Innate Antiviral Defenses Independent of Inducible IFNα/β Production

The matrix protein of respiratory syncytial virus suppresses interferon signaling via RACK1 association

IMPORTANCE

Respiratory syncytial virus (RSV) matrix (M) protein is indispensable for virion assembly and release. It is localized to the nucleus during early infection to perturb host transcription. However, the function of RSV M protein in other cellular activities remains poorly understood. In this study, several interferon response-associated host factors, including RACK1, were identified by proteomic analysis as RSV M interactors. Knockdown of RACK1 attenuates RSV-restricted IFN signaling leading to enhanced host defense against RSV infection, unraveling a role of M protein in antagonizing IFN response via association with RACK1. Our study uncovers a previously unrecognized mechanism of immune evasion by RSV M protein and identifies RACK1 as a novel host factor recruited by RSV, highlighting RACK1 as a potential new target for RSV therapeutics development.

The podocyte: glomerular sentinel at the crossroads of innate and adaptive immunity

Focal segmental glomerulosclerosis (FSGS) is a common glomerular disorder that manifests clinically with the nephrotic syndrome and has a propensity to recur following kidney transplantation. The pathophysiology and therapies available to treat FSGS currently remain elusive. Since the podocyte appears to be the target of apparent circulating factor(s) that lead to recurrence of proteinuria following kidney transplantation, this article is focused on the podocyte. In the context of kidney transplantation, the performance of pre- and post-reperfusion biopsies, and the establishment of in vitro podocyte liquid biopsies/assays allow for the development of clinically relevant studies of podocyte biology. This has given insight into new pathways, involving novel targets in innate and adaptive immunity, such as SMPDL3b, cGAS-STING, and B7-1. Elegant experimental studies suggest that the successful clinical use of rituximab and abatacept, two immunomodulating agents, in our case series, may be due to direct effects on the podocyte, in addition to, or perhaps distinct from their immunosuppressive functions. Thus, tissue biomarker-directed therapy may provide a rational approach to validate the mechanism of disease and allow for the development of new therapeutics for FSGS. This report highlights recent progress in the field and emphasizes the importance of kidney transplantation and recurrent FSGS (rFSGS) as a platform for the study of primary FSGS.

Circulating biomarkers of inflammaging as potential predictors of COVID-19 severe outcomes

The COVID-19 pandemic caused by SARS-CoV-2 infection has been of unprecedented clinical and socio-economic worldwide relevance. The case fatality rate for COVID-19 grows exponentially with age and the presence of comorbidities. In the older patients, COVID-19 manifests predominantly as a systemic disease associated with immunological, inflammatory, and procoagulant responses. Timely diagnosis and risk stratification are crucial steps to define appropriate therapies and reduce mortality, especially in the older patients. Chronically and systemically activated innate immune responses and impaired antiviral responses have been recognized as the results of a progressive remodeling of the immune system during aging, which can be described by the words 'immunosenescence' and 'inflammaging'. These age-related features of the immune system were highlighted in patients affected by COVID-19 with the poorest clinical outcomes, suggesting that the mechanisms underpinning immunosenescence and inflammaging could be relevant for COVID-19 pathogenesis and progression. Increasing evidence suggests that senescent myeloid and endothelial cells are characterized by the acquisition of a senescence-associated pro-inflammatory phenotype (SASP), which is considered as the main culprit of both immunosenescence and inflammaging. Here, we reviewed this evidence and highlighted several circulating biomarkers of inflammaging that could provide additional prognostic information to stratify COVID-19 patients based on the risk of severe outcomes.

