Robust antiviral responses to enterovirus 71 infection in human intestinal epithelial cells

Mechanosensitive extrusion of Enterovirus A71-infected cells from colonic organoids

Enterovirus A71 causes severe disease upon systemic infection, sometimes leading to life-threatening neurological dysfunction. However, in most cases infection is asymptomatic and limited to the gastrointestinal tract, where virus is amplified for transmission. Picornaviruses have previously been shown to exit infected cells via either cell lysis or secretion of vesicles. Here we report that entire Enterovirus A71-infected cells are specifically extruded from the apical surface of differentiated human colon organoids, as observed by confocal microscopy. Differential sensitivity to chemical and peptide inhibitors demonstrated that extrusion of virus-infected cells is dependent on force sensing via mechanosensitive ion channels rather than apoptotic cell death. When isolated and used as inoculum, intact virus-containing extruded cells can initiate new infections. In contrast, when mechanical force sensing is inhibited, large amounts of free virus are released. Thus, extrusion of live, virus-infected cells from intact epithelial tissue is likely to benefit both the integrity of host tissues and the protected spread of this faecal-oral pathogen within and between hosts.

Innate sensing of picornavirus infection involves cGAS-STING-mediated antiviral responses triggered by mitochondrial DNA release

Cyclic GMP-AMP synthase (cGAS) plays a key role in the innate immune responses to both DNA and RNA virus infection. Here, we found that enterovirus 71 (EV-A71), Seneca Valley virus (SVV), and foot-and-mouth disease virus (FMDV) infection triggered mitochondria damage and mitochondrial DNA (mtDNA) release in vitro and vivo. These responses were mediated by picornavirus 2B proteins which induced mtDNA release during viral replication. SVV infection caused the opening of mitochondrial permeability transition pore (mPTP) and led to voltage-dependent anion channel 1 (VDAC1)- and BCL2 antagonist/killer 1 (Bak) and Bak/BCL2-associated X (Bax)-dependent mtDNA leakage into the cytoplasm, while EV-A71 and FMDV infection induced mPTP opening and resulted in VDAC1-dependent mtDNA release. The released mtDNA bound to cGAS and activated cGAS-mediated antiviral immune response. cGAS was essential for inhibiting EV-A71, SVV, and FMDV replication by regulation of IFN-β production. cGAS deficiency contributed to higher mortality of EV-A71- or FMDV-infected mice. In addition, we found that SVV 2C protein was responsible for decreasing cGAS expression through the autophagy pathway. The 9th and 153rd amino acid sites in 2C were critical for induction of cGAS degradation. Furthermore, we also show that EV-A71, CA16, and EMCV 2C antagonize the cGAS-stimulator of interferon genes (STING) pathway through interaction with STING, and highly conserved amino acids Y155 and S156 were critical for this inhibitory effect. In conclusion, these data reveal novel mechanisms of picornaviruses to block the antiviral effect mediated by the cGAS-STING signaling pathway, which will provide insights for developing antiviral strategies against picornaviruses.

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.

DHAV-1 Blocks the Signaling Pathway Upstream of Type I Interferon by Inhibiting the Interferon Regulatory Factor 7 Protein

Duck hepatitis A virus (DHAV), which mainly infects 1- to 4-week-old ducklings, has a fatality rate of 95% and poses a huge economic threat to the duck industry. However, the mechanism by which DHAV-1 regulates the immune response of host cells is rarely reported. This study examined whether DHAV-1 contains a viral protein that can regulate the innate immunity of host cells and its specific regulatory mechanism, further exploring the mechanism by which DHAV-1 resists the host immune response. In the study, the dual-luciferase reporter gene system was used to screen the viral protein that regulates the host innate immunity and the target of this viral protein. The results indicate that the DHAV-1 3C protein inhibits the pathway upstream of interferon (IFN)-β by targeting the interferon regulatory factor 7 (IRF7) protein. In addition, we found that the 3C protein inhibits the nuclear translocation of the IRF7 protein. Further experiments showed that the 3C protein interacts with the IRF7 protein through its N-terminus and that the 3C protein degrades the IRF7 protein in a caspase 3-dependent manner, thereby inhibiting the IFN-β-mediated antiviral response to promote the replication of DHAV-1. The results of this study are expected to serve as a reference for elucidating the mechanisms of DHAV-1 infection and pathogenicity.

