A new procedure for analysing the relationship between different cell surface antigens.

An immunoprecipitation-inhibition procedure is assessing whether different antigenic determinants are carried on the same molecule or on different molecules on cells. The procedure entails (a) exposing NP-40 lysates of cells to antibody against one antigenic specificity; (b) removing free antibody and immune complexes by absorption with protein A-bearing S. aureus bacteria; (c) adsorption of the NP-40 with a detergent binding resin; and (d) measuring the inhibitory activity of the lysates for antibody against another specificity by a rosetting assay. This method has several advantages over the widely used sequential immunoprecipitation procedure.