Flow Cytometry and Cell Sorting

Characterization of cell populations has always been a primary interest of cell biologists. Traditionally, some kind of microscopy—combined with biochemical or immunological techniques—was used to discriminate different cell types or otherwise characterize a new cell population. Microscopy gives very accurate morphological information about the cells, and it may also be used for quantitative measurement of cellular properties. However, these measurements are time-consuming, and so the accuracy of the determined parameter is usually limited by the low number of the cells observed and the consequently high statistical errors. Rare cell types and variants remain undetected in such analyses. The drawbacks of quantitative microscopy can be overcome by automated sampling of cell populations. The first big step in this direction was made by Caspersson et al., who solved the problem of measuring DNA content of cells on slides automatically. High-resolution image analysis microscopy has developed from his approach. A second approach to automated cytology is the analysis of cells in suspension flowing past a detector, known as flow cytometry. Flow cytometry is now a widely applied tool in cell biology and immunology and as well in clinical laboratories, though its potential for characterization of cells is far from fully realized. This chapter deals with the flow cytometric approach to analysis of cell populations. In it we summarize past advances in instrumentation and methodology and also discuss some recent applications of the method to cell biology and biophysics.