Antiviral Immune Mechanisms Research Articles

Temperature-specific vsiRNA confers RNAi-mediated viral resistance at elevated temperature in Capsicum annuum.

Resistance (R) gene-mediated resistance is a robust and efficient antiviral immune system in the plants. Thus, when R-mediated resistance was suppressed at elevated temperatures, resistance towards viruses was expected to be completely collapsed. Nonetheless, the multiplication of Tobacco mosaic virus pathotype P0 (TMV-P0) was inhibited, and TMV-P0 particles were only occasionally present in the systemic leaves of pepper plants (Capsicum annuum). RNAi-mediated RNA silencing is a well-known antiviral immune mechanism. At elevated temperatures, RNAi-mediated antiviral resistance was induced and virus-derived siRNAs (vsiRNAs) were dramatically increased. Through sRNA-sequencing (sRNA-Seq) analysis, we revealed that vsiRNAs derived from TMV-P0 were greatly increased. Intriguingly, virus-infected plants could select the temperature-specific vsiRNAs for antiviral resistance from the amplified vsiRNAs at elevated temperatures. Pre-application of these temperature-specific vsiRNAs endowed antiviral resistance of the plants. Therefore, plants sustain antiviral resistance by activating RNAi-mediated resistance, based on temperature-specific vsiRNAs at elevated temperatures.

Antimicrobial Peptides as Potential Antiviral Factors in Insect Antiviral Immune Response.

Antimicrobial peptides (AMPs) with antiviral activity (antiviral peptides: AVPs) have become a research hotspot and already show immense potential to become pharmaceutically available antiviral drugs. AVPs have exhibited huge potential in inhibiting viruses by targeting various stages of their life cycle. Insects are the most speciose group of animals that inhabit almost all ecosystems and habitats on the land and are a rich source of natural AMPs. However, insect AVP mining, functional research, and drug development are still in their infancy. This review aims to summarize the currently validated insect AVPs, explore potential new insect AVPs and to discuss their possible mechanism of synthesis and action, with a view to providing clues to unravel the mechanisms of insect antiviral immunity and to develop insect AVP-derived antiviral drugs.

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.

Antiviral immune mechanism of Toll-like receptor 4-mediated human alveolar epithelial cells type Ⅱ.

Expression of Toll-like receptor (TLR)4 and its downstream substances, myeloid differentiation factor 88 (MyD88), NF-κB p65, tumor necrosis factor-α (TNF-α) and GR in human alveolar epithelial cells type Ⅱ (AEC Ⅱ) infected with respiratory syncytial virus (RSV) were investigated, and the antiviral immune mechanism mediated by TLR4 was explored. Human AEC Ⅱ were divided into TLR4-/- group, normal group and TLR4+ group, and also into control group, RSV group and RSV+MP (methylprednisolone) group. MTT assay was used to measure the survival of cells after TLR4 knockout and overexpression, and the survival of normal cells after treatment with MP. The concentration of TLR4, MyD88, NF-κB p65, TNF-α, and GR was measured by ELISA after TLR4 knockout and overexpression. Reverse transcription-quantitative PCR (RT-qPCR) was used to measure the mRNA expression of the gene knockout and overexpression groups. RT-qPCR and western blot analysis were used to determine the expression of TLR4, MyD88, NF-κB p65 and GR in RSV and RSV+MP groups. The concentration of the detected substances in the TLR4-/- group was significantly lower than that in the normal group (P<0.01 and <0.001), and in the TLR4+ group was significantly higher than that in the normal group (P<0.05, <0.01 and <0.001); the expression of RSV in the TLR4-/- group was significantly higher than that in the normal group (P<0.001), and in the TLR4+ group was significantly lower than that in the normal group (P<0.05). The expression levels of TLR4, MyD88 and NF-κB p65 in the RSV and RSV+MP groups were significantly higher than those in the control group (P<0.05, <0.01 and <0.001), and the increase presented in the RSV+MP group was significantly lower than that in the RSV group (P<0.05 and <0.01). TLR4-mediated antiviral immunity of human AEC Ⅱ can reduce the levels of TLR4, MyD88, NF-κB p65 and TNF-α and increase the level of GR, participating in the immune defense and reducing the damage of the viral epithelial cells of human type Ⅱ alveoli, thus improving human immunity.

