-A71 agents, because effective therapies are not available to control fatal infection. In EV-A71-infected mice, treatment with the hematopoietic growth factor, Fms-like tyrosine-kinase 3 ligand (Flt3 ligand) before infection reduced the lethality and tissue viral loads. Flt3 ligand failed to enhance the production of type I interferons. Instead, Flt3 ligand boosted the numbers of dendritic cells and, particularly lymphocytes in infected organs with an expansion of spleen B cells, and resulted in an increased titer of virus-specific antibody with neutralizing activity in the serum. The protective effect of Flt3 ligand was abolished in B cell-deficient mice. Our findings revealed that Flt3 ligand administration promotes resistance to EV-A71 infection with enhanced B cell response in a mechanism rarely reported before.

Promyelocytic Leukemia Restricts Enterovirus 71 Replication by Inhibiting Autophagy

The promyelocytic leukemia (PML) protein, also known as TRIM19, functions as a major organizer of PML nuclear bodies (NBs) in most mammalian cells and plays important roles in antiviral activities against both DNA and RNA viruses. In this study, we found that the downregulation of PML rendered HeLa cells more susceptible to infection by enterovirus 71 (EV71), and the overexpression of the PMLIII or PMLIV isoforms inhibited viral protein expression and resulted in viral titers that were 2–3 log units lower than those in the control. Using short interfering RNAs, the downregulation of either the PMLIII or PMLIV isoform increased both viral protein VP1 expression and viral production. The PML repression of EV71 replication was partially mediated by the inhibition of autophagy, and PML deficiency triggered autophagy. Furthermore, the EV71 infection resulted in a reduction in PML independent of the proteasome pathway. Instead, PML degradation was mediated by virus protease 3C^pro. In conclusion, PML contributes to a cellular antiviral effect by inhibiting autophagy, which is countered by a disruption of promyelocytic leukemia protein-nuclear bodies mediated by viral protease 3C^pro.

Enterovirus A71 Proteins: Structure and Function

Enterovirus A71 (EV-A71) infection has grown to become a serious threat to global public health. It is one of the major causes of hand, foot, and mouth disease (HFMD) in infants and young children. EV-A71 can also infect the central nervous system (CNS) and induce diverse neurological complications, such as brainstem encephalitis, aseptic meningitis, and acute flaccid paralysis, or even death. Viral proteins play a crucial role in EV-A71 infection. Many recent studies have discussed the structure and function of EV-A71 proteins, and the findings reported will definitely aid the development of vaccines and therapeutic approaches. This article reviews the progress in the research on the structure and function of EV-A71 proteins. Available literature can provide a basis for studying the pathogenesis of EV-A71 infection in detail.

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

Enterovirus 71 (EV71) is a global infectious disease that affects millions of people. The virus is the main etiological agent for hand, foot, and mouth disease with outbreaks and epidemics being reported globally. Infection can cause severe neurological, cardiac, and respiratory problems in children under the age of 5. Despite on-going efforts, little is known about the pathogenesis of EV71, how the host immune system responds to the virus and the molecular mechanisms behind these responses. Moreover, current animal models remain limited, because they do not recapitulate similar disease patterns and symptoms observed in humans. In this review the role of the host-viral interactions of EV71 are discussed together with the various models available to examine: how EV71 utilizes its proteins to cleave host factors and proteins, aiding virus replication; how EV71 uses its own viral proteins to disrupt host immune responses and aid in its immune evasion. These discoveries along with others, such as the EV71 crystal structure, have provided possible targets for treatment and drug interventions.

