The growth of large megakaryocyte colonies from human bone marrow.

The growth of large, compact megakaryocyte colonies in cultures of human bone marrow is promoted by fresh human plasma and medium conditioned by phyto-hemagglutinin stimulated leukocytes (PHA-LCM). These colonies are typically composed of large cells with translucent cytoplasma, surrounded by a highly refractile border. In addition, they may also contain smaller cells of similar morphology. Independent of their size, all cells react positively with antibodies directed against human factor VIII antigen. The frequency of megakaryocyte colonies may vary for different individuals from 1-35 colonies per 10(5) mononuclear bone marrow cells. The observed linear relationships between the number of cultured cells and the frequency of colonies suggests a single cell origin. The described culture conditions also support the development of a larger megakaryocyte component within multilineage mixed colonies, so that it will now be feasible to investigate the mechanisms involved in directing pluripotent cells towards megakaryocytopoiesis.