The double-stranded RNA bluetongue virus induces type I interferon in plasmacytoid dendritic cells via a MYD88-dependent TLR7/8-independent signaling pathway

The role of plasmacytoid dendritic cells (pDCs) in immunity during viral infections and beyond

Type I and III interferons (IFNs) are essential for antiviral immunity and act through two different but complimentary pathways. First, IFNs activate intracellular antimicrobial programs by triggering the upregulation of a broad repertoire of viral restriction factors. Second, IFNs activate innate and adaptive immunity. Dysregulation of IFN production can lead to severe immune system dysfunction. It is thus crucial to identify and characterize the cellular sources of IFNs, their effects, and their regulation to promote their beneficial effects and limit their detrimental effects, which can depend on the nature of the infected or diseased tissues, as we will discuss. Plasmacytoid dendritic cells (pDCs) can produce large amounts of all IFN subtypes during viral infection. pDCs are resistant to infection by many different viruses, thus inhibiting the immune evasion mechanisms of viruses that target IFN production or their downstream responses. Therefore, pDCs are considered essential for the control of viral infections and the establishment of protective immunity. A thorough bibliographical survey showed that, in most viral infections, despite being major IFN producers, pDCs are actually dispensable for host resistance, which is achieved by multiple IFN sources depending on the tissue. Moreover, primary innate and adaptive antiviral immune responses are only transiently affected in the absence of pDCs. More surprisingly, pDCs and their IFNs can be detrimental in some viral infections or autoimmune diseases. This makes the conservation of pDCs during vertebrate evolution an enigma and thus raises outstanding questions about their role not only in viral infections but also in other diseases and under physiological conditions.

Monitoring longitudinal immunological responses to bluetongue virus 17 in experimentally infected sheep

Bluetongue virus (BTV) is an economically important pathogen of ruminant species with worldwide prevalence. While many BTV infections are asymptomatic, animals with symptomatic presentation deteriorate quickly with the sickest succumbing to disease within one week. Animals that survive the infection often require months to recover. The immune response to BTV infection is thought to play a central role in controlling the disease. Key to understanding BTV disease is profiling vertebrate host immunological cellular and cytokine responses. Studies to characterize immune responses in ruminants have been limited by a lack of species-specific reagents and assay technology. Here we assess the longitudinal immunological response to experimental BTV-17-California (CA) infection in sheep using the most up to date assays. We infected a cohort of sheep with BTV-17-CA and longitudinally monitored each animal for clinical disease, viremia and specific immunological parameters (B cells, T cells, monocytes) by RT-qPCR, traditional flow cytometry and/or fluorescent based antibody arrays. BTV-inoculated sheep exhibited clinical signs characteristic of bluetongue virus disease. Circulating virus was demonstrated after 8 days post inoculation (DPI) and remained detectable for the remainder of the time course (24 DPI). A distinct lymphopenia was observed between 7 and 14 DPI that rebounded to mock-inoculated control levels at 17 DPI. In addition, we observed increased expression of pro-inflammatory cytokines after 8 DPI. Taken together, we have established a model of BTV infection in sheep and have successfully monitored the longitudinal vertebrate host immunological response and viral infection progression using a combination of traditional methods and cutting-edge technology.

Comprehensive immune profiling reveals that Orbivirus infection activates immune checkpoints during acute T cell immunosuppression

Bluetongue virus (BTV) is an arbovirus transmitted by the bite of infected Culicoides midges that affects domestic and wild ruminants producing great economic losses. The infection induces an IFN response, followed by an adaptive immune response that is essential in disease clearance. BTV can nonetheless impair IFN and humoral responses. The main goal of this study was to gain a more detailed understanding of BTV pathogenesis and its effects on immune cell populations. To this end, we combined flow cytometry and transcriptomic analyses of several immune cells at different times post-infection (pi). Four sheep were infected with BTV serotype 8 and blood samples collected at days 0, 3, 7 and 15pi to perform transcriptomic analysis of B-cell marker+, CD4+, CD8+, and CD14+ sorted peripheral mononuclear cells. The maximum number of differentially expressed genes occurred at day 7pi, which coincided with the peak of infection. KEGG pathway enrichment analysis indicated that genes belonging to virus sensing and immune response initiation pathways were enriched at day 3 and 7 pi in all 4 cell population analyzed. Transcriptomic analysis also showed that at day 7pi T cell exhaustion pathway was enriched in CD4+ cells, while CD8+ cells downregulated immune response initiation pathways. T cell functional studies demonstrated that BTV produced an acute inhibition of CD4+ and CD8+ T cell activation at the peak of replication. This coincided with PD-L1 upregulation on the surface of CD4+ and CD8+ T cells as well as monocytes. Taken together, these data indicate that BTV could exploit the PD1/PD-L1 immune checkpoint to impair T cell responses. These findings identify several mechanisms in the interaction between host and BTV, which could help develop better tools to combat the disease.

Whole-transcriptome analyses of sheep embryonic testicular cells infected with the bluetongue virus

Introduction

bluetongue virus (BTV) infection triggers dramatic and complex changes in the host's transcriptional profile to favor its own survival and reproduction. However, there is no whole-transcriptome study of susceptible animal cells with BTV infection, which impedes the in-depth and systematical understanding of the comprehensive characterization of BTV-host interactome, as well as BTV infection and pathogenic mechanisms.

Methods

to systematically understand these changes, we performed whole-transcriptome sequencing in BTV serotype 1 (BTV-1)-infected and mock-infected sheep embryonic testicular cells, and subsequently conducted bioinformatics differential analyses.

Results

there were 1504 differentially expressed mRNAs, 78 differentially expressed microRNAs, 872 differentially expressed long non-coding RNAs, and 59 differentially expressed circular RNAs identified in total. Annotation from the Gene Ontology, enrichment from the Kyoto Encyclopedia of Genes and Genomes, and construction of competing endogenous RNA networks revealed differentially expressed RNAs primarily related to virus-sensing and signaling transduction pathways, antiviral and immune responses, inflammation, and development and metabolism related pathways. Furthermore, a protein-protein interaction network analysis found that BTV may contribute to abnormal spermatogenesis by reducing steroid biosynthesis. Finally, real-time quantitative PCR and western blotting results showed that the expression trends of differentially expressed RNAs were consistent with the whole-transcriptome sequencing data.

Discussion

this study provides more insights of comprehensive characterization of BTV-host interactome, and BTV infection and pathogenic mechanisms.

