Fig. 3— Representative flow cytometry showing apoptosis of human eosinophils at a) 0 h and b–e) 24 h of culture in the absence (b and c) and presence (d and e) of granulocyte-macrophage colony-stimulating factor (GM-CSF; 10 ng·mL−1), and in the absence (b and d) and presence (c and e) of N-acetyl-l-cysteine (NAC; 5 mM). Viable nonapoptotic eosinophils were quantified as the percentage of the total population of cells that were negative for both annexin-V and propidium iodide (PI). Early apoptotic cells were annexin-V-positive and PI-negative. Late apoptotic cells were positive for both annexin-V and PI. The percentage of cells in the bottom left, bottom right and top right quadrants, respectively, were as follows: a) 89.6, 8.32 and 1.73; b) 51.4, 24.7 and 23.5; c) 68.7, 21.4 and 9.44; d) 80.65, 13.6 and 5.31; and e) 71.6, 19.6 and 8.77. Note the decrease in spontaneous apoptosis (absence of GM-CSF) produced by NAC (c versus b) but the increase in apoptotic percentages obtained in the presence of GM-CSF (e versus d).