Hapten-antibody conjugates as probes of the lymphocyte surface

Various forms and applications of the hapten-sandwich method for labeling cell surface antigens are reviewed. This is a two-layer antibody technique: the first antibody that binds antigen has been chemically modified so that a number of hapten groups are attached; the second antibody is directed against the hapten and has been coupled to a marker for amplified detection. This methodology is particularly suited to circumstances where high sensitivity and specificity are required for labeling alloantigens or for discriminating between antigens in double-labeling procedures. It is applicable to fluorescence visualization, electron microscopy, and radioisotopic labeling. It lends itself also to procedures for specific separation of differing lymphoid cell populations, and has been adapted to studies of cell activation in the immune response.