Exosomes Facilitate Transmission of Enterovirus A71 From Human Intestinal Epithelial Cells

BACKGROUND

Enterovirus A71 (EV-A71) has been noted for its tendency to lead to neurological manifestations in young children and infants. Although the alimentary tract has been identified as the primary replication site of this virus, how EV-A71 replicates in the gut and is transmitted to other organs remains unclear.

METHODS

By using differentiated C2BBe1 cells as a model, we observed that intestinal epithelial cells (IECs) were permissive to EV-A71 infection, and viral particles were released in a nonlytic manner.

RESULTS

The coexistence of active caspase 3 and EV-A71 protein was observed in the infected undifferentiated C2BBe1 and RD cells but not in the infected differentiated C2BBe1 cells. Furthermore, EV-A71 infection caused differentiated C2BBe1 and intestinal organoids to secrete exosomes containing viral components and have the ability to establish active infection. Inhibition of the exosome pathway decreased EV-A71 replication and release in IECs and increased the survival rates of infected animals.

CONCLUSIONS

Our findings showed that EV-A71 is able to be actively replicated in enterocytes, and that the exosome pathway is involved in the nonlytic release of viral particles, which may be useful for developing antiviral strategies.

Polar Infection of Echovirus-30 Causes Differential Barrier Affection and Gene Regulation at the Blood-Cerebrospinal Fluid Barrier

Echovirus-30 (E-30) is responsible for the extensive global outbreaks of meningitis in children. To gain access to the central nervous system, E-30 first has to cross the epithelial blood-cerebrospinal fluid barrier. Several meningitis causing bacteria preferentially infect human choroid plexus papilloma (HIBCPP) cells in a polar fashion from the basolateral cell side. Here, we investigated the polar infection of HIBCPP cells with E-30. Both apical and basolateral infections caused a significant decrease in the transepithelial electrical resistance of HIBCPP cells. However, to reach the same impact on the barrier properties, the multiplicity of infection of the apical side had to be higher than that of the basolateral infection. Furthermore, the number of infected cells at respective time-points after basolateral infection was significantly higher compared to apical infection. Cytotoxic effects of E-30 on HIBCPP cells during basolateral infection were observed following prolonged infection and appeared more drastically compared to the apical infection. Gene expression profiles determined by massive analysis of cDNA ends revealed distinct regulation of specific genes depending on the side of HIBCPP cells' infection. Altogether, our data highlights the polar effects of E-30 infection in a human in vitro model of the blood-cerebrospinal fluid barrier leading to central nervous system inflammation.

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.

Aichi Virus Induces Antiviral Host Defense in Primary Murine Intestinal Epithelial Cells

The picornavirus Aichi virus (AiV) is a non-enveloped RNA virus that causes acute gastroenteritis symptoms, such as diarrhea, abdominal pain, nausea, vomiting, and fever. Antiviral host defense involves the fast response of type I interferon (IFN) and the secretion of inflammatory cytokines against pathogens. However, the intestinal inflammatory and antiviral response to AiV infection is poorly understood. This study evaluated the antiviral activity of intestinal epithelial cells (IECs), which form a single-cell layer separating the bowel wall from pathogens. Isolated primary mouse IECs were subjected to AiV infection and virion production, inducing the mRNA expression of type I/type III IFNs and inflammatory cytokines. The mechanism involved induced the expression of phospho-IFN regulatory factor 3 and mitochondrial antiviral-signaling protein of type I IFN signaling. These findings were also observed in AiV-infected human colon carcinoma cells. In summary, a viral productive and pathogenic infection of AiV in primary murine IECs is validated.

Enteroviruses: A Gut-Wrenching Game of Entry, Detection, and Evasion

Enteroviruses are a major source of human disease, particularly in neonates and young children where infections can range from acute, self-limited febrile illness to meningitis, endocarditis, hepatitis, and acute flaccid myelitis. The enterovirus genus includes poliovirus, coxsackieviruses, echoviruses, enterovirus 71, and enterovirus D68. Enteroviruses primarily infect by the fecal–oral route and target the gastrointestinal epithelium early during their life cycles. In addition, spread via the respiratory tract is possible and some enteroviruses such as enterovirus D68 are preferentially spread via this route. Once internalized, enteroviruses are detected by intracellular proteins that recognize common viral features and trigger antiviral innate immune signaling. However, co-evolution of enteroviruses with humans has allowed them to develop strategies to evade detection or disrupt signaling. In this review, we will discuss how enteroviruses infect the gastrointestinal tract, the mechanisms by which cells detect enterovirus infections, and the strategies enteroviruses use to escape this detection.

