COMPARISON OF THE DNA CONTENT OF MEGAKARYOCYTES IDENTIFIED IMMUNOLOGICALLY WITH THAT IDENTIFIED MORPHOLOGICALLY

We devised a new microfluorometric method for determining the ploidy o f megakaryocytes identified immunologically in bone marrow smears. The smears were immunostained by incubation with mouse monoclonal anti-gl ycoproteins (GP) IIb antibodies, followed by fluorescein isothiocyanat e-conjugated goat antimouse IgG antibodies. They were then stained wit h 4',6-diamidino-2-phenylindole (DAPI). Megakaryocytes were identified by their GPIIb immunofluorescence using a microfluorometer and, after the filters were changed, their DNA content was assayed by measuring the intensity of DAPI fluorescence. This intensity was shown to be pro portional to the DNA content when the aperture of the objective lens w as reduced. We compared these results with those obtained when megakar yocytes were identified morphologically, using DAPI staining after Wri ght-Giemsa destaining. In all 12 normal controls, the ploidy peaks wer e shown to be 16N by both methods, and the mean ploidy detected by the immunological method was only reduced 0.961 times relative to the est imate from the morphological method. In contrast, in eight myelodyspla stic syndrome (MDS) :patients, the ploidy peaks were either 8N or 4N a nd the mean was reduced by 0.906 times (P=0.018). Thus we could immuno logically identify small megakaryocytes which we could not identify mo rphologically. Therefore, this method is useful for measuring megakary ocytic ploidy, especially in the pathological megakaryocytes of MDS pa tients.