Antiviral Action Of Interferon Research Articles

RNA helicase SKIV2L limits antiviral defense and autoinflammation elicited by the OAS-RNase L pathway.

The OAS-RNase L pathway is one of the oldest innate RNA sensing pathways that leads to interferon (IFN) signaling and cell death. OAS recognizes viral RNA and then activates RNase L, which subsequently cleaves both cellular and viral RNA, creating "processed RNA" as an endogenous ligand that further triggers RIG-I-like receptor signaling. However, the IFN response and antiviral activity of the OAS-RNase L pathway are weak compared to other RNA-sensing pathways. Here, we discover that the SKIV2L RNA exosome limits the antiviral capacity of the OAS-RNase L pathway. SKIV2L-deficient cells exhibit remarkably increased interferon responses to RNase L-processed RNA, resulting in heightened antiviral activity. The helicase activity of SKIV2L is indispensable for this function, acting downstream of RNase L. SKIV2L depletion increases the antiviral capacity of OAS-RNase L against RNA virus infection. Furthermore, SKIV2L loss exacerbates autoinflammation caused by human OAS1 gain-of-function mutations. Taken together, our results identify SKIV2L as a critical barrier to OAS-RNase L-mediated antiviral immunity that could be therapeutically targeted to enhance the activity of a basic antiviral pathway.

Black carp RIOK3 suppresses MDA5-mediated IFN signaling in the antiviral innate immunity

In mammals, right open reading frame kinase 3 (RIOK3) is related with cancer development and immune regulation. To explore the role of teleost RIOK3 in the antiviral innate immunity, the homolog of RIOK3 (bcRIOK3) from black carp (Mylopharyngodon piceus) has been cloned and characterized in this study. Sequence analysis revealed that bcRIOK3 is conserved in vertebrates. The transcription of bcRIOK3 varied in host cells in response to the stimulation of spring viremia of carp virus (SVCV), poly (I:C), and LPS. Immunoblotting (IB) and immunofluorescence (IF) assays identified bcRIOK3 as a cytoplasmic protein with a molecular weight of ∼60 kDa. It was interesting that bcRIOK3 knockdown led to the decreased basal mRNA levels of IFNa, IFNb and Viperin; however, triggered obviously higher mRNA levels of the above genes after viral infection and enhanced host resistance to SVCV. Like its mammalian counterpart, bcRIOK3 overexpression in EPC cells showed a significant inhibitory effect on black carp MDA5 (bcMDA5)-mediated transcription of interferon promoters and antiviral activity. Co-immunoprecipitation and immunofluorescent assays identified the association between bcRIOK3 and bcMDA5. Further analysis revealed that bcRIOK3 enhanced the K48-linked ubiquitination and proteasome-dependent degradation of bcMDA5, and it weakened the oligomerization of bcMDA5 under poly (I:C) stimulation. In summary, our data conclude that RIOK3 dampens MDA5-mediated IFN signaling by promoting its degradation in black carp, which provide new insights into the regulation of IFN signaling in teleost.

Helicase-independent function of RIG-I against murine gammaherpesvirus 68 via blocking the nuclear translocation of viral proteins

Innate immunity is the first line of defense against viral pathogens. Retinoic Acid-Inducible Gene 1 (RIG-I) is a pattern recognition receptor that recognizes virus-associated double-stranded RNA and initiates the interferon responses. Besides signal transduction, RIG-I exerts direct antiviral functions to displace viral proteins on dsRNA via its Helicase activity. Nevertheless, this effector-like activity of RIG-I against herpesviruses remains largely unexplored. It has been previously reported that herpesviruses deamidate RIG-I, resulting in the abolishment of its Helicase activity and signal transduction. In this study, we discovered that RIG-I possessed signaling-independent antiviral activities against murine gamma herpesviruses 68 (γHV68, murid herpesvirus 4). Importantly, a Helicase-dead mutant of RIG-I (K270A) demonstrated comparable inhibition on herpesviruses lytic replication, indicating that this antiviral activity is Helicase-independent. Mechanistically, RIG-I bound the Replication and Transcription Activator (RTA) and diminished its nuclear localization to repress viral transcription. We further demonstrated that RIG-I blocked the nuclear translocation of ORF21 (Thymidine Kinase), ORF75c (vGAT), both of which form a nuclear complex with RTA and RNA polymerase II (Pol II) to facilitate viral transcription. Moreover, RIG-I retained ORF59 (DNA processivity factor) in the cytoplasm to repress viral DNA replication. Altogether, we illuminated a previously unidentified, Helicase-independent effector-like function of RIG-I against γHV68, representing an exquisite host strategy to counteract viral manipulations on innate immune signaling. ImportanceRetinoic acid-inducible gene I (RIG-I), a member of DExD/H box RNA helicase family, functions as a key pattern recognition receptor (PRR) responsible for the detection of intracellular double-stranded RNA (dsRNA) from virus-infected cells and induction of type I interferon (IFN) responses. Nevertheless, our understanding of the helicase-independent effector-like activity of RIG-I against virus infection, especially herpesvirus infection, remains largely unknown. Herein, by deploying murine gamma herpesviruses 68 (γHV68) as a model system, we demonstrated that RIG-I possessed an interferon and helicase-independent antiviral activity against γHV68 via blocking the nuclear trafficking of viral proteins, which concomitantly repressed the viral early transcription and genome replication thereof. Our work illuminates a previously unidentified antiviral strategy of RIG-I against herpesvirus infection.

