Detection of Single-Cell Apoptosis
Our initial deﬁnitions of the apoptotic process were based on a set of morphological changes that occurred in the cell nucleus and cytoplasm. As ﬁrst described by Kerr using electron microscopy  the earliest visible change in the apoptotic cell was the aggregation of chromatin into compact masses along the nuclear membrane. Eventually, more and more compact granular masses appeared and ﬁlled the nucleus, combined with a gradual reduction in nuclear volume. At the same time the cytoplasm displayed progressive condensation, but with preservation of organelles. “Apoptotic bodies” consisting of discrete spherical or ovoid fragments containing highly condensed chromatin were then phagocytosed and lysed by nearby cells. Initially these changes were thought to encompass the entire apoptotic process, but now it is clear that apoptotic bodies are part of the ﬁnal degradative phase of apoptosis (Fig. 1).