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SARS-CoV-2 Evades immune detection in Alveolar Macrophages

ABSTRACT: Respiratory infections, like the current pandemic SARS-CoV-2 virus, target the epithelial cells in the respiratory tract. However, alveolar macrophages (AMs) are tissue-resident macrophages located within the alveoli of the lung and they play a key role in the early phases of an immune response to respiratory infections. We expect that AMs are the first immune cells to encounter the SARS-CoV-2 and therefore their reaction to SARS-CoV-2 infection will have a profound impact upon the outcome of the infection. Interferons (IFNs) are antiviral cytokines and the first cytokine produced upon viral infection. Here, we challenge AMs with SARS-CoV-2 and to our surprise find that the AMs are incapable of recognising SARS-CoV-2 and produce IFN. This is in contrast to respiratory pathogens, such as influenza A virus and Sendai virus. Callenge of AMs with those viruses resulted in a robust IFN response. The absence of IFN production by AMs upon challenge could explain the initial asymptotic phase of SARS-CoV-2 infections and argues against the AMs as the source of proinflamatory cytokines later in infection.

INSTRUMENT(S): Orbitrap Eclipse

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Primary Cell, Lung, Macrophage

DISEASE(S): Covid-19,Severe Acute Respiratory Syndrome Coronavirus 2

SUBMITTER: Ebbe Toftgaard Poulsen

LAB HEAD: Jan J. Enghild

PROVIDER: PXD021685 | Pride | 2020-10-20

REPOSITORIES: Pride

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Project description:Background: Type I interferons (IFNs) are essential to the clearance of viral diseases, in part by initiating upregulation of IFN regulated genes (IRGs). A clear distinction between genes upregulated directly by virus and genes upregulated by secondary IFN production has not been made. Here we investigated the genes regulated by IFN-a2b compared to the genes regulated by SARS-CoV infection in ferrets. Methods: We characterized early host immune responses in peripheral blood and lung necropsies of ferrets injected with IFN-a2b or infected with SARS-CoV/Tor 2 strain, using microarray analysis on the Affymetrix platform. Results: We identified a common IRG signature that was upregulated in both SARS-CoV infected ferrets as well as in ferrets injected with IFN-a2b. We also identified unique patterns of gene expression for leukocyte activation, cell adhesion and complement pathways between IFN-a2b injection and SARS-CoV infection. Conclusions: Our results define the effects of IFN-a2b on the immune system of ferrets highlighting genes regulated by IFN during SARS-CoV infection. We have shown the similarities and differences of top funcional gene groups as well as pathways that play key roles in early immune responses in ferrets in response to IFN-a2b or SARS-CoV. Key words: ferret, gene expression, SARS, interferon. Keywords: time course In experiments with IFN-a2b, for peripheral blood, 15 ferrets were randomly allocated to 3 groups: Day 0, 5 ferrets (no IFN injection), day 1, 6 ferrets (injected), and day 2, 4 ferrets (injected). For lung necropsies of injected ferrets with IFN-a2b, we used 12 ferrets in 3 groups: 4 ferrets, day 0 (no IFN injection), 4 ferrets, day 1 (injected) and 4 ferrets, day 2 (injected). Experimental groups for SARS-CoV infection was as follows: For peripheral blood, 3 and 4 ferrets for day 0 (no infection) and day 2 (infection) respectively. For lung neceropsies, a total of 9 ferrets in 3 groups, each with 3 replicates for day 0 (no infection), day 1 (infection) and day 2 (infection).

Project description:We previously reported widespread differential expression of long non-protein-coding RNAs (ncRNAs) in response to virus infection. Here, we expanded the study through small RNA transcriptome sequencing analysis of the host response to both severe acute respiratory syndrome coronavirus (SARS-CoV) and influenza virus infections across four founder mouse strains of the Collaborative Cross, a recombinant inbred mouse resource for mapping complex traits. We observed differential expression of over 200 small RNAs of diverse classes during infection. A majority of identified microRNAs (miRNAs) showed divergent changes in expression across mouse strains with respect to SARS-CoV and influenza virus infections and responded differently to a highly pathogenic reconstructed 1918 virus compared to a minimally pathogenic seasonal influenza virus isolate. Novel insights into miRNA expression changes, including the association with pathogenic outcomes and large differences between in vivo and in vitro experimental systems, were further elucidated by a survey of selected miRNAs across diverse virus infections. The small RNAs identified also included many non-miRNA small RNAs, such as small nucleolar RNAs (snoRNAs), in addition to nonannotated small RNAs. An integrative sequencing analysis of both small RNAs and long transcripts from the same samples showed that the results revealing differential expression of miRNAs during infection were largely due to transcriptional regulation and that the predicted miRNA-mRNA network could modulate global host responses to virus infection in a combinatorial fashion. These findings represent the first integrated sequencing analysis of the response of host small RNAs to virus infection and show that small RNAs are an integrated component of complex networks involved in regulating the host response to infection. IMPORTANCE: Most studies examining the host transcriptional response to infection focus only on protein-coding genes. However, mammalian genomes transcribe many short and long non-protein-coding RNAs (ncRNAs). With the advent of deepsequencing technologies, systematic transcriptome analysis of the host response, including analysis of ncRNAs of different sizes, is now possible. Using this approach, we recently discovered widespread differential expression of host long (>200 nucleotide[nt]) ncRNAs in response to virus infection. Here, the samples described in the previous report were again used, but we sequenced another fraction of the transcriptome to study very short (about 20 to 30 nt) ncRNAs. We demonstrated that virus infection also altered expression of many short ncRNAs of diverse classes. Putting the results of the two studies together, we show that small RNAs may also play an important role in regulating the host response to virus infection. The small RNA transcriptome deep sequencing analysis was performed on lung samples from our previously published study (Unique signatures of long noncoding RNA expression in response to virus infection and altered innate immune signaling , X Peng, MBio. 2010 Oct 26;1(5). pii: e00206-10.). We infected four of the eight founder mouse strains used in generating the Collaborative Cross, a recombinant inbred mouse resource for mapping complex traits (41). These strains included 129S1/SvImJ (129/S1), WSB/EiJ (WSB), PWK/PhJ (PWK), and CAST/EiJ (CAST) mice. Ten-week-old mice were intranasally infected with phosphate-buffered saline (PBS) alone or with 1X10^5 PFU of mouse adapted severe acute respiratory syndrome coronavirus (SARS-CoV; rMA15), or 500 PFU of influenza A virus strain A/Pr/8/34 (H1N1; PR8). To match the previous whole-transcriptome analysis, we performed small RNA transcriptome sequencing analysis on the same eight samples from mice with SARS-CoV infections, including one SARS-CoV rMA15-infected mouse and one matched mock-infected mouse from each of the four strains at 2 days postinfection (dpi). In addition, we sequenced the small RNA transcriptome for 12 samples obtained from influenza virus infected mice, including two PR8-infected mice and one matched mockinfected mouse from each of the four strains at 2 dpi.

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SARS-CoV-2 Evades immune detection in Alveolar Macrophages

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