Evidence for a heterogeneous response to erythropoietin in the CFUE pool of human bone marrow.

To determine whether the CFUE pool within human bone marrow is heterogeneous with respect to erythropoietin (Epo) requirements, we studied CFUE growth in vitro as a function of Epo exposure time. We controlled the Epo exposure time by overlaying plasma clot cultures containing 0.5 U/ml Epo with an antibody prepared against human Epo. All cultures were grown for seven days. Benzidine-positive colonies containing eight or more cells were counted as CFUE. Colonies containing eight cells required at least 24-50 h of Epo exposure, and those containing 16 cells required at least 70-90 h of Epo exposure. After 50 h, the number of CFUE progressively increased until it reached a maximum at seven days of Epo exposure. These results suggest that the CFUE pool within human bone marrow is heterogeneous with respect to Epo requirements.