About antiviral effects of vitamin D

Preventing infectious diseases is very important in obstetric and gynaecological practice. Vitamin D is a complex regulator of innate and adaptive immunity. It is known that lack of vitamin D reduces antibacterial and antiviral immunity, stimulates the development of pathologies associated with chronic systemic inflammation. Evidence from evidence-based medicine indicates the importance of using vitamin D preparations to support immunity. The results of fundamental and clinical studies have shown that chronic inflammation and congenital immunity disorders resulting from vitamin D deficiency significantly reduce the body’s resistance not only to tuberculosis, but also to viral hepatitis, acute respiratory infections, papillomavirus and herpesvirus. In addition to a pronounced antibacterial effect, vitamin D is also characterized by its antiviral action. By increasing the expression of interferon-alpha, cathecidine, defensin and antiviral microRNA, vitamin D activates various mechanisms of congenital antiviral immunity. Studies show the need to compensate for vitamin D deficiency for successful therapy of viral hepatitis, respiratory infections, human papillomavirus (HPV) and herpesvirus. In the present article the molecular fundamentals of antiviral action of vitamin D are sequentially considered, as well as the results of fundamental and clinical studies indicating the action of vitamin D against the viruses of hepatitis, herpes, RSV, Epstein-Barr, human papillomavirus, the possibility of using vitamin D in the treatment of these and other viral pathologies is considered. The authors analyzed data on the effect of vitamin D on immunity functions and antiviral protection of the human body.

Thoroughly Remold the Localization and Signaling Pathway of TLR22.

TLR22 exists in nearly all the poikilothermic vertebrates and plays a central role in the initiation of innate immunity and activation of adaptive immunity. TLR22 signaling pathway has been characterized in detail in fugu (Takifugu rubripes). Here, we thoroughly remold the localization and signaling pathways of TLR22. We characterized TLR22a and TLR22b in grass carp (Ctenopharyngodon idella), designated as CiTLR22a and CiTLR22b, and explored the ligand(s), adaptor(s), and signaling pathway(s). Results show that both CiTLR22a and CiTLR22b localize to lysosome, acidic compartment. Correspondingly, CiTLR22a and CiTLR22b directly bind and respond to dsRNA analog poly(I:C) at pH 5, but not at pH 7.4, the physiological pH. Moreover, CiTLR22a and CiTLR22b exhibit antagonistic function in signal transmission, wherein CiTLR22a facilitates the protein and phosphorylation levels of IRF7 and enhances the promoter activities of major IFNs and NF-κBs, while CiTLR22b downregulates IRF7 phosphorylation and IRF3 protein level and suppresses the IFN and NF-κB pathways. Further investigations revealed that CiTLR22a restrains grass carp reovirus (GCRV) replication and protects cells from GCRV infection, whereas CiTLR22b plays a negative role in response to GCRV infection. This is the first time to systematically clarify the signaling pathways of two isotype TLR22s; especially, subcellular localization and adaptor are different from previous TLR22 report, which results from technical limitations. The results will serve the antiviral immune mechanisms in poikilothermic vertebrates and evolutionary immunology.

The activation of antiviral RNA interference not only exists in neural progenitor cells but also in somatic cells in mammals

ABSTRACT The RNA interference (RNAi) pathway directs an important antiviral immunity mechanism in plants and invertebrates. Recently, we and others have demonstrated that the antiviral RNAi response is also conserved in mammals, at least to five distinct RNA viruses, including Zika virus (ZIKV). ZIKV may preferentially infect neuronal progenitor cells (NPCs) in the developing foetal brain. Ex vivo ZIKV infection induces RNAi-mediated antiviral response in human NPCs, but not in the more differentiated NPCs or somatic cells. However, litter is known about the in vivo property or function of the virus-derived small-interfering RNAs (vsiRNAs) targeting ZIKV. Here we report a surprising observation: different from ex vivo observations, viral small RNAs (vsRNAs) targeting ZIKV were produced in vivo upon infection in both central neuron system (CNS) and muscle tissues. In addition, our findings demonstrate the production of canonical vsiRNAs in murine CNS upon antiviral RNAi activation by Sindbis virus (SINV), suggesting the possibility of antiviral immune strategy applied by mammals in the CNS.

Emerging Mechanisms of Insulin-Mediated Antiviral Immunity in Drosophila melanogaster.

