[Flow cytometry measurement of DNA fragmentation in the course of cell death via apoptosis. New techniques for evaluation of DNA status for the pathologist].

Cell death by apoptosis is characterized by DNA fragmentation in 200-250 and/or 30-50 kb followed or not by internucleosomal DNA fragmentation in 180-200 pb. Such characteristics have been used to distinguish between necrotic and apoptotic cells, and also to identify and quantify apoptotic cells by flow cytometry. In the case of internucleosomal DNA fragmentation, the analysis of DNA content constitutes the easiest method to identify apoptotic cells giving an hypoploid cell population commonly called "Sub G1". The identification of the "Sub G1" does not depend on the dyes used; however according to the method of cell fixation and permeabilization, of the divalent cations (Ca2+, Mg2+) present in the staining buffers and of the use of trypsin, the "Sub G1" population may be more or less difficult to identify. To detect apoptotic cells whatever the pattern of DNA fragmentation, the most commonly used methods are either in situ nick-translation or TUNEL (TdT dUTP Nick End Labelling). Thus, flow cytometry offers a wide range of attractive techniques to characterize apoptotic cells but it requires the use of methodological controls for validating results.