Asymmetric synthesis of novel triazole derivatives and their in vitro antiviral activity and mechanism of action

In this study, forty-four chiral triazole derivatives have been prepared via asymmetric synthesis, and which has been successfully characterized by typical spectroscopic techniques including ¹H NMR, ¹³C NMR, EI-MS, elemental analysis and optical rotations. Their in vitro antiviral activities against EV71 and CVB3 were fully investigated in cell-based assays. It was observed that 13 synthetic triazole derivatives inhibited the CPE of EV71 on RD cells, with EC_50S in the 5.3-15.9 μg/ml range and corresponding SIs of 4.0-27.6, while 17 triazole derivatives showed antiviral activities against CVB3, with EC_50S in the 4.7-15.1 μg/ml range and the corresponding SIs of 3.7-14.5. In addition, in some cases, the respective enantiomers showed significantly selective inhibitory effect against EV71, most notably for the enantiomers 9(R) and 10(S), 42(R) and 43(S), which presented an obvious activity difference. The most potential molecules are the compounds 10 and 43 with S-configuration, and which exhibit good SI values compared with the control Ribavirin.

Protective Efficacies of Formaldehyde-Inactivated Whole-Virus Vaccine and Antivirals in a Murine Model of Coxsackievirus A10 Infection

Coxsackievirus A10 (CVA10) is one of the major pathogens associated with hand, foot, and mouth disease (HFMD). CVA10 infection can cause herpangina and viral pneumonia, which can be complicated by severe neurological sequelae. The morbidity and mortality of CVA10-associated HFMD have been increasing in recent years, particularly in the pan-Pacific region. There are limited studies, however, on the pathogenesis and immunology of CVA10-associated HFMD infections, and few antiviral drugs or vaccines have been reported. In the present study, a cell-adapted CVA10 strain was employed to inoculate intramuscularly 5-day-old ICR mice, which developed significant clinical signs, including reduced mobility, lower weight gain, and quadriplegia, with significant pathology in the brain, hind limb skeletal muscles, and lungs of infected mice in the moribund state. The severity of illness was associated with abnormally high expression of the proinflammatory cytokine interleukin 6 (IL-6). Antiviral assays demonstrated that ribavirin and gamma interferon administration could significantly inhibit CVA10 replication both in vitro and in vivo In addition, formaldehyde-inactivated CVA10 whole-virus vaccines induced immune responses in adult mice, and maternal neutralizing antibodies could be transmitted to neonatal mice, providing protection against CVA10 clinical strains. Furthermore, high-titer antisera were effective against CVA10 and could relieve early clinical symptoms and improve the survival rates of CVA10-challenged neonatal mice. In summary, we present a novel murine model to study CVA10 pathology that will be extremely useful in developing effective antivirals and vaccines to diminish the burden of HFMD-associated disease.IMPORTANCE Hand, foot, and mouth disease cases in infancy, arising from coxsackievirus A10 (CVA10) infections, are typically benign, resolving without any significant adverse events. Severe disease and fatalities, however, can occur in some children, necessitating the development of vaccines and antiviral therapies. The present study has established a newborn-mouse model of CVA10 that, importantly, recapitulates many aspects of human disease with respect to the neuropathology and skeletal muscle pathology. We found that high levels of the proinflammatory cytokine interleukin 6 correlated with disease severity and that ribavirin and gamma interferon could decrease viral titers in vitro and in vivo Whole-virus vaccines produced immune responses in adult mice, and immunized mothers conferred protection on neonates against challenge from CVA10 clinical strains. Passive immunization with high-titer antisera could also improve survival rates in newborn animals.

ARRDC4 regulates enterovirus 71-induced innate immune response by promoting K63 polyubiquitination of MDA5 through TRIM65

Enterovirus 71 (EV71) is the main causative agent of hand, foot and mouth disease (HFMD), which induces significantly elevated levels of cytokines and chemokines, leading to local or system inflammation and severe complications, whereas the underlying regulatory mechanisms and the inflammatory pathogenesis remain elusive. ARRDC4 is one member of arrestins family, having important roles in glucose metabolism and G-protein-coupled receptors (GPCRs) related physiological and pathological processes, however, the function of ARRDC4 in innate immune system is largely unknown. Here we identified that ARRDC4 expression was increased after EV71 infection in THP-1-derived macrophages and verified in EV71-infected HFMD patients and the healthy candidates. The expression level of ARRDC4 was positively correlated with the serum concentration of IL-6, TNF-α and CCL3 in clinical specimens. ARRDC4 interacted with MDA5 via the arrestin-like N domain, and further recruited TRIM65 to enhance the K63 ubiquitination of MDA5, resulting in activation of the downstream innate signaling pathway and transcription of proinflammatory cytokines during EV71 infection. Our data highlight new function of ARRDC4 in innate immunity, contributing to the better understanding about regulation of MDA5 activation after EV71 infection, and also suggest ARRDC4 may serve as a potential target for intervention of EV71-induced inflammatory response.

