Effect of neutrophil activation on secretion and membrane expression of PR3, HNE, and MPO. Isolated neutrophils were adjusted to a concentration of 10⁶ cells/mL and stimulated for 15 minutes with 10⁻⁶ mol/L FMLP in the absence or in the presence of cytochalasin B to mobilize specific or azurophil granules, respectively. (A) The concentrations of secreted PR3, HNE, or MPO were measured in the supernatant of stimulated cells using specific sandwich ELISA and are expressed in micrograms per milliliter. Results are given as the mean ± SEM from 9 independent experiments. (B) Neutrophils were labeled for flow cytometry analysis with specific antibodies before (HBSS) or after activation. Membrane expression of PR3, HNE, or MPO is expressed as the percentage of mean fluorescence index (MFI) increase above baseline and is calculated as ([MFI activation] − [MFI HBSS]/[MFI HBSS]) × 100. Results are given as the mean ± SEM from 9 independent experiments.