Proliferative effect of burst-promoting activity upon early erythroid progenitors

The mechanism of action of burst-promoting activity (BPA) was investigated. Rabbit bone marrow conditioned medium (BMCM) was used as a source of BPA for bone marrow derived rabbit erythroid progenitors (BFU-e). The addition of 10% BMCM to methylcellulose cultures resulted in an increase in both burst number (60%) and 59Fe incorporation into heme (1,334%). A strong correlation was observed between cell number and 59 Fe incorporation individual bursts. Analysis of cell number in individual bursts cultured in the presence or absence of BMCM demonstrated that BMCM consistently enhanced burst size. When bone marrow cells were incubated for 4 hours in BMCM prior to culture, a three fold increases in the percentage of S-phase BFU-e was observed. These results show that a major mechanism of action of BMCM burst-promoting activity is to enhance proliferation during the early phase of burst formation.