Fig. 1.

Expression analysis of sialic acid-binding immunoglobulin-like lectin 1 (CD169/SIGLEC1) on circulating monocytes in patients with mild and severe coronavirus disease 2019 (COVID-19). In the early phase of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), 0–9 days after onset of symptoms, CD169/SIGLEC1 expression was strongly upregulated in patients with mild COVID-19 (n = 33) compared to patients with severe COVID-19 (n = 18), and compared to COVID-19 screening patients tested negative for SARS-CoV-2 (n = 27) (a). Longitudinal analyses revealed that monocytic CD169/SIGLEC1 expression in patients with mild COVID-19 (n = 51) gradually decreased over time and eventually reached the normal range as indicated by the dotted line (< 2400 molecules/monocyte) (b). In patients with severe COVID-19 (n = 51), CD169/SIGLEC1 expression undulated around the upper limit of the normal range (b). CD169/SIGLEC1 expression was assessed via flow cytometry with a detection limit of 1200 molecules/monocyte. Mean values are shown if patients were repetitively tested within the same time period (a, b). Data are shown as mean + standard error of mean (SEM) (a, b). For A, one symbol represents one patient. For comparison between groups, Kruskal Wallis test was performed followed by Dunn’s multiple comparison test, ****p ≤ 0.0001, n.s. = not significant