Sustained high levels of interleukin-6 contribute to the pathogenesis of enterovirus 71 in a neonate mouse model

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.

Leflunomide: Traditional immunosuppressant with concurrent antiviral effects

Leflunomide is a classic disease-modifying anti-rheumatic drug that is widely used to treat autoimmune diseases. Studies also show its antiviral effects in in vitro and/or in vivo experiments. Considering glucocorticoids, immunosuppressants and newly emerged antibodies commonly used in autoimmune diseases and autoinflammatory disorders bring risk of infection such as viral infection, leflunomide with combination of anti-viral and immunosuppressive features to maintain the balance between infection and anti-inflammation are attractive. Here we summarize the actions and mechanisms of leflunomide in immunoregulatory and antiviral effects.

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.

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.

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.

Cytokine receptor gp130 promotes postnatal proliferation of cardiomyocytes required for the normal functional development of the heart

Mammalian ventricular cardiomyocytes are premature at birth and exhibit substantial phenotypic changes before weaning. Mouse ventricular myocytes undergo cell division several times after birth; however, the regulatory mechanisms and roles of cardiomyocyte division in postnatal heart development remain unclear. Here, we investigated the physiological role of gp130, the main subunit of multifunctional receptors for the IL-6 family of cytokines, in postnatal cardiomyocyte proliferation. Pharmacological inhibition of gp130 within the first month after birth induced significant systolic dysfunction of the left ventricle in mice. Consistently, mice with postnatal cardiomyocyte-specific gp130 depletion exhibited impaired left ventricular contractility compared to control mice. In these mice, cardiomyocytes exhibited a moderately decreased size and dramatically inhibited proliferation in the left ventricle but not in the right ventricle. Stereological analysis revealed that this change significantly decreased the number of cardiomyocytes in the left ventricle. Furthermore, IL-6 was mainly responsible for promoting ventricular cardiomyocyte proliferation by activating the JAK/STAT3 pathway. Taken together, the IL-6/gp130/JAK/STAT3 axis plays a crucial role in the physiological postnatal proliferation and hypertrophy of left ventricular cardiomyocytes to ensure normal cardiac functional development.

PLAC8 promotes EV71 infected inflammatory lesion by disturbing Th-cell-related cytokines release in neonatal mouse

Enterovirus 71 can cause severe hand, foot, and mouth disease (HFMD) in children. However, little is known about the mechanism of inflammatory disorders caused by EV71 infection and why severe cases are mainly children aged under-three. In current study, using mRNA microarray assay, the differential expression of Placenta-specific 8 (PLAC8) was identified in mice brain. In addition, we found that PLAC8 expression was down-regulated with age in mice lung tissues and human peripheral blood. Then, we further proved that PLAC8 could promote inflammation progress and disturb Th1/Th2/Th17/Treg related cytokines release after EV71 infection using PLAC8 plasmid over-expressed neonatal mouse model. Our data suggest that PLAC8 might play a crucial role in Th cell differentiation and inflammatory damage caused by EV71 infection in infants. Thus, our findings would help understand the causes of severe inflammatory injury in infants during EV71 infection, and provide new insights into the prevention and control of severe HFMD.

Characteristics and therapy of enteroviral encephalitis: case report and systematic literature review

OBJECTIVES

Enterovirus (EV) is a frequent cause of encephalitis. The optimal therapeutic approach remains a matter of debate. We present the case of an immunosuppressed patient with EV encephalitis treated successfully with intravenous immunoglobulin (IVIG) and report the results of a systematic review on the characteristics of EV encephalitis, as well as the safety and efficacy of IVIG therapy.

METHODS

A systematic review was conducted using the PubMed, Cochrane Database, BIOSIS Previews, and ClinicalTrials.gov databases to identify all reports on patients with EV encephalitis as of December 31, 2020. The main outcomes assessed were the efficacy and safety of the respective therapeutic approach.

RESULTS

A total of 73 articles were included: one prospective trial, one retrospective and prospective case series, one purely retrospective case series, and 70 case reports. The case reports included a total of 101 patients. Immunosuppressed patients were at higher risk of contracting EV encephalitis and experiencing a fatal course. Hypogammaglobulinaemia particularly predisposes to EV disease, even with a moderate reduction in serum IgG levels. IVIG therapy in the immunosuppressed may confer a survival advantage.

CONCLUSIONS

IVIG therapy is rarely associated with severe adverse events and may be considered in immunosuppressed patients with EV encephalitis. Future trials should investigate the optimal IVIG dosing and route of application, the benefit of antibody-enriched IVIG preparations, and the serum immunoglobulin level that should trigger prophylactic replacement.

Susceptibility and cytokine responses of human neuronal cells to multiple circulating EV-A71 genotypes in India

Enterovirus-A71 (EV-A71) associated Hand, foot and mouth disease (HFMD) is a highly contagious viral infection affecting children in Asia–Pacific region and has become a major threat to public health. Although several EV-A71 genotypes (C, D, and G) were isolated in India in recent years, no recognizable outbreak of EV-A71 caused HFMD, Acute Flaccid paralysis (AFP) or encephalitis have been reported so far. It is essential to study the pathogenicity or cell tropism of these Indian isolates in order to understand their tendency to cause disease. We investigated the susceptibility and cytokine responses of indigenous EV-A71 genotypes (D and G) isolated from cases of AFP and genotype C viruses isolated from cases of HFMD and encephalitis, in human cells in-vitro. Although all three EV-A71 genotypes could infect and replicate in human muscle and neuronal cells, the genotype D virus showed a delayed response in human neuronal cells. Quantification of cytokine secretion in response to these isolates followed by confirmation with gene expression assays in human neuronal cells revealed significantly higher secretion of pro-inflammatory cytokines TNF-α IL-8, IL-6, IP-10 (p < 0.001) in G genotype infected cells as compared to pathogenic C genotypes whereas the genotype D virus could not induce any of the inflammatory cytokines. These findings will help to better understand the host response to indigenous EV-A71 genotypes for management of future EV-A71 outbreaks in India, if any.