Enterovirus 71 suppresses interferon responses by blocking Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling through inducing karyopherin-α1 degradation

Enterovirus 71 (EV71) has emerged as one of the most important enteroviruses since the eradication of poliovirus, and it causes severe neurological symptoms for which no effective antiviral drugs are available. Type I interferons (IFN) α/β have been used clinically as antiviral therapy as the first line of defense against virus infections successfully for decades. However, treatment with type I interferons has not been effective in patients with EV71 infection. In this study, we found that in cells pretreated with IFN-β, EV71 infection could still lead to a cytopathic effect, and the viral replication was not affected. The mechanism by which EV71 antagonizes interferon signaling, however, has been controversial. Our study indicated that EV71 infection did not inhibit phosphorylation of STAT1/2 induced by IFN-β stimulation, but p-STAT1/2 transport into the nucleus was significantly blocked. We showed that EV71 infection reduced the formation of STAT/karyopherin-α1 (KPNA1) complex upon interferon stimulation and that the virus down-regulated the expression of KPNA1, a nuclear localization signal receptor for p-STAT1. Using specific caspase inhibitors and siRNA for caspase-3, we demonstrated that EV71 infection induced degradation of cellular KPNA1 in a caspase-3-dependent manner, which led to decreased induction of interferon-inducible genes and IFN response. Viral 2A and 3C proteases did not degrade KPNA1, inhibit the activity of ISRE or suppress the transcription of interferon-inducible genes induced by IFN-β. Our study demonstrates a novel mechanism by which antiviral signaling is suppressed through degradation of KPNA1 by activated caspase-3 induced in an enteroviral infection.

A Neonatal Murine Model of Coxsackievirus A6 Infection for Evaluation of Antiviral and Vaccine Efficacy

Hand, foot, and mouth disease (HFMD) is a global health concern. Family Picornaviridae members, particularly enterovirus A71 (EVA71) and coxsackievirus A16 (CVA16), are the primary etiological agents of HFMD; however, a third enterovirus A species, CVA6, has been recently associated with epidemic outbreaks. Study of the pathogenesis of CVA6 infection and development of antivirals and vaccines are hindered by a lack of appropriate animal models. We have developed and characterized a murine model of CVA6 infection that was employed to evaluate the antiviral activities of different drugs and the protective efficacies of CVA6-inactivated vaccines. Neonatal mice were susceptible to CVA6 infection via intramuscular inoculation, and the susceptibility of mice to CVA6 infection was age and dose dependent. Five-day-old mice infected with 10^5.5 50% tissue culture infective doses of the CVA6 WF057R strain consistently exhibited clinical signs, including reduced mobility, lower weight gain, and quadriplegia with significant pathology in the brain, hind limb skeletal muscles, and lungs of the infected mice in the moribund state. Immunohistochemical analysis and quantitative reverse transcription-PCR (qRT-PCR) analyses showed high viral loads (11 log₁₀/mg) in skeletal muscle, and elevated levels of interleukin-6 (IL-6; >2,000 pg/ml) were associated with severe viral pneumonia and encephalitis. Ribavirin and gamma interferon administered prophylactically diminished CVA6-associated pathology in vivo, and treatment with IL-6 accelerated the death of neonatal mice. Both specific anti-CVA6 serum and maternal antibody play important roles in controlling CVA6 infection and viral replication. Collectively, these findings indicate that this neonatal murine model will be invaluable in future studies to develop CVA6-specific antivirals and vaccines.IMPORTANCE Although coxsackievirus A6 (CVA6) infections are commonly mild and self-limiting, a small proportion of children may have serious complications, such as encephalitis, acute flaccid paralysis, and neurorespiratory syndrome, leading to fatalities. We have established a mouse model of CVA6 infection by inoculation of neonatal mice with a CVA6 clinical isolate that produced consistent pathological outcomes. Here, using this model of CVA6 infection, we found that high levels of IL-6 were associated with severe viral pneumonia and encephalitis, as in an evaluation of antiviral efficacy in vivo, IL-6 had no protective effect and instead accelerated death in neonatal mice. We demonstrated that, as antiviral drugs, both gamma interferon and ribavirin played important protective roles in the early stages of infection, with increased survival in treated neonatal mice challenged with CVA6. Moreover, active and passive immunization with the inactivated vaccines and anti-CVA6 serum also protected mice against homologous challenge infections.

