This paper reviews the development of a bioassay that uses apoptosis (a form of cell death) to directly measure the response of cells to a physical or chemical insult. The assay described here is in mid-phase of development and has been applied to various cell lines isolated from humans and mice. Under the assay conditions, apoptotic cells present a isignaturei, or morphology, distinct from other cells. The exposure of cells to ionising radiation, UV light or some chemicals, produces a dose-dependent increase in the apoptotic fraction. The dose response is linear up to about 1 Gy of ionising radiation. A preparation technique for the cells is used that produces a permanent record of the experiment. With automation, the statistical power of the assay is substantial since there are potentially 10/sup 5/ cells that can be examined at each data point. A prototype system is described, it consists of a bright-field microscope and a computer controlled microscope stage integrated with preliminary image analysis software. Trials indicate that 200-400 cells per minute can be assessed for isignaturesi characteristic of apoptotic and unaffected has also begun to determine if the assay can be used to predict the relative radiosensitivities of normal and tumour cells, information that could be used to assist in the planning of dosing schedules for radiotherapy.
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