Flow Sorting for Isolating CFU-E

Erythroid progenitor cells have been classified into three groups of increasing maturity: the primitive burst forming unit (p-BFU-E), the mature burst forming unit (m-BFU-E), and the erythropoietin responsive colony forming unit (CFU-E). This classification is based on their time of maturation in vitro, their proliferative capacity, and their responsiveness to growth factors (1 ). The CFU-E can be distinguished from the more primitive erythroid progenitors by their ability to proliferate and mature in response to a single growth factor, erythropoietin. In clonal assays in vitro, the CFU-E form single or double clusters characteristically containing 8–64 mature or maturing erythroid cells 2 d after cultures have been initiated with mouse bone marrow or fetal liver (2 ,3 ).