FETAL HEMOGLOBIN AND POTASSIUM IN ISOLATED TRANSFERRIN RECEPTOR-POSITIVE DENSE SICKLE RETICULOCYTES

A subset of sickle cells have an increased density at the reticulocyte stage of development, indicating that they are either abnormally dens e upon release from the bone marrow or become dense quickly in the cir culation. These cells are of interest because they most likely have se verely disrupted cation regulation and a short lifespan. Based on the distribution of fetal hemoglobin (HbF) in the density fractions of sic kle red blood cells (RBCs) and in vitro studies of cellular K+ loss, i t seems likely that HbF content is an important in vivo determinant of dense cell formation. In this study, we tested the hypothesis that yo ung, dense cells have low HbF content. Sickle RBCs were first separate d into light and dense fractions. Reticulocytes were isolated from unf ractionated cells and from each density fraction with an immunomagneti c technique directed against transferrin receptors (TfR) and assayed f or the percentage of HbF and K+/Hb ratio. TfR(+) reticulocytes isolate d from unfractionated cells had a much lower HbF content when compared with all the unfractionated RBCs. This is most likely caused by enric hment of F cells because of a longer circulation life span. Heavy TfR( +) reticulocytes had a K+/Hb ratio similar to that measured in the ent ire dense population and contained very low levels of HbF, averaging 2 .5% of the level in all RBCs, 11.7% of the level in all TfR(+) reticul ocytes, and 4.0% of the level in all dense RBCs. These findings sugges t that TfR(+) dense cells derive predominantly from non-F cells. Furth ermore, the amount of HbF in the circulating dense cells suggests that many of these cells do not derive from the TfR(+) dense cells. (C) 19 94 by The American Society of Hematology.