GS-9620 inhibits enterovirus 71 replication mainly through the NF-κB and PI3K-AKT signaling pathways

Human enterovirus 71 (EV71) is the second most common cause of hand, foot, and mouth disease (HFMD), which can occur as a severe epidemic especially among children under 5-years old. New and improved treatment strategies to control EV71 infection are therefore urgently required. The heterocyclic compound GS-9620, a potent and selective agonist of Toll-like receptor 7 (TLR7), has been reported to activate plasmacytoid dendritic cells (pDCs), and suppress HBV as well as HIV replication. In this study, we indicated that GS-9620 also could inhibit EV71 replication in the mouse model of EV71 infection. With three-days treatment after EV71 infection, the levels of proinflammatory cytokines/chemokines, like IFN-α, IFN-γ and MCP-1, were sharply reduced in serum compared to those without treatment. Furthermore, GS-9620 activated TLR7 in the limb muscle cells, which stimulated the NF-κB and PI3K/AKT signaling pathways. When NF-κB or PI3K/AKT inhibitors were used, the antiviral effect of the GS-9620 was impacted. Overall, our data implied GS-9620 probably activates NF-κB and PI3K/AKT signaling pathways to clear the virus.

Antiviral activity of a polysaccharide from Laminaria japonica against enterovirus 71

This in vitro study investigated the antiviral activity of an acidic polysaccharide from Laminaria japonica against enterovirus 71 (EV71) as well as its mechanism of action. The LJ04 polysaccharide was purified from Laminaria japonica by affinity chromatography. To investigate its antiviral activity, an MTT assay, q-PCR, immunofluorescent staining and western-blot analysis were performed. To define its mechanism of action, ELISA, q-PCR and flow cytometry were conducted. LJ04 had a low EC50, high CC50 and high SI. LJ04 inhibited not only JN200804, but also JN200803 in RD cells, and viral proliferation was strongly inhibited, whereas LJ04 suppressed viral-induced apoptosis as detected by flow cytometry. In conclusion, LJ04 was found to have robust antiviral activity by inhibiting apoptosis and inducing IFN-β expression. Our findings indicate that LJ04 is a good candidate for the treatment of EV71.

HRS plays an important role for TLR7 signaling to orchestrate inflammation and innate immunity upon EV71 infection

Enterovirus 71 (EV71) is an RNA virus that causes hand-foot-mouth disease (HFMD), and even fatal encephalitis in children. Although EV71 pathogenesis remains largely obscure, host immune responses may play important roles in the development of diseases. Recognition of pathogens mediated by Toll-like receptors (TLRs) induces host immune and inflammatory responses. Intracellular TLRs must traffic from the endoplasmic reticulum (ER) to the endolysosomal network from where they initiate complete signaling, leading to inflammatory response. This study reveals a novel mechanism underlying the regulation of TLR7 signaling during EV71 infection. Initially, we show that multiple cytokines are differentially expressed during viral infection and demonstrate that EV71 infection induces the production of proinflammatory cytokines through regulating TLR7-mediated p38 MAPK, and NF-κB signaling pathways. Further studies reveal that the expression of the endosome-associated protein hepatocyte growth factor-regulated tyrosine kinase substrate (HRS) is upregulated and highly correlated with the expression of TLR7 in EV71 infected patients, mice, and cultured cells. Virus-induced HRS subsequently enhances TLR7 complex formation in early- and late-endosome by interacting with TLR7 and TAB1. Moreover, HRS is involved in the regulation of the TLR7/NF-κB/p38 MAPK and the TLR7/NF-κB/IRF3 signaling pathways to induce proinflammatory cytokines and interferons, respectively, resulting in the orchestration of inflammatory and immune responses to the EV71 infection. Therefore, this study demonstrates that HRS acts as a key component of TLR7 signaling to orchestrate immune and inflammatory responses during EV71 infection, and provides new insights into the mechanisms underlying the regulation of host inflammation and innate immunity during EV71 infection.

