Isolation and characterization of normal human megakaryocytes.

Human megakaryocytes have been isolated from marrow obtained from ribs removed at thoracotomy. All but one of the patients had normal pre-operative platelet and leucocyte counts. Megakaryocytes averaged 0.37% of all cells in marrow cell suspensions from nine consecutive subjects. A 283-fold purification (to 10.3%) was achieved by a density gradient centrifugation followed by two successive velocity sedimentations at unit gravity. The net yield, 12 800 megakaryocytes per specimen, was sufficient for many kinds of morphological study. Bright-field, phase contrast, and electron microscopy were used to characterize the younger and smaller megakaryocytes. Ploidy analyses were carried out on 100--235 megakaryocytes per specimen; 8N was the predominant ploidy class in isolated megakaryocyte populations from three individuals. The mean megakaryocyte diameter was 24 micrometers in three other specimens and the range was 10--48 micrometers. This data had a normal distribution and overlapped minimally with the size range of all other marrow cells. The presence of a distinct size threshold (at 11.5 micrometers) implied that size alone may be a sufficient objective criterion for identification of human megakaryocytes.