The effect of fetal hemoglobin on the survival characteristics of sickle cells.

The determinants of sickle red blood cell (RBC) life span have not been well-defined but may include both intrinsic factors (eg, the tendency to sickle) and extrinsic factors (eg, the capacity of the reticuloendothelial system to remove defective RBCs). Fetal hemoglobin (HbF) is heterogeneously distributed among sickle RBCs; F cells contain 20% to 25% HbF, whereas the remainder have no detectable HbF (non-F cells). Autologous sickle RBCs were labeled with biotin and reinfused to determine overall survival, non-F- and F-cell survival, and time-dependent changes in HbF content (%HbF) for the surviving F cells.

Phosphatidylserine externalization in sickle red blood cells: associations with cell age, density, and hemoglobin F.

Phosphatidylserine (PS) is normally confined to the cytoplasmic leaflet of the red blood cell (RBC) membrane, but some sickle RBCs expose PS in the outer leaflet (PS+ cells). This study examined the relationships among PS externalization, fetal hemoglobin content, hydration state, and cell age. Sickle RBCs exhibit a wide range of PS externalization.