Enterovirus 71 (EV71) is a highly infectious positive-stranded RNA virus that causes hand-foot-mouth disease (HFMD). As a major pathogen, EV71 infection leads to host immune responses in the disease severity. Toll-like receptors (TLRs) can recognize pathogens to induce host immunity and inflammation. Most TLRs must traffic from the endoplasmic reticulum (ER) to endolysosomal network before responding to ligands. The hepatocyte growth factor-regulated tyrosine kinase substrate (HRS) regulates ESCRT-0 complex and endosomal sorting of membrane proteins. HRS is required for ubiquitin-dependent TLR9 targeting to the endolysosome, however, the mechanism by which HRS regulates inflammation and immunity mediated by TLR7 is still largely unknown. Here, we reveal that HRS is a key component of TLR7 signaling to orchestrate immunity and inflammation during EV71 infection. EV71 infection induces the expression of HRS, which subsequently enhances the TLR7 complex formation by binding with TLR7 and TAB1. HRS facilitates TLR7/NF-κB/p38 MAPK and TLR7/NF-κB/IRF3 signaling pathways to produce proinflammatory cytokines and interferons, leading to induction of inflammatory and immune responses. Thus, we identify HRS as a key regulator of TLR7 signaling and illustrate a novel mechanism underlying the regulation of host immunity and inflammation during viral infection.

Acute Simian Immunodeficiency Virus Infection Triggers Early and Transient Interleukin-7 Production in the Gut, Leading to Enhanced Local Chemokine Expression and Intestinal Immune Cell Homing

The intestinal barrier, one of the first targets of HIV/simian immunodeficiency virus (SIV) is subjected to major physiological changes during acute infection. Having previously shown that pharmaceutical injection of interleukin-7 (IL-7) triggers chemokine expression in many organs leading to massive T-cell homing, in particular to the intestine, we here explored mucosal IL-7 expression as part of the cytokine storm occurring during the acute phase of SIV infection in rhesus macaques. Quantifying both mRNA and protein in tissues, we demonstrated a transient increase of IL-7 expression in the small intestine of SIV-infected rhesus macaques, starting with local detection of the virus by day 3 of infection. We also observed increased transcription levels of several chemokines in the small intestine. In infected macaques, ileal IL-7 expression correlated with the transcription of four of these chemokines. Among these chemokines, the macrophage and/or T-cell attractant chemokines CCL4, CCL25, and CCL28 also demonstrated increased transcription in uninfected IL-7-treated monkeys. Through immunohistofluorescence staining and image analysis, we observed increased CD8⁺ T-cell numbers and stable CD4⁺ T-cell counts in the infected lamina propria (LP) during hyperacute infection. Concomitantly, circulating CCR9⁺beta7⁺ CD4⁺ and CD8⁺ T-cells dropped during acute infection, suggesting augmented intestinal homing of gut-imprinted T-cells. Finally, CD4⁺ macrophages transiently decreased in the submucosa and concentrated in the LP during the first days of infection. Overall, our study identifies IL-7 as a danger signal in the small intestine of Chinese rhesus macaques in response to acute SIV infection. Through stimulation of local chemokine expressions, this overexpression of IL-7 triggers immune cell recruitment to the gut. These findings suggest a role for IL-7 in the initiation of early mucosal immune responses to SIV and HIV infections. However, IL-7 triggered CD4⁺ T-cells and macrophages localization at viral replication sites could also participate to viral spread and establishment of viral reservoirs.

Enterovirus 71-induced has-miR-21 contributes to evasion of host immune system by targeting MyD88 and IRAK1

Enterovirus71(EV71), the etiological agent of hand-foot-and-mouth disease, has increasingly become a public health challenge around the world. Type I interferons (IFNs) are an important family of cytokines that regulate innate and adaptive immune responses to pathogens.These pathways are tightly regulated by the host to prevent an inappropriate cellular response, but viruses can modulate these pathways to proliferate and spread. In this study, we demonstrated that EV71 evades the immune surveillance system to proliferate by activating microRNA-21. We demonstrated that EV71 infection upregulates miR-21, which in turn suppresses EV71-triggered type I IFN production, thus promoting EV71 replication. Furthermore, we demonstrated that miR-21 targets the myeloid differentiation factor 88(MyD88) and interleukin-1 receptor-associated kinase 1(IRAK1), which are involved in EV71-induced type I IFN production.

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.

