Cell differentiation surface marker expression on PLB-985 (top) and NB4 (bottom) cells. Cells were treated with 10⁻⁷ mol/L 9-cis-RA or the selective ligands, and the cell-surface expression of CD11b, CD11c, and CD13 antigens was assessed by flow cytometry at 1, 2, 3, and 4 days after treatment. Graphs indicate percent of positive cells.