Neonatal Murine Model of Coxsackievirus A2 Infection for the Evaluation of Antiviral Therapeutics and Vaccination

Coxsackievirus (CV) A2 has emerged as an important etiological agent in the pathogen spectrum of hand, foot, and mouth disease (HFMD). The symptoms of CVA2 infections are generally mild, but worsen rapidly in some people, posing a serious threat to children’s health. However, compared with enterovirus 71 detected frequently in fatal cases, limited attention has been paid to CVA2 infections because of its benign clinical course. In the present study, we identified three CVA2 strains from HFMD infections and used the cell-adapted CVA2 strain HN202009 to inoculate 5-day-old BALB/c mice intramuscularly. These mice developed remarkably neurological symptoms such as ataxia, hind-limb paralysis, and death. Histopathological determination showed neuronophagia, pulmonary hemorrhage, myofiberlysis and viral myocarditis. Viral replication was detected in multiple organs and tissues, and CVA2 exhibited strong tropism to muscle tissue. The severity of illness was associated with abnormally high levels of inflammatory cytokines, including interleukin (IL)-6, IL-10, tumor necrosis factor α, and monocyte chemotactic protein 1, although the blockade of these proinflammatory cytokines had no obvious protection. We also tested whether an experimental formaldehyde-inactivated CVA2 vaccine could induce protective immune response in adult mice. The CVA2 antisera from the vaccinated mice were effective against CVA2 infection. Moreover, the inactivated CVA2 vaccine could successfully generate immune protection in neonatal mice. Our results indicated that the neonatal mouse model could be a useful tool to study CVA2 infection and to develop CVA2 vaccines.

Enterovirus-A71 exploits peripherin and Rac1 to invade the central nervous system

Enterovirus-A71 (EV-A71) has been associated with severe neurological forms of hand, foot, and mouth disease (HFMD). EV-A71 infects motor neurons at neuromuscular junctions (NMJs) to invade the central nervous system (CNS). Here, we investigate the role of peripherin (PRPH) during EV-A71 infection, a type III intermediate neurofilament involved in neurodegenerative conditions. In mice infected with EV-A71, PRPH co-localizes with viral particles in the muscles at NMJs and in the spinal cord. In motor neuron-like and neuroblastoma cell lines, surface-expressed PRPH facilitates viral entry, while intracellular PRPH influences viral genome replication through interactions with structural and non-structural viral components. Importantly, PRPH does not play a role during infection with coxsackievirus A16, another causative agent of HFMD rarely associated with neurological complications, suggesting that EV-A71 ability to exploit PRPH represents a unique attribute for successful CNS invasion. Finally, we show that EV-A71 also exploits some of the many PRPH-interacting partners. Of these, small GTP-binding protein Rac1 represents a potential druggable host target to limit neuroinvasion of EV-A71.

Efficacy of a coxsackievirus A6 vaccine candidate in an actively immunized mouse model

Coxsackievirus A6 (CV-A6) has been emerging as a major pathogen of hand, foot and mouth disease (HFMD). Study on the pathogenesis of CV-A6 infection and development of vaccines is hindered by a lack of appropriate animal models. Here, we report an actively immunized-challenged mouse model to evaluate the efficacy of a Vero-cell-based, inactivated CV-A6 vaccine candidate. The neonatal Kunming mice were inoculated with a purified, formaldehyde-inactivated CV-A6 vaccine on days 3 and 9, followed by challenging on day 14 with a naturally selected virulent strain at a lethal dose. Within 14 days postchallenge, all mice in the immunized groups survived, while 100% of the Alum-only inoculated mice died. Neutralizing antibodies (NtAbs) were detected in the serum of immunized suckling mice, and the NtAb levels correlated with the survival rate of the challenged mice. The virus loads in organs were reduced, and pathological changes and viral protein expression were weak in the immunized mice compared with those in Alum-only inoculated control mice. Elevated levels of interleukin-4, 6, interferon γ and tumour necrosis factor α were also observed in Alum-only control mice compared with immunized mice. Importantly, the virulent CV-A6 challenge strain was selected quickly and conveniently from a RD cell virus stock characterized with the natural multi-genotypes. The virulent determinants were mapped to V124M and I242 V at VP1. Together, our results indicated that this actively immunized mouse model is invaluable for future studies to develop multivalent vaccines containing the major component of CV-A6 against HFMD.

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.

Targeting Macrophages as a Therapeutic Option in Coronavirus Disease 2019

Immune cells of the monocyte/macrophage lineage are characterized by their diversity, plasticity, and variety of functions. Among them, macrophages play a central role in antiviral responses, tissue repair, and fibrosis. Macrophages can be reprogrammed by environmental cues, thus changing their phenotype during an antiviral immune response as the viral infection progresses. While M1-like macrophages are essential for the initial inflammatory responses, M2-like macrophages are critical for tissue repair after pathogen clearance. Numerous reports have evaluated the detrimental effects that coronaviruses, e.g., HCoV-229E, SARS-CoV, MERS-CoV, and SARS-CoV-2, have on the antiviral immune response and macrophage functions. In this review, we have addressed the breadth of macrophage phenotypes during the antiviral response and provided an overview of macrophage-coronavirus interactions. We also discussed therapeutic approaches to target macrophage-induced complications, currently under evaluation in clinical trials for coronavirus disease 2019 patients. Additionally, we have proposed alternative approaches that target macrophage recruitment, interferon signaling, cytokine storm, pulmonary fibrosis, and hypercoagulability.

The anti-viral facet of anti-rheumatic drugs: Lessons from COVID-19

The outbreak of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has posed the world at a pandemic risk. Coronavirus-19 disease (COVID-19) is an infectious disease caused by SARS-CoV-2, which causes pneumonia, requires intensive care unit hospitalization in about 10% of cases and can lead to a fatal outcome. Several efforts are currently made to find a treatment for COVID-19 patients. So far, several anti-viral and immunosuppressive or immunomodulating drugs have demonstrated some efficacy on COVID-19 both in vitro and in animal models as well as in cases series. In COVID-19 patients a pro-inflammatory status with high levels of interleukin (IL)-1B, IL-1 receptor (R)A and tumor necrosis factor (TNF)-α has been demonstrated. Moreover, high levels of IL-6 and TNF-α have been observed in patients requiring intensive-care-unit hospitalization. This provided rationale for the use of anti-rheumatic drugs as potential treatments for this severe viral infection. Other agents, such as hydroxychloroquine and chloroquine might have a direct anti-viral effect. The anti-viral aspect of immunosuppressants towards a variety of viruses has been known since long time and it is herein discussed in the view of searching for a potential treatment for SARS-CoV-2 infection.

