An Accessory to the ‘Trinity’: SR-As Are Essential Pathogen Sensors of Extracellular dsRNA, Mediating Entry and Leading to Subsequent Type I IFN Responses

Extracellular RNA is becoming increasingly recognized as a signaling molecule. Virally derived double stranded (ds)RNA released into the extracellular space during virus induced cell lysis acts as a powerful inducer of classical type I interferon (IFN) responses; however, the receptor that mediates this response has not been identified. Class A scavenger receptors (SR-As) are likely candidates due to their cell surface expression and ability to bind nucleic acids. In this study, we investigated a possible role for SR-As in mediating type I IFN responses induced by extracellular dsRNA in fibroblasts, a predominant producer of IFNβ. Fibroblasts were found to express functional SR-As, even SR-A species thought to be macrophage specific. SR-A specific competitive ligands significantly blocked extracellular dsRNA binding, entry and subsequent interferon stimulated gene (ISG) induction. Candidate SR-As were systematically investigated using RNAi and the most dramatic inhibition in responses was observed when all candidate SR-As were knocked down in unison. Partial inhibition of dsRNA induced antiviral responses was observed in vivo in SR-AI/II-/- mice compared with WT controls. The role of SR-As in mediating extracellular dsRNA entry and subsequent induced antiviral responses was observed in both murine and human fibroblasts. SR-As appear to function as ‘carriers’, facilitating dsRNA entry and delivery to the established dsRNA sensing receptors, specifically TLR3, RIGI and MDA-5. Identifying SR-As as gatekeepers of the cell, mediating innate antiviral responses, represents a novel function for this receptor family and provides insight into how cells recognize danger signals associated with lytic virus infections. Furthermore, the implications of a cell surface receptor capable of recognizing extracellular RNA may exceed beyond viral immunity to mediating other important innate immune functions

The Nitric Oxide Pathway Provides Innate Antiviral Protection in Conjunction with the Type I Interferon Pathway in Fibroblasts

The innate host response to virus infection is largely dominated by the production of type I interferon and interferon stimulated genes. In particular, fibroblasts respond robustly to viral infection and to recognition of viral signatures such as dsRNA with the rapid production of type I interferon; subsequently, fibroblasts are a key cell type in antiviral protection. We recently found, however, that primary fibroblasts deficient for the production of interferon, interferon stimulated genes, and other cytokines and chemokines mount a robust antiviral response against both DNA and RNA viruses following stimulation with dsRNA. Nitric oxide is a chemical compound with pleiotropic functions; its production by phagocytes in response to interferon-γ is associated with antimicrobial activity. Here we show that in response to dsRNA, nitric oxide is rapidly produced in primary fibroblasts. In the presence of an intact interferon system, nitric oxide plays a minor but significant role in antiviral protection. However, in the absence of an interferon system, nitric oxide is critical for the protection against DNA viruses. In primary fibroblasts, NF-κB and interferon regulatory factor 1 participate in the induction of inducible nitric oxide synthase expression, which subsequently produces nitric oxide. As large DNA viruses encode multiple and diverse immune modulators to disable the interferon system, it appears that the nitric oxide pathway serves as a secondary strategy to protect the host against viral infection in key cell types, such as fibroblasts, that largely rely on the type I interferon system for antiviral protection

Successful aging, change in sexual interest and sexual satisfaction in couples from four European countries

Although the importance of sexuality and physical intimacy for well-being of older adults has been recognized, the role of sexuality in successful aging (SA) has been largely neglected. Building on our previous work, here we further validated a three-dimensional model of SA and examined its associations with sexual satisfaction and change in sexual interest among older heterosexual couples (aged 60–75 years). Participants were recruited in a probability-based survey, which was carried out in 2016–2017 in four European countries. Using structural equation modeling of the Actor–Partner Interdependence, we observed significant relationships between SA and sexual satisfaction for both male and female partners across countries. Among women, their retrospectively assessed change in sexual interest over the past 10 years was consistently associated with sexual satisfaction. Partner effects were gender-specific: male partners’ SA was significantly related to their female partners’ change in sexual interest, which in turn was linked to male partners’ sexual satisfaction. The findings point to substantial ties between successful aging and sexuality in older European couples. Taking into account the prevalent stereotypes about old age and sexuality, this study’s findings can assist professionals working with aging couples

Interferon Regulatory Factor-1 (IRF-1) Shapes Both Innate and CD8+ T Cell Immune Responses against West Nile Virus Infection