Herpes simplex virus 1 evades cellular antiviral response by inducing microRNA-24, which attenuates STING synthesis

STING is a nodal point for cellular innate immune response to microbial infections, autoimmunity and cancer; it triggers the synthesis of the antiviral proteins, type I interferons. Many DNA viruses, including Herpes Simplex Virus 1 (HSV1), trigger STING signaling causing inhibition of virus replication. Here, we report that HSV1 evades this antiviral immune response by inducing a cellular microRNA, miR-24, which binds to the 3’ untranslated region of STING mRNA and inhibits its translation. Expression of the gene encoding miR-24 is induced by the transcription factor AP1 and activated by MAP kinases in HSV1-infected cells. Introduction of exogenous miR-24 or prior activation of MAPKs, causes further enhancement of HSV1 replication in STING-expressing cells. Conversely, transfection of antimiR-24 inhibits virus replication in those cells. HSV1 infection of mice causes neuropathy and death; using two routes of infection, we demonstrated that intracranial injection of antimiR-24 alleviates both morbidity and mortality of the infected mice. Our studies reveal a new immune evasion strategy adopted by HSV1 through the regulation of STING and demonstrates that it can be exploited to enhance STING’s antiviral action.

The type I interferon system is the first line of cellular antiviral innate immune response. Virus infection is recognized by various pattern recognition receptors in the infected cell and it activates the interferon system to inhibit virus replication. However, viruses have evolved various mechanisms to evade the cellular immune response and enhance viral replication. Our study uncovers an immune evasion strategy used by the Herpes Simplex virus to circumvent the cGAS/STING signaling pathway which is the pivotal innate immune response to combat DNA virus replication. miR-24 induction by HSV1 targets STING and hence, dampens Type I Immune response against the virus. The induction of miR-24 is regulated by virus induced MAPK activation, which are also required during early lytic cycles of HSV1 replication and is indispensable for HSV1 reactivation from latency in neurons; depicting a new direct co-relation between MAPK activation and HSV1 replication orchestrated through cellular miR-24. Silencing of miR-24 in mice brain curtails viral replication and disease severity. Overall, these results indicate possible therapeutic use of stable antimiR-24 against HSV1 and other diseases that are alleviated by STING.

Type I Interferon-Mediated Regulation of Antiviral Capabilities of Neutrophils

Interferons (IFNs) are induced by viruses and are the main regulators of the host antiviral response. They balance tissue tolerance and immune resistance against viral challenges. Like all cells in the human body, neutrophils possess the receptors for IFNs and contribute to antiviral host defense. To combat viruses, neutrophils utilize various mechanisms, such as viral sensing, neutrophil extracellular trap formation, and antigen presentation. These mechanisms have also been linked to tissue damage during viral infection and inflammation. In this review, we presented evidence that a complex cross-regulatory talk between IFNs and neutrophils initiates appropriate antiviral immune responses and regulates them to minimize tissue damage. We also explored recent exciting research elucidating the interactions between IFNs, neutrophils, and severe acute respiratory syndrome-coronavirus-2, as an example of neutrophil and IFN cross-regulatory talk. Dissecting the IFN-neutrophil paradigm is needed for well-balanced antiviral therapeutics and development of novel treatments against many major epidemic or pandemic viral infections, including the ongoing pandemic of the coronavirus disease that emerged in 2019.

Innate immune evasion by SARS-CoV-2: Comparison with SARS-CoV

SARS-CoV-2 virus, a member of the Coronaviridae family, causes Covid-19 pandemic disease with severe respiratory illness. Multiple strategies enable SARS-CoV-2 to eventually overcome antiviral innate immune mechanisms which are important components of viral pathogenesis. This review considers several mechanisms of SARS-CoV-2 innate immune evasion including suppression of IFN-α/β production at the earliest stage of infection, mechanisms that exhaust natural killer cell-mediated cytotoxicity, overstimulation of NLRP3 inflammasome and induction of a cytokine storm. A comparison with SARS-CoV is made. Greater knowledge of these and other immune evasion tactics may provide us with improved possibilities for research into this novel deadly virus.

