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

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Abstract
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.