Arboviruses (arthropod-borne viruses), such as Zika (ZIKV), West Nile (WNV), and dengue (DENV) virus, include some of the most significant global health risks to human populations. The steady increase in the number of cases is of great concern due to the debilitating diseases associated with each viral infection. Because these viruses all depend on the mosquito as a vector for disease transmission, current research has focused on identifying immune mechanisms used by insects to effectively harbor these viruses and cause disease in humans and other animals. Drosophila melanogaster are a vital model to study arboviral infections and host responses as they are a genetically malleable model organism for experimentation that can complement analysis in the virus' natural vectors. D. melanogaster encode a number of distinct mechanisms of antiviral defense that are found in both mosquito and vertebrate animal systems, providing a viable model for study. These pathways include canonical antiviral modules such as RNA interference (RNAi), JAK/STAT signaling, and the induction of STING-mediated immune responses like autophagy. Insulin signaling plays a significant role in host-pathogen interactions. The exact mechanisms of insulin-mediated immune responses vary with each virus type, but nevertheless ultimately demonstrates that metabolic and immune signaling are coupled for antiviral immunity in an arthropod model. This mini review provides our current understanding of antiviral mechanisms in D. melanogaster, with a focus on insulin-mediated antiviral signaling, and how such immune responses pertain to disease models in vertebrate and mosquito species.

The Activation of Antiviral RNA Interference Not Only Exist in Neural Progenitor Cells But Also in Somatic Cells in Mammals

The RNA interference (RNAi) pathway directs an important antiviral immunity mechanism in plants and invertebrates. Recently, we and others have demonstrated that the induction and suppression of antiviral RNAi response are also conserved in mammals, at least to five distinct RNA viruses, including Zika virus (ZIKV). ZIKV preferentially infects neuronal progenitor cells (NPCs) in the developing fetal brain. Xu et al. have revealed that ex vivo ZIKV infection induces RNAi-mediated antiviral response in human NPCs, but not in the more differentiated NPCs or somatic cells. However, less is known about the in vivo property or function of the virus-derived small-interfering RNAs (vsiRNAs) targeting Zika virus. Here we report a surprising observation: viral small RNAs (vsRNAs) targeting ZIKV were produced in vivo upon infection in both central neuron system (CNS) and muscle tissues. In addition, our findings demonstrate the production of canonical vsiRNAs in murine CNS upon antiviral RNAi activation by Sindbis virus, suggesting the possibility of antiviral immune strategy applied by mammals in the CNS.

Sec62 Suppresses Foot-and-Mouth Disease Virus Proliferation by Promotion of IRE1α-RIG-I Antiviral Signaling.

Foot-and-mouth disease virus (FMDV) is highly infectious and causes a major plague in animal farming. Unfolded protein response is one of the major cellular responses to pathogenic infections, which performs a crucial role in cell survival, apoptosis, and antiviral innate immune response. In this study, we showed that FMDV infection activated two unfolded protein response branches (PERK-eIF2α and ATF6 signaling) in both baby hamster kidney cells (BHK-21) and porcine kidney (PK-15) cells, whereas it suppressed the IRE1α-XBP1 signaling by decreasing IRE1α level. Further study revealed IRE1α signaling as an important antiviral innate immune mechanism against FMDV. Sec62, the transport protein, was greatly decreased at the late stages of FMDV infection. By overexpression and knockdown study, we also found that the expression of Sec62 was positively involved in the levels of IRE1α and RIG-I and subsequent activation of downstream antiviral signaling pathways in FMDV-infected PK-15 cells. Taken together, our study demonstrates that Sec62 is an important antiviral factor that upregulates IRE1α-RIG-I-dependent antiviral innate immune responses, and FMDV evades antiviral host defense mechanism by downregulating Sec62-IRE1α/RIG-I.

Diminished secretion and function of IL-29 is associated with impaired IFN-α response of neonatal plasmacytoid dendritic cells.

