Erythropoiesis: Making a Red Blood Cell

Cell differentiation along the erythroid lineage occurs over a two week span in humans. The earliest erythroid progenitor, the BFU-E (burst forming unit-erythroid), is small and without distinguishing histologic characteristics. BFU-Es express the cell surface antigen, CD34, as do all other early hematopoietic progenitors allowing for its isolation using anti-CD34 antibodies. The stage after the BFU-E is the CFU-E (colony forming unit-erythroid) which is larger and is the stage right before hemoglobin production begins. Immature erythroblasts which start producing hemoglobin also start condensing their nucleus. Mature erythroblasts are smaller with a tightly compacted nucleus which is expelled as the cells become reticulocytes.

Stages of Adult Human Red Cell Differentiation Grown In Vitro:

CD34+ progenitors were isolated from adult peripheral blood or cord blood and grown in liquid medium in fibronectin-coated wells. Growth factors were added or removed as indicated below the the graph. Benzidine staining is a marker for hemoglobin.
H. Ni, X.-D. Yang,C.J. Stoeckert, Jr., Maturation and developmental stage-related changes in fetal globin gene expression are reproduced in transiently transfected primary adult human erythroblasts. Exp Hematol. 1999 Jan;27(1):46-53.

The pictures shown correspond to BFU-E (day 3), CFU-E (day 7), immature erythroblast (day 11) and mature erythroblast (day 15). Cells were stained by the Romanowski water-based adaptation of Wright-Giemsa.