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Dynamin-like GTPase proteins, including myxoma (Mx) and guanylate-binding proteins (GBPs), are among the many interferon stimulated genes induced following viral infections. While studies report that human (h)GBPs inhibit different viruses in vitro, few have convincingly demonstrated that mouse (m)GBPs mediate antiviral activity, although mGBP-deficient mice have been used extensively to define their importance in immunity to diverse intracellular bacteria and protozoa. Herein, we demonstrate that individual (overexpression) or collective (knockout (KO) mice) mGBPs of the chromosome 3 cluster (mGBPchr3) do not inhibit replication of five viruses from different virus families in vitro, nor do we observe differences in virus titres recovered from wild type versus mGBPchr3 KO mice after infection with three of these viruses (influenza A virus, herpes simplex virus type 1 or lymphocytic choriomeningitis virus). These data indicate that mGBPchr3 do not appear to be a major component of cell-intrinsic antiviral immunity against the diverse viruses tested in our studies. Mouse guanylate binding proteins of the chromosome 3 cluster (mGBPchr3) do not mediate potent antiviral activity against different human or mouse viruses in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Many interferon (IFN)‐stimulated genes are upregulated within host cells following infection with influenza and other viruses. While the antiviral activity of some IFN‐stimulated genes, such as the IFN‐inducible GTPase myxoma resistance (Mx)1 protein 1, has been well defined, less is known regarding the antiviral activities of related IFN‐inducible GTPases of the guanylate‐binding protein (GBP) family, particularly mouse GBPs, where mouse models can be used to assess their antiviral properties in vivo. Herein, we demonstrate that mouse GBP1 (mGBP1) was upregulated in a mouse airway epithelial cell line (LA‐4 cells) following pretreatment with mouse IFNα or infection by influenza A virus (IAV). Whereas doxycycline‐inducible expression of mouse Mx1 (mMx1) in LA‐4 cells resulted in reduced susceptibility to IAV infection and reduced viral growth, inducible mGBP1 did not. Moreover, primary cells isolated from mGBP1‐deficient mice (mGBP1−/−) showed no difference in susceptibility to IAV and mGBP1−/− macrophages showed no defect in IAV‐induced NLRP3 (NLR family pyrin domain containing 3) inflammasome activation. After intranasal IAV infection, mGBP1−/− mice also showed no differences in virus replication or induction of inflammatory responses in the airways during infection. Thus, using complementary approaches such as mGBP1 overexpression, cells from mGBP1−/− mice and intranasal infection of mGBP1−/− we demonstrate that mGBP1 does not play a major role in modulating IAV infection in vitro or in vivo. [ABSTRACT FROM AUTHOR]

Moraxella catarrhalis is an important human respiratory pathogen and a major causative agent of otitis media and chronic obstructive pulmonary disease. Toll‐like receptors contribute to, but cannot fully account for, the complexity of the immune response seen in M. catarrhalis infection. Using primary mouse bone marrow‐derived macrophages to examine the host response to M. catarrhalis infection, our global transcriptomic and targeted cytokine analyses revealed activation of immune signalling pathways by both membrane‐bound and cytosolic pattern‐recognition receptors. We show that M. catarrhalis and its outer membrane vesicles or lipooligosaccharide (LOS) can activate the cytosolic innate immune sensor caspase‐4/11, gasdermin‐D‐dependent pyroptosis, and the NLRP3 inflammasome in human and mouse macrophages. This pathway is initiated by type I interferon signalling and guanylate‐binding proteins (GBPs). We also show that inflammasomes and GBPs, particularly GBP2, are required for the host defence against M. catarrhalis in mice. Overall, our results reveal an essential role for the interferon‐inflammasome axis in cytosolic recognition and immunity against M. catarrhalis, providing new molecular targets that may be used to mitigate pathological inflammation triggered by this pathogen. Synopsis: The human respiratory pathogen Moraxella catarrhalis causes otitis media and chronic obstructive pulmonary disease. Multiple innate immune components mediate a host response against M. catarrhalis infection, including Toll‐like receptors, cGAS and STING, guanylate‐binding proteins (GBPs), and the caspase‐11‐NLRP3 inflammasome. M. catarrhalis and its secreted outer membrane vesicles deliver lipooligosaccharide (LOS) to activate the caspase‐11‐NLRP3 inflammasome.GBP1, GBP2, GBP3 and GBP5 (but not GBP4, GBP7, GBP8, GBP9 and GBP11) contribute to M. catarrhalis‐induced inflammasome activation by targeting intracellular bacteria.GBP recruitment to M. catarrhalis is independent of LOS, but GBPs facilitate membrane disruption and bacteriolysis to promote LOS release.The caspase‐11‐NLRP3 inflammasome and GBPs contribute to host defence against systemic M. catarrhalis infection. [ABSTRACT FROM AUTHOR]

Inflammasomes are cytosolic signaling complexes capable of sensing microbial ligands to trigger inflammation and cell death responses. Here, we show that guanylate-binding proteins (GBPs) mediate pathogen-selective inflammasome activation. We show that mouse GBP1 and GBP3 are specifically required for inflammasome activation during infection with the cytosolic bacterium Francisella novicida. We show that the selectivity of mouse GBP1 and GBP3 derives from a region within the N-terminal domain containing charged and hydrophobic amino acids, which binds to and facilitates direct killing of F. novicida and Neisseria meningitidis, but not other bacteria or mammalian cells. This pathogen-selective recognition by this region of mouse GBP1 and GBP3 leads to pathogen membrane rupture and release of intracellular content for inflammasome sensing. Our results imply that GBPs discriminate between pathogens, confer activation of innate immunity, and provide a host-inspired roadmap for the design of synthetic antimicrobial peptides that may be of use against emerging and re-emerging pathogens. Guanylate-binding proteins (GBP) have a function in inflammasome formation and pathogen defence. Here the authors show that these GBP proteins are able to kill certain bacteria and promote selective inflammasome activation and that this is mediated by specific GBP protein regions. [ABSTRACT FROM AUTHOR]

RIG-I is an innate sensor of RNA virus infection and its activation induces interferon-stimulated genes (ISGs). In vitro studies using human cells have demonstrated the ability of synthetic RIG-I agonists (3pRNA) to inhibit IAV replication. However, in mouse models of IAV the effectiveness of 3pRNA reported to date differs markedly between studies. Myxoma resistance (Mx)1 is an ISG protein which mediates potent anti-IAV activity, however most inbred mouse strains do not express a functional Mx1. Herein, we utilised C57BL/6 mice that do (B6.A2G-Mx1) and do not (B6-WT) express functional Mx1 to assess the ability of prophylactic 3pRNA treatment to induce ISGs and to protect against subsequent IAV infection. In vitro, 3pRNA treatment of primary lung cells from B6-WT and B6.A2G-Mx1 mice resulted in ISG induction however inhibition of IAV infection was more potent in cells from B6.A2G-Mx1 mice. In vivo, a single intravenous injection of 3pRNA resulted in ISG induction in lungs of both B6-WT and B6.A2G-Mx1 mice, however potent and long-lasting protection against subsequent IAV challenge was only observed in B6.A2G-Mx1 mice. Thus, despite broad ISG induction, expression of a functional Mx1 is critical for potent and long-lasting RIG-I agonist-mediated protection in the mouse model of IAV infection. [ABSTRACT FROM AUTHOR]