Purification of erythroblastic nests

We describe a method for preparing purified erythroblastic nests in large numbers (approximately 10(6)/run) in three steps: (1) induction of splenic erythropoiesis in mice, (2) preparative differential centrifugation for the removal of erythrocytes and single cells from spleen cell suspensions, and (3) sedimentation in an isokinetic gradient of Ficoll 400 in Joklik's modification of minimum essential medium. Viability of isolated EN is very high, as demonstrated by the trypan blue exclusion and in vitro erythrocyte formation methods.