Analysis of Flt3 receptor expression on human marrow mononuclear cells using three-color flow cytometry. Cells were stained for CD34, CD38, and Flt3 receptor. A scatter gate was first drawn to exclude dead cells (R1, not shown). (A) Expression of CD34 and CD38 on all live marrow mononuclear cells. Two cell populations were defined by gates: (R2) CD34⁺ and (R3) CD34⁻. (B) Expression of CD34 and Flt3 receptor on total marrow mononuclear cells. Using the gates set in (A), expression of Flt3 receptor versus CD38 was examined on gated CD34⁺ cells (C) or CD34⁻cells (D). Percentages of cells are provided in each plot by quadrant. Quadrants were drawn based on isotype control profiles (E). The results shown are representative of three experiments.