Demonstration of erythroblastic differentiation after 14 days in blood in vitro during Vaquez's disease without addition of erythropoietin]

Leucocytes of normal individuals and patients with polycythemia vera were isolated from the peripheral blood by Ficoll-Hipaque density gradient centrifugation and cultured in vitro suing the bovine plasma clot culture technique with a minor modification: the addition of fresh normal serum. After 14 days in the presence of sheep erythropo?etin (3U/ml) erythropo?etic bursts containing between 3 and 10 subcolonies were observed in normal and polycythemia vera cultures. Blood leucocytes of patients with polycythemia vera rise to these erythropo?etic bursts without addition of erythropo?etin to the culture. This behavior was never observed in the blood of normal individuals. These results indicate that in polycythemia vera commited erythro?d stem cells of high proliferative capacity closely resembling the murine erythro?d burst forming unit have an abnormal sensitivity to erythropo?etin as well as the immediate precursors of the proerythroblasts. The culture of these cells from the peripheral blood offers some practical advantages.