A neonatal murine model of coxsackievirus A4 infection for evaluation of vaccines and antiviral drugs

Coxsackievirus A4 (CVA4) infection can cause hand, foot and mouth disease (HFMD), an epidemic illness affecting neonatal and paediatric cohorts, which can develop to severe neurological disease with high mortality. In this study, we established the first ICR mouse model of CVA4 infection for the evaluation of inactivated vaccines and antiviral drug screening. The CVA4 YT226R strain was selected to infect the neonatal mice and three infectious factors were optimized to establish the infection model. The 3-day-old neonatal mice exhibited clinical symptoms such as hind limb paralysis and death. The severe inflammatory reactions were closely related to the abnormal expression of the acute phase response proinflammatory cytokine IL-6 and an imbalance in the IFN-γ/IL-4 ratio. Importantly, the inactivated CVA4 whole-virus vaccine induced humoral immune responses in adult females and the maternal antibodies afforded mice complete protection against lethal dose challenges of homologous or heterologous CVA4 strains. Both IFN-α2a and antiserum inhibited the replication of CVA4 and increased the survival rates of neonatal mice during the early stages of infection. This neonatal murine model of CVA4 infection will be useful for the development of prophylactic and therapeutic vaccines and for screening of antiviral drugs targeting CVA4 to decrease morbidity and mortality.

Mechanism for the lethal effect of enterovirus A71 intracerebral injection in neonatal mice

Enterovirus A71 (EV-A71) infection is primarily responsible for fatal hand, foot, and mouth disease (HFMD) cases. Infants and younger children are more likely to suffer central nervous system damage as a result of EV-A71 infection, but this virus mostly does not affect older children and adults. This study investigated the possible mechanism underlying the age-dependent lethal effect of EV-A71 infection by comparing neonatal and adult mouse models of EV-A71 infection. Although viral proliferation is absent in both neonatal and adult mice, we observed that EV-A71, as a stimulus for astrocytes, elevates the levels of cytokines and monoamine neurotransmitters in neonatal mice. Then, we selected IL-6 and adrenaline as targets in a pharmacological approach to further validate the roles of these factors in mediating the mortality of neonatal mice after EV-A71 infection. Intracerebral injection of IL-6 and adrenaline enhanced the severity of EV-A71 infection, while treatment with an anti-IL-6-neutralizing antibody or the adrenergic-antagonist phenoxybenzamine reversed the lethal effect of EV-A71 in neonatal mice. These results suggest that the central nervous system (CNS) damage in neonatal cases of EV-A71 infection might be caused by an activated fetal cerebral immune response to the virus, including the disruption of brainstem function through increased levels of cytokines and neurotransmitters, rather than the typical cytopathic effect (CPE) of viral infection.

Characterization of inflammatory cytokine profiles in cerebrospinal fluid of hand, foot, and mouth disease children with enterovirus 71-related encephalitis in Hangzhou, Zhejiang, China

Enterovirus 71 (EV71) is an important etiological agent of hand, foot, and mouth disease (HFMD), which can also lead to severe neurological complications (eg, encephalitis) in young children. Although a series of reports on EV71 infection have been published, the pathogenic mechanism of EV71 infection is still not fully understood.We evaluated the cerebrospinal fluid (CSF) levels of the inflammatory cytokines interleukin (IL)-8, IL-1β, IL-6, IL-10, tumor necrosis factor (TNF)-α, and IL-12p70 in 88 children with EV71-related encephalitis and 19 children with febrile convulsion (FC) with the use of commercial cytometric bead array kits.The levels of IL-8, IL-1β, IL-6, and IL-10 in CSF were significantly higher in encephalitis group when compared with those observed in FC group, while no significant changes were noted in the levels of TNF-α and IL-12p70. In addition, significant and positive correlations among CSF IL-8, IL-1β, IL-6, and IL-10 were observed in encephalitis group. Furthermore, receiver operator characteristic analysis determined a cut-off value of 10.62 pg/mL for IL-6 to discriminate encephalitis patients from FCs with the sensitivity and specificity of 89.8% and 84.2%, respectively. Moreover, logistic regression analyses revealed that IL-6 was an independent predictor of EV71-related encephalitis (odds ratio = 23.241, P < .001).Our results indicate that 4 inflammatory cytokines (IL-8, IL-1β, IL-6, and IL-10) play important roles in the pathogenesis of EV71 infection. IL-6 may be used for the evaluation of EV71-related encephalitis and as a potential therapy candidate for EV71 infection.

EV71 infection induces neurodegeneration via activating TLR7 signaling and IL-6 production

As a neurotropic virus, human Enterovirus 71 (EV71) infection causes hand-foot-and-mouth disease (HFMD) and may develop severe neurological disorders in infants. Toll-like receptor 7 (TLR7) acts as an innate immune receptor and is also a death receptor in the central nervous system (CNS). However, the mechanisms underlying the regulation of TLR7-mediated brain pathogenesis upon EV71 infection remain largely elusive. Here we reveal a novel mechanism by which EV71 infects astrocytes in the brain and induces neural pathogenesis via TLR7 and interleukin-6 (IL-6) in C57BL/6 mice and in human astroglioma U251 cells. Upon EV71 infection, wild-type (WT) mice displayed more significant body weight loss, higher clinical scores, and lower survival rates as compared with TLR7^-/- mice. In the cerebral cortex of EV71-infected mice, neurofilament integrity was disrupted, and inflammatory cell infiltration and neurodegeneration were induced in WT mice, whereas these were largely absent in TLR7^-/- mice. Similarly, IL-6 production, Caspase-3 cleavage, and cell apoptosis were significantly higher in EV71-infected WT mice as compared with TLR7^-/- mice. Moreover, EV71 preferentially infected and induced IL-6 in astrocytes of mice brain. In U251 cells, EV71-induced IL-6 production and cell apoptosis were suppressed by shRNA-mediated knockdown of TLR7 (shTLR7). Moreover, in the cerebral cortex of EV71-infected mice, the blockade of IL-6 with anti-IL-6 antibody (IL-6-Ab) restored the body weight loss, attenuated clinical scores, improved survival rates, reduced the disruption of neurofilament integrity, decreased cell apoptotic induction, and lowered levels of Caspase-3 cleavage. Similarly, in EV71-infected U251 cells, IL-6-Ab blocked EV71-induced IL-6 production and cell apoptosis in response to viral infection. Collectively, it’s exhibited TLR7 upregulation, IL-6 induction and astrocytic cell apoptosis in EV71-infected human brain. Taken together, we propose that EV71 infects astrocytes of the cerebral cortex in mice and human and triggers TLR7 signaling and IL-6 release, subsequently inducing neural pathogenesis in the brain.

