Fluorometric quantitation of fluorescein-coupled antibodies attached to the cell membrane.

A method was devised which allows the measurement, by direct and indirect fluorescence assay, of the binding of fluorescein-coupled antibodies directed against cell-membrane antigens. The systems used were: (1) species-specific antigens, (2) genetically determined isoantigens, (3) virus-determined, tumor-specific antigens, and (4) membrane-bound immunoglobulin in a Burkitt cell line. Titration of antibodies gave straight lines in the log versus log scale, the slope of the titration curve probably being dependent on the density of antigen receptors on the cell surface.