Coexpression of CD antigens and SIRP on BM subsets. Mononuclear BM cells were analyzed by 2-color immunofluorescence. Cells were labeled with MoAb P3C4 (IgG2a) and stained with FITC-conjugated goat anti-mouse IgG2a-specific antiserum, as well as with PE-conjugated MoAbs against CD33, CD34, CD19, CD117, CD3, CD56, glycophorin A (Gly A), and AC133 antigen. Gated mononuclear cells were analyzed on a FACSCalibur flow cytometer (n = 6).