Activation Of Antiviral Response Research Articles

Antiviral responses are shaped by heterogeneity in viral replication dynamics.

Antiviral signalling, which can be activated in host cells upon virus infection, restricts virus replication and communicates infection status to neighbouring cells. The antiviral response is heterogeneous, both quantitatively (efficiency of response activation) and qualitatively (transcribed antiviral gene set). To investigate the basis of this heterogeneity, we combined Virus Infection Real-time IMaging (VIRIM), a live-cell single-molecule imaging method, with real-time readouts of the dsRNA sensing pathway to analyse the response of human cells to encephalomyocarditis virus (EMCV) infection. We find that cell-to-cell heterogeneity in viral replication rates early in infection affect the efficiency of antiviral response activation, with lower replication rates leading to more antiviral response activation. Furthermore, we show that qualitatively distinct antiviral responses can be linked to the strength of the antiviral signalling pathway. Our analyses identify variation in early viral replication rates as an important parameter contributing to heterogeneity in antiviral response activation.

Abstract 4495: DNA demethylation promotes ERV expression and activation of immune signaling in renal cell cancer cells

Abstract Recently, we reported that expression of endogenous retroviruses (ERVs), a class of transposable element, is associated with response to immune checkpoint blockade (ICB) in renal cell carcinoma (RCC). Aberrant expression of ERVs can activate host antiviral responses, as well as produce neoantigens. ERV expression is repressed by DNA methylation and can be activated by DNA hypomethylating agents. Here, we investigate whether Decitabine, a DNA hypomethylating agent, can activate ERV expression and host antiviral defenses in RCC to potentially enhance response to ICB. Decitabine induced expression of ERV3-2 and ERV4700 in RCC cells lines, which was accompanied by activation of host antiviral defense genes and increased secretion of inflammatory cytokines. We validated this effect in primary human RCC cell lines. Knockout of RIG-I and MDA5 dsRNA sensors attenuated activation of antiviral responses associated with Decitabine treatment, and RIG-I and MDA5 immunoprecipitations showed increased ERV binding in RCC cells treated with Decitabine. Bioinformatic analysis of RNAseq data showed the Decitabine-induced gene signature could be associated with increased CD8 infiltration and response to ICB. Conditioned media from Decitabine treated RCC cells was capable of inducing host anti-viral defense in naïve RCC cells and could modestly improve activation of T-cells from healthy donors. Further, conditioned media from RCC cells treated with Decitabine significantly enhanced T-cell migration. In a small retrospective cohort of metastatic RCC patients treated with single-agent PD-1/PD-L1 blockade, activation of some host antiviral defense genes was significantly higher in responders compared with nonresponders. Thus, modulation of ERV expression by Decitabine to activate host antiviral defenses could represent a novel therapeutic strategy to enhance RCC patient response to immune checkpoint blockade. Citation Format: Aguirre A. de Cubas, William Dunker, Rachel Hongo, Anuj Bhatia, Andrew Zaninovich, Anshuman Panda, Kathryn E. Beckermann, Gyan Bhanot, Shridar Ganesan, John Karijolich, W K. Rathmell. DNA demethylation promotes ERV expression and activation of immune signaling in renal cell cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4495.

Influence of Dietary Supplementation of Probiotic Pediococcus acidilactici MA18/5M During the Transition From Freshwater to Seawater on Intestinal Health and Microbiota of Atlantic Salmon (Salmo salar L.).

The aim of this study was to assess the effect of the transfer from freshwater to seawater on the distal intestinal bacterial communities of Atlantic salmon (Salmo salar L.) and to evaluate the effect of dietary inclusion of Pediococcus acidilactici MA18/5M (at 1.19 × 106 CFU/g). In this context, fish health and antiviral response were also investigated. A 12-week feeding trial was conducted in a flow-through rearing system involving 6 weeks in freshwater and 6 weeks in seawater. Fish received a control and probiotic diet. The composition of the salmon gut bacterial communities was determined by high-throughput sequencing of digesta and mucosa samples from both the freshwater and seawater stage. The main phyla detected during both freshwater and seawater stages were Firmicutes, Proteobacteria, Fusobacteria, and Actinobacteria. Significant differences were observed between the intestinal microbiota in the digesta and the mucosa. Both probiotic supplementation and the seawater transfer (SWT) had a substantial impact on the microbial communities, with most pronounced changes detected in the mucosal communities after SWT. This last finding together with a significantly higher antiviral response (mx-1 and tlr3 gene expression) in the distal intestine of fish fed the probiotic diet suggest a causal link between the microbiota modulation and activation of antiviral response. Feeding probiotics during the freshwater stage did not significantly increase survival after infectious pancreatic necrosis virus (IPNV) challenge after SWT, although higher survival was observed in one out of two replicate challenge tanks. In conclusion, this study demonstrated that both dietary probiotic supplementation and transfer from freshwater to seawater have an important role in modulating the bacterial communities in the distal intestine of Atlantic salmon. Furthermore, supplementation of the diet with P. acidilactici MA18/5M can modulate antiviral response.

