Preparation of a Relatively Acid-Stable Antigen (CEA) by Disruption of its Specific Precipitate with Antibody

Abstract

The carcinoembryonic antigen (CEA) of intestinal tract cancers is presently purified by extraction from a homogen-ate of such tissues with 1.0M perchloric acid (PCA), followed by two steps of chromatography and one of electrophoresis. In this study, rabbit antisera prepared against such purified CEA, and absorbed with normal human plasma, liver, kidney, spleen and brain, gave a conventional precipitin curve with a water homogenate or with a dialyzed PCA extract of intestinal tract cancers. The immune precipitate was almost completely soluble in PCA. Following dialysis of this solution against cold water, a new precipitate composed mainly of denatured antibody appeared. The remaining solution contained purified antigen. Recovery of this antigen (CEA-R), as judged by radioimmunoassay, appeared optimal when 3.0M PCA was used for disruption of the immune precipitate, and presence of 1.8M urea was helpful. When injected into rabbits, CEA-R was not as strongly antigenic as CEA. Comparison by immunodiffusion and immunoelectrophoresis against their specific rabbit anti-sera indicated that CEA and CEA-R share some specificities but are not identical.