Quantification of apoptosis by FACS analysis after staining with Annexin V–FITC and propidium iodide.

Density gradient-purified monocytes were cultured for 6 days with GM-CSF plus IL-4 in the absence (A,C,E) or presence (B,D,F) of 1000 U/mL IFN-α plus 1 ng/mL LPS. Shown are the results of a single experiment by 3 alternative modes of representations displaying the forward/side scatter profile (A-B), Annexin V–FITC versus propidium iodide (PI) (C-D), and forward scatter versus Annexin V–FITC (E-F). Gates G1 (apoptotic cells) and G2 (viable cells) were drawn arbitrarily in the representation forward scatter versus Annexin (E-F), because in this representation both populations could best be discriminated. In this experiment cells in gate G1 (apoptotic cells) amounted to 12.2% of total cells in panel E (control culture) and 64.8% in panel F (culture with IFN-α plus LPS), whereas the cells in gate G2 were considered as viable cells (75% of total cells in panel E and 22% in panel F). The small population of lymphocytes (best visible in panel A) amounted to 8.3% of total events in this experiment.