Plasmacytoid dendritic cells (pDCs) are key players in the antiviral immune response and type III IFNs such as IL‐29 appear to play a pivotal role in pDC function. Pronounced susceptibility to viral infections in neonates is partly resulting from diminished antiviral immune mechanisms. Accordingly, the aim of the present study was to investigate the impact of IL‐29 in the altered immune response of neonatal pDCs. PBMCs of adult and term newborns were stimulated with CpG‐ODN2216 in the presence or absence of IL‐29 and assessed for IFN‐α production, downstream‐signaling, and activation marker expression. A significantly lower IL‐29 production after TLR9‐specific stimulation was demonstrated in neonatal pDCs. IL‐29 enhanced the IFN‐α production of pDCs in adults compared to newborns. Newborn pDCs displayed a significantly lower surface expression of IL‐10 and IL‐28Rα receptor resulting in diminished STAT1 and IRF7 activation. Interestingly, concomitant stimulation with CpG‐ODN2216/IL‐29 had no impact on the expression of surface activation and maturation markers of pDCs in neither population. The diminished antiviral immune response of neonatal pDCs is associated with reduced production and cellular responses toward IL‐29. Potential therapeutic agents enhancing the IL‐29 response in neonatal pDCs possibly augment viral protection in newborns.

Grass carp STK38 regulates IFN I expression by decreasing the phosphorylation level of GSK3β

As a member of NDR protein kinase family and a novel protein kinase of Hippo signal pathway, Serine/threonine kinase 38 (STK38) plays a very significant role in the innate immune. In mammals, STK38 performs its function by combining with GSK3β. Nowadays, there are few reports of STK38 in fish. In order to explain the function of fish STK38 in the innate immunity, we cloned the ORF of grass carp (Ctenopharyngodon idella) STK38 (CiSTK38) and the related kinase GSK3β (CiGSK3β). Phylogenetic trees revealed that CiSTK38 and CiGSK3β evolved closer kinship with sinocyclocheilus grahami STK38 and siniperca chuatsi GSK3β respectively. CiSTK38 and CiGSK3β can respond to the intradermal injection of poly (I:C) in grass carp different tissues and the transfection of poly I:C in CIK cells. Subcellular localization revealed the CiGSK3β were broadly distributed through the cytoplasm, whereas CiSTK38 were observed both in cytoplasm and nucleus. However, when they were co-transferred into cells, the two proteins were found to aggregate in the nucleus. GST-pulldown and co-immunoprecipitation analysis revealed that CiSTK38 can physically interact with CiGSK3β. Phos-tag PAGE illustrated CiSTK38 can decrease the phosphorylation and auto-phosphorylation level of CiGSK3β at Ser9 and at Tyr216. To investigate the functional correlation between CiSTK38 and CiGSK3β, we overexpressed CiSTK38 and CiGSK3β in CIK cells and found that they can up-regulate the expression of IFN I. In short, we demonstrated that CiSTK38 can confer CiGSK3β kinase activity by reducing its phosphorylation level. Result from this study strongly suggested that the anti-viral immune effects elicited by poly (I:C) in part were mediated through activation of CiGSK3β. The findings provided scientific basis for the anti-viral immune mechanism of STK38 and GSK3β in fish.

Antiviral ARGONAUTEs Against Turnip Crinkle Virus Revealed by Image-Based Trait Analysis.

RNA-based silencing functions as an important antiviral immunity mechanism in plants. Plant viruses evolved to encode viral suppressors of RNA silencing (VSRs) that interfere with the function of key components in the silencing pathway. As effectors in the RNA silencing pathway, ARGONAUTE (AGO) proteins are targeted by some VSRs, such as that encoded by Turnip crinkle virus (TCV). A VSR-deficient TCV mutant was used to identify AGO proteins with antiviral activities during infection. A quantitative phenotyping protocol using an image-based color trait analysis pipeline on the PlantCV platform, with temporal red, green, and blue imaging and a computational segmentation algorithm, was used to measure plant disease after TCV inoculation. This process captured and analyzed growth and leaf color of Arabidopsis (Arabidopsis thaliana) plants in response to virus infection over time. By combining this quantitative phenotypic data with molecular assays to detect local and systemic virus accumulation, AGO2, AGO3, and AGO7 were shown to play antiviral roles during TCV infection. In leaves, AGO2 and AGO7 functioned as prominent nonadditive, anti-TCV effectors, whereas AGO3 played a minor role. Other AGOs were required to protect inflorescence tissues against TCV. Overall, these results indicate that distinct AGO proteins have specialized, modular roles in antiviral defense across different tissues, and demonstrate the effectiveness of image-based phenotyping to quantify disease progression.

