Megakaryocyte precursors (promegakaryoblasts and megakaryoblasts) in the normal human bone marrow. An immunohistochemical and morphometric study on routinely processed trephine biopsies.

On routinely processed trephine biopsies of the normal human bone marrow derived from 15 patients, immunostaining with a monoclonal antibody against platelet glycoprotein IIIa (Y2/51) and morphometric measurements were performed for the determination of megakaryocyte precursor cells. Based on cell sizes and on comparison with (1) specimens stained by the periodic acid-Schiff reaction and (2) smears, the smallest elements clearly identifiable as belonging to the megakaryocyte series were classified as promegakaryoblasts. Promegakaryoblasts had a frequency of 1.7/sq mm and 140/cu mm of bone marrow and constituted about 8% of the total positively stained megakaryocytic elements; they were characterized by a size of 41.5 sq microns, a diameter of 7.7 microns, a high nuclear-cytoplasmic ratio (0.32) and a nearly circular outline of their nuclear and cellular perimeters.