Acceleration of the hemoglobin switch in cultures in neonate erythroid precursors by adult cells.

Erythroid colonies from cord blood in which both late (CFU-E) and early (BFU-E) erythroid precursors are present, were grown by the plasma clot technique. Hemoglobin (Hb) synthesis was studied and compared in fresh reticulocytes. 7-day-old colonies. and 14-day-old colonies. In the 8 cases studied, the proportion of HbA synthesis progresssively increased from circulating reticulocytes to 7-day-old colonies and finally in 14-day-old colonies. This result brings evidence that Hb switch is programmed at least at the level of early erythroid precursors. In order to modify the cellular environment of the culture and to examine their influence on globin genes expression. neonate and adult irradiated light density blood cells were added. Irradiated cells from adults. in contrast to those from neonates. were able to increase HbA synthesis in colonies derived from early erythroid progenitors. Under optimal conditions of culture (i.e.. a high concentration of neonate plated cells), adult cells elicited a constant increase (22%) in the proportion of HbA synthesis. A linear relationship between this increase of HbA synthesis and the number of added cells was observed. In contrast. the plating efficiency was not significantly modified; however. the size of the erythroid bursts was increased upon the addition of adult irradiated cells. Under suboptimal conditions of culture (i.e.. a low concentration of plated cells). adult irradiated cells markedly increased the plating efficiency, the size of the colonies. and HbA synthesis (85%). In contrast to the dramatic effects of irradiated adult cells, the cord blood irradiated cells had a very slight effect on HbA synthesis. the plating efficiency. and the size of the colonies derived from cord blood precursors. All these results suggest that only adult cells are able to amplify the Hb switch in the newborn at the level of BFU-E. Two possible mechanisms can be hypothesized: the adult irradiated cells may either modify the differentiation of the BFU-E or recruit precursors that have a higher capacity to express HbA in their progeny.