Expression of SIRPα and SIRPβ on hematopoietic cells.

(A) PB cells and in vitro–generated DCs were immunolabeled with MoAbs P3C4 (IgG2a) or B1D5 (IgG2a) and PE-conjugated goat antimouse IgG2a-specific antiserum (filled histograms). Nonbinding IgG2a antibody was used as negative control (black line). Cultured DCs were further labeled with FITC-conjugated CD1a-specific MoAb. Gated lymphocytes, monocytes, and granulocytes, as well as CD1a⁺ DCs were analyzed on a FACSCalibur flow cytometer (n = 3). (B) Ficoll- isolated BM cells were labeled with MoAbs P3C4 or B1D5 and stained with FITC-conjugated goat antimouse IgG2a-specific antiserum, as well as with PE-conjugated MoAbs against CD19, CD33, CD34, and AC133 antigen. Gated mononuclear cells were analyzed on a FACSCalibur flow cytometer (n = 3). (C) Expression of SIRP on CD34⁺CD38⁻ BM cells. Cells were stained with CD34-FITC, CD38-APC, CD133-PE, and either P3C4 (SIRPα) or B1D5 (SIRPβ) plus anti-IgG2a-FITC, and analyzed on a FACSCalibur flow cytometer. The plots show coexpression of CD133 and SIRP on gated CD34⁺CD38⁻ cells.