Dysfunctional immune response in the COVID-19 patients is a recurrent theme impacting symptoms and mortality, yet the detailed understanding of pertinent immune cells is not complete. We applied single-cell RNA sequencing to 284 samples from 196 COVID-19 patients and controls and created a comprehensive immune landscape with 1.46 million cells. The large dataset enabled us to identify that different peripheral immune subtype changes were associated with distinct clinical features including age, sex, severity, and disease stages of COVID-19. SARS-CoV-2 RNAs were found in diverse epithelial and immune cell types, accompanied by dramatic transcriptomic changes within viral positive cells. Systemic up-regulation of S100A8/A9, mainly by megakaryocytes and monocytes in the peripheral blood, may contribute to the cytokine storms frequently observed in severe patients. Our data provide a rich resource for understanding the pathogenesis and developing effective therapeutic strategies for COVID-19.

30Qing Mao (Phone +86 135 9418 0020;Abstract: An excessive immune response contributes to SARS-CoV, MERS-CoV and SARS-CoV-2 pathogenesis and lethality, but the mechanism remains unclear. In this study, the N proteins of SARS-CoV, MERS-CoV and SARS-CoV-2 were found to bind to MASP-2, the key serine protease in the lectin pathway of complement activation, resulting in aberrant complement activation and aggravated inflammatory lung injury. Either blocking the N protein:MASP-2 5 interaction or suppressing complement activation can significantly alleviate N protein-induced complement hyper-activation and lung injury in vitro and in vivo. Complement hyper-activation was also observed in COVID-19 patients, and a promising suppressive effect was observed when the deteriorating patients were treated with anti-C5a monoclonal antibody. Complement suppression may represent a common therapeutic approach for pneumonia induced by these 10 highly pathogenic coronaviruses. Short Title: SARS-CoV N over-activates complement by MASP-2One Sentence Summary: The lectin pathway of complement activation is a promising target for 15 the treatment of highly pathogenic coronavirus induced pneumonia.All rights reserved. No reuse allowed without permission.(which was not certified by peer review) is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity.

Several studies show that the immunosuppressive drugs targeting the interleukin-6 (IL-6) receptor, including tocilizumab, ameliorate lethal inflammatory responses in COVID-19 patients infected with SARS-CoV-2. Here, by employing single-cell analysis of the immune cell composition of two severe-stage COVID-19 patients prior to and following tocilizumabinduced remission, we identify a monocyte subpopulation that contributes to the inflammatory cytokine storms. Furthermore, although tocilizumab treatment attenuates the inflammation, immune cells, including plasma B cells and CD8 + T cells, still exhibit robust humoral and cellular antiviral immune responses. Thus, in addition to providing a highdimensional dataset on the immune cell distribution at multiple stages of the COVID-19, our work also provides insights into the therapeutic effects of tocilizumab, and identifies potential target cell populations for treating COVID-19-related cytokine storms.

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LET-767 from Caenorhabditis elegans belongs to a family of short chain dehydrogenases/reductases and is homologous to 17␤-hydroxysterol dehydrogenases of type 3 and 3-ketoacylCoA reductases. Worms subjected to RNA interference (RNAi) of let-767 displayed multiple growth and developmental defects in the first generation and arrested in the second generation as L1 larvae. To determine the function of LET-767 in vivo, we exploited a biochemical complementation approach, in which let-767 (RNAi)-arrested larvae were rescued by feeding with compounds isolated from wild type worms. The arrest was only rescued by the addition of triacylglycerides extracted from worms but not from various natural sources, such as animal fats and plant oils. The mass spectrometric analyses showed alterations in the fatty acid content of triacylglycerides. Essential for the rescue were odd-numbered fatty acids with monomethyl branched chains. The rescue was improved when worms were additionally supplemented with long chain even-numbered fatty acids. Remarkably, let-767 completely rescued the yeast 3-ketoacyl-CoA reductase mutant (ybr159⌬). Because worm ceramides exclusively contain a monomethyl branched chain sphingoid base, we also investigated ceramides in let-767 (RNAi). Indeed, the amount of ceramides was greatly reduced, and unusual sphingoid bases were observed. Taken together, we conclude that LET-767 is a major 3-ketoacyl-CoA reductase in C. elegans required for the bulk production of monomethyl branched and long chain fatty acids, and the developmental arrest in let-767 (RNAi) worms is caused by the deficiency of the former.The nematode Caenorhabditis elegans has emerged as a valuable model organism for studying metabolism, storage, and function of lipids (1-4). The worm genome encodes a large number of proteins implicated potentially into lipid binding or metabolism (5). These include more than 270 nuclear hormone receptors (6, 7), which might interact with the putative products of more than 80 cytochrome P450s (8) and several short chain dehydrogenases (9).Functional genomics and proteomics do not directly reveal substrate specificity, activity, and function of metabolic enzymes. In model organisms, such as C. elegans, their identification and functional annotation are typically achieved either (i) by classical biochemical genetics approach, where mutants are selected that fail to synthesize known metabolites, or (ii) by the reverse approach, where metabolites are identified based on their ability to complement mutations in a particular gene. A successful example of the first approach is delineating the synthesis of polyunsaturated fatty acids in C. elegans (10, 11), in which several mutants with abnormal fatty acid composition were isolated. The reverse complementation approach was used to identify a lipophilic fraction, which rescued reproductive development in dauer constitutive daf-2 and daf-9 mutants and contained the product of the cytochrome P450 DAF-9 dafachronic acid (12-14). Similarly, a sterol-related activity, which ...