Upregulation of membrane PR3 expression during sequential degranulation of isolated neutrophils. (A) Isolated neutrophils were adjusted to a concentration of 10⁶ cells/mL and labeled for flow cytometry analysis with the specific MoAb before (HBSS) or after activation with various concentrations of FMLP in the absence or in the presence of cytochalasin B. Membrane expression of CR1 and CD63 are expressed as the mean fluorescence index (MFI). For PR3 membrane expression, results are expressed as the MFI of the mPR3⁺subset. Results are given as the percentage increase in MFI defined as (MFI MoAb − MFI control IgG1) ± SEM from 6 independent experiments. (B) Representative experiment of double-labeling PR3 and CR1, a marker of secretory vesicle mobilization, in resting neutrophils and in neutrophils stimulated with 10⁻⁸ mol/L FMLP (indicated with an arrow) from an individual having a 28% mPR3⁺subset. Labeling with the MoAb anti-CR1 shows an homogeneous population. (C) Representative experiment of double-labeling PR3 and CD63, a marker of azurophil degranulation in resting neutrophils and in neutrophils stimulated with 10⁻⁶ mol/L FMLP in the presence of cytochalasin B (indicated with an arrow), from an individual having a 43% mPR3⁺ subset. Labeling with the MoAb anti-CD63 shows a homogeneous population.