Fetal hemoglobin production in cultures of primitive and mature human erythroid progenitors: Differentiation affects the quantity of fetal hemoglobin produced per fetal-hemoglobin-containing cell

Single-cell microscopic immunodiffusion assays were used to determine the cellular mechanisms that regulate fetal hemoglobin (HbF) levels in cultures of primitive and late erythroid precursors obtained from human adult bone marrow. Two variables - the percentage of cells containing HbF (F cells) and the picograms (pg) of HbF/F cell - were assayed in cells derived from erythroid colony-forming units (CFU-E) and from erythroid burst-forming units (BFU-E) at 7 and 14 days in culture, respectively. The percentage of F cells among all nucleated cells from CFU-E-derived colonies (29.4% ± 12.5%, mean ± SD) was not significantly different (p = 0.2) from the percentage of F cells from BFU-E-derived bursts (37.3% ± 10.1%). Serial daily assays of all cells in cultures on days 3 through 7 and on day 14 revealed a marked increase in F cells between days 4 and 6 in culture. The average amount of HbF/F cell was less in CFU-E-derived F cells than in BFU-E-derived cells (3.5 ± 0.3 pg versus 6.2 ± 3.3 pg; p <0.01), while adult hemoglobin (HbA) levels in CFU-E- and BFU-E-derived cells remained comparable (19.9 ± 2.2 pg versus 21.9 ± 5.3 pg, p = 0.3). These findings indicate that F cell number in culture is not significantly influenced by the relative maturity of the erythroid precursors from which the cells are derived. Differences in the levels of HbF between CFU-E- and BFU-E-derived cells are due to differences in the amount of HbF per F cell, not F cell number.