Respiratory epithelial cells as master communicators during viral infections.

Purpose of ReviewCommunication by epithelial cells during respiratory viral infections is critical in orchestrating effective antiviral responses but also can lead to excessive inflammation. This review will evaluate studies that investigate how respiratory epithelial cells influence the behavior of immune cells and how epithelial cell/immune cell interactions contribute to antiviral responses and immunopathology outcomes.Recent FindingsPrevious studies have characterized cytokine responses of virus-infected epithelial cells. More recent studies have carefully demonstrated the effects of these cytokines on cellular behaviors within the infected lung. Infected epithelial cells release exosomes that specifically regulate responses of monocytes and neighboring epithelial cells without promoting spread of virus. In contrast, rhinovirus-infected cells induce monocytes to upregulate expression of the viral receptor, promoting spread of the virus to alternate cell types. The precise alteration of PDL expression on infected epithelial cells has been shown to switch between inhibition and activation of antiviral responses.SummaryThese studies have more precisely defined the interactions between epithelial and immune cells during viral infections. This level of understanding is critical for the development of novel therapeutic strategies that promote effective antiviral responses or epithelial repair or inhibit damaging inflammatory responses during severe respiratory viral infections.

Post-translational regulation of antiviral innate signaling.

The innate immune system initiates immune responses by pattern‐recognition receptors (PRR). Virus‐derived nucleic acids are sensed by the retinoic acid‐inducible gene I (RIG‐I)‐like receptor (RLR) family and the toll‐like receptor (TLR) family as well as the DNA sensor cyclic GMP‐AMP (cGAMP) synthase (cGAS). These receptors activate IRF3/7 and NF‐κB signaling pathways to induce the expression of type I interferons (IFNs) and other cytokines firing antiviral responses within the cell. However, to achieve a favorable outcome for the host, a balanced production of IFNs and activation of antiviral responses is required. Post‐translational modifications (PTMs), such as the covalent linkage of functional groups to amino acid chains, are crucial for this immune homeostasis in antiviral responses. Canonical PTMs including phosphorylation and ubiquitination have been extensively studied and other PTMs such as methylation, acetylation, SUMOylation, ADP‐ribosylation and glutamylation are being increasingly implicated in antiviral innate immunity. Here we summarize our recent understanding of the most important PTMs regulating the antiviral innate immune response, and their role in virus‐related immune pathogenesis.

Rapid induction and persistence of paracrine-induced cellular antiviral states arrest viral infection spread in A549 cells

The virus/host interaction is a complex interplay between pro- and anti-viral factors that ultimately determines the spread or halt of virus infections in tissues. This interplay develops over multiple rounds of infection. The purpose of this study was to determine how cellular-level processes combine to impact the spatial spread of infection. We measured the kinetics of virus replication (VSV), antiviral paracrine signal upregulation and secretion, spatial spread of virus and paracrine antiviral signaling, and inhibition of virus production in antiviral-exposed A549 human lung epithelial cells. We found that initially infected cells released antiviral signals 4-to-7h following production of virus. However, the subsequent rapid dissemination of signal and fast induction of a robust and persistent antiviral state ultimately led to a suppression of infection spread. This work shows how cellular responses to infection and activation of antiviral responses can integrate to ultimately control infection spread across host cell populations.

Phosphorylation and Dephosphorylation of the RIG-I-like Receptors: A Safety Latch on a Fateful Pathway

Activation of antiviral responses by RNA sensors RIG-I and MDA5 must be stringently controlled. In this issue of Immunity, Wies etal. (2013) show that a requirement for activation-induced dephosphorylation of these proteins reinforces this restriction.

