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Mast cells (MCs) play a pathobiologic role in type 2 (T2) allergic inflammatory diseases of the airway, including asthma and chronic rhinosinusitis with nasal polyposis (CRSwNP). Distinct MC subsets infiltrate the airway mucosa in T2 disease, including subepithelial MCs expressing the proteases tryptase and chymase (MC TC ) and epithelial MCs expressing tryptase without chymase (MC T ). However, mechanisms underlying MC expansion and the transcriptional programs underlying their heterogeneity are poorly understood. Here, we use flow cytometry and single-cell RNA-sequencing (scRNA-seq) to conduct a comprehensive analysis of human MC hyperplasia in CRSwNP, a T2 cytokine-mediated inflammatory disease. We link discrete cell surface phenotypes to the distinct transcriptomes of CRSwNP MC T and MC TC , which represent polarized ends of a transcriptional gradient of nasal polyp MCs. We find a subepithelial population of CD38 high CD117 high MCs that is markedly expanded during T2 inflammation. These CD38 high CD117 high MCs exhibit an intermediate phenotype relative to the expanded MC T and MC TC subsets. CD38 high CD117 high MCs are distinct from circulating MC progenitors and are enriched for proliferation, which is markedly increased in CRSwNP patients with aspirin-exacerbated respiratory disease, a severe disease subset characterized by increased MC burden and elevated MC activation. We observe that MCs expressing a polyp MC T -like effector program are also found within the lung during fibrotic diseases and asthma, and further identify marked differences between MC TC in nasal polyps and skin. These results indicate that MCs display distinct inflammation-associated effector programs and suggest that in situ MC proliferation is a major component of MC hyperplasia in human T2 inflammation., (Copyright © 2021 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

There is pressing urgency to understand the pathogenesis of the severe acute respiratory syndrome coronavirus clade 2 (SARS-CoV-2), which causes the disease COVID-19. SARS-CoV-2 spike (S) protein binds angiotensin-converting enzyme 2 (ACE2), and in concert with host proteases, principally transmembrane serine protease 2 (TMPRSS2), promotes cellular entry. The cell subsets targeted by SARS-CoV-2 in host tissues and the factors that regulate ACE2 expression remain unknown. Here, we leverage human, non-human primate, and mouse single-cell RNA-sequencing (scRNA-seq) datasets across health and disease to uncover putative targets of SARS-CoV-2 among tissue-resident cell subsets. We identify ACE2 and TMPRSS2 co-expressing cells within lung type II pneumocytes, ileal absorptive enterocytes, and nasal goblet secretory cells. Strikingly, we discovered that ACE2 is a human interferon-stimulated gene (ISG) in vitro using airway epithelial cells and extend our findings to in vivo viral infections. Our data suggest that SARS-CoV-2 could exploit species-specific interferon-driven upregulation of ACE2, a tissue-protective mediator during lung injury, to enhance infection., Competing Interests: Declaration of Interests A.R. is an SAB member of ThermoFisher Scientific, Neogene Therapeutics, Asimov, and Syros Pharmaceuticals; a co-founder of and equity holder in Celsius Therapeutics; and an equity holder in Immunitas Therapeutics. A.K.S. reports compensation for consulting and/or SAB membership from Merck, Honeycomb Biotechnologies, Cellarity, Cogen Therapeutics, Orche Bio, and Dahlia Biosciences. L.S.K. is on the SAB for HiFiBio; she reports research funding from Kymab Limited, Bristol Meyers Squibb, Magenta Therapeutics, BlueBird Bio, and Regeneron Pharmaceuticals and consulting fees from Equillium, FortySeven, Inc, Novartis, Inc, EMD Serono, Gilead Sciences, and Takeda Pharmaceuticals. A.S. is an employee of Johnson and Johnson. N.K. is an inventor on a patent using thyroid hormone mimetics in acute lung injury that is now being considered for intervention in COVID-19 patients. J.L. is a scientific consultant for 10X Genomics, Inc. O.R.R, is a co-inventor on patent applications filed by the Broad Institute to inventions relating to single-cell genomics applications, such as in PCT/US2018/060860 and US Provisional Application No. 62/745,259. S.T. in the last three years was a consultant at Genentech, Biogen, and Roche and is a member of the SAB of Foresite Labs. M.H.W. is now an employee of Pfizer. F.J.T. reports receiving consulting fees from Roche Diagnostics GmbH and ownership interest in Cellarity, Inc. P.H. is a co-inventor on a patent using artificial intelligence and high-resolution microscopy for COVID-19 infection testing based on serology., (Copyright © 2020 The Authors. Published by Elsevier Inc. All rights reserved.)