Fetal characteristics of erythrocytes in sickle cell anemia: an immunofluorescence study of individual cells.

In a group of disease states that includes sickle cell anemia (SS disease), two fetal erythrocyte markers, Hb F and i antigen, persist into adulthood. Using the technique of single-cell immunofluorescence, we determined the expression of l-i antigens and the presence of Hb F within populations of erythrocytes. Subjects tested included normal adults, normal newborns, patients with SS disease, and individuals with sickle cell trait. We classified erythrocytes reacting to anti-i as i cells and those reacting to anti-l as l cells, a terminology analogous to that used to identify erythrocytes containing increased amounts of Hb F as F cells. The expression of l and i antigens within populations of both normal and SS erythrocytes was found to be heterogeneous. The proporations of both i cells and l cells in all SS patients studied exceeded those found in normal adults, and an overall stronger-than-normal reactivity of individual SS cells to the two antibodies was observed. Proportions of F cells showed no correlation with proportions of i cells; and with double fluroescence staining for both Hb F and i, a significant proportion of each total SS red cell population was found to carry only one or the other marker. These findings confirm and clarify on a cellular level our previous demonstration, by means of quantitative hemagglutination, that there is increased expression of both l and i by whole populations of SS erythrocytes. In addition, we provide here new information on the expression of l and i within populations of normal human erythrocytes.