Toll-Like Receptor Tag Team

Cell Signaling How many receptors does it take to initiate an antiviral response? Yamashita et al. say it's two, plus an additional tyrosine kinase. First, you need Toll-like Receptor 3 (TLR3), which has a well-characterized role in the detection of double-stranded RNA (dsRNA) and initiation of protective cellular responses. Earlier findings showed that TLR3 differs from other TLRs in requiring phosphorylation of two tyrosine residues in its cytoplasmic tail for activation. Here, another receptor is implicated in the activation of antiviral responses by TLR3—the epidermal growth factor receptor (EGFR), which is itself a tyrosine kinase. The EGFR was found to associate with dsRNA-activated TLR3 in endosomal membranes along with another tyrosine kinase, Src. Both EGFR and Src appeared to phosphorylate a particular tyrosine residue in TLR3, and inhibition of the kinases inhibited TLR3-dependent antiviral responses. Thus, antiviral responses may involve interactions between signaling systems controlling cell growth and those mediating innate immune responses. Sci. Signal. 5 , ra50 (2012).

Polyinosinic‐polycytidylic acid suppresses acetaminophen‐induced hepatotoxicity independent of type I interferons and toll‐like receptor 3

Viral infections are often linked to altered drug metabolism in patients; however, the underlying molecular mechanisms remain unclear. Here we describe a mechanism by which activation of antiviral responses by the synthetic double-stranded RNA ligand, polyinosinic-polycytidylic acid (polyI:C), leads to decreased acetaminophen (APAP) metabolism and hepatotoxicity. PolyI:C administration down-regulates expression of retinoic X receptor-α (RXRα) as well as its heterodimeric partner pregnane X receptor (PXR) in mice. This down-regulation results in suppression of downstream cytochrome P450 enzymes involved in conversion of APAP to its toxic metabolite. Although the effects of polyI:C on drug metabolism are often attributed to interferon production, we report that polyI:C can decrease APAP metabolism in the absence of the type I interferon receptor. Furthermore, we demonstrate that polyI:C can attenuate APAP metabolism through both its membrane-bound receptor, Toll-like receptor 3 (TLR3), as well as cytoplasmic receptors. This is the first study to illustrate that in vivo administration of polyI:C affects drug metabolism independent of type I interferon production or in the absence of TLR3 through crosstalk between nuclear receptors and antiviral responses.

Influenza A Virus Polymerase Inhibits Type I Interferon Induction by Binding to Interferon β Promoter Stimulator 1

Type I interferons (IFNs) are known to be critical factors in the activation of host antiviral responses and are also important in protection from influenza A virus infection. Especially, the RIG-I- and IPS-1-mediated intracellular type I IFN-inducing pathway is essential in the activation of antiviral responses in cells infected by influenza A virus. Previously, it has been reported that influenza A virus NS1 is involved in the inhibition of this pathway. We show in this report that the influenza A virus utilizes another critical inhibitory mechanism in this pathway. In fact, the viral polymerase complex exhibited an inhibitory activity on IFNβ promoter activation mediated by RIG-I and IPS-1, and this activity was not competitive with the function of NS1. Co-immunoprecipitation analysis revealed that each polymerase subunit bound to IPS-1 in mammalian cells, and each subunit inhibited the activation of IFNβ promoter by IPS-1 independently. In addition, by a combinational expression of each polymerase subunit, IPS-1-induced activation of IFNβ promoter was more efficiently inhibited by the expression of PB2 or PB2-containing complex. Moreover, the expression of PB2 inhibited the transcription of the endogenous IFNβ gene induced after influenza A virus infection. These findings demonstrate that the viral polymerase plays an important role for regulating host anti-viral response through the binding to IPS-1 and inhibition of IFNβ production.

Competition between wild-type virus and a reassortant from subgroups I and II of CMV and activation of antiviral responses in cowpea

To investigate the interactions between RNA3 and RNA4 from subgroups I and II in mixed infections, accumulation of CMV RNA were analyzed. In the mixed inoculation assays with CMV-LE (LE, subgroup I) and a reassortant LLm consisting of RNA1 and RNA2 from LE, and RNA3 from CMV-m2 (m2, subgroup II), LE RNA3 and RNA4 could systemically spread in the plants, whereas those of m2 could not. Furthermore, accumulation of virus short RNA and a cowpea-encoded RNA-directed RNA polymerase gene (VuRdRP1) mRNA were found in the plants, suggesting that VIGS and/or distinct antiviral responses (was) were activated by infection with CMV.