Erythroid progenitors in polycythemia vera.

Recent data concerning in vitro studies of erythroid progenitors in polycythemia vera (PV) are reviewed. As shown by different laboratories, at least two populations of CFUE seem to coexist in the bone marrow of such patients: one exhibits normal in vitro behavior; the other, probably of clonal origin, is abnormally sensitive to erythropoietin. This abnormal population of CFUE is highly sensitive to trace amounts of erythropoietin and is probably responsible for the in vivo development of polycythemia despite a depressed level of erythropoietin. At the BFUE level, two populations also seem to coexist. However, the abnormal behavior of erythroid progenitors is probably not expressed at this early level of differentiation but only at the late CFUE level. This is in agreement with some of the data, which suggest that in the differentiation of erythroid progenitors into erythroblasts, erythropoietin is only needed at a level very close to CFUE.