Interferon regulatory factor (IRF)-1 is an immunomodulatory transcription factor that functions downstream of pathogen recognition receptor signaling and has been implicated as a regulator of type I interferon (IFN)-αβ expression and the immune response to virus infections. However, this role for IRF-1 remains controversial because altered type I IFN responses have not been systemically observed in IRF-1-/- mice. To evaluate the relationship of IRF-1 and immune regulation, we assessed West Nile virus (WNV) infectivity and the host response in IRF-1-/- cells and mice. IRF-1-/- mice were highly vulnerable to WNV infection with enhanced viral replication in peripheral tissues and rapid dissemination into the central nervous system. Ex vivo analysis revealed a cell-type specific antiviral role as IRF-1-/- macrophages supported enhanced WNV replication but infection was unaltered in IRF-1-/- fibroblasts. IRF-1 also had an independent and paradoxical effect on CD8+ T cell expansion. Although markedly fewer CD8+ T cells were observed in naïve animals as described previously, remarkably, IRF-1-/- mice rapidly expanded their pool of WNV-specific cytolytic CD8+ T cells. Adoptive transfer and in vitro proliferation experiments established both cell-intrinsic and cell-extrinsic effects of IRF-1 on the expansion of CD8+ T cells. Thus, IRF-1 restricts WNV infection by modulating the expression of innate antiviral effector molecules while shaping the antigen-specific CD8+ T cell response

Effects of viral hemorrhagic septicemia virus (VHSV) on the rainbow trout (Oncorhynchus mykiss) monocyte cell line RTS-11

The effect of viral hemorrhagic septicemia virus (VHSV) was studied on the established rainbow trout (Oncorhynchus mykiss) monocyte/macrophage-like cell line RTS11. The virus was not able to complete its replication cycle as infectious viral particles were not released from the cells. However, in RTS11, the virus was capable of producing mRNA from at least its N and G genes. At the protein level, only N protein was detected 2 days post-infection, whereas a faint band corresponding to the G protein was also observed after 5 days post-infection. These results suggest an interruption of viral protein translation at some point. The expression of N mRNA was significantly inhibited in cells pre-treated with Poly IC, but not affected by 2-aminopurine (2-AP), an inhibitor of the dsRNA-dependent protein kinase (PKR), thus indicating that PKR has no effect on mRNA expression directly. However, when cells were preincubated with Poly IC in the presence of 2-AP, the levels of N mRNA were restored suggesting that Poly IC can limit viral transcription through an antiviral mechanism dependent of PKR. The effect of VHSV on the expression of transcripts for different immune genes was determined, but significant induction was found only for genes related to the type I interferon (IFN) response, such as IFN-1 and -2 and the three Mx isoforms. Heat-inactivated virus failed to induce IFN-1 and -2, suggesting that early events in the VHSV life cycle were necessary for the type I IFN response. Poly IC alone also induced transcripts for the antiviral Mx proteins. Prior exposure of RTS11 to VHSV did not prevent Poly IC from inducing transcripts for Mx1, Mx2 and Mx3. Perhaps the failure of VHSV to disable antiviral mechanisms in RTS11 accounts for the aborted infections. © 2007 Elsevier Ltd. All rights reserved

Extracellular dsRNA induces a type I interferon response mediated via class A scavenger receptors in a novel Chinook salmon derived spleen cell line

Despite increased global interest in Chinook salmon aquaculture, little is known of their viral immune defenses. This study describes the establishment and characterization of a continuous cell line derived from Chinook salmon spleen, CHSS, and its use in innate immune studies. Optimal growth was seen at 14–18 °C when grown in Leibovitz\u27s L-15 media with 20% fetal bovine serum. DNA analyses confirmed that CHSS was Chinook salmon and genetically different from the only other available Chinook salmon cell line, CHSE-214. Unlike CHSE-214, CHSS could bind extracellular dsRNA, resulting in the rapid and robust expression of antiviral genes. Receptor/ ligand blocking assays confirmed that class A scavenger receptors (SR-A) facilitated dsRNA binding and subsequent gene expression. Although both cell lines expressed three SR-A genes: SCARA3, SCARA4, and SCARA5, only CHSS appeared to have functional cell-surface SR-As for dsRNA. Collectively, CHSS is an excellent cell model to study dsRNA-mediated innate immunity in Chinook salmon

Membrane Perturbation Elicits an IRF3-Dependent, Interferon-Independent Antiviral Response ▿ †

We previously found that enveloped virus binding and penetration are necessary to initiate an interferon-independent, IRF3-mediated antiviral response. To investigate whether membrane perturbations that accompany membrane fusion-dependent enveloped-virus entry are necessary and sufficient for antiviral-state induction, we utilized a reovirus fusion-associated small transmembrane (FAST) protein. Membrane disturbances during FAST protein-mediated fusion, in the absence of additional innate immune response triggers, are sufficient to elicit interferon-stimulated gene induction and establishment of an antiviral state. Using sensors of membrane disruption to activate an IRF3-dependent, interferon-independent antiviral state may provide cells with a rapid, broad-spectrum innate immune response to enveloped-virus infections