Representative dot blot to show apoptosis of Gr-1–positive cells as detected by MC-540 staining.

Bone marrow cells were harvested from G-CSF–deficient and wild-type mice and immediately stained with MC-540 dye and Gr-1 FITC antibody. The cells were analyzed by 2-color flow cytometry using Cell Quest software. Regions R2 and R4 represent apoptotic cells in Gr-1^lo and Gr-1^bright populations, respectively. Regions R3 and R5 represent nonapoptotic cells in Gr-1^lo and Gr-1^bright populations, respectively. In the bottom panel, cells were stained only with Gr-1-FITC antibody, and their red autofluorescence under the same settings was determined. The regions were adjusted to take into account background autofluorescence.