Preservation of cells sorted individually onto microscope slides with a fluorescence-activated cell sorter

Fluorescence-activated cell sorters permit analyses and separation of cell populations based on light scatter and surface immunofluorescence parameters. Since a sorter can deposit individually identifiable cells onto a microscope slide, it was considered of interest to combine the flow measurements with analyses available on cells adhering to a surface as in, for example, morphological studies, cytoplasmic immunofluorescent staining, and mRNA in situ hybridization. A necessary condition for these studies is the preservation of cell structures after sorting. We report here a procedure suitable for this purpose. The most important features of this procedure are A) reducing the saline content of the sorter sheath fluid to about 0.0015 M (one-hundredth that of normal saline) to prevent cell damage due to hypertonicity during drying, and B) coating the substrate with a thin layer of newborn calf serum to promote the adherence of the cells to the substrate during subsequent fixing and staining.