Enterovirus 71 (EV71) infection causes aseptic meningitis, poliomyelitis-like paralysis and fatal encephalitis in infants. Besides an immune receptor, toll-like receptor 7 (TLR7) serves as a death receptor in central nervous system (CNS). However, the role of TLR7 in EV71-induced neural pathogenesis remains ambiguous. This study reveals a distinct mechanism by which EV71 induces neurodegeneration via TLR7 and interleukin-6 (IL-6). Upon EV71 infection, TLR7^-/- mice displayed less body weight loss, lower clinical score, and higher survival rate as compared with wild-type (WT) mice. Meanwhile, a severer histopathologic neurofilaments disruption, neurodegeneration and cell apoptosis were observed in brain of EV71-infected WT mice. IL-6 release, cell apoptosis, and Caspase-3 cleavage were attenuated by shRNA targeting TLR7 (shTLR7) in EV71-infected U251 cells. Moreover, anti-IL-6 antibody (IL-6-Ab) suppressed EV71-induced body weight loss, clinical score increase, and survival rate decrease as well as neurofilaments disruption and neurodegeneration in mice, and it also attenuated EV71-induced cell apoptosis and Caspase-3 cleavage in U251 cells. It’s retrospectively observed that TLR7 upregulation, IL-6 induction and astrocytic cell apoptosis in EV71-infected human brain. Therefore, TLR7 is required for neural pathogenesis by IL-6 induction upon EV71 infection.

Low frequency, weak MCP-1 secretion and exhausted immune status of peripheral monocytes were associated with progression of severe enterovirus A71-infected hand, foot and mouth disease

A minority of hand, foot and mouth disease (HFMD) caused by enterovirus A71 (EV-A71) results in severe neural complications. However, whether monocyte-mediated immunity is involved in the disease progression of HFMD remains unknown. One hundred and twenty mild and 103 severe HFMD patients were recruited and enzyme-linked immunosorbent assay (ELISA), flow cytometry and Transwell culture were performed in the study. Peripheral monocyte counts were lower in both absolute counts and frequencies in severe cases compared to mild cases. After screening 10 monocyte-related cytokines by ELISA, only monocyte chemoattractant protein-1 (MCP-1) was found at higher levels in sera of mild cases compared to those with severe symptoms. Monocytes purified from mild cases produced more MCP-1 than the cells from severe patients when stimulated in vitro. We observed that immune exhaustion markers programmed death 1 (PD-1) and programmed death ligand 1 (PD-L1) were highly regulated on the surface of monocytes from severe cases compared to mild cases. PD-L1 blockade induced a higher production of MCP-1 in the supernatant of a Transwell system. The production of MCP-1 also increased following PD-L1 blockade of purified monocytes activated by granulocyte-macrophage colony-stimulating factor (GM-CSF) combined with R848 or EV-A71 virus. Our results indicate that absolute count, frequency and levels of MCP-1 secretion of peripheral monocytes, together with their immune status, probably contribute to differential disease prognosis in EV-A71-associated HFMD.

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.

Virulent Pseudorabies Virus Infection Induces a Specific and Lethal Systemic Inflammatory Response in Mice

Pseudorabies virus (PRV) is an alphaherpesvirus that infects the peripheral nervous system (PNS). The natural host of PRV is the swine, but it can infect most mammals, including cattle, rodents, and dogs. In these nonnatural hosts, PRV always causes a severe acute and lethal neuropathy called the "mad itch," which is uncommon in swine. Thus far, the pathophysiological and immunological processes leading to the development of the neuropathic itch and the death of the animal are unclear. Using a footpad inoculation model, we established that mice inoculated with PRV-Becker (virulent strain) develop a severe pruritus in the foot and become moribund at 82 h postinoculation (hpi). We found necrosis and inflammation with a massive neutrophil infiltration only in the footpad and dorsal root ganglia (DRGs) by hematoxylin and eosin staining. PRV load was detected in the foot, PNS, and central nervous system tissues by quantitative reverse transcription-PCR. Infected mice had elevated plasma levels of proinflammatory cytokines (interleukin-6 [IL-6] and granulocyte colony-stimulating factor [G-CSF]) and chemokines (Gro-1 and monocyte chemoattractant protein 1). Significant IL-6 and G-CSF levels were detected in several tissues at 82 hpi. High plasma levels of C-reactive protein confirmed the acute inflammatory response to PRV-Becker infection. Moreover, mice inoculated with PRV-Bartha (attenuated, live vaccine strain) did not develop pruritus at 82 hpi. PRV-Bartha also replicated in the PNS, and the infection spread further in the brain than PRV-Becker. PRV-Bartha infection did not induce the specific and lethal systemic inflammatory response seen with PRV-Becker. Overall, we demonstrated the importance of inflammation in the clinical outcome of PRV infection in mice and provide new insights into the process of PRV-induced neuroinflammation.IMPORTANCE Pseudorabies virus (PRV) is an alphaherpesvirus related to human pathogens such as herpes simplex virus 1 and varicella-zoster virus (VZV). The natural host of PRV is the swine, but it can infect most mammals. In susceptible animals other than pigs, PRV infection always causes a characteristic lethal pruritus known as the "mad itch." The role of the immune response in the clinical outcome of PRV infection is still poorly understood. Here, we show that a systemic host inflammatory response is responsible for the severe pruritus and acute death of mice infected with virulent PRV-Becker but not mice infected with attenuated strain PRV-Bartha. In addition, we identified IL-6 and G-CSF as two main cytokines that play crucial roles in the regulation of this process. Our findings give new insights into neuroinflammatory diseases and strengthen further the similarities between VZV and PRV infections at the level of innate immunity.

[Role of p38MAPK signaling pathway in autophagy of Henle-407 cells induced by spvB of Salmonella typhimurium]

OBJECTIVE

To investigate the role of p38MAPK signaling pathway in autophagy of intestinal epithelial cells induced by spvB of S.typhimurium.

METHODS

Henle-407 cells in exponential growth were infected with wild-type S.typhimurium strain STM-211 (with spvB gene), spvB mutated strain STM-delata;spvB, or with delata;spvB-complemented strain STM-c-spvB after treatment of the cells with the p38MAPK inhibitor SB203580. At different time points of co-culture, the cells were collected and the intracellular bacteria were counted. Western blotting was performed to detect the expressions of phosphorylated p38 and autophagy-related proteins LC3 and p62; immunofluorescence staining was used to observe the expression and distribution of LC3.

RESULTS

At 1, 2 and 4 h after the infection, the phosphorylation levels of p38 in STM-211 group and STM-c-spvB group were significantly lower than that in STM-delata;spvB group (P<0.05). At 2 and 4 h of co-culture, the intracellular bacterial counts were significantly greater in STM-211 and STM-c-spvB infection groups than in STM-delata;spvB group (P<0.05). Pretreatment with p38 inhibitor SB203580 did no significantly affect the expression levels of LC3 II or P62 in STM-211 and STM-c-spvB groups, but caused significant reduction in their expressions in STM-delata;spvB group at 1 h (P<0.05), and such changes were more obvious at 3 h (P<0.05).

