DIFFERENTIAL KINETICS OF PROPIDIUM IODIDE UPTAKE IN APOPTOTIC AND NECROTIC THYMOCYTES

Apoptosis and necrosis represent two different mechanisms by which cel ls die. The dynamics of cellular lesions in these two processes differ . Ill particular we demonstrate that plasma membrane damage, occurring as a primary event during necrosis represents, on the contrary, a del ayed but massive phenomenon during apoptosis. In consequence there are different kinetics of propidium iodide incorporation by necrotic and apoptotic thymocytes. This represents the basis for the flow cytometri c identification of different cellular subsets. Analysis of these subs ets after sorting showed that clearly apoptotic cells, which are not a ble to exclude propidium iodide for long incubation periods, do not sh ow any morphologically detectable membrane damage. The kinetics of pro pidium iodide incorporation in vivo in isolated rat thymocytes can the refore be used in flow cytometric analysis. This technique can be used instead of DNA staining of ethanol-treated cells or nick translation to recognize apoptotic cells, and distinguish apoptosis from necrosis, without killing the cell.