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Kinetics of the formation of pure and heterogeneous megakaryocyte colonies by megakaryocyte progenitor cells in vitro.

The formation of pure and heterogeneous megakaryocyte colonies in vitro by megakaryocyte progenitor cells was studied using a whole plate stain for acetylcholinesterase to identify megakaryocyte colonies. In cultures of 75,000 C57BL marrow cells, maximal numbers of 11 +/- 5 (mean +/- standard deviation) pure and 6 +/- 1 heterogeneous colonies were reached after 6-7 days of incubation, after which megakaryocyte colony degeneration was marked. The ratio of pure: heterogeneous colonies remained constant at 2:1 both during the incubation period, and when different concentrations of megakaryocyte colony stimulating factor (MEG-CSF) and different numbers of cells per culture were used. The average size of both pure and heterogeneous colonies increased during the incubation period to maximal colony sizes of 15 +/- 13 cells per pure colony and 264 +/- 300 cells per heterogeneous colony. Sequential analysis of individual colonies in situ failed to demonstrate an increase in the size of individual pure colonies, but the enlargement of individual heterogeneous colonies was observed.