Differential effects of human erythroid burst stimulating activity (HuEBSA) on human cord blood burst forming units-erythroid (BFU-Es) as a function of their differentiation state

An erythroid stimulating activity which promotes the growth of small bursts probably arising from mature burst forming units-erythroid (BFU-Es) of adu lt human bone marrow cells and called human erythroid burst stimulating act ivity (HuEBSA), was previously found in media conditioned by a fetal human kidney cell line. In the present work we report that adding HuEBSA to cultu res did not increase the burst number but increased the size of bursts from cord blood (CB) cells. A similar observation was made using stem cell fact or (SCP), However, a synergistic effect on the burst number was noted when both HuEBSA and SCE were introduced to cultures. We also noticed that CB er ythroid progenitors pre-cultured with 5637-Conditioned Medium [as a source of burst promoting activity (BPA)I and erythopoietin (Epo) for 3 days could be stimulated by HuEBSA but not by SCF, Similar results were obtained when interleukin 3 (IL-3) was introduced with Epo to the pre-cultures. These results suggest that two different populations of erythroid progenito rs coexist in cord blood, one is Epo- and IL-3-sensitive, the other solely Epo-sensitive. It also seems probable that HuEBSA acts on erythroid progeni tors arising from the more immature erythroid population, since its stimula ting activity was evident after a 3-day pre-culture of cord blood cells in Epo and IL-3, (C) 1999 Academic Press.