Monocyte differentiation into macrophages is specifically associated with caspase activation.

Human monocytes purified from healthy donor peripheral blood were exposed to 100 ng/mL M-CSF or 100 ng/mL GM-CSF plus 10 ng/mL IL-4. (A,B) Flow cytometry assay analysis of caspase-3 active fragments at indicated times following M-CSF (A) or GM-CSF/IL-4 (B) exposure (white curves indicate untreated monocytes at time 0; gray curves, cytokine-treated cells). (C) Flow cytometry assay analysis of caspase-9 active fragments after 72 hours of exposure to indicated cytokines (white curves indicate untreated monocytes at time 0; gray curves, cytokine-treated cells). (D) Fluorescence microscopy analysis of caspase-3 and -9 active fragments and Hoechst 33342 staining of nuclear chromatin in cells exposed to indicated cytokines for 3 days. Cleaved caspase-3 and -9 were assigned the color green, and nuclei labeled with Hoechst were stained in blue. In each panel, 1 representative of at least 4 experiments is shown.