Competitive induction of erythroid progenitors by relative concentration of BPA to erythropoietin: possible existence of intermediate compartment between BFU-E and CFU-E.
Crude preparations of erythropoietin (Epo) have been found to contain burst-promoting activity (BPA) as a contaminant. When anti-Epo antiserum was added to the culture of erythroid progenitor cells stimulated in vitro with crude Epo, the number of colonies derived from late erythroid progenitors (CFUe) was reduced, while that from early erythroid progenitors (BFUe) was increased. On the other hand, when the culture was stimulated with BPA-free Epo, which was purified from human urine, addition of anti-Epo antiserum enhanced neither BFUe nor CFUe. These results suggest that the ratio of BPA and Epo may be crucial in the assay of erythroid progenitors. Addition of anemic mouse spleen-conditioned medium (AMSCM) to the culture as a source of BPA resulted in the increase of BFUe and the reduction of CFUe under various concentrations of Epo. These findings might be explained by the existence of intermediate compartment of erythroid progenitors depending on both BPA and Epo.