CD66b⁺CD16^highgranulocytes display increased nigericin-triggered caspase-1 activation in severe COVID-19 whereas CD66b⁺CD16^dimgranulocytes of severe COVID-19 lost their capacity to respond to the NLRP3 stimulation. Whole peripheral blood cells of healthy donors or COVID-19 patients were analyzed by flow cytometry using CD45, CD66b, and CD16 markers. (A-E) Whole peripheral blood was treated with vehicle (control) or nigericin (5 µM) for 30 minutes and granulocyte subsets were analyzed for FAM-FLICA MFI (caspase-1 activation) (A-B) and nigericin-induced fold of FAM-FLICA MFI compared with control (C-D). (E) Histogram of FAM-FLICA signal in CD66b⁺CD16^dim cells. Light colors, FAM-FLICA in the control condition; dark colors, FAM-FLICA in the nigericin-treated condition. The dotted line represents the gate used to determine the percentage of FAM-FLICA⁺ cells. (F-G) Leukocytes were defined as CD45⁺ and the frequency of granulocyte subsets among leukocytes was analyzed. *P ≤ .05; **P ≤ .01; ****P < .0001.