Optimal detection of apoptosis by flow cytometry depends on cell morphology

Flow cytometry has recently become a choice technique for the quantitative analysis of apoptosis. Monoparametric DNA analysis usually allows identification of apoptotic cells as a 'subdiploid' peak. Progression through apoptosis leads to chromatin condensation, nuclear fragmentation and eventually to cell disruption. Thus, a major problem for the flow cytometric analysis of apoptotic populations is discrimination between debris and apoptotic cells. Here we demonstrate that the best parameter on which to make such a distinction is the DNA content, no matter what type of cell is studied. In contrast, discrimination between apoptotic, non-apoptotic cells, and debris is possible on the basis of scattering signals only in few selected cases, depending on the morphology of the intact cells.