| Abstract: | Human bone marrow cells were sequentially fractionated by three negative selection steps to remove adherent cells and Fc receptor-bearing cells, followed by immune adsorption (panning) to deplete maturing cells that react with a panel of monoclonal antibodies. This nonadherent Fc receptor and antibody negative fraction could be further enriched by a positive selection "panning" step, using an antibody to HLA-DR antigen; 12-27% of the cells formed erythroid burst-forming unit (BFU-E), erythroid colony-forming unit, granulocyte-monocyte colony-forming unit, and erythroid and granulocyte and/or monocyte colony-forming unit-derived colonies with recovery of 0.5-1% of the cells and 20-100% of the colony-forming cells. Sequential fractionation resulted in increasing dependence of a subset of BFU-E-derived colonies on exogenous burst-promoting activity (BPA) for proliferation in culture, but the most enriched progenitor fraction still contained a proportion of accessory cell or BPA-independent BFU-E that responded to either natural or biosynthetic erythropoietin when added to cultures on day 0 in the absence of BPA. If the addition of erythropoietin was delayed until day 3, the data suggest that this population of BFU-E either died or became unresponsive to erythropoietin. Delayed addition of erythropoietin to cultures of enriched progenitors provided a sensitive BPA assay, since BPA-independent but erythropoietin-responsive BFU-E were eliminated. The surviving BFU-E that were dependent for their proliferation on the presence of both BPA and erythropoietin showed a characteristic dose response to increasing BPA concentrations. |
