title: Affinity in radioimmunoassay of antibody cross-reactive with carcinoembryonic antigen (CEA) and colon carcinoma antigen-III (CCA-III).
abstract: Several antisera raised against purified carcinoembryonic antigen (CEA) were evaluated for their content of antibody cross-reactive with colon carcinoma antigen-III (CCA-III). All antisera gave a reaction of partial identity between CEA and CCA-III and demonstrated a high titer in CEA radioimmunoassay (RIA). Between 50 and 70% of the CEA RIA activity was removed, however, by absorption with soluble CCA-III or adsorption onto CCA-III-containing immunoadsorbents. Immunoadsorbent retained antibody gave a line of complete identity between CEA and CCA-III. Purified CCA-III (2 mug) only partially depressed CEA binding by this common site antibody, whereas nanogram quantities of CCA-III inhibited the reaction between specific CCA-III antibody and radioiodinated CCA-III. In addition, low levels of CEA were equally effective in depressing CEA binding by the common site or CEA-specific antibody. The higher affinity in RIA of the common site antibody for CEA over CCA-III suggests that the common determinant expressed on CEA is stereochemically different from that on CCA-III. The results further demonstrate that interference by plasma CCA-III is not a significant factor in the measurement of CEA by RIA.
mesh_terms: D000230:Adenocarcinoma / Q000276:immunology; D000912:Antibodies, Neoplasm / Q000302:isolation & purification; D000918:Antibody Specificity; D000951:Antigens, Neoplasm; D002272:Carcinoembryonic Antigen; D003110:Colonic Neoplasms / Q000276:immunology*; D003429:Cross Reactions; D000939:Epitopes; D005779:Immunodiffusion; D007164:Immunosorbents; D009994:Osmolar Concentration; D011863:Radioimmunoassay
chemical_list: D000912:Antibodies, Neoplasm; D000951:Antigens, Neoplasm; D002272:Carcinoembryonic Antigen; D000939:Epitopes; D007164:Immunosorbents