Cell sorting by continuous flow cytometry

Abstract

Cell sorters have been commercially avail- able for several years, and the principles on which they work have been with us for over 200 years. They allow rapid and accurate determination of cellular and subcellular characteristics, and can accurately sort cells with required features into purified popula- tions. Cell sorters are often known as FAtS (fluorescent activated cell sorter), which is the trade mark of a particular instrument; other makes are available, under the general description of flow cytometers. In flow cytometry, cells (or subcellular components such as isolated chromo- somes) flowing at high speeds in aqueous solution are illuminated briefly and give off optical signals detected by photosensors. Cells are often stained with a fluorescent dye which emits a fluorescent signal when illuminated by the incident light. Scattering of the incident light beam by each cell allows determination of cell size, shape, granularity and surface topography. Signals are analysed by a computer which can then control electrostatic deflection plates enabling desired populations of cells to be physically isolated according to any combi- nation of the measured parameters. A typical flow cytometer is shown in Fig. I. Under nitrogen pressure a suspension of cells stained with a fluorochrome is in- jected into the flow chamber through a small needle and encounters a much larger reservoir of faster flowing sheath fluid (usually physiological saline). The cells are confined to the centre of