CONCLUSION

The inhibitory effect of spvB gene on autophagy in intestinal epithelial cells is related with the negative regulation of p38MAPK signaling pathway.

Pyroptosis induced by enterovirus 71 and coxsackievirus B3 infection affects viral replication and host response

Enterovirus 71 (EV71) is the primary causative pathogen of hand, foot, and mouth disease (HFMD), affecting children with severe neurological complications. Pyroptosis is a programmed cell death characterized by cell lysis and inflammatory response. Although proinflammatory response has been implicated to play important roles in EV71-caused diseases, the involvement of pyroptosis in the pathogenesis of EV71 is poorly defined. We show that EV71 infection induced caspase-1 activation. Responding to the activation of caspase-1, the expression and secretion of both IL-1β and IL-18 were increased in EV71-infected cells. The treatment of caspase-1 inhibitor markedly improved the systemic response of the EV71-infected mice. Importantly, caspase-1 inhibitor suppressed EV71 replication in mouse brains. Similarly, pyroptosis was activated by the infection of coxsackievirus B3 (CVB3), an important member of the Enterovirus genus. Caspase-1 activation and the increased expression of IL-18 and NLRP3 were demonstrated in HeLa cells infected with CVB3. Caspase-1 inhibitor also alleviated the overall conditions of virus-infected mice with markedly decreased replication of CVB3 and reduced expression of caspase-1. These results indicate that pyroptosis is involved in the pathogenesis of both EV71 and CVB3 infections, and the treatment of caspase-1 inhibitor is beneficial to the host response during enterovirus infection.

Murine model of acute myocarditis and cerebral cortical neuron edema induced by coxsackievirus B4

Globally, coxsackievirus B4 (CV-B4) has been continuously isolated and evidence suggests an association with the development of pancreatitis and type I diabetes. In addition, CV-B4 is also associated with myocarditis and severe central nervous system (CNS) complications, which remain poorly studied and understood. In the present study, we established an Institute for Cancer Research (ICR) mouse model of CV-B4 infection and examined whether CV-B4 infection resulted in a predisposition to myocarditis and CNS infection. We found high survival in both the treatment and control group, with no significant differences in clinical outcomes observed. However, pathological lesions were evident in both brain and heart tissue of the CV-B4-infected mice. In addition, high viral loads were found in the neural and cardiac tissues as early as 2 days post infection. Expressions of IFN-γ and IL-6 in sera were significantly higher in CV-B4-infected mice compared to uninfected negative controls, suggesting the involvement of these cytokines in the development of histopathological lesions. Our murine model successfully reproduced the acute myocarditis and cerebral cortical neuron edema induced by CV-B4, and may be useful for the evaluation of vaccine candidates and potential antivirals against CV-B4 infection.

T Cell Immunity To Enterovirus 71 Infection In Humans And Implications For Vaccine Development

Enterovirus 71 (EV-A71) is one of the major pathogens causing hand, foot and mouth disease (HFMD). Some strains can lead to neurological disease and fatality in children. Up to date, there is no FDA-approved vaccine to prevent severe HFMD and mortality. Although the inactivated vaccine has advanced to production in China, lack of long-term protection and the requirement of multiple boosters have necessitated the development of other types of vaccines. Recent studies indicate that cellular and not humoral immunity determines the clinical outcome of EV-A71 infections. High levels of cytokines such as IL-1β, IL-6, IL-10 and IFN-γ tend to correlate with clinical severity in patients with pulmonary edema and encephalitis. The live attenuated vaccine may serve as the preferred choice as it can induce excellent humoral and cellular immunity as well as live-long immunity. Expression of certain HLA alleles such as TNF-α promoter type II (-308 allele), HLA-A33 and HLA-DR17 responses have been linked to severe HFMD. However, the high variability of MHC genes could restrict T cell recognition and be a major obstacle in the design of peptide vaccines. Hence, the development of a T cell universal vaccine (incorporating both CD4⁺ and CD8⁺ T cell epitopes) that induces broad, multifunctional and cross-reactive CD8⁺ T cell responses maybe desirable.

Pulmonary edema following central nervous system lesions induced by a non- mouse-adapted EV71 strain in neonatal BALB/c mice

Background

Enterovirus (EV) infection has been a serious health issue in Asia-Pacific region. It has been indicated that the occurrence of fatal hand foot and mouth disease (HFMD) cases following EV71 infection is mainly attributed to pulmonary edema. However, the development of pulmonary disorders after EV71 infection remains largely unknown. To establish an EV71-infected animal model and further explore the underlying association of central nervous system (CNS) invasion with pulmonary edema, we isolated a clinical source EV71 strain (ZZ1350) from a severe case in Henan Province.

Methods

We evaluated the cytotoxicity of ZZ1350 strain and the susceptibility in 3-day-old BALB/c mice with intraperitoneal, intracerebral and intramuscular inoculation. Various histopathological and immunohistochemical techniques were applied to determine the target organs or tissue damage after infection. Correlation analysis was used to identify the relationship between CNS injury and pulmonary disorders.

Results

Our experimental results suggested that ZZ1350 (C4 subtype) had high cytotoxicity against African green monkey kidney (Vero) cells and human rhabdomyosarcoma (RD) cells and neonatal BALB/c mice were highly susceptible to the infection with ZZ1350 through three different inoculation routes (2 × 10⁶ pfu/mouse) exhibiting severe neurological and respiratory symptoms that were similar to clinical observation. Viral replication was found in brain, spinal cord, skeletal muscle, lung, spleen, liver, heart of infected mice and these sections also showed histopathological changes. We found that brain histology score was positive correlated with lung histology score in total experimental mice and mice under the three inoculation routes (P < 0.05). At the same time, there were positive correlations between spinal cord score and lung score in total experimental mice and mice with intracerebral inoculation (P < 0.05).

Conclusions

ZZ1350 strain is effective to establish animal model of EV71 infection with severe neurological and respiratory symptoms. The development of pulmonary disorders after EV71 infection is associated with severity of CNS damage.

Electronic supplementary material

The online version of this article (doi: 10.1186/s12985-017-0911-5) contains supplementary material, which is available to authorized users.