Influenza A virus inhibits TET2 expression by endoribonuclease PA-X to attenuate type I interferon signaling and promote viral replication.

Influenza A virus (IAV) expresses several accessory proteins to limit host anti-viral restriction factors to facilitate viral replication. The Ten-Eleven Translocation 2 (TET2) is a methylcytosine dioxygenase that promotes DNA demethylation by catalyzing the oxidation of 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), which plays a vital role in hematopoiesis and immunity. Here we report that TET2 is a host restriction factor that limits IAV replication. But IAV endoribonuclease PA-X is able to remove the replication restriction by binding to TET2 mRNA and driving TET2 mRNA degradation to reduce TET2 expression during infection. Genetic inactivation of TET2 markedly enhances IAV replication in vitro and in vivo. Mechanistically, we found that TET2 regulates demethylation and transcription of STAT1 and some interferon-stimulated genes (ISGs), including ISG15, ISG20, and IFIT5, so the loss of TET2 greatly impairs type I Interferon signaling. Furthermore, we confirmed that TET2-mediated demethylation of the STAT1 gene is critical for interferon anti-viral activity. Our study demonstrates that the host TET2 is essential to the innate immune response against IAV infection.

COVID-19 and thyroid function: What do we know so far?

Coronavirus disease 2019 (COVID-19) was characterized as a pandemic in March, 2020 by the World Health Organization. COVID-19 is a respiratory syndrome that can progress to acute respiratory distress syndrome, multiorgan dysfunction, and eventually death. Despite being considered a respiratory disease, it is known that other organs and systems can be affected in COVID-19, including the thyroid gland. Thyroid gland, as well as hypothalamus and pituitary, which regulate the functioning of most endocrine glands, express angiotensin-converting enzyme 2 (ACE2), the main protein that functions as a receptor to which SARS-CoV-2 binds to enter host cells. In addition, thyroid gland is extremely sensitive to changes in body homeostasis and metabolism. Immune system cells are targets for thyroid hormones and T3 and T4 modulate specific immune responses, including cell-mediated immunity, natural killer cell activity, the antiviral action of interferon (IFN) and proliferation of T- and B-lymphocytes. However, studies show that patients with controlled hypothyroidism and hyperthyroidism do not have a higher prevalence of COVID-19, nor do they have a worse prognosis when infected with the virus. On the other hand, retrospective observational studies, prospective studies, and case reports published in the last two years reported abnormal thyroid function related to acute SARS-CoV-2 infection or even several weeks after its resolution. Indeed, a variety of thyroid disorders have been documented in COVID-19 patients, including non-thyroidal illness syndrome (NTIS), subacute thyroiditis and thyrotoxicosis. In addition, thyroid disease has already been reported as a consequence of the administration of vaccines against SARS-CoV-2. Overall, the data revealed that abnormal thyroid function may occur during and in the convalescence post-COVID condition phase. Although the cellular and molecular mechanisms are not completely understood, the evidence suggests that the "cytokine storm" is an important mediator in this context. Thus, future studies are needed to better investigate the pathophysiology of thyroid dysfunction induced by COVID-19 at both molecular and clinical levels.

SARS-CoV-2 ORF3a inhibits cGAS-STING-mediated autophagy flux and antiviral function.