Early Events in Reovirus Infection Influence Induction of Innate Immune Response

Mammalian orthoreovirus (reovirus) is a double-stranded RNA (dsRNA) virus which encapsidates its 10 genome segments within a double-layered viral particle. Reovirus infection triggers an antiviral response in host cells which serves to limit viral replication. This antiviral response is initiated by recognition of the incoming viral genome by host sensors present in the cytoplasm. However, how host sensors gain access to the reovirus genome is unclear, as this dsRNA is protected by the viral particle proteins throughout infection. To initiate infection, reovirus particles are endocytosed and the outer viral particle layer is disassembled through the action of host proteases. This disassembly event is required for viral escape into the cytoplasm to begin replication. We show that endosomal proteases are required even late in infection, when disassembly is complete, to induce an immune response to reovirus. Additionally, counter to dogma, our data demonstrate that at least some viral dsRNA genome is exposed and detectable during entry. We hypothesize that some proportion of reovirus particles remain trapped within endosomes, allowing for the breakdown of these particles and release of their genome. We show that rapidly uncoating mutants escape the endosome more rapidly and induce a diminished immune response. Further, we show that particles entering through dynamin-independent pathways evade detection by host sensors. Overall, our data provide new insight into how genomes from entering reovirus particles are detected by host cells. IMPORTANCE Viruses must infect host cells to replicate, often killing the host cell in the process. However, hosts can activate defenses to limit viral replication and protect the organism. To trigger these host defenses to viral infections, host cells must first recognize that they are infected. Mammalian orthoreovirus (reovirus) is a model system used to study host-virus interactions. This study identifies aspects of host and virus biology which determine the capacity of host cells to detect infection. Notably, entry of reovirus into host cells plays a critical role in determining the magnitude of immune response triggered during infection. Mutants of reovirus which can enter cells more rapidly are better at avoiding detection by the host. Additionally, reovirus can enter cells through multiple routes. Entry through some of these routes also helps reovirus evade detection.

ISG20 Inhibits Bluetongue Virus Replication

ISG20 is an interferon-inducible exonuclease that inhibits virus replication. Although ISG20 is thought to degrade viral RNA, the antiviral mechanism and specificity of ISG20 remain unclear. In this study, the antiviral role of ovine ISG20 (oISG20) in bluetongue virus ​(BTV) infection was investigated. It was found that BTV infection up-regulated the transcription of ovine ISG20 (oISG20) in a time- and BTV multiplicity of infection (MOI)-dependent manner. Overexpression of oISG20 suppressed the production of BTV genome, proteins, and virus titer, whereas the knockdown of oISG20 increased viral replication. oISG20 was found to co-localize with BTV proteins VP4, VP5, VP6, and NS2, but only directly interacted with VP4. Exonuclease defective oISG20 significantly decreased the inhibitory effect on BTV replication. In addition, the interaction of mutant oISG20 and VP4 was weakened, suggesting that binding to VP4 was associated with the inhibition of BTV replication. The present data characterized the anti-BTV effect of oISG20, and provides a novel clue for further exploring the inhibition mechanism of double-stranded RNA virus by ISG20.

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BTV infection significantly up-regulated the transcription level of oISG20 in vitro.

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The oISG20 showed a high similarity with other ISG20s from different species.

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The oISG20 had antiviral activity against BTV infection.

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The inhibitory effect of oISG20 on BTV replication is mediated by BTV VP4 protein.

Inhibition of the IFN Response by Bluetongue Virus: The Story So Far

Bluetongue virus (BTV) is the prototypical orbivirus that belongs to the Reoviridae family. BTV infection produces a disease in ruminants, particularly in sheep, that results in economic losses through reduced productivity. BTV is transmitted by the bite of Culicoides spp. midges and is nowadays distributed globally throughout subtropical and even temperate regions. As most viruses, BTV is susceptible to the IFN response, the first line of defense employed by the immune system to combat viral infections. In turn, BTV has evolved strategies to counter the IFN response and promote its replication. The present review we will revise the works describing how BTV interferes with the IFN response.

The VP3 Protein of Bluetongue Virus Associates with the MAVS Complex and Interferes with the RIG-I-Signaling Pathway

Bluetongue virus (BTV), an arbovirus transmitted by Culicoides biting midges, is a major concern of wild and domestic ruminants. While BTV induces type I interferon (alpha/beta interferon [IFN-α/β]) production in infected cells, several reports have described evasion strategies elaborated by this virus to dampen this intrinsic, innate response. In the present study, we suggest that BTV VP3 is a new viral antagonist of the IFN-β synthesis. Indeed, using split luciferase and coprecipitation assays, we report an interaction between VP3 and both the mitochondrial adapter protein MAVS and the IRF3-kinase IKKε. Overall, this study describes a putative role for the BTV structural protein VP3 in the control of the antiviral response.

Recognition of Reovirus RNAs by the Innate Immune System

Mammalian orthoreovirus (reovirus) is a dsRNA virus, which has long been used as a model system to study host–virus interactions. One of the earliest interactions during virus infection is the detection of the viral genomic material, and the consequent induction of an interferon (IFN) based antiviral response. Similar to the replication of related dsRNA viruses, the genomic material of reovirus is thought to remain protected by viral structural proteins throughout infection. Thus, how innate immune sensor proteins gain access to the viral genomic material, is incompletely understood. This review summarizes currently known information about the innate immune recognition of the reovirus genomic material. Using this information, we propose hypotheses about host detection of reovirus.

Comparative Evaluation of T-Cell Immune Response to BTV Infection in Sheep Vaccinated with Pentavalent BTV Vaccine When Compared to Un-Vaccinated Animals

Recent invasion of multiple bluetongue virus serotypes (BTV) in different regions of the world necessitates urgent development of efficient vaccine that is directed against multiple BTV serotypes. In this experimental study, cell mediated immune response and protective efficacy of binary ethylenimine (BEI) inactivated Montanide^™ ISA 206 adjuvanted pentavalent (BTV-1, 2, 10, 16 and 23) vaccine was evaluated in sheep and direct challenge with homologous BTV serotypes in their respective group. Significant (P < 0.05) up-regulation of mRNA transcripts of IFN-α, IL-2, IL-6, IL-12, IFN-γ and TNF-α in PBMCs of vaccinated animals as compared to control (un-vaccinated) animals at certain time points was observed. On the other hand, there was a significant increase in mean ± SD percentage of CD8⁺ T cells after 7 days post challenge (DPC) but, the mean ± SD percentage of CD4⁺ T-cell population slightly declined at 7 DPC and enhanced after 14 DPC. Significant differences (P < 0.05) of CD8⁺ and CD4⁺T cells population was also observed between vaccinated and unvaccinated sheep. The vaccine also significantly (P < 0.05) reduced BTV RNA load in PBMCs of vaccinated animals than unvaccinated animals following challenge. There were no significant difference (P > 0.05) in cytokine induction, BTV RNA load and CD8⁺ and CD4⁺cell count among BTV-1, 2, 10, 16 and 23 serotype challenges except significant increase in mean ± SD percentage of CD8⁺ in BTV-2 group. These findings put forwarded that binary ethylenimine inactivated montanide adjuvanted pentavalent bluetongue vaccine has stimulated cell mediated immune response and most importantly reduced the severity of BTV-1, 2, 10, 16 and 23 infections following challenge in respective group.

