FACS analysis of adult bone marrow cells stained for GPIIb-IIIa expression. Four-week-old bone marrow cells were immunostained with anti–GPIIb-IIIa MoAb. (A) Two populations with high and low fluorescence intensity were sorted. The percentages of cells in the GPIIb-IIIa^hi (high) and GPIIb-IIIa^lo (low) groups are indicated in the windows. The cell morphology of each fraction is illustrated in B and C, respectively. (B) Morphology of GPIIb-IIIa highly fluorescent cells (thrombocytes). (C) Thromboblasts in the GPIIb-IIIa weakly fluorescent cell population. (D) GPIIb-IIIa^lo (+low) and GPIIb-IIIa^hi(+high) cells, as well as the negative (−) and unsorted populations were cultured in erythroid differentiation medium. Each column represents the number of colonies arising from 1,000 cells in duplicate cultures.