5,6-carboxyfluorescein diacetate succinimidyl ester-labeled apoptotic and necrotic as well as detergent-treated cells can be traced in composite cell samples.

Detection of dividing cells by staining with 5,6-carboxyfluorescein diacetate succinimidyl ester (CFSE) has been widely used in flow-cytometric protocols. We analyzed the fate of CFSE in cells undergoing apoptotic or necrotic cell death, respectively. Peripheral blood mononuclear cells (PBMC) were stained with CFSE. Apoptosis was induced by UVB irradiation and necrosis by incubation at 56 degrees C for 30 min. In some experiments, labeled cells were permeabilized with detergent and CFSE association with nuclei was assessed. We observed that (i) CFSE remains stably detectable in apoptotic and necrotic cells; (ii) CFSE remains stably associated with the nuclei of cells even after their lysis by detergent; (iii) CFSE labeling does not interfere with the induction of cell death; and (iv) CFSE is not transferred from stained dying cells to unstained neighboring counterparts. We conclude that, in addition to tracking viable cells, CFSE can be used to trace dying cells in composite samples. We demonstrated that CFSE labeling does not influence the induction and the execution of apoptosis or necrosis.