Cytofluorimetric measurement of cytoplasmic myeloperoxidase by permeabilisation of blood cells with the FACS lysing solution

We read with great interest the paper by Tiirikainen dealing with the use of different red blood cell Lysing solutions for the cytofluorimetricd etection of intracellular antigens in normal blood cells. Our experience with either a Facstarplus or a Facscan flow cytometer coin- cided with that of Tiirikainen. However, we wish to point out that our first reports regarding the use of the FACS Lysing solution (Becton-Dickinson) for the simultaneous cytofluorimetric evaluation of a cytoplasmic antigen (my- eloperoxidase; MPO) and surface membrane antigens were published several years ago (1990 and 1991). In these studies as well as in others published more re- cently, we showed that peripheral blood cells ob- tained from both healthy subjects and patients with hematological disorders can be successfully labelled with monoclonal antibodies (mAbs) directed against cytoplas- mic and nuclear antigens, using this commercial red blood cell lysing solution before cell staining, allowing the measurement of several antigenic determinants localized within the cell membrane. It is conceivable that these studies will allow the identification of the best reagent for the analysis of the various cytoplasmic and nuclear antigens in both normal and leukemic cells. However, it should be kept in mind that the pattern of reactivity for each mAb directed against an internal antigen should be carefully evaluated in many cell types before making any diagnostic and prognostic assumptions regarding acute leukemias.