Virus-induced autophagic degradation of STAT2 as a mechanism for interferon signaling blockade

The mammalian interferon (IFN) signaling pathway is a primary component of the innate antiviral response, and viral pathogens have evolved multiple mechanisms to antagonize this pathway and to facilitate infection. Bluetongue virus (BTV), an orbivirus of the Reoviridae family, is transmitted by midges to ruminants and causes a disease that produces important economic losses and restriction to animal trade and is of compulsory notification to the World Organization for Animal Health (OIE). Here, we show that BTV interferes with IFN-I and IFN-II responses in two ways, by blocking STAT1 phosphorylation and by degrading STAT2. BTV-NS3 protein, which is involved in virion egress, interacts with STAT2, and induces its degradation by an autophagy-dependent mechanism. This STAT2 degradative process requires the recruitment of an E3-Ub-ligase to NS3 as well as NS3 K63 polyubiquitination. Taken together, our study identifies a new mechanism by which a virus degrades STAT2 for IFN signaling blockade, highlighting the diversity of mechanisms employed by viruses to subvert the IFN response.

A low-passage insect-cell isolate of bluetongue virus uses a macropinocytosis-like entry pathway to infect natural target cells derived from the bovine host

Bluetongue virus (BTV) causes an economically important disease in domestic and wildlife ruminants and is transmitted by Culicoides biting midges. In ruminants, BTV has a wide cell tropism that includes endothelial cells of vascular and lymphatic vessels as important cell targets for virus replication, and several cell types of the immune system including monocytes, macrophages and dendritic cells. Thus, cell-entry represents a particular challenge for BTV as it infects many different cell types in widely diverse vertebrate and invertebrate hosts. Improved understanding of BTV cell-entry could lead to novel antiviral approaches that can block virus transmission from cell to cell between its invertebrate and vertebrate hosts. Here, we have investigated BTV cell-entry using endothelial cells derived from the natural bovine host (BFA cells) and purified whole virus particles of a low-passage, insect-cell isolate of a virulent strain of BTV-1. Our results show that the main entry pathway for infection of BFA cells is dependent on actin and dynamin, and shares certain characteristics with macropinocytosis. The ability to use a macropinocytosis-like entry route could explain the diverse cell tropism of BTV and contribute to the efficiency of transmission between vertebrate and invertebrate hosts.

Tellurium/Bovine Serum Albumin Nanocomposites Inducing the Formation of Stress Granules in a Protein Kinase R-Dependent Manner

The effect of nanoparticles (NPs) on cellular stress responses is important to the understanding of nanotoxicities and developing safe therapies. Although the relationship between NPs and cellular stress responses has been preliminarily investigated, stress responses to NPs remain unclear. Here, tellurium/bovine serum albumin (Te/BSA) nanocomposites were prepared using sodium tellurite, BSA, and glutathione as precursors. The as-prepared Te/BSA nanocomposites, with particle size similar to that of many viruses, are found to induce the formation of stress granules (SGs), a kind of cytoplasmic RNA granule formed under various stresses. The SGs in Te/BSA nanocomposite-treated cells are composed of T-cell internal antigen 1 (TIA1), TIA1-related protein, and eukaryotic initiation factor 3η. Using chemical inhibitors and small interfering RNA-mediated silencing, protein kinase R (PKR) is identified as the α-subunit of eukaryotic initiation factor 2 (eIF2α)-kinase activated upon Te/BSA nanocomposite incubation, which is also the dominant kinase responsible for eIF2α activation under virus infection. Mechanistically, PKR is activated in a heparin-dependent manner. This study reveals a biological effect of Te/BSA nanocomposites on stress responses, providing a preliminary basis for further research on viruslike particles and the application of NPs in biology.

Role of the myeloid differentiation primary response (MYD88) and TIR-domain-containing adapter-inducing interferon-β (TRIF) pathways in dengue

AIMS

Dengue disease courses with high viremia titers and high cytokine production suggesting viral replication and active immune response that could be related to viral evasion. One of the main targets of dengue virus (DENV) is monocyte/macrophage cells; however, little information regarding viral evasive mechanisms and pathway activation in monocytes infected by DENV is available. The aim of this study was to determine the role of myeloid differentiation primary response (MyD88), TIR-domain-containing adapter- inducing interferon-β (TRIF) and NF-kB pathways in viral replication and cytokine production in human monocyte cultures infected by DENV2.

MAIN METHODS

In this regard Pepinh- TRIF, Pepinh- MYD and pyrrolidine dithiocarbamate (PDTC) were used to inhibit TRIF, MYD88 and NF-kB pathways. Cytokine production was measured by ELISA.

KEY FINDINGS

Increased DENV replication and IFNα/β, TNF-α, IL-12 and IL-18 in infected cultures at 24h were found. All of these parameters were significantly decreased after TRIF, MYD88 or NF-kB inhibition. Association analysis between viral replication and cytokine production showed high significant positive correlation in TRIF and MYD88 treated cultures.

SIGNIFICANCE

This study shows that DENV2 induces activation of innate-immune response and transcription factors to drive viral expression and replication in the face of pro-inflammatory antiviral responses in vitro.

TREM-1 activation modulates dsRNA induced antiviral immunity with specific enhancement of MAPK signaling and the RLRs and TLRs on macrophages

Triggering receptor expressed on myeloid cells 1(TREM-1) is a newly identified member of the immunoglobulin superfamily and is extensively involved in the regulation of innate immunity. To determine the role of TREM-1 in innate antiviral immunity, we investigated TREM-1 expression and its downstream signaling effect in the murine bone marrow-derived macrophages or RAW264.7 macrophage-like mouse cell line by double-stranded RNA (dsRNA) stimulation. The level of TREM-1 expression was low at the baseline and could up-regulate markedly in dose- and time-dependent manners upon stimulation by dsRNA/poly IC. Inhibitor studies disclosed mitogen-activated protein kinase (MAPK) p38 and PI3K pathways were involved in dsRNA-induced up-regulation of TREM-1. Compared with lipopolysaccharide (LPS), the peak response of poly IC-induced TREM-1 expression is delayed, and cells pretreated with scrambled RNA presented higher expression of TREM-1 upon LPS challenge. After ligation with the agonist antibody, TREM-1 can potentiate type I interferon (IFN) production and antiviral inflammation induced by dsRNA, which is ralated to the enhanced phosphorylation of MAPKs and expression of RLRs and TLRs by TREM-1 ligation. This study is the first to show the regulatory role of TREM-1 in RLRs and TLRs expression, and these findings might enrich the understanding of the up-regulation mechanism and the function of TREM-1.

