Caspase-1 activation level in myeloid cells in the blood of COVID-19 patients. Whole peripheral blood cells of healthy donors or COVID-19 patients with mild to critical symptoms were stained for active caspase-1 (detected using the FAM-FLICA probe) and for CD45, CD14, CD16, and CD66b markers. Cells were immunophenotyped by flow cytometry. Leukocytes were defined as CD45⁺ and were analyzed for monocyte and granulocyte surface markers. (A-D) Monocytes were defined as CD14⁺ and subpopulations were gated as indicated in panel A using CD14 and CD16 markers. The indicated monocyte subsets were analyzed for the mean fluorescence intensity (MFI) of FAM-FLICA corresponding to the activation of caspase-1 (B-D). (E-G) Granulocytes were defined as CD66b⁺ and the different subsets were gated as indicated using CD66b and CD16 markers (E). (F-G) The indicated granulocyte subsets were analyzed for the FAM-FLICA MFI. **P ≤ .01.