Fig. 1

Example of flow cytometry biparametric histograms showing the gating strategy used to identify immature granulocytes (IG) in peripheral blood of COVID-19 patients. The examples shown here are merged data of one same patient on day 0 (in blue dot) and day 7 (in red dot) to illustrate gating strategy. A Hematopoietic cells were selected on specific morphological parameter (Side Scatter channel, reflecting the granularity of the cytoplasm) and expression of CD45 (a pan-leukocyte marker). B Hematopoietic cells positive for CD14 (monocyte maker) were considered as monocytes, and the ones positive for CD3 (T cell marker) as T lymphocytes. The red square corresponds to cells that are negative for these two markers (Not T not mono). C Side scatter (cytoplasm granularity) and CD19 (B cell marker) were used to separate the neutrophils (red gate) and the B lymphocytes, respectively. D Neutrophils were divided into two subtypes (i) mature granulocytes strongly positive for CD16 (CD16+) and (ii) Immature granulocyte (IG) low or negative for CD16. CD64 was used as an activation marker