Analyse Influenza A Virus-vermittelter Veränderungen in der Reaktionsfähigkeit alveolarer Typ II Epithelzellen als zugrundeliegender Mechanismus einer erhöhten Anfälligkeit gegenüber sekundärer Pneumokokkeninfektionen
Zusammenfassung der Projektergebnisse
Infections with influenza A virus (IAV) lead to an increased susceptibility to secondary infections with opportunistic bacteria, especially Streptococcus pneumoniae. This hypersensitivity to pneumococci persists even after the IAV has been eliminated by the immune system and the organism is in the phase of recovery and regeneration of the lung tissue damaged by the viral infection. Alveolar epithelial cells type II (AECII) are primary targets of IAV and important effectors of antibacterial immune defense in the lung. Whether and how IAV infection alters AECII responses to pneumococci and whether such altered antibacterial AECII responses in the lung contribute to increased susceptibility to pneumococci was largely unclear and was the central question addressed in this project. To investigate this questions, we used a mouse model of IAV / S. pneumoniae superinfection. Specifically, mice were infected with a sublethal dose of mouse-adapted IAV PR/8/34 and superinfected with clinical pneumococcal isolates of varying invasiveness (serotypes 4>7F>19F) on day 14 after IAV infection. Animals infected exclusively with IAV or any of the 3 pneumococcal serotypes served as control groups. AECII were isolated by fluorescence-activated cell sorting, gene expression was analyzed by microarray, and epigenetic analyses were performed by Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq). The cytokine environment in the airways was analyzed by multiplex and enzyme immunoassays. Our analyses revealed that superinfection with both potentially invasive S. pneumoniae serotypes 4 and 7F, but not infection with the noninvasive serotype 19F, resulted in enhanced bacterial growth and dissemination of bacteria into the blood in the post-IAV lung. Interestingly, IAV infection prior to secondary pneumococcal infection favored a bacterial strain-dependent hyperinflammatory cytokine profile in the airways. This was characterized by, among others, increased interferon (IFN)-alpha and IFN-gamma production by alveolar macrophages and induction of a number of IFN response genes (IRGs) in AECII. The transcriptional response of AECII to 7F infection surprisingly resembled that to serotype 4 after a previous IAV infection, i.e., an isolate that is less pathogenic in monoinfection induces an immune response whose pattern resembles that of a highly pathogenic serotype. This particularly affected genes that correlate with the expression of two key regulators of the interferon response: Irf7 and Stat1. Epigenetic ATAC-seq analyses of AECII in prior IAV infection revealed increased expression of the ARACNE network genes Hist1h2bf, Igtp, Mki67, Rasl10b, H2-Q6, and H2-Q7, which are associated with increased chromatin accessibility in promoter regions. ATAC-seq analyses of AECII from healthy lungs compared with lungs 14 days after IAV infection revealed that several of the previously identified IRG DNA regions in AECII were more accessible after IAV infection, i.e., the increased expression of these genes in the course of bacterial superinfection was due to epigenetic changes induced in AECII by the previous IAV infection. Overall, we demonstrated that susceptibility to pneumococci persists after resolved IAV infection, but that this susceptibility is highly dependent on the pneumococcal serotype. We further show that AECII persistently retain an IAV-associated transcriptional pattern that, at least in part through epigenetic imprinting, serotype-specifically influences proliferation and accelerates and amplifies the AECII transcriptional response, mainly to interferons, upon secondary pneumococcal infection. Fortunately, the scientific impact of our research has been demonstrated by a broad interest in this project at international conferences. In addition, the clinical relevance of bacterial superinfection after previous viral infection - probably due to the broad public discussion about respiratory infections in connection with the SARS-CoV-2 pandemic - is obviously perceived more strongly. This is expressed, for example, by recent invitations to contribute and article on IAV-pneumococcal coinfections to the recognized German Medical Journal Deutsches Ärzteblatt and the invitation to give a lecture to the interested public on our current research in this field at the "Medical Sunday” in Magdeburg in October. The data from this project also formed the basis for three new successfully acquired projects in third-party funded scientific consortia.
Projektbezogene Publikationen (Auswahl)
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In vivo transcriptional program of type II alveolar epithelial cells in influenza and bacterial (co)infection. 19th Fraunhofer Seminar "Models of Lung Disease", Hannover, Germany
Dunja Bruder
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It ain’t over when it’s over – recovery from flu involves profound changes in antipneumococcal functions of alveolar type II epithelial cells. Gordon Research Conference "Biology of Acute Respiratory Infection”, 2020, Galveston, Texas, USA
Julia D. Boehme
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CD47 restricts antiviral function of alveolar macrophages during influenza virus infection. iScience, 25(12), 105540.
Wenzek, Christina; Steinbach, Philine; Wirsdörfer, Florian; Sutter, Kathrin; Boehme, Julia D.; Geffers, Robert; Klopfleisch, Robert; Bruder, Dunja; Jendrossek, Verena; Buer, Jan; Westendorf, Astrid M. & Knuschke, Torben
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FOCIS annual meeting, 2022, San Francisco, California, USA – Hybrid meeting "Maladapted antibacterial epithelial response in the post-influenza lung as a potential driver for enhanced susceptibility to bacterial superinfection” (invited talk)
Julia D. Boehme; Dunja Bruder
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Maladapted epithelial response in the post-influenza lung as a potential driver for enhanced susceptibility to bacterial superinfection. 2nd Summer School "Infection Biology" 2022, Greifswald, Germany
Dunja Bruder
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Resolved Influenza A virus infection rewires epithelial gene regulatory networks and antipneumococcal interferon responses in a bacterial strain-dependent manner. 50th Annual Meeting of the Australian and New Zealand Society for Immunology, 2022, Melbourne, Australia
Julia D. Boehme