Susceptibility of human tonsillar epithelial cells to enterovirus 71 with normal cytokine response

A recent histopathologic study implicated human tonsillar crypt epithelium as an important site for EV71 replication in EV71-caused fatal cases. This study aimed to confirm the susceptibility of human tonsillar epithelium to EV71. Two human tonsillar epithelial cell lines (UT-SCC-60A and UT-SCC-60B) were susceptive to EV71, and PI3K/AKT, p38, ERK1/2, and JNK1/2 signal pathways were activated. Interferon-α, IL-8, IL-1β, IL-6 and IL-12p40 were induced and regulated by PI3K/AKT, p38, ERK1/2, and JNK1/2 signal pathways. PI3K/AKT pathway activation appeared to suppress the induction of TNF-α, which induced cell survival by inhibiting GSK-3β. The activation of NF-κB was observed but inhibited by these pathways in EV71 infection. Furthermore, ERK1/2 and JNK1/2 were essential for efficient EV71 replication. Human tonsillar epithelial cells support EV71 replication and display innate antiviral immunity in vitro, indicating that human tonsillar epithelial cells may be novel targets for EV71 infection and replication in vivo.

Interleukin-27 as a Novel Biomarker for Early Cardiopulmonary Failure in Enterovirus 71-Infected Children with Central Nervous System Involvement

Enterovirus 71 (EV71) is a major pathogen for severe hand, foot, and mouth disease (HFMD), which leads to severe neurological complications and has high morbidity and mortality. Reliable biomarker for the prediction of deterioration in EV71-infected children with central nervous system (CNS) involvement may reduce the cardiopulmonary failure and mortality. Here, we found that serum IL-27 levels were significantly higher in stage III EV71-infected HFMD patients with early cardiopulmonary failure and strong correlation with CRP levels. IL27p28 polymorphisms (rs153109, rs17855750, and rs181206) did not influence IL-27 production, and these three SNPs were not associated with EV71 infection risk and clinical stage. IL-27 can be used as an prediction indicator for early cardiopulmonary failure in EV71-infected children with CNS involvement.

Differential Regulation of TLR Signaling on the Induction of Antiviral Interferons in Human Intestinal Epithelial Cells Infected with Enterovirus 71

Enterovirus 71 (EV71) causes hand-foot-and-mouth disease, which can lead to fatal neurological complications in young children and infants. Few gastrointestinal symptoms are observed clinically, suggesting the presence of a unique immunity to EV71 in the gut. We reported a robust induction of interferons (IFNs) in human intestinal epithelial cells (HT-29), which was suppressed in other types such as RD and HeLa cells. The underlying mechanism for the apparent difference remains obscure. In this study we report that in EV71-infected HT-29 cells, TLR/TRIF signaling was essential to IFN induction; viral replication increased and the induction of IFN-α, -β, -ω, -κ, and -ε decreased markedly in TRIF-silenced HT-29 cells. Importantly, TRIF was degraded by viral 3C^pro in RD cells, but resisted cleavage, and IRF3 was activated and translocated into the nucleus in HT-29 cells. Taken together, our data suggest that IFNs were induced differentially in human HT-29 cells through an intact TLR/TRIF signaling, which differs from other cell types and may be implicated in viral pathogenesis in EV71 infection.

Enterovirus-related diarrhoea in Guangdong, China: clinical features and implications in hand, foot and mouth disease and herpangina

Background

A series of complications caused by enteroviruses, including meningitis, encephalitis, acute flaccid paralysis, acute cardiopulmonary failure, respiratory infection, and myocardial injury have been reported in hand, foot and mouth disease/herpangina (HFMD/HA). However, the complication of diarrhoea caused by enteroviruses has been neglected, and a summary of its clinical features and impact on HFMD/HA is unavailable.

Methods

We included inpatients with HFMD/HA admitted to the Paediatric Department of Zhujiang Hospital during 2009–2012. We summarised and compared clinical data for cases with and without diarrhoea, and determined enterovirus serotypes by reverse transcriptase polymerase chain reaction and genotyping based on a partial-length fragment of viral protein 1 or the 5’-untranslated region.

Results

There were 804 inpatients with HFMD/HA and 28 (3.5 %) presented with diarrhoea. Gastrointestinal symptoms were mild in most cases of diarrhoea (82.1 %), with high prevalence of no dehydration (82.1 %), short duration of diarrhoea (78.6 %) and watery stools (75.0 %). The prevalence of multi-organ dysfunction syndrome (10.7 vs 0.40 %) (p = 0.001), hepatic injury (14.3 vs 3.4 %) (p = 0.019), myocardial injury (21.4 vs 6.1 %) (p = 0.002) and convulsion (21.4 vs 7.2 %) (p = 0.016) was significantly higher in the diarrhoea than no diarrhoea group. There was no significant difference between the two groups regarding prevalence of death, altered consciousness, paralysis, central nervous system involvement, or acute respiratory infection.