Recognizing aberrant cytoplasmic dsDNA and stimulating cGAS‐STING‐mediated innate immunity are essential for the host defense against viruses. Recent studies have reported that SARS‐CoV‐2 infection, responsible for the COVID‐19 pandemic, triggers cGAS‐STING activation. cGAS‐STING activation can trigger IRF3‐type I interferon (IFN) and autophagy‐mediated antiviral activity. Although viral evasion of STING‐triggered IFN‐mediated antiviral function has been well studied, studies concerning viral evasion of STING‐triggered autophagy‐mediated antiviral function are scarce. In the present study, we have discovered that SARS‐CoV‐2 ORF3a is a unique viral protein that can interact with STING and disrupt the STING‐LC3 interaction, thus blocking cGAS‐STING‐induced autophagy but not IRF3‐type I IFN induction. This novel function of ORF3a, distinct from targeting autophagosome‐lysosome fusion, is a selective inhibition of STING‐triggered autophagy to facilitate viral replication. We have also found that activation of bat STING can induce autophagy and antiviral activity despite its defect in IFN induction. Furthermore, ORF3a from bat coronaviruses can block bat STING‐triggered autophagy and antiviral function. Interestingly, the ability to inhibit STING‐induced autophagy appears to be an acquired function of SARS‐CoV‐2 ORF3a, since SARS‐CoV ORF3a lacks this function. Taken together, these discoveries identify ORF3a as a potential target for intervention against COVID‐19.This article is protected by copyright. All rights reserved.

An Integrated View of Deubiquitinating Enzymes Involved in Type I Interferon Signaling, Host Defense and Antiviral Activities.

Viral infectious diseases pose a great challenge to human health around the world. Type I interferons (IFN-Is) function as the first line of host defense and thus play critical roles during virus infection by mediating the transcriptional induction of hundreds of genes. Nevertheless, overactive cytokine immune responses also cause autoimmune diseases, and thus, tight regulation of the innate immune response is needed to achieve viral clearance without causing excessive immune responses. Emerging studies have recently uncovered that the ubiquitin system, particularly deubiquitinating enzymes (DUBs), plays a critical role in regulating innate immune responses. In this review, we highlight recent advances on the diverse mechanisms of human DUBs implicated in IFN-I signaling. These DUBs function dynamically to calibrate host defenses against various virus infections by targeting hub proteins in the IFN-I signaling transduction pathway. We also present a future perspective on the roles of DUB-substrate interaction networks in innate antiviral activities, discuss the promises and challenges of DUB-based drug development, and identify the open questions that remain to be clarified. Our review provides a comprehensive description of DUBs, particularly their differential mechanisms that have evolved in the host to regulate IFN-I-signaling-mediated antiviral responses.

Baseline pro-inflammatory gene expression in whole blood is related to adverse long-term outcomes after transcatheter aortic valve replacement: a case control study

BackgroundAge-associated inflammation and immune system dysfunction have been implicated as mechanisms that increase risk for adverse long-term procedural outcomes in older adults. The purpose of this study was to investigate relationships between baseline inflammatory and innate antiviral gene expression and outcomes after transcatheter aortic valve replacement (TAVR) in older adults with severe aortic stenosis.MethodsWe performed a retrospective case–control study comparing pre-procedural pro-inflammatory and Type 1 interferon (IFN) gene expression in 48 controls with favorable outcomes (alive 1 year after TAVR with improved quality of life [QoL]) versus 48 individuals with unfavorable outcomes (dead by 1 year or alive at 1 year but with reduced QoL). Gene expression was evaluated in whole blood via (1) pre-defined composite scores of 19 inflammation-associated genes and 34 Type I IFN response genes, and (2) pro-inflammatory and antiviral transcription factor activity inferred from promotor based bioinformatics analyses of genes showing > 25% difference in average expression levels across groups. All analyses were adjusted for age, gender, body mass index, diabetes, immunosuppression, cardiovascular disease (CVD), and frailty.ResultsRelative to controls, those with unfavorable outcomes demonstrated higher expression of the pro-inflammatory gene composite prior to TAVR (p < 0.01) and bioinformatic indicators of elevated Nuclear Factor kB (p < 0.001) and Activator Protein 1 (p < 0.001) transcription factor activity, but no significant differences in Type I IFN-related gene expression.ConclusionsThese results demonstrate that a pro-inflammatory state prior to TAVR, independent of CVD severity and frailty status, is associated with worse long-term procedural outcomes.