Innate Immune Response to Influenza Virus at Single-Cell Resolution in Human Epithelial Cells Revealed Paracrine Induction of Interferon Lambda 1

Early interactions of influenza A virus (IAV) with respiratory epithelium might determine the outcome of infection. The study of global cellular innate immune responses often masks multiple aspects of the mechanisms by which populations of cells work as organized and heterogeneous systems to defeat virus infection, and how the virus counteracts these systems. In this study, we experimentally dissected the dynamics of IAV and human epithelial respiratory cell interaction during early infection at the single-cell level. We found that the number of viruses infecting a cell (multiplicity of infection [MOI]) influences the magnitude of virus antagonism of the host innate antiviral response. Infections performed at high MOIs resulted in increased viral gene expression per cell and stronger antagonist effect than infections at low MOIs. In addition, single-cell patterns of expression of interferons (IFN) and IFN-stimulated genes (ISGs) provided important insights into the contributions of the infected and bystander cells to the innate immune responses during infection. Specifically, the expression of multiple ISGs was lower in infected than in bystander cells. In contrast with other IFNs, IFN lambda 1 (IFNL1) showed a widespread pattern of expression, suggesting a different cell-to-cell propagation mechanism more reliant on paracrine signaling. Finally, we measured the dynamics of the antiviral response in primary human epithelial cells, which highlighted the importance of early innate immune responses at inhibiting virus spread.IMPORTANCE Influenza A virus (IAV) is a respiratory pathogen of high importance to public health. Annual epidemics of seasonal IAV infections in humans are a significant public health and economic burden. IAV also causes sporadic pandemics, which can have devastating effects. The main target cells for IAV replication are epithelial cells in the respiratory epithelium. The cellular innate immune responses induced in these cells upon infection are critical for defense against the virus, and therefore, it is important to understand the complex interactions between the virus and the host cells. In this study, we investigated the innate immune response to IAV in the respiratory epithelium at the single-cell level, providing a better understanding on how a population of epithelial cells functions as a complex system to orchestrate the response to virus infection and how the virus counteracts this system.

Innate Immune Evasion by Human Respiratory RNA Viruses

The impact of respiratory virus infections on the health of children and adults can be very significant. Yet, in contrast to most other childhood infections as well as other viral and bacterial diseases, prophylactic vaccines or effective antiviral treatments against viral respiratory infections are either still not available, or provide only limited protection. Given the widespread prevalence, a general lack of natural sterilizing immunity, and/or high morbidity and lethality rates of diseases caused by influenza, respiratory syncytial virus, coronaviruses, and rhinoviruses, this difficult situation is a genuine societal challenge. A thorough understanding of the virus-host interactions during these respiratory infections will most probably be pivotal to ultimately meet these challenges. This review attempts to provide a comparative overview of the knowledge about an important part of the interaction between respiratory viruses and their host: the arms race between host innate immunity and viral innate immune evasion. Many, if not all, viruses, including the respiratory viruses listed above, suppress innate immune responses to gain a window of opportunity for efficient virus replication and setting-up of the infection. The consequences for the host's immune response are that it is often incomplete, delayed or diminished, or displays overly strong induction (after the delay) that may cause tissue damage. The affected innate immune response also impacts subsequent adaptive responses, and therefore viral innate immune evasion often undermines fully protective immunity. In this review, innate immune responses relevant for respiratory viruses with an RNA genome will briefly be summarized, and viral innate immune evasion based on shielding viral RNA species away from cellular innate immune sensors will be discussed from different angles. Subsequently, viral enzymatic activities that suppress innate immune responses will be discussed, including activities causing host shut-off and manipulation of stress granule formation. Furthermore, viral protease-mediated immune evasion and viral manipulation of the ubiquitin system will be addressed. Finally, perspectives for use of the reviewed knowledge for the development of novel antiviral strategies will be sketched.

