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?:abstract
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OBJECTIVE: Infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can lead to severe pneumonia, but also thrombotic complications and non-pulmonary organ failure Recent studies suggest intravascular neutrophil activation and subsequent immune cell triggered immunothrombosis as a central pathomechanism linking the heterogenous clinical picture of Coronavirus Disease 2019 (COVID-19) We sought to study whether immunothrombosis is a pathognomonic factor in COVID-19 or a general feature of (viral) pneumonia, as well as to better understand its upstream regulation APPROACH AND RESULTS: By comparing histopathological specimens of SARS-CoV-2 with influenza affected lungs, we show that vascular neutrophil recruitment, NETosis, and subsequent immunothrombosis are typical features of severe COVID-19, but less prominent in influenza pneumonia Activated neutrophils were typically found in physical association with monocytes To explore this further, we combined clinical data of COVID-19 cases with comprehensive immune cell phenotyping and bronchoalveolar lavage fluid scRNA-seq data We show that a HLADR(low) CD9(low) monocyte population expands in severe COVID-19, which releases neutrophil chemokines in the lung, and might in turn explain neutrophil expansion and pulmonary recruitment in the late stages of severe COVID-19 CONCLUSIONS: In summary, our data underline an innate immune cell axis causing vascular inflammation and immunothrombosis in severe SARS-CoV-2 infection
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