Black carp TUFM collaborates with NLRX1 to inhibit MAVS-mediated antiviral signaling pathway

TUFM is a mitochondrial protein and serves as a regulator of antiviral signaling; nevertheless, the character of TUFM in teleosts remains unidentified. In this study, TUFM homologue of black carp (Mylopharyngodon piceus) has been characterized and its role in innate immunity has been explored. Black carp TUFM (bcTUFM) comprises 447 amino acids and shows the high similarity to human TUFM. bcTUFM was about 50 kDa in the Western blot assay and was determined as a cytosolic protein by immunofluorescent microscopy. Knockdown of bcTUFM by shRNA enhanced the antiviral ability of the host cells. The induction fold of interferon promoter transcription in the cells co-expressing bcTUFM and bcMAVS was much lower than that of the cells expressing bcMAVS alone. Our previous study has identified that bcNLRX1 interacted with bcMAVS and functioned as an inhibitor of bcMAVS. The interaction between bcTUFM and bcNLRX1, but not bcTUFM and bcMAVS, was detected through co-immunoprecipitation. The subsequent reporter assay and plaque assay demonstrated that the inhibition of bcMAVS-mediated interferon production and antiviral activity by bcNLRX1 was enhanced by co-expressed bcTUFM. Thus, our data suggests that bcTUFM cooperates with bcNLRX1 to inhibit bcMAVS-mediated antiviral signaling during host antiviral innate immune response against SVCV.

TRIF-mediated antiviral signaling is differentially regulated by TRAF2 and TRAF6 in black carp

TRIF is an antiviral adaptor downstream of Toll-like receptors, the roles of teleost TRIF and their regulation remain largely unknown. In this study, a TRIF homologue (bcTRIF) of black carp (Mylopharyngodon piceus) has been cloned, and the transcription of bcTRIF in vivo and ex vivo increased in response to different stimuli. Overexpressed bcTRIF induced the transcription of interferon promoter in the EPC cells and enhanced protection of cells against infection of spring viremia of carp virus (SVCV). The previous study has identified that black carp TRAF2 (bcTRAF2) and TRAF6 (bcTRAF6) functioned positively in RIG-I/MAVS signaling. When co-expressed with bcTRAF2, bcTRIF-induced the transcription of interferon promoter in EPC cells was decreased, and the antiviral activity of bcTRIF was dampened accordingly. On the contrary, co-expressed bcTRAF6 enhanced both bcTRIF-mediated interferon promoter transcription and antiviral activity. The subsequent co-immunoprecipitation identified the interaction between bcTRAF2/6 and bcTRIF. Thus, bcTRIF-mediated antiviral signaling is up-regulated by bcTRAF6 and down-regulated by bcTRAF2.

Hyperlipidemia management during the COVID-19 pandemic: PCSK9 inhibitors to enhance the antiviral action of interferon.

Hyperlipidemia management during the COVID-19 pandemic: PCSK9 inhibitors to enhance the antiviral action of interferon.

Comparative evaluation of mono- and polyclonal antibodies used in identification of interferon alpha-2b products

Quality control of recombinant interferon (rIFN) products with the help of modern analytical methods, including those used for identification, is becoming increasingly relevant nowadays. Identification is especially challenging in the case of Russian rIFN products that contain not only interferon (IFN) alpha-2b, but also other active ingredients and excipients that hinder the use of physical and chemical methods. Manufacturers of such products use IFN neutralization assay with mono- and/or polyclonal antibodies for identification. The aim of the study was to assess the feasibility of using different types of antibodies in the identification test based on neutralization of IFN antiviral activity in IFN alpha-2b products containing other active ingredients and excipients in addition to IFN. Materials and methods: the following materials were used in the study: MDBK cells, vesicular stomatitis virus, samples of IFN alpha-2b products with different composition and by different manufacturers, mono- and polyclonal antibodies by different manufacturers. Identification of rINFs was carried out by a biological method based on neutralization by specific antibodies of IFN ability to suppress the cytopathic effect of the indicator virus in a cell culture using a reference standard for comparison. Results: both polyclonal and monoclonal antibodies were shown to neutralize the activity of the tested IFN alpha-2b substances. Polyclonal antibodies interact with all products containing the same active ingredients, irrespective of their composition. Monoclonal antibodies interact selectively with some products. Conclusions: polyclonal antibodies can be used for identification of any product containing IFN alpha-2b. The use of monoclonal antibodies for this purpose is limited and depends on the composition of the product.

Antagonism of Type I Interferon by Severe Acute Respiratory Syndrome Coronavirus 2.

The coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), warranting urgent study of the molecular mechanisms of SARS-CoV-2 infection and host immune response. Type I interferon (IFN-I) is a key component of host innate immune system responsible for eliminating the virus at the early stage of infection. In contrast, SARS-CoV-2 has evolved multiple strategies to evade innate immune response to facilitate viral replication, transmission, and pathogenesis. This review summarizes the recent progresses on SARS-CoV-2 proteins that antagonize host IFN-I production and/or signaling. These progresses have provided knowledge for new vaccine and antiviral development to prevent and control COVID-19.

Efficiency of potato and garlic virus control by interferon use

Efficiency of potato and garlic virus control by interferon use

Aspects of a Methodological Approach to Determination of Interferon Alpha Specific Activity

Specific antiviral activity is one of the key indicators characterising pharmaceutical quality and pharmacological efficacy of interferon alpha products (IFN-α). Specific activity is determined using a bioassay measuring antiviral activity in cell culture. The aim of the study was to select the most appropriate conditions for in vitro determination of IFN-α product specific activity. Materials and methods: Vero, MDBK, Hep-2, and A-549 homologous and heterologous cell cultures, as well as vesicular stomatitis Indiana virus (VSV) and murine encephalomyocarditis (EMC) virus at a dose of 100 TCD50 /0.1 mL were used for determination of specific antiviral activity. The international reference standard of recombinant interferon alpha-2b activity (Interferon alpha 2b, human, rDNA, E. coli-derived, 2nd WHO International Standard, 1999, NIBSC Code No. 95/566) and human recombinant interferon alpha 2b in the form of solution (batch No. 040214, Pharmapark LLC, Russia) were used as IFN-α samples. Results: the analysis of the obtained data helped to determine: the combinations of cell lines and the indicator virus most sensitive to IFN-α; the optimal concentration of fetal serum in the medium, and the optimal time parameters; the preferred method of reporting test results. Conclusions: the following test conditions were found to be optimal: the MDBK/VSV and Hep-2/EMC combinations proved to be the most sensitive to IFN-α; the optimal period of interferon and cell culture incubation—24 hours; the optimal concentration of fetal bovine serum in the culture medium used for diluting interferon products—2–5%. The instrumental procedure is preferred for reporting the results of interferon antiviral activity determination, because it is up-to-date, reliable, accurate and time-efficient.

Additive Effects of Zinc Chloride on the Suppression of Hepatitis A Virus Replication by Interferon in Human Hepatoma Huh7 Cells.

Hepatitis A virus (HAV) infection is still one of the serious health problems worldwide, despite the existence of effective vaccines for HAV. Zinc compounds have antiviral activities against various DNA and RNA viruses. Therefore, we investigated the effects of zinc compounds on the antiviral activity of interferon against HAV. The effects of zinc compounds with or without interferon on HAV genotype IIIA HA11-1299 replication were examined in human hepatoma Huh7 cells. Cell viability was examined by the MTS assay. Inflammasome associated gene expression was examined by real-time reverse transcription-polymerase chain reaction. Both zinc sulfate and zinc chloride had an inhibitory effect on HAV replication. Zinc sulfate tended to enhance while zinc chloride significantly enhanced the anti-HAV effect induced by interferon-alpha-2a. Zinc chloride significantly up-regulated mitogen-activated protein kinase 12 (MAPK12) and down-regulated 6 related genes [baculoviral IAP repeat containing 3 (BIRC3), interleukin 1 beta (IL1B), proline-serine-threonine phosphatase interacting protein 1 (PSTPIP1), prostaglandin-endoperoxide synthase 2 (PTGS2), PYD and CARD domain containing (PYCARD), and tumor necrosis factor (TNF)]. Zinc chloride inhibits HAV replication and has additive effects on the anti-HAV activities of interferon.

Transcriptional response of USP18 predicts treatment outcomes of interferon-alpha in HBeAg-positive chronic hepatitis B patientsefere.

