Expression of granulocyte and monocyte/macrophage markers after the delayed addition of ATRA during liquid suspension culture. One thousand FACS-enriched lin⁻c-kit⁺Sca-1⁺hematopoietic precursors were added to wells containing media and cytokines (SCF, IL-6, IL-11, and Flt-3 ligand). At daily intervals from 0 to 7 days after culture initiation, ATRA (1 μmol/L final concentration) was added to a separate group of wells for each time point. Cells were harvested at day 8 and washed, and the surface phenotypes of granulocytes (Gr-1) and monocyte/macrophages (F4/80) were analyzed by flow cytometry. Results are expressed as the percentage and absolute number of Gr-1–expressing (A and B) or F4/80-expressing (C and D) cells per well for each day of addition. Results are shown from one experiment, but multiple repeat experiments yielded similar results.