BCL6 modulates tissue neutrophil survival and exacerbates pulmonary inflammation following influenza virus infection

Neutrophils are vital for antimicrobial defense; however, their role during viral infection is less clear. Furthermore, the molecular regulation of neutrophil fate and function at the viral infected sites is largely elusive. Here we report that BCL6 deficiency in myeloid cells exhibited drastically enhanced host resistance to severe influenza A virus (IAV) infection. In contrast to the notion that BCL6 functions to suppress innate inflammation, we find that myeloid BCL6 deficiency diminished lung inflammation without affecting viral loads. Using a series of Cre-transgenic, reporter, and knockout mouse lines, we demonstrate that BCL6 deficiency in neutrophils, but not in monocytes or lung macrophages, attenuated host inflammation and morbidity following IAV infection. Mechanistically, BCL6 bound to the neutrophil gene loci involved in cellular apoptosis in cells specifically at the site of infection. As such, BCL6 disruption resulted in increased expression of apoptotic genes in neutrophils in the respiratory tract, but not in the circulation or bone marrow. Consequently, BCL6 deficiency promoted tissue neutrophil apoptosis. Partial neutrophil depletion led to diminished pulmonary inflammation and decreased host morbidity. Our results reveal a previously unappreciated role of BCL6 in modulating neutrophil apoptosis at the site of infection for the regulation of host disease development following viral infection. Furthermore, our studies indicate that tissue-specific regulation of neutrophil survival modulates host inflammation and tissue immunopathology during acute respiratory viral infection.

IRF1 Maintains Optimal Constitutive Expression of Antiviral Genes and Regulates the Early Antiviral Response

Viral defense at mucosal sites depends on interferons (IFN) and IFN stimulated genes (ISGs), either of which may be constitutively expressed to maintain an “antiviral state” (AVS). However, the mechanisms that govern the AVS are poorly defined. Using a BEAS-2B respiratory epithelial cell line deficient in IRF1, we demonstrate higher susceptibility to infection with vesicular stomatitis virus (VSV) and influenza virus. IRF1-mediated restriction of VSV is IFN-independent, as blockade of types I and III IFNs and JAK-STAT signaling before infection did not affect VSV infection of either parent or IRF1 KO cells. Transcriptome analysis revealed that IRF1 regulates constitutive expression of ~300 genes, including antiviral ISGs: OAS2, BST2, and RNASEL and knockdown of any of these IRF1-dependent genes increased VSV infection. Additionally, IRF1 enhances rapid expression of IFNβ and IFNλ after stimulation with poly I:C and also regulates ISG expression. Mechanistically, IRF1 enhances recruitment of BRD4 to promotor-enhancer regions of ISGs for rapid expression and maintains levels of histone H3K4me1 for optimal constitutive expression. Finally, IRF1 also regulates constitutive expression of TLR2 and TLR3 and promotes signaling through these pattern recognition receptors (PRR). These data reveal multiple roles for IRF1 toward effective anti-viral responses by maintaining IFN-independent constitutive expression of anti-viral ISGs and supporting early IFN-dependent responses to PRR stimulation.

Cytokine gene transcription in the trachea, Harderian gland, and trigeminal ganglia of chickens inoculated with virulent infectious laryngotracheitis virus (ILTV) strain

The objective of this study was to determine how cytokine transcription profiles correlate with patterns of infectious laryngotracheitis virus (ILTV) replication in the trachea, Harderian gland, and trigeminal ganglia during the early and late stages of infection after intratracheal inoculation. Viral genomes and transcripts were detected in the trachea and Harderian gland but not in trigeminal ganglia. The onset of viral replication in the trachea was detected at day one post-infection and peaked by day three post-infection. The peak of pro-inflammatory (CXCLi2, IL-1β, IFN-γ) and anti-inflammatory (IL-13, IL-10) cytokine gene transcription, 5 days post-infection, coincided with the increased recruitment of inflammatory cells, extensive tissue damage, and limiting of virus replication in the trachea. In contrast, transcription of the IFN-β gene in the trachea remained unaffected suggesting that ILTV infection blocks type I interferon responses. In the Harderian gland, the most evident transcription change was the early and transient upregulation of the IFN-γ gene at 1 day post-infection, which suggests that the Harderian gland is prepared to rapidly respond to ILTV infection. Overall, results from this study suggest that regulation of Th1 effector cells and macrophage activity by Th1/2 cytokines was pertinent to maintain a balanced immune response capable of providing an adequate Th1-mediated protective immunity, while sustaining some immune homeostasis in preparation for the regeneration of the tracheal mucosa.

