F reticulocytes assay: a method to evaluate fetal hemoglobin production

Production of fetal hemoglobin (Hb F) involves molecular as well as cellular aspects as, among red blood cells, it is restricted to a specific population referred as the F cells. Thus understanding the mechanisms involved in persistence or re-emergence of Hb F production in various inherited or acquired conditions requires the measurement of both Hb F and F cells. In addition, in disorders with a hemolytic component, including sickle cell disease (SCD), because of a probable preferential survival of F cells as compared to non-F cells, the true parameter of F cell production is the F reticulocyte count. The F cells/F reticulocytes ratio then selectively reflects this preferential survival. Here we describe an original immunofluorescence microscopy assay that permits the simultaneous measurement of F cells and F reticulocytes. For this assay to be widely usable, we chose to use commercially available monoclonal antibodies.