Ubiquitin-specific protease 18 (USP18) is an important inhibitor of interferon (IFN) antiviral activity, and the aim of this study was to investigate the association between the USP18 mRNA level change in peripheral blood mononuclear cells (PBMCs) when stimulated with IFN in vitro before initiating treatment and the treatment outcomes in HBeAg-positive chronic hepatitis B (CHB) patients treated with IFN. A total of 44 patients who received standard IFN-based anti-HBV therapy and follow-up were enrolled in the study. The in vitro IFN-induced USP18 mRNA change (USP18IFN-N ) was measured via comparison of quantitative PCR-determined USP18 transcription levels of BPMCs cultured with and without IFN stimulation. Either for virological (VR) or serological response (SR), the baseline USP18IFN-N was significantly higher (P=0.018 for VR, P=0.008 for SR) among nonresponders (n=23 for VR, n=33 for SR) than that of responders (n=21 for VR, n=11 for SR). Multivariate analyses revealed baseline USP18IFN-N was a novel independent predictor for either VR (OR=0.292, 95% CI=0.102-0.835, P=0.022) or SR (OR=0.173, 95% CI=0.035-0.849, P=0.031) in our cohort. In addition, baseline USP18IFN-N in combination with HBV DNA loads or HBeAg levels showed improved accuracy of pretreatment prediction for VR or SR responders, respectively. Baseline USP18IFN-N levels are associated with both virological and serological response, and have the potential to become a clinical predictor for treatment outcomes in HBeAg-positive CHB patients before initiating IFN-α therapy.

Anti-H7N9 avian influenza A virus activity of interferon in pseudostratified human airway epithelium cell cultures

BackgroundSince H7N9 influenza A virus (H7N9) was first reported in 2013, five waves of outbreaks have occurred, posing a huge threat to human health. In preparation for a potential H7N9 epidemic, it is essential to evaluate the efficacy of anti-H7N9 drugs with an appropriate model.MethodsWell-differentiated pseudostratified human airway epithelium (HAE) cells were grown at the air–liquid interface, and the H7N9 cell tropism and cytopathic effect were detected by immunostaining and hematoxylin-eosin (HE) staining. The H7N9 replication kinetics and anti-H7N9 effect of recombinant human α2b (rhIFN-α2b) and rhIFN-λ1 were compared with different cell lines. The H7N9 viral load and interferon-stimulated gene (ISG) expression were quantified by real-time PCR assays.ResultsH7N9 could infect both ciliated and non-ciliated cells within the three-dimensional (3D) HAE cell culture, which reduced the number of cilia and damaged the airways. The H7N9 replication kinetics differed between traditional cells and 3D HAE cells. Interferon had antiviral activity against H7N9 and alleviated epithelial cell lesions; the antiviral activity of rhIFN-α2b was slightly better than that of rhIFN-λ1. In normal cells, rhIFN-α2b induced a greater amount of ISG expression (MX1, OAS1, IFITM3, and ISG15) compared with rhIFN-λ1, but in 3D HAE cells, this trend was reversed.ConclusionsBoth rhIFN-α2b and rhIFN-λ1 had antiviral activity against H7N9, and this protection was related to the induction of ISGs. The 3D cell culture model is suitable for evaluating interferon antiviral activity because it can demonstrate realistic in vivo-like effects.

Crosstalk Between Mammalian Antiviral Pathways.

As part of their innate immune response against viral infections, mammals activate the expression of type I interferons to prevent viral replication and dissemination. An antiviral RNAi-based response can be also activated in mammals, suggesting that several mechanisms can co-occur in the same cell and that these pathways must interact to enable the best antiviral response. Here, we will review how the classical type I interferon response and the recently described antiviral RNAi pathways interact in mammalian cells. Specifically, we will uncover how the small RNA biogenesis pathway, composed by the nucleases Drosha and Dicer can act as direct antiviral factors, and how the type-I interferon response regulates the function of these. We will also describe how the factors involved in small RNA biogenesis and specific small RNAs impact the activation of the type I interferon response and antiviral activity. With this, we aim to expose the complex and intricate network of interactions between the different antiviral pathways in mammals.

LY6E mediates an evolutionarily conserved enhancement of virus infection by targeting a late entry step

Interferons (IFNs) contribute to cell-intrinsic antiviral immunity by inducing hundreds of interferon-stimulated genes (ISGs). In a screen to identify antiviral ISGs, we unexpectedly found that LY6E, a member of the LY6/uPAR family, enhanced viral infection. Here, we show that viral enhancement by ectopically expressed LY6E extends to several cellular backgrounds and affects multiple RNA viruses. LY6E does not impair IFN antiviral activity or signaling, but rather promotes viral entry. Using influenza A virus as a model, we narrow the enhancing effect of LY6E to uncoating after endosomal escape. Diverse mammalian orthologs of LY6E also enhance viral infectivity, indicating evolutionary conservation of function. By structure-function analyses, we identify a single amino acid in a predicted loop region that is essential for viral enhancement. Our study suggests that LY6E belongs to a class of IFN-inducible host factors that enhance viral infectivity without suppressing IFN antiviral activity.