New method for quantitative determination of fetal hemoglobin-containing red blood cells by flow cytometry: application to sickle-cell disease.

A new method to quantify red blood cells (RBCs) containing fetal hemoglobin (HbF), or F cells, by flow cytometry was developed. The use of formaldehyde as fixative agent and sodium dodecyl sulfate (SDS) to permeabilize fixed RBCs resulted in a low staining background, a negligible Hb leakage, and minimal cell clumping. HbF was detected by immunofluorescence with a murine monoclonal antibody directed to the gamma chain of human Hb. The accuracy of the F-cell count was evaluated on mixed-field populations of adult and cord RBCs. The results of flow cytometry were highly correlated with HbF dosage in the hemolysate by high-pressure liquid chromatography (HPLC) (R > 0.99). The sensitivity of the method allowed the study of HbF distribution at the single-cell level in normal controls and patients with sickle-cell disease (SCD). All patients exhibited a heterocellular distribution of HbF, with highly variable percentages of F cells and non-F cells. As an additional and valuable biological parameter in SCD, the mean HbF content per F cell could be deduced from the measurement of HbF level by HPLC and F-cell count by flow cytometry. Results were unchanged after storing the cells for several weeks in an optimized resuspending solution. Since it does not need uncommon reagents or devices and allows the simultaneous detection of membrane antigens by two-color flow cytometry, this method is convenient for routine laboratories as well as for research purposes.