Enterovirus 71 infection and vaccines

Hand, foot and mouth disease (HFMD) is a highly contagious viral infection affecting young children during the spring to fall seasons. Recently, serious outbreaks of HFMD were reported frequently in the Asia-Pacific region, including China and Korea. The symptoms of HFMD are usually mild, comprising fever, loss of appetite, and a rash with blisters, which do not need specific treatment. However, there are uncommon neurological or cardiac complications such as meningitis and acute flaccid paralysis that can be fatal. HFMD is most commonly caused by infection with coxsackievirus A16, and secondly by enterovirus 71 (EV71). Many other strains of coxsackievirus and enterovirus can also cause HFMD. Importantly, HFMD caused by EV71 tends to be associated with fatal complications. Therefore, there is an urgent need to protect against EV71 infection. Development of vaccines against EV71 would be the most effective approach to prevent EV71 outbreaks. Here, we summarize EV71 infection and development of vaccines, focusing on current scientific and clinical progress.

A Case-control Study on Risk Factors for Severe Hand, Foot and Mouth Disease

The objective of this study was to identify potential risk factors for severe hand, foot and mouth disease (HFMD). In this case-control study, 459 severe HFMD patients and 246 mild HFMD patients from Guangdong province and Henan province, China were included. Data comprising demographic characteristics, clinical symptoms and signs, laboratory findings and other factors were collected. Univariate analysis revealed 30 factors associated with severe cases. Further multivariate analysis indicated four independent risk factors: fatigue (p < 0.01, odd ratio [OR] = 204.7), the use of glucocorticoids (p = 0.03, OR = 10.44), the use of dehydrant drugs (p < 0.01, OR = 73.7) and maculopapular rash (p < 0.01, OR = 84.4); and one independent protective factor: herpes or ulcers in mouth (p = 0.01, OR = 0.02). However, more systematic research and validation are needed to understand the underlying risk factors for severe HFMD.

Enterovirus 71 inhibits cellular type I interferon signaling by inhibiting host RIG-I ubiquitination

Enterovirus 71 (EV71) is a human pathogen that induces hand, foot, and mouth disease (HFMD) and fatal neurological diseases in young children and infants. Pathogenicity of EV71 is likely related to its ability to evade host innate immunity through inhibiting cellular type I interferon signaling. However, it is less well understood the molecular events governing this process. In this study, we found that EV71 infection suppressed the induction of antiviral immunity by inhibiting the expression levels of IFN-β and IFN-stimulated genes (ISGs), such as ISG54 and ISG56, at the late stage of viral infection. At the same time, our results showed that EV71 infection significantly inhibited ubiquitination of RIG-I. In contrast, up-regulation of RIG-I ubiquitination promoted expression of IFN-β and ISGs, suggesting that inhibition of cellular type I interferon signaling was caused by down-regulation of RIG-I ubiquitination during EV71 infection. These results suggest that inhibition of RIG-I-mediated type I IFN responses by EV71 may contribute to the pathogenesis of viral infection.