Disappearance of Hb F and i antigen during the first year of life.

In order to investigate whether a common control mechanism is involved in the diminution of i antigen expression and that of Hb F content in human erythrocytes during the postnatal period, we compared changes in 72 normal infants aged from 0 to 12 months. The proportion of hemoglobins (Hb F, Hb A, Hb A2) and the quantitation of "i" antigen were determined on the total population of red blood cells. In addition, the percentage of individual cells containing Hb F or "i" antigen or both (F cells, "i" cells, and F + "i" cells) were evaluated by using a rhodamine-conjugated anti-Hb F and a fluorescein conjugated anti-system on the same smear preparation. The results provided by the two most sensitive techniques (F cell counting and "i agglutinability) indicated that the curves of disappearance of Hb F and "i" antigen along the 12 first months after birth were identical. A strong correlation (r = 0.97, P < 0.0001) existed between the percentage of F cells and "i" antigen expression. In addition, the progressive increase in Hb A2 concentration was inversely correlated firstly with the proportion of Hb F and second with the expression of the "i" antigen. These results suggest that the switch from fetal to adult hemoglobin and the transformation of "i" antigen expression occurring during the first year following birth are governed by a common control mechanism.