Transcriptomic Profiles of Senegalese Sole Infected With Nervous Necrosis Virus Reassortants Presenting Different Degree of Virulence

Betanodaviruses [nervous necrosis virus (NNV)] are the causative agent of the viral encephalopathy and retinopathy, a disease that affects cultured Senegalese sole (Solea senegalensis). NNV reassortants, combining genomic segments from redspotted grouper nervous necrosis virus (RGNNV) and striped jack nervous necrosis virus (SJNNV) genotypes, have been previously isolated from several fish species. The wild-type reassortant wSs160.03, isolated from Senegalese sole, has been proven to be more virulent to sole than the parental genotypes (RGNNV and SJNNV), causing 100% mortality. Mutations at amino acids 247 (serine to alanine) and 270 (serine to asparagine) in the wSs160.03 capsid protein have allowed us to obtain a mutant reassortant (rSs160.03_247+270), which provokes a 40% mortality decrease. In this study, the RNA-Seq technology has been used to comparatively analyze Senegalese sole transcriptomes in two organs (head kidney and eye/brain) after infection with wild-type and mutant strains. A total of 633 genes were differentially expressed (DEGs) in animals infected with the wild-type isolate (with higher virulence), whereas 393 genes were differentially expressed in animals infected with the mutant strain (37.9% decrease in the number of DEGs). To study the biological functions of detected DEGs involved in NNV infection, a gene ontology (GO) enrichment analysis was performed. Different GO profiles were obtained in the following subclasses: (i) biological process; (ii) cellular component; and (iii) molecular function, for each viral strain tested. Immune response and proteolysis have been the predominant biological process after the infection with the wild-type isolate, whereas the infection with the mutant strain induces proteolysis in head kidney and inhibition of vasculogenesis in nervous tissue. Regarding the immune response, genes coding for proteins acting as mediators of type I IFN expression (DHX58, IRF3, IRF7) and IFN-stimulated genes (ISG15, Mx, PKR, Gig1, ISG12, IFI44, IFIT-1, to name a few) were upregulated in animals infected with the wild-type isolate, whereas no-differential expression of these genes was observed in samples inoculated with the mutant strain. The different transcriptomic profiles obtained could help to better understand the NNV pathogenesis in Senegalese sole, setting up the importance as virulence determinants of amino acids at positions 247 and 270 within the RNA2 segment.

B cells are the predominant mediators of early systemic viral dissemination during rectal LCMV infection

Determining the magnitude of local immune response during mucosal exposure to viral pathogens is critical to understanding the mechanism of viral pathogenesis. We previously showed that vaginal inoculation of lymphocytic choriomeningitis virus (LCMV) fails to induce a robust innate immune response in the lower female reproductive tract (FRT), allowing high titer viral replication and a delay in T-cell-mediated viral control. Despite this immunological delay, LCMV replication remained confined mainly to the FRT and the draining iliac lymph node. Here, we show that rectal infection with LCMV triggers type I/III interferon responses, followed by innate immune activation and lymphocyte recruitment to the colon. In contrast to vaginal exposure, innate immunity controls LCMV replication in the colon, but virus rapidly disseminates systemically. Virus-induced inflammation promotes the recruitment of LCMV target cells to the colon followed by splenic viral dissemination by infected B cells, and to a lesser extent by CD8 T cells. These findings demonstrate major immunological differences between vaginal and rectal exposure to the same viral pathogen, highlighting unique risks associated with each of these common routes of sexual viral transmission.

