Changes in haemoglobin and antigenic constitution of erythrocytes during embryonic and postembryonic chick development.

Between the 18th and 20th day of incubation, the proportion of haemoglobin F (Hb F) synthesis decreases in the embryo bone marrow from the value found in the yolk sac (10% of the total haemoglobin synthesis) to the value found in the bone marrow of young chicks (2%). A similar drop in Hb F synthesis is observed with a delay of 48 hours in the blood. Two membrane antigens each specific of either embryo or adult erythrocytes have been detected. The study by immunofluorescence of their cellular distribution shows that 3 erythrocyte populations are successively produced: a population E bearing the embryonic antigen only, a population EA bearing both antigens and a population A bearing the adult antigen only. The presence of a relatively high proportion of Hb F in population E is strongly suggested by the similar kinetics of Hb F and E cells disappearance within the first posthatching month.