Fixing and Binding Antibodies to Suspension Cells in Preparation for Staining

Cell Staining

When labeled antibodies are used to detect antigens in cells or tissues, several characteristics of an antigen can be readily determined. Most importantly, cell staining will show both the presence and subcellular localization of an antigen. Double-labeling techniques permit the simultaneous detection of two antigens, allowing comparisons of the relative distribution of different antigens. Many cell-staining methods can also be used in conjunction with conventional histological stains and autoradiographic methods to compare the localization of the antigen with other markers. Cell staining can also be used in pathology studies for determining such variables as the type of infectious organism, the progenitor of a neoplastic cell, or the presence of an inflammatory response. With certain modifications, the procedure can be used to purify cells on the basis of the antigenic composition of their cell surface. Cell staining is a versatile technique and, if the antigen is highly localized, can detect as few as a thousand antigen molecules in a cell or tissue. In some circumstances, cell staining may also be used to determine the approximate concentration of an antigen. Improvements in antibody labeling methods, microscopes, cameras, and image analyzers are rapidly extending the sensitivity of cell-staining procedures and are making these techniques more quantitative. Even without these improvements, cell staining can yield important qualitative and semiquantitative data. This introduction describes protocols for cell staining techniques and includes a discussion of major constraints, antibody selection, and troubleshooting.

Detecting Fluorochrome-Labeled Cells

This protocol describes cell staining using fluorochrome-labeled antibodies. The resolution of subcellular structures using fluorochrome-labeled antibodies exceeds that of the transmitted light microscope because of the visualization of an expanding cone of emitted light from the excited fluorochrome in the specimen. The most commonly used fluorochromes are fluorescein and rhodamine. In recent years, a number of advances in the development of fluorochromes have resulted in brighter and longer-lasting dyes with narrow emission spectra. These are available from a number of commercial suppliers. They can be conjugated to anti-immunoglobulin antibodies, Protein A, Protein G, avidin, or streptavidin. These conjugates are available from many commercial sources. Filter sets are commonly available that will permit independent observation of these two fluorochromes in the same sample. The fluorochrome Texas Red is also used for immunofluorescence, and can be detected using the same filter sets as rhodamine.