RSAD2 and AIM2 Modulate Coxsackievirus A16 and Enterovirus A71 Replication in Neuronal Cells in Different Ways That May Be Associated with Their 5' Nontranslated Regions

Coxsackievirus A16 (CV-A16) and enterovirus A71 (EV-A71) are closely related enteroviruses that cause the same hand, foot, and mouth disease (HFMD), but neurological complications occur only very rarely in CV-A16 compared to EV-A71 infections. To elucidate host responses that may be able to explain these differences, we performed transcriptomic analysis and real-time quantitative PCR (RT-qPCR) in CV-A16-infected neuroblastoma cells (SK-N-SH), and the results showed that the radical S-adenosylmethionine domain containing 2 (RSAD2) was the highest upregulated gene in the antimicrobial pathway. Increased RSAD2 expression was correlated with reduced viral replication, while RSAD2 knockdown cells were correlated with increased replication. EV-A71 replication showed no apparent correlation to RSAD2 expressions. Absent in melanoma 2 (AIM2), which is associated with pyroptotic cell death, was upregulated in EV-A71-infected neurons but not in CV-A16 infection, suggesting that the AIM2 inflammasome played a significant role in suppressing EV-A71 replication. Chimeric viruses derived from CV-A16 and EV-A71 but containing swapped 5' nontranslated regions (5' NTRs) showed that RSAD2 expression/viral replication and AIM2 expression/viral replication patterns may be linked to the 5' NTRs of parental viruses. Differences in secondary structure of internal ribosomal entry sites within the 5' NTR may be responsible for these findings. Overall, our results suggest that CV-A16 and EV-A71 elicit different host responses to infection, which may help explain the apparent lower incidence of CV-A16-associated neurovirulence in HFMD outbreaks compared to EV-A71 infection.IMPORTANCE Although coxsackievirus A16 (CV-A16) and enterovirus A17 (EV-A71) both cause hand, foot, and mouth disease, EV-A71 has emerged as a leading cause of nonpolio, enteroviral fatal encephalomyelitis among young children. The significance of our research is in the identification of the possible differing and novel mechanisms of CV-A16 and EV-A71 inhibition in neuronal cells that may impact viral neuropathogenesis. We further showed that viral 5' NTRs may play significant roles in eliciting different host response mechanisms.

Stage-specific IFN-induced and IFN gene expression reveal convergence of type I and type II IFN and highlight their role in both acute and chronic stage of pathogenic SIV infection

Interferons (IFNs) play a major role in controlling viral infections including HIV/SIV infections. Persistent up-regulation of interferon stimulated genes (ISGs) is associated with chronic immune activation and progression in SIV/HIV infections, but the respective contribution of different IFNs is unclear. We analyzed the expression of IFN genes and ISGs in tissues of SIV infected macaques to understand the respective roles of type I and type II IFNs. Both IFN types were induced in lymph nodes during early stage of primary infection and to some extent in rectal biopsies but not in PBMCs. Induction of Type II IFN expression persisted during the chronic phase, in contrast to undetectable induction of type I IFN expression. Global gene expression analysis with a major focus on ISGs revealed that at both acute and chronic infection phases most differentially expressed ISGs were inducible by both type I and type II IFNs and displayed the highest increases, indicating strong convergence and synergy between type I and type II IFNs. The analysis of functional signatures of ISG expression revealed temporal changes in IFN expression patterns identifying phase-specific ISGs. These results suggest that IFN-γ strongly contribute to shape ISG upregulation in addition to type I IFN.

Differential responses of innate immunity triggered by different subtypes of influenza a viruses in human and avian hosts

BACKGROUND

Innate immunity provides first line of defense against viral infections. The interactions between hosts and influenza A virus and the response of host innate immunity to viral infection are critical determinants for the pathogenicity or virulence of influenza A viruses. This study was designed to investigate global changes of gene expression and detailed responses of innate immune systems in human and avian hosts during the course of infection with various subtypes of influenza A viruses, using collected and self-generated transcriptome sequencing data from human bronchial epithelial (HBE), human tracheobronchial epithelial (HTBE), and A549 cells infected with influenza A virus subtypes, namely H1N1, H3N2, H5N1 HALo mutant, and H7N9, and from ileum and lung of chicken and quail infected with H5N1, or H5N2.

