Detecting Gold-Labeled Cells

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.

Fixing and Binding Antibodies to Suspension Cells in Preparation for Staining

Staining of suspension cells after fixation, described here, is normally used only to detect cell-surface antigens. Once cells are fixed and permeabilized, the antibodies are added. The antibodies can be labeled directly or they can be detected by using a labeled secondary reagent that will bind specifically to the primary antibody. Detection reagents for cell staining can be labeled with fluorochromes, enzymes, gold, or iodine. Because the cells are in suspension, the washing steps are tedious, and care should be taken not to centrifuge for long durations or at high speeds.

Binding Antibodies to Attached Cells or Tissues in Preparation for Staining

Cells for staining are usually prepared from one of three sources: adherent cells, suspension cells, or whole tissues. Antibodies generally are applied directly to the area of the cells or tissues that is being studied. The antibodies can be labeled directly or they can be detected by using a labeled secondary reagent that will bind specifically to the primary antibody. Detection reagents for cell staining can be labeled with fluorochromes, enzymes, gold, or iodine.