Bluetongue Virus NS4 Protein Is an Interferon Antagonist and a Determinant of Virus Virulence

Bluetongue virus (BTV) is the causative agent of bluetongue, a major infectious disease of ruminants with serious consequences to both animal health and the economy. The clinical outcome of BTV infection is highly variable and dependent on a variety of factors related to both the virus and the host. In this study, we show that the BTV nonstructural protein NS4 favors viral replication in sheep, the animal species most affected by bluetongue. In addition, NS4 confers a replication advantage on the virus in interferon (IFN)-competent primary sheep endothelial cells and immortalized cell lines. We determined that in cells infected with an NS4 deletion mutant (BTV8ΔNS4), there is increased synthesis of type I IFN compared to cells infected with wild-type BTV-8. In addition, using RNA sequencing (RNA-seq), we show that NS4 modulates the host IFN response and downregulates mRNA levels of type I IFN and interferon-stimulated genes. Moreover, using reporter assays and protein synthesis assays, we show that NS4 downregulates the activities of a variety of promoters, such as the cytomegalovirus immediate-early promoter, the IFN-β promoter, and a promoter containing interferon-stimulated response elements (ISRE). We also show that the NS4 inhibitory activity on gene expression is related to its nucleolar localization. Furthermore, NS4 does not affect mRNA splicing or cellular translation. The data obtained in this study strongly suggest that BTV NS4 is an IFN antagonist and a key determinant of viral virulence.

IMPORTANCE Bluetongue is one of the main infectious diseases of ruminants and is caused by bluetongue virus (BTV), an arthropod-borne virus transmitted from infected to susceptible animals by Culicoides biting midges. Bluetongue has a variable clinical outcome that can be related to both virus and host factors. It is therefore critical to understand the interplay between BTV and the host immune responses. In this study, we show that a nonstructural protein of BTV (NS4) is critical to counteract the innate immune response of the host. Infection of cells with a BTV mutant lacking NS4 results in increased synthesis of IFN-β and upregulation of interferon-stimulated genes. In addition, we show that NS4 is a virulence factor for BTV by favoring viral replication in sheep, the animal species most susceptible to bluetongue.

Vaccines for Prevention of Bluetongue and Epizootic Hemorrhagic Disease in Livestock: A North American Perspective

Bluetongue (BT) and epizootic hemorrhagic disease (EHD) are noncontagious, insect-transmitted diseases of domestic and wild ruminants caused by related but distinct viruses. There are significant gaps in our scientific knowledge and available countermeasures to control an outbreak of orbivirus-induced disease, whether BT or EHD. Both BT virus (BTV) and EHD virus (EHDV) cause hemorrhagic fevers in susceptible ruminants; however, BT is principally a disease of domestic livestock whereas EHD is principally a disease of certain species of wild, non-African ungulates, notably white-tailed deer. The live-attenuated (modified live virus [MLV]) vaccines available in the United States for use in small ruminant livestock do provide good protection against clinical disease following infection with the homologous virus serotype. Although there is increasing justification that the use of MLV vaccines should be avoided if possible, these are the only vaccines currently available in the United States. Specifically, MLVs are used in California to protect sheep against infection with BTV serotypes 10, 11, and 17, and a MLV to BTV serotype 10 is licensed for use in sheep throughout the United States. These MLV vaccines may need to continue to be used in the immediate future for protective immunization of sheep and goats against BT. There are currently no licensed vaccines available for EHD in the United States other than autogenous vaccines. If there is a need to rapidly develop a vaccine to meet an emerging crisis associated with either BTV or EHDV infections, development of an inactivated virus vaccine in a conventional adjuvanted formulation will likely be required. With two doses of vaccine (and in some instances just one dose), inactivated vaccines can provide substantial immunity to the epizootic serotype of either BTV or EHDV. This strategy is similar to that used in the 2006-2008 BTV serotype 8 outbreaks in northern Europe that provided vaccine to the field within 2 years of the initial incursion (by 2008). Further research and development are warranted to provide more efficacious and effective vaccines for control of BTV and EHDV infections.

Proteomic analysis of sheep primary testicular cells infected with bluetongue virus

Bluetongue virus (BTV) causes a non‐contagious, arthropod‐transmitted disease in wild and domestic ruminants, such as sheep. In this study, we used iTRAQ labeling coupled with LC‐MS/MS for quantitative identification of differentially expressed proteins in BTV‐infected sheep testicular (ST) cells. Relative quantitative data were obtained for 4455 proteins in BTV‐ and mock‐infected ST cells, among which 101 and 479 proteins were differentially expressed at 24 and 48 h post‐infection, respectively, indicating further proteomic changes during the later stages of infection. Ten corresponding genes of differentially expressed proteins were validated via real‐time RT‐PCR. Expression levels of three representative proteins, eIF4a1, STAT1 and HSP27, were further confirmed via western blot analysis. Bioinformatics analysis disclosed that the differentially expressed proteins are primarily involved in biological processes related to innate immune response, signal transduction, nucleocytoplasmic transport, transcription and apoptosis. Several upregulated proteins were associated with the RIG‐I‐like receptor signaling pathway and endocytosis. To our knowledge, this study represents the first attempt to investigate proteome‐wide dysregulation in BTV‐infected cells with the aid of quantitative proteomics. Our collective results not only enhance understanding of the host response to BTV infection but also highlight multiple potential targets for the development of antiviral agents.

Baicalin Protects Keratinocytes from Toll-like Receptor-4 Mediated DNA Damage and Inflammation Following Ultraviolet Irradiation

UVB radiation contributes to both direct and indirect damage to the skin including the generation of free radicals and reactive oxygen species (ROS), inflammatory responses, immunosuppression and gene mutations, which can ultimately lead to photocarcinogenesis. A plant-derived flavonoid, baicalin, has been shown to have antioxidant, anti-inflammatory and free radical scavenging activities. Previous studies from our laboratory have shown that in murine skin, Toll-like receptor-4 (TLR4) enhanced both UVB-induced DNA damage and inflammation. The aim of this study was to investigate the efficacy of baicalin against TLR4-mediated processes in the murine keratinocyte PAM 212 cell line. Our results demonstrate that treating keratinocytes with baicalin both before and after UV radiation (100 mJ cm(-2) ) significantly inhibited the level of intracellular ROS and decreased cyclobutane pyrimidine dimers and 8-Oxo-2'-deoxyguanosine (8-oxo-dG)-markers of DNA damage. Furthermore, cells treated with baicalin demonstrated an inhibition of TLR4 and its downstream signaling molecules, MyD88, TRIF, TRAF6 and IRAK4. TLR4 pathway inhibition resulted in NF-κB inactivation and down-regulation of iNOS and COX-2 protein expression. Taken together, baicalin treatment effectively protected keratinocytes from UVB-induced inflammatory damage through TLR pathway modulation.

Activation of TLR3/interferon signaling pathway by bluetongue virus results in HIV inhibition in macrophages

Bluetongue virus (BTV), a nonenveloped double-stranded RNA virus, is a potent inducer of type Ι interferons in multiple cell systems. In this study, we report that BTV16 treatment of primary human macrophages induced both type I and III IFN expression, resulting in the production of multiple antiviral factors, including myxovirus resistance protein A, 2',5'-oligoadenylate synthetase, and the IFN-stimulated gene 56. Additionally, BTV-treated macrophages expressed increased HIV restriction factors (apolipoprotein B mRNA-editing enzyme catalytic polypeptide 3 G/F/H) and CC chemokines (macrophage inflammatory protein 1-α, macrophage inflammatory protein 1-β, regulated on activation of normal T cell expressed and secreted), the ligands for HIV entry coreceptor CC chemokine receptor type 5. BTV16 also induced the expression of tetherin, which restricts HIV release from infected cells. Furthermore, TLR3 signaling of macrophages by BTV16 resulted in the induction of several anti-HIV microRNAs (miRNA-28, -29a, -125b, -150, -223, and -382). More importantly, the induction of antiviral responses by BTV resulted in significant suppression of HIV in macrophages. These findings demonstrate the potential of BTV-mediated TLR3 activation in macrophage innate immunity against HIV.