TANK-binding kinase 1 as a novel therapeutic target for viral diseases

ABSTRACTIntroduction: TANK-binding kinase 1 (TBK1) is vital for the induction of antiviral innate immune responses. Both RNA and DNA viral infection induces TBK1 activation, triggers phosphorylation of interferon regulatory factor (IRF) 3 and subsequent expression of type I interferons (IFNs; IFN-α/β). Type I IFNs can induce the expression of numerous antiviral genes called interferon-stimulated genes (ISGs) to build a remarkable antiviral state and limit viral replication. Thus, optimal TBK1 activity is crucial for IRF3-induced type I IFNs expression and ISGs-mediated viral elimination.Areas covered: This review provides an overview of the diverse roles of TBK1 in antiviral innate immune responses, the regulatory mechanisms of TBK1 activity and the implication in antiviral development.Expert opinion: TBK1 is a key kinase against antiviral infection via inducing type I IFNs expression. Multiple types of post-translational modifications of TBK1 tightly regulate TBK1 activity and subsequent TBK1-dependent antiviral responses. The identified regulators of TBK1 unveil regulatory mechanisms of host antiviral innate immunity and immuno-escape mechanism of virus provide strategies to control viral diseases by modulating TBK1 activity.

Poly-ADP Ribosyl Polymerase 1 (PARP1) Regulates Influenza A Virus Polymerase.

Influenza A viruses (IAV) are evolutionarily successful pathogens, capable of infecting a number of avian and mammalian species and responsible for pandemic and seasonal epidemic disease in humans. To infect new species, IAV typically must overcome a number of species barriers to entry, replication, and egress, even while virus replication is counteracted by antiviral host factors and innate immune mechanisms. A number of host factors have been found to regulate the replication of IAV by interacting with the viral RNA-dependent RNA polymerase (RdRP). The host factor PARP1, a poly-ADP ribosyl polymerase, was required for optimal functions of human, swine, and avian influenza RdRP in human 293T cells. In IAV infection, PARP1 was required for efficient synthesis of viral nucleoprotein (NP) in human lung A549 cells. Intriguingly, pharmacological inhibition of PARP1 enzymatic activity (PARylation) by 4-amino-1,8-naphthalimide led to a 4-fold increase in RdRP activity, and a 2.3-fold increase in virus titer. Exogenous expression of the natural PARylation inhibitor PARG also enhanced RdRP activity. These data suggest a virus-host interaction dynamic where PARP1 protein itself is required, but cellular PARylation has a distinct suppressive modality, on influenza A viral polymerase activity in human cells.

Zika virus infection induces RNAi-mediated antiviral immunity in human neural progenitors and brain organoids.

The re-emergence of Zika virus (ZIKV) in the Western Hemisphere has resulted in global public health crisis since 2015. ZIKV preferentially infects and targets human neural progenitor cells (hNPCs) and causes fetal microcephaly upon maternal infection. hNPCs not only play critical roles during fetal brain development, but also persist in adult brain throughout life. Yet the mechanism of innate antiviral immunity in hNPCs remains largely unknown. Here, we show that ZIKV infection triggers the abundant production of virus-derived small interfering RNAs in hNPCs, but not in the more differentiated progenies or somatic cells. Ablation of key RNAi machinery components significantly enhances ZIKV replication in hNPCs. Furthermore, enoxacin, a broad-spectrum antibiotic that is known as an RNAi enhancer, exerts potent anti-ZIKV activity in hNPCs and other RNAi-competent cells. Strikingly, enoxacin treatment completely prevents ZIKV infection and circumvents ZIKV-induced microcephalic phenotypes in brain organoid models that recapitulate human fetal brain development. Our findings highlight the physiological importance of RNAi-mediated antiviral immunity during the early stage of human brain development, uncovering a novel strategy to combat human congenital viral infections through enhancing RNAi.

