Isolation and characterization of human erythroblasts at distinct stages of development by cell sorting using GPA, band 3, and α4 integrin as surface markers. (A) The in vitro cultured day 7 or day 14 erythroblasts were stained with GPA, α4 integrin, and band 3. The expression levels of α4 integrin of all GPA⁺ cells were plotted again the expression levels of band 3. The data are displayed using both contour and density plots. Band 3 negative cells are gated as population I. Population III is represented by the cluster expressing medium level of band 3 and high level of α4 integrin. The region between I and III is gated as population II. Two distinct populations (IV and V) are clearly separated on cells cultured for 14 days. (B) Representative images of erythroblast morphology on stained cytospins from the 6 distinct regions shown in Figure 4A. Pro, proerythroblast; early baso, early basophilic erythroblast; late baso, late basophilic erythroblast; poly, polychromatic erythroblast; ortho, orthochromatic erythroblast. (C) Mitotic ability of purified staged human erythroblasts. Left panel: representative growth curves of staged human erythroblasts. Right panel: number of cell divisions of staged human erythroblasts. Data shown are from 4 independent experiments.