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Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has infected more than 35 million people globally, with more than 1 million deaths recorded by WHO as of Oct 12, 2020. As a second wave of COVID-19 affects Europe, and with winter approaching, we need clear communication about the risks posed by COVID-19 and effective strategies to combat them. Here, we share our view of the current evidence-based consensus on COVID-19.

Management of the global crisis of the coronavirus disease 2019 pandemic requires detailed appraisal of evidence to support clear, actionable, and consistent public health messaging. The use of cloth masks for general public use is being debated, and is in flux. We searched the MEDLINE and EMBASE databases and Google for articles reporting the filtration properties of flat cloth or cloth masks. We reviewed the reference lists of relevant articles to identify further articles and identified articles through social and conventional news media. We found 25 articles. Study of protection for the wearer used healthy volunteers, or used a manikin wearing a mask, with airflow to simulate different breathing rates. Studies of protection of the environment, also known as source control, used convenience samples of healthy volunteers. The design and execution of the studies was generally rigorously described. Many descriptions of cloth lacked the detail required for reproducibility; no study provided all the expected details of material, thread count, weave, and weight. Some of the homemade mask designs were reproducible. Successful masks were made of muslin at 100 threads per inch (TPI) in 3 to 4 layers (4-layer muslin or a muslin-flannel-muslin sandwich), tea towels (also known as dish towels), made using 1 layer (2 layers would be expected to be better), and good-quality cotton T-shirts in 2 layers (with a stitched edge to prevent stretching). In flat-cloth experiments, linen tea towels, 600-TPI cotton in 2 layers, and 600-TPI cotton with 90-TPI flannel performed well but 80-TPI cotton in 2 layers did not. We therefore recommend cotton or flannel at least 100 TPI, at least 2 layers. More layers, 3 or 4, will provide increased filtration but there is a trade-off in that more layers increases the resistance to breathing. Although this is not a systematic review, we included all the articles that we identified in an unbiased way. We did not include gray literature or preprints. A plain language summary of these data and recommendations, as well as information on making, wearing and cleaning cloth masks is available at www.clothmasks.ca.

We document here that intensive care COVID19 patients suffer a profound decline in hemoglobin levels but show an increase of circulating nucleated red cells, suggesting that SARS-CoV-2 infection either directly or indirectly induces stress erythropoiesis. However, the impact of SARS-CoV-2 on erythropoiesis has not been well investigated. We show that ACE2 expression peaks during erythropoiesis and renders erythroid progenitors vulnerable to infection by SARS-CoV-2. In particular, we characterize two erythroid progenitor populations as primary targets for the virus. Early erythroid progenitors, defined as CD34-CD117+CD71+CD235a-, show the highest levels of ACE2 and constitute the primary target cell to be infected during erythropoiesis. In addition, SARS-CoV-2 can also bind and infect mid-late erythroid precursors, defined as CD34-CD117-CD71+CD235a+. Our findings constitute the first report of SARS-CoV-2 infectivity in erythroid progenitor cells and can contribute to understanding both the clinical symptoms of severe COVID19 patients and how the virus can spread through the circulation to produce local inflammation in tissues, including the bone marrow. Funding: This work was supported by the Francis Crick Institute, which receives its core funding from Cancer Research UK (FC001045), the UK Medical Research Council (FC001045) and the Wellcome Trust (FC001045) to DB. Conflict of Interest: The authors declare no competing interests. Ethical Approval: Peripheral blood was isolated from consenting unscreened healthy adult volunteers following approved protocols by the ethics board of the Francis Crick Institute and the regulations of the Human Tissue act 2004. Peripheral blood mononuclear cells (PBMCs) were isolated by centrifugation over a Histopaque-1119 gradient (Sigma-Aldrich 11191).

Summary Although commonly associated with autophagosomes, LC3 can also be recruited to membranes by covalent lipidation in a variety of non-canonical contexts. These include responses to ionophores such as the M2 proton channel of influenza A virus. We report a subtractive CRISPR screen that identifies factors required for non-canonical LC3 lipidation. As well as the enzyme complexes directly responsible for LC3 lipidation in all contexts, we show the RALGAP complex is important for M2-induced, but not ionophore drug-induced, LC3 lipidation. In contrast, ATG4D is responsible for LC3 recycling in M2-induced and basal LC3 lipidation. Identification of a vacuolar ATPase subunit in the screen suggests a common mechanism for non-canonical LC3 recruitment. Influenza-induced and ionophore drug-induced LC3 lipidation lead to association of the vacuolar ATPase and ATG16L1 and can be antagonized by Salmonella SopF. LC3 recruitment to erroneously neutral compartments may therefore represent a response to damage caused by diverse invasive pathogens., Graphical abstract, Highlights • Subtractive CRISPR screen identifies genes involved in non-canonical LC3 lipidation • v-ATPase regulates LC3 lipidation at erroneously neutral compartments • RALGAP complex involved in M2 proton channel induced LC3 lipidation • ATG4D is responsible for LC3 recycling in M2-induced and basal LC3 lipidation, Ulferts et al. identify v-ATPase as the central regulator of ATG16L1 WD40 domain-dependent of LC3 lipidation. This lipidation can be prevented by Salmonella SopF and counteracted by ATG4D, the predominant ATG4 paralog responsible for LC3 delipidation. The RalGAP complex affects influenza virus M2-induced LC3 lipidation by affecting M2 trafficking.

Background In autophagy, cellular components are engulfed in a double membrane and recycled for their nutritional value. This mechanism has been adapted to defend cells against intracellular pathogens. Although viruses must evade autophagocytic destruction, they can also benefit from the resources that autophagy provides. We explored the molecular mechanisms by which influenza manipulates the autophagocytic machinery. Methods We used pull-down and fluorescence anisotropy assays to investigate the binding of the influenza A virus M2 proton channel to the essential autophagy protein LC3. The distribution of autophagosomes in infected cells was investigated by confocal microscopy. Construction of LIR-mutant viruses allowed us to investigate the importance of the interaction for subverting autophagy and the consequences for virion morphology and stability. Findings We found that binding to LC3 is mediated by a highly conserved LC3 interacting region (LIR) in the cytoplasmic tail of M2, the first such motif discovered in a pathogen. The M2 LIR is required for the redistribution of LC3 to the unusual destination of the plasma membrane in virus-infected cells. Mutations in M2 that abolish binding to LC3 interfere with filamentous budding and reduce virion stability. Interpretation We conclude that influenza A virus subverts autophagy by mimicking a host short linear protein–protein interaction motif. We suggest that this process occurs to provide adequate supply of membrane for virion production. This efficient strategy might facilitate transmission of infection between organisms by enhancing the stability of viral progeny. Funding Academy of Medical Sciences.