Suppression of interleukin-6 increases enterovirus A71 lethality in mice

Background

Enterovirus A71 (EV-A71) infection can induce fatal encephalitis in young children. Clinical reports show that interleukin-6 (IL-6) levels in the serum and cerebrospinal fluid of infected patients with brainstem encephalitis are significantly elevated. We used a murine model to address the significance of endogenous IL-6 in EV-A71 infection.

Results

EV-A71 infection transiently increased serum and brain IL-6 protein levels in mice. Most importantly, absence of IL-6 due to gene knockout or depletion of IL-6 using neutralizing monoclonal antibody enhanced the mortality and tissue viral load of infected mice. Absence of IL-6 increased the damage in the central nervous system and decreased the lymphocyte and virus-specific antibody responses of infected mice.

Conclusions

Endogenous IL-6 functions to clear virus and protect the host from EV-A71 infection. Our study raises caution over the use of anti-IL-6 antibody or pentoxifylline to reduce IL-6 for patient treatment.

Electronic supplementary material

The online version of this article (10.1186/s12929-017-0401-5) contains supplementary material, which is available to authorized users.

Neurotropism In Vitro and Mouse Models of Severe and Mild Infection with Clinical Strains of Enterovirus 71

Enterovirus 71 (EV71) is a common etiological agent of hand, foot, and mouth disease and fatal neurological diseases in children. The neuropathogenicity of severe EV71 infection has been documented, but studies comparing mouse models of severe and mild EV71 infection are lacking. The aim of the study was to investigate the neurovirulence of EV71 strains and the differences in serum cytokine and chemokine levels in mouse models of severe and mild EV71 infection. Nine EV71 isolates belonging to the C4 subgenogroup (proposed as genotype D) displayed infectivity in human neuroblastoma SK-N-SH cells; moreover, ultrastructural observation confirmed viral particle replication. The survival rate of the severe model was 71.43% (5/7), and 60% (3/5) of the surviving severe model mice displayed sequelae of paralysis, whereas the only symptom in mild model mice was ruffled fur. Dynamic detection of serum cytokine and chemokine levels demonstrated that interleukin (IL)-5, IL-13, IL-6, monocyte chemotactic protein 1 (MCP-1), and chemokine (C-C motif) ligand 5 (also called Regulated upon Activation, Normal T-cell Expressed, and Secreted (CCL5/RANTES) were significantly up-regulated at the early period of infection, indicating that these factors might herald a severe outcome. Our findings suggest that elevated cytokines and chemokines may have potential value as prognostic markers in mouse models.

Airway CD8(+) T Cells Are Associated with Lung Injury during Infant Viral Respiratory Tract Infection

Infants and young children are disproportionately susceptible to severe complications from respiratory viruses, although the underlying mechanisms remain unknown. Recent studies show that the T cell response in the lung is important for protective responses to respiratory infections, although details on the infant/pediatric respiratory immune response remain sparse. The objectives of the present study were to characterize the local versus systemic immune response in infants and young children with respiratory failure from viral respiratory tract infections and its association to disease severity. Daily airway secretions were sampled from infants and children 4 years of age and younger receiving mechanical ventilation owing to respiratory failure from viral infection or noninfectious causes. Samples were examined for immune cell composition and markers of T cell activation. These parameters were then correlated with clinical disease severity. Innate immune cells and total CD3(+) T cells were present in similar proportions in airway aspirates derived from infected and uninfected groups; however, the CD8:CD4 T cell ratio was markedly increased in the airways of patients with viral infection compared with uninfected patients, and specifically in infected infants with acute lung injury. T cells in the airways were phenotypically and functionally distinct from those in blood with activated/memory phenotypes and increased cytotoxic capacity. We identified a significant increase in airway cytotoxic CD8(+) T cells in infants with lung injury from viral respiratory tract infection that was distinct from the T cell profile in circulation and associated with increasing disease severity. Airway sampling could therefore be diagnostically informative for assessing immune responses and lung damage.

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.

An inactivated hand-foot-and-mouth disease vaccine using the enterovirus 71 (C4a) strain isolated from a Korean patient induces a strong immunogenic response in mice

Enterovirus 71 (EV71) is a major causative agent of hand-foot-and-mouth disease (HFMD) frequently occurring in children. HFMD induced by EV71 can cause serious health problems and has been reported worldwide, particularly in the Asia-Pacific region. In this study, we assessed the immunogenicity of a formalin-inactivated HFMD vaccine using an EV71 strain (FI-EV71 C4a) isolated from a Korean patient. The vaccine candidate was evaluated in mice to determine the vaccination doses and vaccine schedules. BALB/c mice were intramuscularly administered 5, 10, or 20 μg FI-EV71 vaccine, followed by a booster 2 weeks later. EV71-specific antibodies and neutralizing antibodies were induced and maintained until the end of the experimental period in all vaccinated groups. To determine the effectiveness of adjuvant for the EV71 vaccine, three adjuvants, i.e., aluminium hydroxide gel, monophosphoryl lipid A, and polyinosinic-polycytidylic acid, were administered separately with the FI-EV71 vaccine to mice via the intramuscular route. Mice administered the FI-EV71 vaccine formulated with all three adjuvants induced a significantly increased antibody response compared with that of the single adjuvant groups. The vaccinated group with triple adjuvants exhibited more rapid induction of EV71-specific and neutralizing antibodies than the other groups. These results suggested that the role of adjuvant in inactivated vaccine was important for eliciting effective immune responses against EV71. In conclusion, our results showed that FI-EV71 was a potential candidate vaccine for prevention of EV71 infection.

Thiamine and riboflavin inhibit production of cytokines and increase the anti-inflammatory activity of a corticosteroid in a chronic model of inflammation induced by complete Freund's adjuvant

BACKGROUND

The effects induced by thiamine and riboflavin, isolated or in association with corticosteroids, in models of chronic inflammation are not known. Thus, we evaluated the effect induced by these B vitamins, isolated or in association with dexamethasone, on the mechanical allodynia, paw edema and cytokine production induced by complete Freund's adjuvant (CFA) in rats.

METHODS

Chronic inflammation was induced by two injections of CFA. Nociceptive threshold, paw volume and body temperature were evaluated for 21days. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) contents were determined in paw tissue. Riboflavin (125, 250 or 500mg/kg) or thiamine (150, 300 or 600mg/kg) were administered per os (po), twice daily. Dexamethasone (0.5mg/kgday, po) was administered every three days.

