Regulation of human megakaryocytopoiesis: analysis of proliferation, ploidy and maturation in liquid cultures.

A liquid culture technique associated with either double staining and flow cytometry or electron microscopy was used to study human megakaryocytopoiesis. During development from the embryo to the adult, a progressive increase in ploidy classes associated with an enhancement of megakaryocyte (meg) size was observed. Granulocyte-macrophage colony-stimulating factor had no effects on adult marrow cultures. In contrast, interleukin (IL) 3 induced a marked proliferation, but was unable to promote polyploidization. Furthermore, it abrogated the effects on endomitosis of aplastic plasma (AP). This negative effect on polyploidization of IL-3 could be partially dissociated from its effects on proliferation by a delayed addition in culture. AP acted on both proliferation and endoreplication, which was not due to the main hematopoietic growth factors, including IL-6. A synthesis of IL-6 was detected by in situ hybridization in cultured cells including megs which also express receptors for IL-6. These results suggest that terminal meg differentiation may be regulated by an autocrine IL-6 loop, and that megakaryocytopoiesis may be independently regulated at early and late stages of differentiation.