Autophagy Activated by Bluetongue Virus Infection Plays a Positive Role in Its Replication

Bluetongue virus (BTV) is an important pathogen of wild and domestic ruminants. Despite extensive study in recent decades, the interplay between BTV and host cells is not clearly understood. Autophagy as a cellular adaptive response plays a part in many viral infections. In our study, we found that BTV1 infection triggers the complete autophagic process in host cells, as demonstrated by the appearance of obvious double-membrane autophagosome-like vesicles, GFP-LC3 dots accumulation, the conversion of LC3-I to LC3-II and increased levels of autophagic flux in BSR cells (baby hamster kidney cell clones) and primary lamb lingual epithelial cells upon BTV1 infection. Moreover, the results of a UV-inactivated BTV1 infection assay suggested that the induction of autophagy was dependent on BTV1 replication. Therefore, we investigated the role of autophagy in BTV1 replication. The inhibition of autophagy by pharmacological inhibitors (3-MA, CQ) and RNA interference (siBeclin1) significantly decreased viral protein synthesis and virus yields. In contrast, treating BSR cells with rapamycin, an inducer of autophagy, promoted viral protein expression and the production of infectious BTV1. These findings lead us to conclude that autophagy is activated by BTV1 and contributes to its replication, and provide novel insights into BTV-host interactions.

Defining Mononuclear Phagocyte Subset Homology Across Several Distant Warm-Blooded Vertebrates Through Comparative Transcriptomics

Mononuclear phagocytes are organized in a complex system of ontogenetically and functionally distinct subsets, that has been best described in mouse and to some extent in human. Identification of homologous mononuclear phagocyte subsets in other vertebrate species of biomedical, economic, and environmental interest is needed to improve our knowledge in physiologic and physio-pathologic processes, and to design intervention strategies against a variety of diseases, including zoonotic infections. We developed a streamlined approach combining refined cell sorting and integrated comparative transcriptomics analyses which revealed conservation of the mononuclear phagocyte organization across human, mouse, sheep, pigs and, in some respect, chicken. This strategy should help democratizing the use of omics analyses for the identification and study of cell types across tissues and species. Moreover, we identified conserved gene signatures that enable robust identification and universal definition of these cell types. We identified new evolutionarily conserved gene candidates and gene interaction networks for the molecular regulation of the development or functions of these cell types, as well as conserved surface candidates for refined subset phenotyping throughout species. A phylogenetic analysis revealed that orthologous genes of the conserved signatures exist in teleost fishes and apparently not in Lamprey.

Multiple genome segments determine virulence of bluetongue virus serotype 8

Bluetongue virus (BTV) causes bluetongue, a major hemorrhagic disease of ruminants. In order to investigate the molecular determinants of BTV virulence, we used a BTV8 strain minimally passaged in tissue culture (termed BTV8L in this study) and a derivative strain passaged extensively in tissue culture (BTV8H) in in vitro and in vivo studies. BTV8L was pathogenic in both IFNAR(-/-) mice and in sheep, while BTV8H was attenuated in both species. To identify genetic changes which led to BTV8H attenuation, we generated 34 reassortants between BTV8L and BTV8H. We found that partial attenuation of BTV8L in IFNAR(-/-) mice was achieved by simply replacing genomic segment 2 (Seg2, encoding VP2) or Seg10 (encoding NS3) with the BTV8H homologous segments. Fully attenuated viruses required at least two genome segments from BTV8H, including Seg2 with either Seg1 (encoding VP1), Seg6 (encoding VP6 and NS4), or Seg10 (encoding NS3). Conversely, full reversion of virulence of BTV8H required at least five genomic segments of BTV8L. We also demonstrated that BTV8H acquired an increased affinity for glycosaminoglycan receptors during passaging in cell culture due to mutations in its VP2 protein. Replication of BTV8H was relatively poor in interferon (IFN)-competent primary ovine endothelial cells compared to replication of BTV8L, and this phenotype was determined by several viral genomic segments, including Seg4 and Seg9. This study demonstrated that multiple viral proteins contribute to BTV8 virulence. VP2 and NS3 are primary determinants of BTV pathogenesis, but VP1, VP5, VP4, VP6, and VP7 also contribute to virulence.

IMPORTANCE

Bluetongue is one of the major infectious diseases of ruminants, and it is listed as a notifiable disease by the World Organization for Animal Health (OIE). The clinical outcome of BTV infection varies considerably and depends on environmental and host- and virus-specific factors. Over the years, BTV serotypes/strains with various degrees of virulence (including nonpathogenic strains) have been described in different geographical locations. However, no data are available to correlate the BTV genotype to virulence. This study shows that BTV virulence is determined by different viral genomic segments. The data obtained will help to characterize thoroughly the pathogenesis of bluetongue. The possibility to determine the pathogenicity of virus isolates on the basis of their genome sequences will help in the design of control strategies that fit the risk posed by new emerging BTV strains.

Plasmacytoid dendritic cells, a role in neoplastic prevention and progression

BACKGROUND

Plasmacytoid dendritic cells (pDCs) are multifunctional bone-marrow-derived immune cells that are key players in bridging the innate and adaptive immune systems. Activation of pDCs through toll-like receptor agonists has proven to be an effective treatment for some neoplastic disorders.

MATERIALS AND METHODS

In this mini-review, we will explore the fascinating contribution of pDCs to neoplastic pathology and discuss their potential utilization in cancer immunotherapy.

RESULTS

Current research suggests that pDCs have cytotoxic potential and can effectively induce apoptosis of tumour-derived cells lines. They are also reported to display tolerogenic function with the ability to suppress T-cell proliferation, analogous to regulatory T cells. In this capacity, they are critical in the suppression of autoimmunity but can be exploited by tumour cells to circumvent the expansion of tumour-specific T cells, thereby allowing tumours to persist.

CONCLUSION

Several forms of skin cancer are successfully treated with the topical drug Imiquimod, which activates pDCs through toll-like receptor 7 engagement. Additionally, pDC-based anticancer vaccines have shown encouraging results for the treatment of melanoma in early trials. Future studies regarding the contributions of pDCs to malignancy will likely afford many opportunities for immunotherapy strategies.

