Megakaryocyte colonies from peripheral blood progenitors.

After 14 days of incubation, megakaryocyte colonies were visualized by immunostaining to detect GPIIb/IIIa-expressing cells (pink-red). (A) (right) Typical small (3-20 cells) CFU-Mks from an asymptomatic carrier (original magnification, 200 ×; II-7). (left) Cluster of small GPIIb/IIIa cells seen in cultures of thrombocytopenic control subjects (II-5). (B) Representative atypical colonies seen in thrombocytopenic members. Cells are large but weakly positive for GPIIb/IIIa (original magnification as indicated; II-4 and II-5).