THE STUDY OF ACUTE-LEUKEMIA CELLS BY MEANS OF ACRIDINE-ORANGE STAINING AND FLOW-CYTOMETRY

The studies described here explored the staining of acute leukemia cel ls with acridine orange (AO). The red fluorescence curve of AML specim ens was usually bimodal, suggesting the presence of subpopulations of cells which have different RNA contents. In almost every AML specimen, small leukemic blast cells comprised at least part of the ''low RNA c ontent'' subpopulation. Residual granulocytes and lymphocytes also con tributed to this population. Frequently, the green fluorescence, indic ative of the binding of AO to DNA, was slightly less in these cells th an in the majority of cells present. There was no evidence however, th at the leukemia cells with these characteristics represented a G(0) or kinetically quiescent population of cells. In ALL specimens, the pres ence of multiple cytogenetically distinct clones was easily detectable in AO stained specimens. The red fluorescence curve of G(0)/G(1) ALL cells was unimodal.