Preclinical Characterization of AFM26, a Novel B Cell Maturation Antigen (BCMA)-Directed Tetravalent Bispecific Antibody for High Affinity Retargeting of NK Cells Against Myeloma

Natural killer (NK) cells are crucial effector cells of the innate immune system capable of rapidly recognizing and eliminating infected, stressed and malignant cells. NK cells are also the prime mediators of antibody-dependent cell-mediated cytotoxicity (ADCC), a potent mechanism of anti-viral immunity that has been applied to cancer therapy by targeting tumor-expressed surface antigens using monoclonal antibodies (mAbs). Classical ADCC is mediated by low affinity Fc-mediated engagement of NK cells via FcγRIIIA (CD16A) and is modulated by differences in target antigen expression levels. While high potency of therapeutic mAbs is achieved when target antigen is available at high density, potency and efficacy decrease substantially when copy numbers are low. Classical ADCC also needs to overcome the inhibitory effect of competing serum IgG and is negatively affected by a low affinity polymorphism of CD16A (158F) that is prevalent in approximately 8 of 10 individuals. Hence, classical Fc-mediated ADCC does not fully utilize the therapeutic potential of NK cell cytotoxicity.B cell maturation antigen (BCMA) has emerged as a promising target for treatment of multiple myeloma (MM) due to its near universal expression on tumor cells and restricted expression in non-malignant tissues. Numerous therapeutic approaches are currently investigated clinically and pre-clinically and target BCMA, however, none of these are aimed at fully utilizing NK cell-mediated ADCC. Low copy numbers of BCMA (approx. 40-15,000) might limit the activity of classical mAbs against BCMA, especially in the presence of high serum concentrations of paraprotein. In addition, NK cells may be ideally suited to target minimal residual disease immediately before or after autologous stem cell transplantation. Consequently, by efficiently redirecting NK cell cytotoxicity to BCMA+ myeloma, AFM26 used alone or in combination with other approaches may provide a novel, optimized treatment strategy.Here we describe development of AFM26, a BCMA and CD16A-directed tetravalent bispecific antibody that selectively engages CD16A+ effector cells, including NK cells, and is designed to overcome the limitations of classical ADCC. AFM26 is based on the recently launched Redirected, Optimized Cell Killing (ROCK) antibody platform and combines high affinity CD16A-directed effector cell engagement with IgG-like pharmacokinetics and manufacturability. We demonstrate that AFM26 interacts with NK cells with high avidity independently of CD16A polymorphism and in presence of competing IgG. NK cell-mediated lysis of BCMA+ target cell lines induced by AFM26 is largely independent of BCMA expression levels with high potency and efficacy observed at low copy numbers (<200), as confirmed by autologous lysis of primary MM cells in vitro. Despite more potent and efficacious in vitro lysis, release of inflammatory cytokines is comparable with classical antibody formats. We further demonstrate anti-tumor activity of AFM26 in combination with adoptive transfer of primary human NK cells in vivo using human IL-15-transgenic NOG mice.AFM26 therefore is a promising agent currently in preclinical development to fully unlock NK cell cytotoxicity for BCMA-directed immunotherapy of MM. DisclosuresRoss:Affimed: Employment. Reusch:Affimed: Employment. Wingert:Affimed: Employment. Haneke:Affimed: Employment. Klausz:Affimed: Research Funding. Otte:Affimed: Research Funding. Schub:Affimed: Research Funding. Knackmuss:Affimed: Employment. Müller:Affimed: Employment. Ellwanger:Affimed: Employment. Fucek:Affimed: Employment. Schniegler-Mattox:Affimed: Employment. Koch:Affimed GmbH: Employment. Valerius:Affimed: Research Funding. Gramatzki:Affimed: Research Funding. Peipp:Affimed: Research Funding. Tesar:Affimed: Employment. Rajkovic:Affimed: Employment. Treder:Affimed GmbH: Employment.

Insights into ZIKV-Mediated Innate Immune Responses in Human Dermal Fibroblasts and Epidermal Keratinocytes

Zika virus (ZIKV) has emerged as a global pathogen causing significant public health concern. ZIKV infections in humans principally occur via mosquito bites. Thus, host skin cells are permissive to ZIKV infection and are the first line of defense against the virus. Here, we examined the role and mechanisms of antiviral skin immunity against ZIKV infection. ZIKV infection (African lineage MR766) in human dermal fibroblasts, human epidermal keratinocytes, and HaCaT keratinocytes resulted in distinct expression changes in RIG-I-like receptors, such as RIG-I and MDA5. Inhibition of RIG-I using small interfering RNA resulted in increased viral gene expression and reduced induction of IFNs and IFN-stimulated genes. Furthermore, ZIKV NS1 directly interacted with RIG-I or MDA5 and down-regulated RIG-I-like receptor-mediated antiviral signaling pathways. Asian lineage ZIKV (PRVABC59) infection also showed a distinct pattern of antiviral immunity in human skin cells, compared with other ZIKV strains. Additionally, ZIKV infections in human neural progenitor cells induced the robust activation of RIG-I-like receptor-mediated signaling, followed by highly enhanced IFN-stimulated gene expression. Our findings provide important insights into ZIKV tropism and subsequent antiviral signaling pathways that regulate ZIKV replication in human dermal fibroblasts and human epidermal keratinocytes.

