Use of soluble and Staphylococcus aureus-immobilized second antibody compared in a radioimmunoassay for human alpha-fetoprotein.

Staphylococcus aureus cells coated with rabbit anti-goat immunoglobulin G were compared with soluble second antibody in a radioimmunoassay for human serum alphafetoprotein. Recovery of primary immune complexes with use of the bacterial immunoadsorbant (a) allowed second-antibody incubation time to be shortened from 3 h to 20 min at 37 degrees C, (b) decreased by 80% the amount of second antibody required per assay, thereby significantly reducing assay costs, and (c) provided a convenient and reproducible method for separation of free and bound antigen. The ease of preparation and the uniformity and stability of the S. aureus second-antibody reagent are additional advantages that may be useful in other radioimmunoassay procedures.