Study of the virulence of serotypes 4 and 9 of African horse sickness virus in IFNAR(-/-), Balb/C and 129 Sv/Ev mice

African horse sickness virus (AHSV) is a double-stranded RNA virus which belongs to the family Reoviridae, genus Orbivirus. Recent studies have focused on the interferon-α/β receptor knock-out mice (IFNAR(-/-)) as a small animal laboratory for the development of AHSV vaccines. The aim of this work was to study in vivo the virulence of two strains of AHSV and to compare the outcome of the infection of three mouse strains. To address this, AHSV serotypes 4 (AHSV-4) and 9 (AHSV-9) were inoculated subcutaneously (SC) and intranasally (IN) in two immunocompetent mouse strains (Balb/C and 129 Sv/Ev (129 WT)) as well as IFNAR(-/-) mice (on 129 Sv/Ev genetic background). In IFNAR(-/-) mice, fatality up to 50% was measured and significantly more clinical signs were observed in comparison with SC inoculated immunocompetent mice. The observed clinical signs were significantly more severe after AHSV-4 infection, in particular in immunocompetent mice inoculated by IN route. Considering RNAemia, significantly higher viral loads were measured following AHSV-4 infection. In the organs of 129 WT inoculated by IN route, significantly higher viral loads were detected after AHSV-4 infection. Together the results support a higher virulence for AHSV-4 compared to AHSV-9 and a higher clinical impact following infections in IN inoculated mice, at least in the investigated strains. The study also brought indirect evidences for type I IFN involvement in the control of AHSV infection.

Dual modulation of type I interferon response by bluetongue virus

Bluetongue virus (BTV) is a double-stranded RNA (dsRNA) virus that causes an economically important disease in ruminants. BTV infection is a strong inducer of type I interferon (IFN-I) in multiple cell types. It has been shown recently that BTV and, more specifically, the nonstructural protein NS3 of BTV are able to modulate the IFN-I synthesis pathway. However, nothing is known about the ability of BTV to counteract IFN-I signaling. Here, we investigated the effect of BTV on the IFN-I response pathway and, more particularly, the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. We found that BTV infection triggered the expression of IFN-stimulated genes (ISGs) in A549 cells. However, when BTV-infected cells were stimulated with external IFN-I, we showed that activation of the IFN-stimulated response element (ISRE) promoter and expression of ISGs were inhibited. We found that this inhibition involved two different mechanisms that were dependent on the time of infection. After overnight infection, BTV blocked specifically the phosphorylation and nuclear translocation of STAT1. This inhibition correlated with the redistribution of STAT1 in regions adjacent to the nucleus. At a later time point of infection, BTV was found to interfere with the activation of other key components of the JAK/STAT pathway and to induce the downregulation of JAK1 and TYK2 protein expression. Overall, our study indicates for the first time that BTV is able to interfere with the JAK/STAT pathway to modulate the IFN-I response.

IMPORTANCE

Bluetongue virus (BTV) causes a severe disease in ruminants and has an important impact on the livestock economy in areas of endemicity such as Africa. The emergence of strains, such as serotype 8 in Europe in 2006, can lead to important economic losses due to commercial restrictions and prophylactic measures. It has been known for many years that BTV is a strong inducer of type I interferon (IFN-I) in vitro and in vivo in multiple cell types. However, the ability of BTV to interact with the IFN-I system remains unclear. Here, we report that BTV is able to modulate the IFN-I response by interfering with the Janus tyrosine kinase (JAK)/signal transducer and activator of transcription protein (STAT) signaling pathway. These findings contribute to knowledge of how BTV infection interferes with the host's innate immune response and becomes pathogenic. This will also be important for the design of efficacious vaccine candidates.

Rotavirus activates lymphocytes from non-obese diabetic mice by triggering toll-like receptor 7 signaling and interferon production in plasmacytoid dendritic cells

It has been proposed that rotavirus infection promotes the progression of genetically-predisposed children to type 1 diabetes, a chronic autoimmune disease marked by infiltration of activated lymphocytes into pancreatic islets. Non-obese diabetic (NOD) mice provide a model for the human disease. Infection of adult NOD mice with rhesus monkey rotavirus (RRV) accelerates diabetes onset, without evidence of pancreatic infection. Rather, RRV spreads to the pancreatic and mesenteric lymph nodes where its association with antigen-presenting cells, including dendritic cells, induces cellular maturation. RRV infection increases levels of the class I major histocompatibility complex on B cells and proinflammatory cytokine expression by T cells at these sites. In autoimmunity-resistant mice and human mononuclear cells from blood, rotavirus-exposed plasmacytoid dendritic cells contribute to bystander polyclonal B cell activation through type I interferon expression. Here we tested the hypothesis that rotavirus induces bystander activation of lymphocytes from NOD mice by provoking dendritic cell activation and proinflammatory cytokine secretion. NOD mouse splenocytes were stimulated with rotavirus and assessed for activation by flow cytometry. This stimulation activated antigen-presenting cells and B cells independently of virus strain and replicative ability. Instead, activation depended on virus dose and was prevented by blockade of virus decapsidation, inhibition of endosomal acidification and interference with signaling through Toll-like receptor 7 and the type I interferon receptor. Plasmacytoid dendritic cells were more efficiently activated than conventional dendritic cells by RRV, and contributed to the activation of B and T cells, including islet-autoreactive CD8+ T cells. Thus, a double-stranded RNA virus can induce Toll-like receptor 7 signaling, resulting in lymphocyte activation. Our findings suggest that bystander activation mediated by type I interferon contributes to the lymphocyte activation observed following RRV infection of NOD mice, and may play a role in diabetes acceleration by rotavirus.

The molecular biology of Bluetongue virus replication

The members of Orbivirus genus within the Reoviridae family are arthropod-borne viruses which are responsible for high morbidity and mortality in ruminants. Bluetongue virus (BTV) which causes disease in livestock (sheep, goat, cattle) has been in the forefront of molecular studies for the last three decades and now represents the best understood orbivirus at a molecular and structural level. The complex nature of the virion structure has been well characterised at high resolution along with the definition of the virus encoded enzymes required for RNA replication; the ordered assembly of the capsid shell as well as the protein and genome sequestration required for it; and the role of host proteins in virus entry and virus release. More recent developments of Reverse Genetics and Cell-Free Assembly systems have allowed integration of the accumulated structural and molecular knowledge to be tested at meticulous level, yielding higher insight into basic molecular virology, from which the rational design of safe efficacious vaccines has been possible. This article is centred on the molecular dissection of BTV with a view to understanding the role of each protein in the virus replication cycle. These areas are important in themselves for BTV replication but they also indicate the pathways that related viruses, which includes viruses that are pathogenic to man and animals, might also use providing an informed starting point for intervention or prevention.

Induction and control of the type I interferon pathway by Bluetongue virus

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A general review describing the current knowledge on the type I IFN pathway.

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Description of several mechanisms evolved by viruses to counteract this antiviral response.

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An up-to-date review on the interaction of BTV and the type I IFN pathway in vivo and in vitro.

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Description of the cellular sensors involved in the induction of IFN-α/β synthesis upon BTV infection in haematopoietic and non-haematopoietic cells.

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Description of the strategies evolved by BTV to counteract this cellular antiviral response.

