ABSTRACT
Background: Excessive monocyte/macrophage activation with the development of a cytokine storm and subsequent acute lung injury, leading to acute respiratory distress syndrome (ARDS) is a feared consequence of infection with COVID-19. The ability to recognize and potentially intervene early in those patients at greatest risk of developing this complication could be of great clinical utility. Methods: We performed detailed flow cytometric analysis of peripheral blood samples from 28 COVID-19 patients treated at Xian No.8 Hospital and the First Affiliated Hospital of Xian Jiaotong University in early 2020 in an attempt to identify factors that could help predict severity of disease and patient outcome. Findings: While we did not detect significant differences in the number of monocytes between patients with COVID-19 and normal healthy individuals,we did identify significant morphological and functional differences, which are more pronounced in patients requiring prolonged hospitalization and ICU admission. Patients with COVID-19 have larger than normal monocytes, easily identified on forward scatter, side scatter analysis by routine flow cytometry,with the presence of a distinct population of monocytes with high forward scatter (FSC-high). On more detailed analysis, these FSC-high monocytes are CD11b+, CD14+, CD16+, CD68+, CD80+, CD163+, CD206+ and secrete IL-6, IL-10 and TNF-alpha, consistent with an inflammatory phenotype. Conclusions: The detection and serial monitoring of this subset of inflammatory monocytes using flow cytometry could be of great help in guiding the prognostication and treatment of patients with COVID-19 and merits further evaluation.