Plasmatic L-arginine level in SARS-CoV-2 patients correlated with PMN-MDSC frequency. (a) Plasmatic Arginine level of SARSCoV-2 ICU (ICU, n = 31) and no ICU (no ICU, n = 31) patients and healthy donors (HD, n = 9). Results are shown as box and whiskers plot. Kruskal-Walliswith Dunn’s post hoc test was applied. (b) Flow-cytometry gating strategy used to identify MDSC among PBMC. Dead cells were excluded by selecting DRAQ7neg cells. One representative COVID-19 patient and one HD are shown. (c) Correlation between plasmatic L-arginine level and PMN-MDSC percentage from SARSCoV-2 infected patients and HD. Non-parametric Spearman correlation was applied. (d) Representative plots of the adopted gating strategy to evaluate platelet activation. Platelets were selected as CD41a+ (SSC/CD41a plot), and PAC-1 expression (mean fluorescence intensity, mfi) was evaluated. (e) PAC-1 expression (mfi) on platelets from ICU (n = 21), no ICU (n = 15) patients, and HD (n = 9). Results are shown as box and whiskers plot. Kruskal-Walliswith Dunn’s post hoc test was applied. (f) Correlation between PAC-1 platelet expression (mfi) and L-arginine plasmatic level.