Coexpression of CD antigens and SIRP on CD34⁺ BM cells. CD34⁺ cells were isolated from BM aspirates of healthy donors using MACS separation columns and analyzed by 3-color immunofluorescence. Cells were labeled with CD34-PerCP and MoAb P3C4 (IgG2a), as well as with PE-conjugated MoAbs against CD19, CD71, CD90, CD117, or the nonconjugated CD164-specific MoAb 103B2 (IgG3). After washing, the cells were stained with FITC-conjugated goat anti-mouse IgG2a-specific antiserum and with PE-conjugated IgG3-specific goat anti-mouse antiserum. Immunolabeled cells were analyzed on a FACSCalibur flow cytometer (n = 3).