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Update on flow cytometry, introduction.

The development of flow cytometers and advances in computer technology have greatly advanced our ability to detect and quantitate biologic, biochemical and morphologic alterations on a cellular level, permitting measurements unobtainable by other means. Since Kamentsky et al. (1) reported the development of the first such instrument, the impact of these devices on biology and medicine has intensified, adding weight to the statement (2) that, “the potential impact of flow systems on biology. . . equals that of the electron microscope” and to the prediction (3) that, “by the end of the next decade, flow cytophotometers may be as important in research and clinical medicine as the scintillation counter or the autoanalyzer”. The presentations of the past three meetings at the Engineering Foundation Conferences on Automated Cytology have been published as special issues in this Journal. Significantly, the first in 1974, contained 147 pages and the most recent 1979 contained 635 pages. The Panel Session “Update on Flow Cytophotometry” was an attempt to cover selected aspects ofinstrumentation and applications. Dr. Fulwyler, a pioneer in the development of cell sorters was to have discussed the current status of flow system instrumentation but was unable to participate. Dr. Kamentsky also could not attend but did submit a presentation which is included in this series. As the original architect of flow instrumentation, his outspoken opinions and predictions about future directions for flow systems carry particular weight. Dr. Crissman and associates have been leading contributors to the development, testing and application of fluorescent DNA probes for flow-systems. Their concern about the effects of preparatory procedures on fluorescent emission intensity and their caution concerning interpretation of data without adequate controls needs emphasis. Dr. Krshan has been able to assess amounts of chemotherapeutic antibiotics in cultured human or mouse leukemic lymphoblasts based on quantitation ofquenching offluorescence by adriomycin upon binding to DNA, or by measuring enhancement of fluorescence of propidium iodide on binding to double stranded nucleic acids. These and similar studies (4) suggest an important role for flow cytometry in monitoring the intracellular distribution of anti-cancer drugs. Dr. Dolbeare and associates used flow cytometry to study intracellular enzyme activity of individual cells using fluorogenic substrates. This approach parallels and complements our own studies with nonfluorescent technics (5). Both approaches have limitations. As pointed out by Dolbeare, there is a need to find fluorescent reaction products which are insoluble and/or which do not diffuse out of the cell. The major problems with nonfluorescent reactions relate to interference by unstained cells and to the higher sensitivity of fluorescent over nonfluorescent detection systems. A hint of the possibilities in applying flow systems to immunological studies is indicated by the presentation by Loken who described changes in phenotypic expression of myeloma cells during tumor growth upon exposure to chemotherapeutic agents. In addition, flow analyses permitted detection of clonal variants in cultured myeloma cells which were then sorted, subcultured and studied for a variety of immunologic markers.