RESULTS

CFA induced long lasting mechanical allodynia and paw edema. Elevation of body temperature was observed for a short period. Riboflavin reduced neither paw edema nor mechanical allodynia. Thiamine did not change paw edema, but partially inhibited mechanical allodynia. Riboflavin (500mg/kg) and thiamine (600mg/kg) exacerbated the anti-inflammatory activity of dexamethasone. Riboflavin, thiamine and dexamethasone reduced TNF-α and IL-6 production. The association of dexamethasone with thiamine induced greater inhibition of IL-6 production when compared with that induced by dexamethasone.

CONCLUSIONS

Riboflavin and thiamine exacerbate the anti-inflammatory activity of dexamethasone and reduce production of TNF-α and IL-6.

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.

Motor coordination and balance measurements reveal differential pathogenicity of currently spreading enterovirus 71 strains in human SCARB2 transgenic mice

Enterovirus 71 (EV71) has caused large-scale epidemics with neurological complications in the Asia-Pacific region. The C4a and B5 strains are the two major genotypes circulating in many countries recently. This study used a new protocol, a motor coordination task, to assess the differential pathogenicity of C4a and B5 strains in human SCARB2 transgenic mice. We found that the pathogenicity of C4a viruses was more severe than that of B5 viruses. Moreover, we discovered that an increased level of monocyte chemoattractant protein-1 was positively correlated with severely deficient motor function. This study provides a new method for evaluating EV71 infection in mice and distinguishing the severity of the symptoms caused by different clinical strains, which would contribute to studies of pathogenesis and development of vaccines and antivirals in EV71 infections.

Antiviral effects of Reduning injection against Enterovirus 71 and possible mechanisms of action

The present study was designed to evaluate the protective effects of Reduning injection against Enterovirus 71 (EV71) in Vero cells and in mice. The Vero cells were infected with 100 and 50 TCID50 (50% tissue culture infective dose) of EV71, respectively. The inhibition of Reduning injection on cytopathic effect (CPE) was detected. Meanwhile, a mouse model produced by intraperitoneal EV71-infection (10(6) TCID50), was used to investigate the protective effects of Reduning injection. The total survival rate, living time, daily survival rate, weight ratio, and score for symptoms were examined. The viral loads in Vero cells and muscle tissues were detected using real-time PCR. Finally, the content of cytokines was analyzed by ELISA. In the Vero cells, 2.5 mg crude drug·mL(-1) of Reduning injection inhibited CPE induced by EV71 infection. In the mice, 1.3 g crude drug·kg(-1) of Reduning injection rescued death triggered by infection, in comparison with model group. Moreover, the survival rate, weight ratio, and clinical scores were also improved. The viral RNA copies in the Vero cells and the mice muscle tissues were reduced. Besides, the steep EV71-induced accumulations of TNF-α and MCP-1 were decreased by Reduning injection. In conclusion, Reduning injection showed promising protective effects against EV71 in Vero cells and in mice.

Cerebrospinal fluid Th1/Th2 cytokine profiles in children with enterovirus 71-associated meningoencephalitis

Enterovirus 71 (EV71) infection can cause severe neurological complications including meningoencephalitis (ME) in some patients with hand, foot and mouth disease (HFMD). However, to date no studies have reported changes in cytokine concentrations and their correlations with clinical variables in patients with ME following EV71 infection. In this study, responses of Th1/Th2 cytokine, including IL-2, IL-4, IL-6, IL-10, TNF-α and IFN-γ, in cerebrospinal fluid (CSF) from patients with EV71-related HFMD with ME and patients with febrile convulsions (FC) were analyzed using cytometric bead array technology. It was found that CSF IL-6 and IFN-γ concentrations were significantly higher in patients with EV71-related ME than in those with FC. Additionally, both CSF IL-6 and IFN-γ concentrations were correlated with CSF cytology, fever duration and duration of hospital stay. More interestingly, a positive correlation between CSF IL-6 and IFN-γ concentrations was observed. Finally, receiver operating characteristic analysis revealed that when a cutoff value of 9.40 pg/mL was set for IL-6, the sensitivity and specificity were 84.5% and 85.5%, respectively, for discriminating EV71-related ME from FC. In conclusion, IL-6 and IFN-γ may be associated with EV71-induced neuropathology.

MicroRNA and Pathogenesis of Enterovirus Infection

There are no currently available specific antiviral therapies for non-polio Enterovirus infections. Although several vaccines have entered clinical trials, the efficacy requires further evaluation, particularly for cross-strain protective activity. Curing patients with viral infections is a public health problem due to antigen alterations and drug resistance caused by the high genomic mutation rate. To conquer these limits in the development of anti-Enterovirus treatments, a comprehensive understanding of the interactions between Enterovirus and host cells is urgently needed. MicroRNA (miRNA) constitutes the biggest family of gene regulators in mammalian cells and regulates almost a half of all human genes. The roles of miRNAs in Enterovirus pathogenesis have recently begun to be noted. In this review, we shed light on recent advances in the understanding of Enterovirus infection-modulated miRNAs. The impacts of altered host miRNAs on cellular processes, including immune escape, apoptosis, signal transduction, shutdown of host protein synthesis and viral replication, are discussed. Finally, miRNA-based medication provides a promising strategy for the development of antiviral therapy.

Neurotropic Enterovirus Infections in the Central Nervous System

Enteroviruses are a group of positive-sense single stranded viruses that belong to the Picornaviridae family. Most enteroviruses infect humans from the gastrointestinal tract and cause mild symptoms. However, several enteroviruses can invade the central nervous system (CNS) and result in various neurological symptoms that are correlated to mortality associated with enteroviral infections. In recent years, large outbreaks of enteroviruses occurred worldwide. Therefore, these neurotropic enteroviruses have been deemed as re-emerging pathogens. Although these viruses are becoming large threats to public health, our understanding of these viruses, especially for non-polio enteroviruses, is limited. In this article, we review recent advances in the trafficking of these pathogens from the peripheral to the central nervous system, compare their cell tropism, and discuss the effects of viral infections in their host neuronal cells.

Norepinephrine and Epinephrine Enhanced the Infectivity of Enterovirus 71

Background

Enterovirus 71 (EV71) infections may be associated with neurological complications, including brainstem encephalitis (BE). Severe EV71 BE may be complicated with autonomic nervous system (ANS) dysregulation and/or pulmonary edema (PE). ANS dysregulation is related to the overactivation of the sympathetic nervous system, which results from catecholamine release.

Objective

The aims of this study were to explore the effects of catecholamines on severe EV71 infection and to investigate the changes in the percentages of EV71-infected cells, virus titer, and cytokine production on the involvement of catecholamines.

