SIRPα and SIRPβ expression on AML blasts.

Ficoll-isolated PB or BM cells from patients with AML were immunolabeled with MoAb P3C4 or B1D5, followed by PE-conjugated goat antimouse IgG2a-specific antiserum (filled histograms). Nonbinding IgG2a antibody was used as negative control (black line). Cells were further stained with FITC-conjugated CD45-specific MoAb and gated CD45^low leukemic blasts were analyzed. AML samples were divided into 3 groups: (1) normal SIRPα/β expression; (2) reduced SIRPα, no SIRPβ expression; (3) no SIRPα/β expression. The histograms show representative examples of each group. The number of analyzed samples is given in parentheses.