key: cord-1004927-rs33hw5n
authors: Pence, Brandt D.
title: Atypical monocytes in COVID‐19: Lighting the fire of cytokine storm?
date: 2020-11-19
journal: J Leukoc Biol
DOI: 10.1002/jlb.5ce0920-613r
sha: eaad7a6a0cac4f432cb6d1c5883faed42bb4ef48
doc_id: 1004927
cord_uid: rs33hw5n

nan

The emergence of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) and its attendant pandemic coronavirus disease 2019 (COVID-19) has precipitated an enormous research effort into characterizing immune system responses to the virus. Given the public health and economic burdens of the pandemic, a great deal of this research has focused on efforts to produce immunogenic vaccines and develop effective antiviral treatments against SARS-CoV-2. Early in the pandemic, however, it was observed that a pronounced inflammatory cytokine storm associated with severe COVID-19, 1 and as such, some effort has been made to characterize the etiology of this phenomenon. In a sample of COVID-19 patients, a population of monocytes is observed with high forward scatter by flow cytometry. A more extensive profiling of these cells demonstrated that they are highly vacuolated and produce pro-inflammatory cytokines such as tumor necrosis factor (TNF)-and interleukin (IL)-6. Additionally, they express the intermediate/nonclassical phenotype marker CD16 as well as mature macrophage markers CD80 and CD206. Finally, circulating monocytes are shown to express ACE2, the SARS-CoV-2 receptor. Questions (marked with a red "?") remain as to whether direct binding of SARS-CoV-2 to monocytes mediates these changes, or whether the mechanism of actions result from indirect stimulation expression of the virus receptor (ACE2) on monocytes. While others have described these as well, this remains important in that (a) the virus must be in the blood in order to encounter circulating monocytes, and (b) those monocytes must express a receptor for the virus in order to mount an inflammatory response. Increases in monocyte-derived macrophages in the lungs during COVID-19 has been described, 8 

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