RESULTS

We examined the induction of various cytokines and chemokines in human hosts infected with different subtypes of influenza A viruses. Type I and III interferons were found to be differentially induced with each subtype. H3N2 caused abrupt and the strongest response of IFN-β and IFN-λ, followed by H1N1 (though much weaker), whereas H5N1 HALo mutant and H7N9 induced very minor change in expression of type I and III interferons. Similarly, differential responses of other innate immunity-related genes were observed, including TMEM173, MX1, OASL, IFI6, IFITs, IFITMs, and various chemokine genes like CCL5, CX3CL1, and chemokine (C-X-C motif) ligands, SOCS (suppressors of cytokine signaling) genes. Third, the replication kinetics of H1N1, H3N2, H5N1 HALo mutant and H7N9 subtypes were analyzed, H5N1 HALo mutant was found to have the highest viral replication rate, followed by H3N2, and H1N1, while H7N9 had a rate similar to that of H1N1 or H3N2 though in different host cell type.

CONCLUSION

Our study illustrated the differential responses of innate immunity to infections of different subtypes of influenza A viruses. We found the influenza viruses which induced stronger innate immune responses replicate slower than those induces weaker innate immune responses. Our study provides important insight into links between the differential innate immune responses from hosts and the pathogenicity/ virulence of different subtypes of influenza A viruses.

Double deficiency of Trex2 and DNase1L2 nucleases leads to accumulation of DNA in lingual cornifying keratinocytes without activating inflammatory responses

The cornification of keratinocytes on the surface of skin and oral epithelia is associated with the degradation of nuclear DNA. The endonuclease DNase1L2 and the exonuclease Trex2 are expressed specifically in cornifying keratinocytes. Deletion of DNase1L2 causes retention of nuclear DNA in the tongue epithelium but not in the skin. Here we report that lack of Trex2 results in the accumulation of DNA fragments in the cytoplasm of cornifying lingual keratinocytes and co-deletion of DNase1L2 and Trex2 causes massive accumulation of DNA fragments throughout the cornified layers of the tongue epithelium. By contrast, cornification-associated DNA breakdown was not compromised in the epidermis. Aberrant retention of DNA in the tongue epithelium was associated neither with enhanced expression of DNA-driven response genes, such as Ifnb, Irf7 and Cxcl10, nor with inflammation. Of note, the expression of Tlr9, Aim2 and Tmem173, key DNA sensor genes, was markedly lower in keratinocytes and keratinocyte-built tissues than in macrophages and immune tissues, and DNA-driven response genes were not induced by introduction of DNA in keratinocytes. Altogether, our results indicate that DNase1L2 and Trex2 cooperate in the breakdown and degradation of DNA during cornification of lingual keratinocytes and aberrant DNA retention is tolerated in the oral epithelium.

ISG15 Modulates Type I Interferon Signaling and the Antiviral Response during Hepatitis E Virus Replication