Conclusions

Most patients with diarrhoea caused by enteroviruses circulating in Guangdong Province in 2009–2012 had mild or moderate gastrointestinal symptoms. Although enterovirus-related diarrhoea caused additional multi-organ dysfunction syndrome, hepatic injury and myocardial injury in children with HFMD/HA, timely intervention efficiently reduced disease severity and improved outcome.

Clonal evolution of CD8+ T cell responses against latent viruses: relationship among phenotype, localization, and function

Human cytomegalovirus (hCMV) infection is characterized by a vast expansion of resting effector-type virus-specific T cells in the circulation. In mice, interleukin-7 receptor α (IL-7Rα)-expressing cells contain the precursors for long-lived antigen-experienced CD8(+) T cells, but it is unclear if similar mechanisms operate to maintain these pools in humans. Here, we studied whether IL-7Rα-expressing cells obtained from peripheral blood (PB) or lymph nodes (LNs) sustain the circulating effector-type hCMV-specific pool. Using flow cytometry and functional assays, we found that the IL-7Rα(+) hCMV-specific T cell population comprises cells that have a memory phenotype and lack effector features. We used next-generation sequencing of the T cell receptor to compare the clonal repertoires of IL-7Rα(+) and IL-7Rα(-) subsets. We observed limited overlap of clones between these subsets during acute infection and after 1 year. When we compared the hCMV-specific repertoire between PB and paired LNs, we found many identical clones but also clones that were exclusively found in either compartment. New clones that were found in PB during antigenic recall were only rarely identical to the unique LN clones. Thus, although PB IL-7Rα-expressing and LN hCMV-specific CD8(+) T cells show typical traits of memory-type cells, these populations do not seem to contain the precursors for the novel hCMV-specific CD8(+) T cell pool during latency or upon antigen recall. IL-7Rα(+) PB and LN hCMV-specific memory cells form separate virus-specific compartments, and precursors for these novel PB hCMV-specific CD8(+) effector-type T cells are possibly located in other secondary lymphoid tissues or are being recruited from the naive CD8(+) T cell pool.

IMPORTANCE

Insight into the self-renewal properties of long-lived memory CD8(+) T cells and their location is crucial for the development of both passive and active vaccination strategies. Human CMV infection is characterized by a vast expansion of resting effector-type cells. It is, however, not known how this population is maintained. We here investigated two possible compartments for effector-type cell precursors: circulating acute-phase IL-7Rα-expressing hCMV-specific CD8(+) T cells and lymph node (LN)-residing hCMV-specific (central) memory cells. We show that new clones that appear after primary hCMV infection or during hCMV reactivation seldom originate from either compartment. Thus, although identical clones may be maintained by either memory population, the precursors of the novel clones are probably located in other (secondary) lymphoid tissues or are recruited from the naive CD8(+) T cell pool.

Toll-like receptor 9-mediated protection of enterovirus 71 infection in mice is due to the release of danger-associated molecular patterns

