The proportion of mitoses in different cell lineages changes during short-term culture of normal human bone marrow

To determine the hematopoietic cell lineage of mitotic cells in human bone marrow on direct examination and after 24-hour culture, marrow mitoses from four healthy individuals were studied, using a new technique that allows analysis of karyotypes in cells whose cell membrane and cytoplasm have been preserved. Mitoses were identified as being of erythroid lineage by immunofluorescent staining for surface glycophorin A and as being of granulocytic lineage by cytoplasmic staining for Sudan black B. On direct marrow examination without prior culture, the great majority of mitoses (74% to 90%) were of erythroid lineage; only a few (0% to 10%) were granulocytic. After 24-hour culture, the percentage of erythroid mitoses (15% to 40%) decreased, while the percentage of granulocytic mitoses (58% to 87%) increased strikingly. These data indicate that mitotic cells of different hematopoietic cell lineages predominate in marrow at different culture times and offer a plausible explanation for the high frequency of normal karyotypes in acute myeloid leukemia after direct marrow cytogenetic evaluation.