Radioimmunoprecipitation Assay for Australia Antigen, Antibody, and Antigen-Antibody Complexes 1

Summary Purified Australia antigen [Au(1)], conjugated with 125I, was reacted with and quantitatively precipitated by human anti-Au(1) in the presence of heterologous antihuman IgG and “dilute” ammonium sulfate. The sensitivity of the devised radioim-munoprecipitation assay procedure proved to be up to 1000 times more sensitive for the detection of antigen and up to 20,000 times more sensitive for the detection of antibody when compared with either immunodiffusion or complement fixation assays. This method is extremely valuable not only in the quantitative detection of antigen and antibody but also in the delineation of naturally occurring antigen-antibody complexes.