Herpes Simplex Virus 1 UL36USP Antagonizes Type I Interferon-Mediated Antiviral Innate Immunity.

Type I interferons (IFNs), as major components of the innate immune system, play a vital role in host resistance to a variety of pathogens. Canonical signaling mediated by type I IFNs activates the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway through binding to the IFN-α/β receptor (IFNAR), resulting in transcription of IFN-stimulated genes (ISGs). However, viruses have evolved multiple strategies to evade this process. Here, we report that herpes simplex virus 1 (HSV-1) ubiquitin-specific protease (UL36USP) abrogates the type I IFN-mediated signaling pathway independent of its deubiquitinase (DUB) activity. In this study, ectopically expressed UL36USP inhibited IFN-β-induced activation of ISRE promoter and transcription of ISGs, and overexpression of UL36USP lacking DUB activity did not influence this effect. Furthermore, UL36USP was demonstrated to antagonize IFN-β-induced activation of JAKs and STATs via specifically binding to the IFNAR2 subunit and blocking the interaction between JAK1 and IFNAR2. More importantly, knockdown of HSV-1 UL36USP restored the formation of JAK1-IFNAR2 complex. These findings underline the roles of UL36USP-IFNAR2 interaction in counteracting the type I IFN-mediated signaling pathway and reveal a novel evasion mechanism of antiviral innate immunity by HSV-1.IMPORTANCE Type I IFNs mediate transcription of numerous antiviral genes, creating a remarkable antiviral state in the host. Viruses have evolved various mechanisms to evade this response. Our results indicated that HSV-1 encodes a ubiquitin-specific protease (UL36USP) as an antagonist to subvert type I IFN-mediated signaling. UL36USP was identified to significantly inhibit IFN-β-induced signaling independent of its deubiquitinase (DUB) activity. The underlying mechanism of UL36USP antagonizing type I IFN-mediated signaling was to specifically bind with IFNAR2 and disassociate JAK1 from IFNAR2. For the first time, we identify UL36USP as a crucial suppressor for HSV-1 to evade type I IFN-mediated signaling. Our findings also provide new insights into the innate immune evasion by HSV-1 and will facilitate our understanding of host-virus interplay.

Establishment of fin cell lines and their use to study the immune gene expression in cyprinid fishes with different ploidy in rhabdovirus infection

Triploid hybrid (3n = 150) of red crucian carp (♀, 2n = 100) and allotetraploid (♂, 4n = 200) display improved disease resistance and stress resistance than their parents. In order to elucidate their innate immune mechanisms, three novel cell lines from the caudal fin of red crucian carp, triploid hybrid and allotetraploid (named 2nFC, 3nFC and 4nFC accordingly) were established and characterized respectively. 2nFC, 3nFC and 4nFC showed fibroblast-like morphology and characteristics. They have been subcultured for more than 100 passages since the initial primary culture. Viral infection experiments showed that 2nFC, 3nFC and 4nFC were susceptible to spring viraemia of carp virus (SVCV) infection. Intriguingly, 3nFC performed the stronger resistance ability against SVCV than 2nFC and 4nFC, which indicated that 2nFC, 3nFC and 4nFC might be used as the suitable in vitro models for exploring and analyzing the differences among these three cyprinid fishes in antiviral innate immune mechanisms. Based on this, we analyzed the transcriptome profile of 2nFC, 3nFC and 4nFC in the context of SVCV infection. The KEGG enrichment analysis showed that the differentially expressed genes (DEGs) were primarily enriched to immune-related signaling pathways. However, some signaling pathways against viral infection were activated remarkably in 2nFC and 3nFC but not in 4nFC. Overall, the establishment of 2nFC, 3nFC and 4nFC provided us a suitable platform to elucidate the innate immunity of fishes with different ploidy and clear genetic relationship.