INDUCTION OF ERYTHROPOIETIN RESPONSIVENESS IN VITRO BY A DISTINCT POPULATION OF BONE MARROW CELLS

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Abstract
Bone marrow contains a small population of primitive erythroid progenitor [mouse] cells which can be detected by their capacity to form large numbers of erythroid progeny in viscous cultures containing erythropoietin (EP). These cells were termed erythroid burst-forming units (BFUe). Expression of the [mouse] erythroid differentiation potential of BFUe required the presence of an activity additional to EP. This activity was designated as BFA (burst feeder activity). The number of BFUe detected and their apparent sensitivity to EP were directly related to the BFA concentration of the cultures. BFA was associated with a population of bone marrow cells of high buoyant density and small volume, which were sensitive to irradiation. The radiation dose-effect curve provided strong evidence that bone marrow BFA was independent of cell proliferation; BFA was unaffected by in vivo treatment with hydroxyurea. The findings were compatible with a 2-step regulation model for erythroid differentiation in which BFA-induced progeny of BFUe sensitivity to EP.