Enterovirus 71 (EV71), a positive-stranded RNA virus, is the major cause of hand, foot, and mouth disease (HFMD) with severe neurological symptoms. Antiviral type I interferon (alpha/beta interferon [IFN-α/β]) responses initiated from innate receptor signaling are inhibited by EV71-encoded proteases. It is less well understood whether EV71-induced apoptosis provides a signal to activate type I interferon responses as a host defensive mechanism. In this report, we found that EV71 alone cannot activate Toll-like receptor 9 (TLR9) signaling, but supernatant from EV71-infected cells is capable of activating TLR9. We hypothesized that TLR9-activating signaling from plasmacytoid dendritic cells (pDCs) may contribute to host defense mechanisms. To test our hypothesis, Flt3 ligand-cultured DCs (Flt3L-DCs) from both wild-type (WT) and TLR9 knockout (TLR9KO) mice were infected with EV71. More viral particles were produced in TLR9KO mice than by WT mice. In contrast, alpha interferon (IFN-α), monocyte chemotactic protein 1 (MCP-1), tumor necrosis factor-alpha (TNF-α), IFN-γ, interleukin 6 (IL-6), and IL-10 levels were increased in Flt3L-DCs from WT mice infected with EV71 compared with TLR9KO mice. Seven-day-old TLR9KO mice infected with a non-mouse-adapted EV71 strain developed neurological lesion-related symptoms, including hind-limb paralysis, slowness, ataxia, and lethargy, but WT mice did not present with these symptoms. Lung, brain, small intestine, forelimb, and hind-limb tissues collected from TLR9KO mice exhibited significantly higher viral loads than equivalent tissues collected from WT mice. Histopathologic damage was observed in brain, small intestine, forelimb, and hind-limb tissues collected from TLR9KO mice infected with EV71. Our findings demonstrate that TLR9 is an important host defense molecule during EV71 infection. Importance: The host innate immune system is equipped with pattern recognition receptors (PRRs), which are useful for defending the host against invading pathogens. During enterovirus 71 (EV71) infection, the innate immune system is activated by pathogen-associated molecular patterns (PAMPs), which include viral RNA or DNA, and these PAMPs are recognized by PRRs. Toll-like receptor 3 (TLR3) and TLR7/8 recognize viral nucleic acids, and TLR9 senses unmethylated CpG DNA or pathogen-derived DNA. These PRRs stimulate the production of type I interferons (IFNs) to counteract viral infection, and they are the major source of antiviral alpha interferon (IFN-α) production in pDCs, which can produce 200- to 1,000-fold more IFN-α than any other immune cell type. In addition to PAMPs, danger-associated molecular patterns (DAMPs) are known to be potent activators of innate immune signaling, including TLR9. We found that EV71 induces cellular apoptosis, resulting in tissue damage; the endogenous DNA from dead cells may activate the innate immune system through TLR9. Therefore, our study provides new insights into EV71-induced apoptosis, which stimulates TLR9 in EV71-associated infections.

Apigenin inhibits enterovirus 71 replication through suppressing viral IRES activity and modulating cellular JNK pathway

Enterovirus 71 (EV71) is a member of genus Enterovirus in Picornaviridae family, which is one of the major causative agents for hand, foot and mouth disease (HFMD), and sometimes associated with severe central nervous system diseases in children. Currently there are no effective therapeutic medicines or vaccines for the disease. In this report, we found that apigenin and luteolin, two flavones that differ only in the number of hydroxyl groups could inhibit EV71-mediated cytopathogenic effect (CPE) and EV71 replication with low cytotoxicity. Both molecules also showed inhibitory effect on the viral polyprotein expression. They prevented EV71-induced cell apoptosis, intracellular reactive oxygen species (ROS) generation and cytokines up-regulation. Time-of-drug addition study demonstrated that apigenin and luteolin acted after viral entry. We examined the effect of apigenin and luteolin on 2A(pro) and 3C(pro) activity, two viral proteases responsible for viral polyprotein processing, and found that they showed less inhibitory activity on 2A(pro) or 3C(pro). Further studies demonstrated that apigenin, but not luteolin could interfere with viral IRES activity. Also, apigenin inhibited EV71-induced c-Jun N-terminal kinase (JNK) activation which is critical for viral replication, in contrast to luteolin that did not. This study demonstrated that apigenin may inhibit EV71 replication through suppressing viral IRES activity and modulating cellular JNK pathway. It also provided evidence that one hydroxyl group difference in the B ring between apigenin and luteolin resulted in the distinct antiviral mechanisms. This study will provide the basis for better drug development and further identification of potential drug targets.

Elucidating the host-pathogen interaction between human colorectal cells and invading Enterovirus 71 using transcriptomics profiling

•

Enterovirus 71 (EV71) is one of the main etiological agents for Hand, Foot and Mouth Disease (HFMD).

•

Types I, II and III interferon may be a key antiviral response against EV71.

•

We examine the transcriptomic changes in human colorectal cells during EV71 infection.

•

The intestinal epithelial immune system plays a key role in the progression of HFMD.

Enterovirus 71 (EV71) is one of the main etiological agents for Hand, Foot and Mouth Disease (HFMD) and has been shown to be associated with severe clinical manifestation. Currently, there is no antiviral therapeutic for the treatment of HFMD patients owing to a lack of understanding of EV71 pathogenesis. This study seeks to elucidate the transcriptomic changes that result from EV71 infection. Human whole genome microarray was employed to monitor changes in genomic profiles between infected and uninfected cells. The results reveal altered expression of human genes involved in critical pathways including the immune response and the stress response. Together, data from this study provide valuable insights into the host–pathogen interaction between human colorectal cells and EV71.