The innate immune response is the first line of defence against viruses, involving the production of type I IFN (IFN-α/β) and other pro-inflammatory cytokines that control the infection. It also shapes the adaptive immune response generated by both T and B cells. Production of type I IFN occurs both in vivo and in vitro in response to Bluetongue virus (BTV), an arthropod-borne virus. However, the mechanisms responsible for the production of IFN-β in response to BTV remained unknown until recently and are still not completely understood. In this review, we describe the recent advances in the identification of cellular sensors and signalling pathways involved in this process. The RNA helicases retinoic acid-inducible gene-I (RIG-I) and melanoma differentiation-associated gene 5 (MDA5) were shown to be involved in the expression of IFN-β as well as in the control of BTV infection in non-haematopoietic cells. In contrast, induction of IFN-α/β synthesis in sheep primary plasmacytoid dendritic cells (pDCs) required the MyD88 adaptor independently of the Toll-like receptor 7 (TLR7), as well as the kinases dsRNA-activated protein kinase (PKR) and stress-activated protein kinase (SAPK)/Jun N-terminal protein kinase (JNK). As type I IFN is essential for the establishment of an antiviral cellular response, most of viruses have elaborated counteracting mechanisms to hinder its action. This review also addresses the ability of BTV to interfere with IFN-β synthesis and the recent findings describing the non-structural viral protein NS3 as a powerful antagonist of the host cellular response.

Type I interferon limits the capacity of bluetongue virus to infect hematopoietic precursors and dendritic cells in vitro and in vivo

Hematopoietic stem cells (HSCs) give rise to progenitors with potential to produce multiple cell types, including dendritic cells (DCs). DCs are the principal antigen-presenting cells and represent the crucial link between innate and adaptive immune responses. Bluetongue virus (BTV), an economically important Orbivirus of the Reoviridae family, causes a hemorrhagic disease mainly in sheep and occasionally in other species of ruminants. BTV is transmitted between its mammalian hosts by certain species of biting midges (Culicoides spp.) and is a potent alpha interferon (IFN-α) inducer. In the present report, we show that BTV infects cells of hematopoietic origin but not HSCs in immunocompetent sheep. However, BTV infects HSCs in the absence of type I IFN (IFN-I) signaling in vitro and in vivo. Infection of HSCs in vitro results in cellular death by apoptosis. Furthermore, BTV infects bone marrow-derived DCs (BM-DCs), interfering with their development to mature DCs in the absence of type I IFN signaling. Costimulatory molecules CD80 and CD86 and costimulatory molecules CD40 and major histocompatibility complex class II (MHC-II) are affected by BTV infection, suggesting that BTV interferes with DC antigen-presenting capacity. In vivo, different DC populations are also affected during the course of infection, probably as a result of a direct effect of BTV replication in DCs and the production of infectious virus. These new findings suggest that BTV infection of HSCs and DCs can impair the immune response, leading to persistence or animal death, and that this relies on IFN-I.

Pathogen recognition receptors: ligands and signaling pathways by Toll-like receptors

Toll-like receptors (TLRs) play critical roles in host defense against microbes. In the past decade, growing numbers of in vitro, in vivo and in silico studies have been performed and revealed the physiological significance and structural basis of their ligands and signal transduction, which involves various extracellular, membrane-bound, cytoplasmic and nuclear signaling molecules for the activation of TLR signaling. However, negative regulation of TLR-mediated responses is also essential for the prevention of autoimmunity and is mediated by a number of molecules. In this review, we will introduce recent advances in the understanding of TLR biology in terms of their ligands and signaling pathways.

Interferon α/β receptor knockout mice as a model to study bluetongue virus infection

Bluetongue is an arthropod-borne disease caused by a virus of the genus Orbivirus, the bluetongue virus (BTV), which affects ruminant livestock such as cattle, sheep, and goats and wild ruminants such as deer, and camelids. Recently, adult mice with gene knockouts of the interferon α/β receptor (IFNAR-/-) have been described as a model of lethal BTV infection. IFNAR(-/-) mice are highly susceptible to BTV-1, BTV-4 and BTV-8 infection when the virus is administered intravenously or subcutaneosuly. Disease progression and pathogenesis closely mimics signs of bluetongue disease in ruminants. In the present paper we review the studies where IFNAR(-/-) mice have been used as an animal model to study BTV transmission, pathogenesis, virulence, and protective efficacy of inactivated and new recombinant marker BTV vaccines. Furthermore, we report new data on protective efficacy of different strategies of BTV vaccination and also on induction of interferon α/β and proinflammatory immune responses in IFNAR(-/-) mice infected with BTV.

Comparative analysis of innate immune response following in vitro stimulation of sheep and goat peripheral blood mononuclear cells with bluetongue virus - serotype 23

Bluetongue is an infectious disease caused by bluetongue virus (BTV), which affects sheep, goat, cattle and certain wild ruminants. However severe clinical signs are usually seen with significant mortality in sheep than cattle and goat. To date, comparative studies on innate immune responses of sheep and goat infected with BTV is lacking. In this study, we compared the innate immune response of sheep and goat by infecting the peripheral blood mononuclear cells (PBMCs) with BTV serotype 23. In our study, we observed that sheep PBMCs supports higher virus replication than goat PBMCs. To delineate the role of innate immune response in differential viral replication observed in this study, we examined TLR3 (Receptor for dsRNA virus) mRNA expression and cytokine profiles (IL-1β, Il-6, IL-8, Il-10, IL-12p40, TNF-α, IFN-γ and IFN-α) following Poly I:C (TLR3 ligand) stimulation and BTV 23 infection. In our present study, sheep PBMCs had significantly higher TLR3 mRNA levels, TLR3 specific ligand (Poly I:C) stimulation resulted in increased levels of IFN-γ at transcriptional and translational levels along with IL-8 and IL-10 at transcriptional levels. Whereas, the levels of TNF-α was higher in goat PBMCs at transcriptional levels. BTV infected sheep PBMCs expressed significantly higher levels of IFN-γ at transcriptional and translational levels along with IL-6, IL-8 and IL-10 at transcriptional levels. Whereas the expression levels of TNF-α and IFN-α at transcriptional and translational levels were significantly high in goat PBMCs. To examine the potential factor for consistent increase in the expression of TNF-α, we sequenced the promoter region of TNF-α and identified a total of five single nucleotide polymorphisms (SNP) and one indel in goat TNF-α promoter region. Luciferase assay for transcriptional activity of the promoter showed that goat TNF-α has significantly enhanced transcriptional activity in comparison with sheep TNF-α promoter. Altogether, our data suggests that the expression levels of TNF-α and IFN-α and/or IL-10 plays crucial role in replication of BTV 23.

NS3 of bluetongue virus interferes with the induction of type I interferon

Upon infection with Bluetongue virus (BTV), an arthropod-borne virus, type I interferon (IFN-I) is produced in vivo and in vitro. IFN-I is essential for the establishment of an antiviral cellular response, and most if not all viruses have elaborated strategies to counteract its action. In this study, we assessed the ability of BTV to interfere with IFN-I synthesis and identified the nonstructural viral protein NS3 as an antagonist of the IFN-I system.