Study Design

Plasma levels of norepinephrine (NE) and epinephrine (EP) in EV71-infected patients were measured using an enzyme-linked immunoassay. The expression of adrenergic receptors (ADRs) on RD, A549, SK-N-SH, THP-1, Jurkat and human peripheral blood mononuclear cells (hPBMCs) were detected using flow cytometry. The percentages of EV71-infected cells, virus titer, and cytokine production were investigated after treatment with NE and EP.

Results

The plasma levels of NE and EP were significantly higher in EV71-infected patients with ANS dysregulation and PE than in controls. Both α_1A- and β₂-ADRs were expressed on A549, RD, SK-N-SH, HL-60, THP-1, Jurkat cells and hPBMCs. NE treatment elevated the percentages of EV71-infected cells to 62.9% and 22.7% in THP-1 and Jurkat cells, respectively. Via treatment with EP, the percentages of EV71-infected cells were increased to 64.6% and 26.9% in THP-1 and Jurkat cells. The percentage of EV71-infected cells increased upon NE or EP treatment while the α- and β-blockers reduced the percentages of EV71-infected cells with NE or EP treatment. At least two-fold increase in virus titer was observed in EV71-infected A549, SK-N-SH and hPBMCs after treatment with NE or EP. IL-6 production was enhanced in EV71-infected hPBMCs at a concentration of 10² pg/mL NE.

Conclusion

The plasma levels of NE and EP elevated in EV71-infected patients with ANS dysregulation and PE. Both NE and EP enhanced the percentages of infected cells and virus titers in EV71 infection in vitro. NE and EP may play a role in the pathogenesis of EV71 BE complicated with ANS dysregulation and PE.

Intrinsic apoptosis and proinflammatory cytokines regulated in human astrocytes infected with enterovirus 71

Enterovirus 71 (EV71) has emerged as a clinically important neurotropic virus following poliovirus eradication. However, the mechanism of EV71-induced neurological manifestation remains largely unclear. In this study, we showed that human astrocytes were susceptible to EV71 and viral RNA was first detected at 12 h post-infection (p.i.), whilst viral proteins were detected at 36 h p.i. EV71-infected astrocytes underwent apoptosis, in which cytochrome c was released from mitochondria to the cytosol and caspase-9 was activated. Interestingly, caspase-2 and -8 were not cleaved or activated during the infection, whilst a selective inhibitor of caspase-9, Z-LEHD-FMK, blocked the cleavage of caspase-3 and -7, indicating that only the mitochondria-mediated intrinsic apoptotic pathway was activated in EV71-infected astrocytes. EV71 infection also induced proinflammatory cytokines, including IL-6, IL-8, CCL5 and IFN-γ-inducible protein (IP)-10 in astrocytes, which may play a critical role in EV71-induced neuroinflammation and neurological complications. By using inhibitors of mitogen-activated protein kinases (MAPKs), we demonstrated that the induction of the cytokines was mainly regulated by the MAPK p38 signalling pathway as a significant reduction of the cytokines was observed when treated with p38 inhibitors. This study demonstrated that human astrocytes were susceptible to EV71, and the infection led to intrinsic apoptosis and induction of p38-regulated proinflammatory cytokines. These findings further our understanding of the neuropathogenesis in severe cases of EV71 infection.

Etiology, pathogenesis, antivirals and vaccines of hand, foot, and mouth disease

Hand, foot, and mouth disease (HFMD), caused by enteroviruses, is a syndrome characterized by fever with vesicular eruptions mainly on the skin of the hands, feet, and oral cavity. HFMD primarily affects infants and young children. Although infection is usually self-limited, severe neurological complications in the central nervous system can present in some cases, which can lead to death. Widespread infection of HFMD across the Asia-Pacific region over the past two decades has made HFMD a major public health challenge, ranking first among the category C notifiable communicable diseases in China every year since 2008. This review summarizes our understanding of HFMD, focusing on the etiology and pathogenesis of the disease, as well as on progress toward antivirals and vaccines. The review also discusses the implications of these studies as they relate to the control and prevention of the disease.

Enterovirus 71 Proteins 2A and 3D Antagonize the Antiviral Activity of Gamma Interferon via Signaling Attenuation

Enterovirus 71 (EV71) infection causes severe mortality involving multiple possible mechanisms, including cytokine storm, brain stem encephalitis, and fulminant pulmonary edema. Gamma interferon (IFN-γ) may confer anti-EV71 activity; however, the claim that disease severity is highly correlated to an increase in IFN-γ is controversial and would indicate an immune escape initiated by EV71. This study, investigating the role of IFN-γ in EV71 infection using a murine model, showed that IFN-γ was elevated. Moreover, IFN-γ receptor-deficient mice showed higher mortality rates and more severe disease progression with slower viral clearance than wild-type mice. In vitro results showed that IFN-γ pretreatment reduced EV71 yield, whereas EV71 infection caused IFN-γ resistance with attenuated IFN-γ signaling in IFN regulatory factor 1 (IRF1) gene transactivation. To study the immunoediting ability of EV71 proteins in IFN-γ signaling, 11 viral proteins were stably expressed in cells without cytotoxicity; however, viral proteins 2A and 3D blocked IFN-γ-induced IRF1 transactivation following a loss of signal transducer and activator of transcription 1 (STAT1) nuclear translocation. Viral 3D attenuated IFN-γ signaling accompanied by a STAT1 decrease without interfering with IFN-γ receptor expression. Restoration of STAT1 or blocking 3D activity was able to rescue IFN-γ signaling. Interestingly, viral 2A attenuated IFN-γ signaling using another mechanism by reducing the serine phosphorylation of STAT1 following the inactivation of extracellular signal-regulated kinase without affecting STAT1 expression. These results demonstrate the anti-EV71 ability of IFN-γ and the immunoediting ability by EV71 2A and 3D, which attenuate IFN-γ signaling through different mechanisms.

IMPORTANCE

Immunosurveillance by gamma interferon (IFN-γ) may confer anti-enterovirus 71 (anti-EV71) activity; however, the claim that disease severity is highly correlated to an increase in IFN-γ is controversial and would indicate an immune escape initiated by EV71. IFN-γ receptor-deficient mice showed higher mortality and more severe disease progression, indicating the anti-EV71 property of IFN-γ. However, EV71 infection caused cellular insusceptibility in response to IFN-γ stimulation. We used an in vitro system with viral protein expression to explore the novel IFN-γ inhibitory properties of the EV71 2A and 3D proteins through the different mechanisms. According to this study, targeting either 2A or 3D pharmacologically and/or genetically may sustain a cellular susceptibility in response to IFN-γ, particularly for IFN-γ-mediated anti-EV71 activity.