Megakaryocytes are the bone marrow cells that generate platelets. They are relatively rare cells, comprising between 0.03 and 0.06% of all nucleated marrow cells (R. L. Berkow et al., J. Lab. Clin. Med., 103: 811-818, 1984). The study of human megakaryocyte differentiation and function has been hampered by the small number of these cells available for study. Recently we have established a human cell line (EST-IU) from the marrow of a patient with an acute nonlymphocytic leukemia and a

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... l germ cell tumor. While this cell line seems to express many of the phenotypic characteristics of human megakaryocytes, it does not appear to express any phenotypic properties associated with cells of the erythroid, lymphoid, granulocytic, or monocytic lineages. Transmission electron microscopy demonstrates frequent multinucleated cells. Staining for platelet peroxidase reactivity revealed darkening of the perinuclear envelope and the endoplasmic reticulum, a characteristic of cells of the megakaryocytic lineage. Indirect immunofluorescence assays reveal that EST-IU expresses reactivity with anti-platelet glycoprotein antisera, anti-Factor VIII-related antigen antisera, anti-Factor V antisera, anti-thrombocyte antisera, Tab (monoclonal anti-platelet glycoprotein IIb-IIIa), and anti-fibronectin antisera. Flow cytometry-derived DNA histograms demonstrate populations with multiple ploidies, ranging from approximately 4N to 32N. Based upon morphological and histochemical characteristics, antigenic expression, and nuclear characteristics, EST-IU cells appear to have a phenotype that closely resembles human megakaryocytes. This cell line should be useful in the further cell study of the molecular and cell biology of human megakaryocytopoiesis.