Dendritic cell subtypes from lymph nodes and blood show contrasted gene expression programs upon Bluetongue virus infection

Human and animal hemorrhagic viruses initially target dendritic cells (DCs). It has been proposed, but not documented, that both plasmacytoid DCs (pDCs) and conventional DCs (cDCs) may participate in the cytokine storm encountered in these infections. In order to evaluate the contribution of DCs in hemorrhagic virus pathogenesis, we performed a genome-wide expression analysis during infection by Bluetongue virus (BTV), a double-stranded RNA virus that induces hemorrhagic fever in sheep and initially infects cDCs. Both pDCs and cDCs accumulated in regional lymph nodes and spleen during BTV infection. The gene response profiles were performed at the onset of the disease and markedly differed with the DC subtypes and their lymphoid organ location. An integrative knowledge-based analysis revealed that blood pDCs displayed a gene signature related to activation of systemic inflammation and permeability of vasculature. In contrast, the gene profile of pDCs and cDCs in lymph nodes was oriented to inhibition of inflammation, whereas spleen cDCs did not show a clear functional orientation. These analyses indicate that tissue location and DC subtype affect the functional gene expression program induced by BTV and suggest the involvement of blood pDCs in the inflammation and plasma leakage/hemorrhage during BTV infection in the real natural host of the virus. These findings open the avenue to target DCs for therapeutic interventions in viral hemorrhagic diseases.

Recognition of pathogen-associated nucleic acids by endosomal nucleic acid-sensing toll-like receptors

Foreign nucleic acids, the essential signature molecules of invading pathogens that act as danger signals for host cells, are detected by endosomal nucleic acid-sensing toll-like receptors (TLRs) 3, 7, 8, 9, and 13. These TLRs have evolved to recognize ‘non-self’ nucleic acids within endosomal compartments and rapidly initiate innate immune responses to ensure host protection through induction of type I interferons, inflammatory cytokines, chemokines, and co-stimulatory molecules and maturation of immune cells. In this review, we highlight our understanding of the recognition of pathogen-associated nucleic acids and activation of corresponding signaling pathways through endosomal nucleic acid-sensing TLRs 3, 7, 8, 9, and 13 for an enormous diversity of pathogens, with particular emphasis on their compartmentalization, intracellular trafficking, proteolytic cleavage, autophagy, and regulatory programs.

Shrimp MyD88 responsive to bacteria and white spot syndrome virus

The myeloid differentiation factor 88 (MyD88) is an important adapter protein which links members of the toll-like receptor (TLR) to the downstream components to activate related signaling pathways. In the present study, a MyD88 homolog (FcMyD88) was cloned from penaeid shrimp Fenneropenaeus chinensis. The ORF of FcMyD88 consisted of 1434 bp encoding a polypeptide of 477 amino acids which contains a death domain (DD) and a typical TLR and interleukin-1 receptor (IL-1R)-related (TIR) domain. Homology analysis revealed that the predicted amino acid (aa) sequence of FcMyD88 shared high similarities with a variety of previously reported MyD88s. The time-dependent expression patterns of FcMyD88 in cephalothoraxes of shrimp injected with Vibrio anguillarum (Gram-negative bacteria, G(-)), Micrococcus lysodeikticu (Gram-positive bacteria, G(+)) and white syndrome spot virus (WSSV) were analyzed at transcription and protein level by real-time PCR and western blotting, respectively. The expression level of FcMyD88 mRNA was significantly up-regulated at one hour (h), 12 h and 24 h after stimulation with both V. anguillarum and M. lysodeikticu. The expression level of FcMyD88 protein was 2-fold up-regulated at 12 h post injection (hpi) of inactivated V. anguillarum while it didn't change after M. lysodeikticu injection during this period. After WSSV injection, the expression level of FcMyD88 mRNA remained relatively constant, while the FcMyD88 protein was significantly up-regulated at 12 and 24 hpi. These results suggested that the MyD88-dependent signaling pathway could be involved in the defense of both bacteria and WSSV infection.

Sensing and control of bluetongue virus infection in epithelial cells via RIG-I and MDA5 helicases

Bluetongue virus (BTV), an arthropod-borne member of the Reoviridae family, is a double-stranded RNA virus that causes an economically important livestock disease that has spread across Europe in recent decades. Production of type I interferon (alpha/beta interferon [IFN-α/β]) has been reported in vivo and in vitro upon BTV infection. However, the cellular sensors and signaling pathways involved in this process remain unknown. Here we studied the mechanisms responsible for the production of IFN-β in response to BTV serotype 8. Upon BTV infection of A549 cells, expression of IFN-β and other proinflammatory cytokines was strongly induced at both the protein and mRNA levels. This response appeared to be dependent on virus replication, since exposure to UV-inactivated virus failed to induce IFN-β. We also demonstrated that BTV infection activated the transcription factors IFN regulatory factor 3 and nuclear factor κB. We investigated the role of several pattern recognition receptors in this response and showed that expression of IFN-β was greatly reduced after small-interfering-RNA-mediated knockdown of the RNA helicase encoded by retinoic acid-inducible gene I (RIG-I) or melanoma differentiation-associated gene 5 (MDA5). In contrast, silencing of MyD88, Toll-like receptor 3, or the recently described DexD/H-box helicase DDX1 sensor had no or a weak effect on IFN-β induction, suggesting that the RIG-I-like receptor pathway is specifically engaged for BTV sensing. Moreover, we also showed that overexpression of either RIG-I or MDA5 impaired BTV expression in infected A549 cells. Overall, this indicates that RIG-I and MDA5 can both contribute to the recognition and control of BTV infection.

dsRNA-dependent protein kinase PKR and its role in stress, signaling and HCV infection

The double-stranded RNA-dependent protein kinase PKR plays multiple roles in cells, in response to different stress situations. As a member of the interferon (IFN)‑Stimulated Genes, PKR was initially recognized as an actor in the antiviral action of IFN, due to its ability to control translation, through phosphorylation, of the alpha subunit of eukaryotic initiation factor 2 (eIF2α). As such, PKR participates in the generation of stress granules, or autophagy and a number of viruses have designed strategies to inhibit its action. However, PKR deficient mice resist most viral infections, indicating that PKR may play other roles in the cell other than just acting as an antiviral agent. Indeed, PKR regulates several signaling pathways, either as an adapter protein and/or using its kinase activity. Here we review the role of PKR as an eIF2α kinase, its participation in the regulation of the NF-κB, p38MAPK and insulin pathways, and we focus on its role during infection with the hepatitis C virus (HCV). PKR binds the HCV IRES RNA, cooperates with some functions of the HCV core protein and may represent a target for NS5A or E2. Novel data points out for a role of PKR as a pro-HCV agent, both as an adapter protein and as an eIF2α-kinase, and in cooperation with the di-ubiquitin-like protein ISG15. Developing pharmaceutical inhibitors of PKR may help in resolving some viral infections as well as stress-related damages.