High erythroid burst-promoting activity in sera from umbilical cord blood

Using methylcellulose clonal cell cultures, we examined human erythroid burst-promoting activity (BPA) in sera obtained from umbilical cord blood. BPA was measured on the basis of the number of erythroid bursts (BFU-E) and hemoglobin synthesis when peripheral blood mononuclear cells were cultured with cord blood serum in the presence of 1.0 U/ml erythropoietin (Epo) at low fetal calf serum concentration (10%). Controls were cultured with adult serum. The number of BFU-E and hemoglobin synthesis increased in culture to which cord blood serum had been added, and the enhancing effects of cord blood serum on erythroid burst formation were more pronounced than in control cultures with 2.0 U/ml Epo. No erythroid bursts, however, grew in the cultures with cord blood serum in the absence of Epo. Increased sensitivity of erythroid burst formation to low concentrations of Epo was observed in cultures containing cord blood serum. Dose-relationships between the concentrations of cord blood serum and the number of BFU-E and hemoglobin synthesis were clearly observed. We therefore concluded that the stimulatory effects of cord blood serum on erythroid burst formation may be due to BPA, one of the factors required for the proliferation of erythroid precursors at an early stage.