Flow cytometry analysis of the shedding of membrane microparticles from PNH (P) and control (T) RBC after calcium ionophore treatment. Dot plot representations of AV^FITC-labeled cell and particle suspensions. Cells have the highest forward scatter signal (FSC), whereas derived microparticles have a lower one. The proportion of events in each gate is indicated. Stimulation was achieved by 5 μmol/L calcium ionophore A23187 in the presence of 2 mmol/L external CaCl₂ for 90 minutes at 37°C. Fluorescence intensity reflects the extent of AV^FITC labeling of the population of interest, testifying to the degree of phosphatidylserine externalization. Each dot plot corresponds to 10,000 events and is representative of three experiments performed likewise.