Hepatitis E virus (HEV), a single-stranded positive-sense RNA virus, generally causes self-limiting acute viral hepatitis, although chronic HEV infection has recently become a significant clinical problem in immunocompromised individuals, especially in solid-organ transplant recipients. Innate immunity, via the type I interferon (IFN) response, plays an important role during the initial stages of a viral infection. IFN-stimulated gene 15 (ISG15), an IFN-induced ubiquitin-like protein, is known to have an immunomodulatory role and can have a direct antiviral effect on a wide spectrum of virus families. In the present study, we investigated the antiviral effect as well as the potential immunomodulatory role of ISG15 during HEV replication. The results revealed that HEV induced high levels of ISG15 production both in vitro (Huh7-S10-3 liver cells) and in vivo (liver tissues from HEV-infected pigs); however, ISG15 is not required for virus replication. We also demonstrated that ISG15 silencing potentiates enhanced type I IFN-mediated signaling, resulting in an increase in the type I IFN-mediated antiviral effect during HEV replication. This observed enhanced type I IFN signaling correlated with an increase in IFN-stimulated gene expression levels during HEV replication. Furthermore, we showed that PKR and OAS1 played important roles in the ISG15-mediated type I IFN sensitivity of HEV. Taken together, the results from this study suggest that ISG15 plays an important immunomodulatory role and regulates HEV sensitivity to exogenous type I IFN.IMPORTANCE Hepatitis E virus (HEV) infection typically causes self-limiting acute viral hepatitis. However, chronic HEV infection has recently become a significant clinical problem in immunocompromised patients. Pegylated interferon (IFN) has been used to treat chronic HEV infection in solid-organ transplant patients with some success. However, the mechanism behind the type I IFN-mediated antiviral effect against HEV remains unclear. This report demonstrates that ISG15 induced by HEV replication in Huh7-S10-3 human liver cells plays an immunomodulatory role by negatively regulating type I IFN signaling and, thus, HEV sensitivity to type I IFN. Our results also show that PKR and OAS1 play important roles in the ISG15-mediated type I IFN sensitivity of HEV.

Roles of Interferons in Pregnant Women with Dengue Infection: Protective or Dangerous Factors

Dengue infection is a serious public health problem in tropical and subtropical areas. With the recent outbreaks of Zika disease and its reported correlation with microcephaly, the large number of pregnancies with dengue infection has become a serious concern. This review describes the epidemiological characteristics of pregnancy with dengue and the initial immune response to dengue infection, especially in IFNs production in this group of patients. Dengue is much more prevalent in pregnant women compared with other populations. The severity of dengue is correlated with the level of IFNs, while the serum IFN level must be sufficiently high to maintain the pregnancy and to inhibit virus replication.

RIG-I is a key antiviral interferon-stimulated gene against hepatitis E virus regardless of interferon production

Interferons (IFNs) are broad antiviral cytokines that exert their function by inducing the transcription of hundreds of IFN-stimulated genes (ISGs). However, little is known about the antiviral potential of these cellular effectors on hepatitis E virus (HEV) infection, the leading cause of acute hepatitis globally. In this study, we profiled the antiviral potential of a panel of important human ISGs on HEV replication in cell culture models by overexpression of an individual ISG. The mechanism of action of the key anti-HEV ISG was further studied. We identified retinoic acid-inducible gene I (RIG-I), melanoma differentiation-associated protein 5, and IFN regulatory factor 1 (IRF1) as the key anti-HEV ISGs. We found that basal expression of RIG-I restricts HEV infection. Pharmacological activation of the RIG-I pathway by its natural ligand 5'-triphosphate RNA potently inhibits HEV replication. Overexpression of RIG-I activates the transcription of a wide range of ISGs. RIG-I also mediates but does not overlap with IFN-α-initiated ISG transcription. Although it is classically recognized that RIG-I exerts antiviral activity through the induction of IFN production by IRF3 and IRF7, we reveal an IFN-independent antiviral mechanism of RIG-I in combating HEV infection. We found that activation of RIG-I stimulates an antiviral response independent of IRF3 and IRF7 and regardless of IFN production. However, it is partially through activation of the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) cascade of IFN signaling. RIG-I activated two distinct categories of ISGs, one JAK-STAT-dependent and the other JAK-STAT-independent, which coordinately contribute to the anti-HEV activity.

CONCLUSION

We identified RIG-I as an important anti-HEV ISG that can be pharmacologically activated; activation of RIG-I stimulates the cellular innate immunity against HEV regardless of IFN production but partially through the JAK-STAT cascade of IFN signaling. (Hepatology 2017;65:1823-1839).