Reaction of anti-idiotypic antibody with the hapten-binding site of a myeloma protein.

Rabbit antiserum was prepared against mouse myeloma Protein-315, an IgA protein with specificiy toward the 2,4-dinitrophenyl group. After absorption of the antiserum with another IgA myeloma protein and with affinity-labeled Protein-315, the antiserum was specific for idiotypic determinants on Protein-315. Monovalent ligands that bind to Protein-315 with high affinity strongly inhibited the reaction of the protein with its anti-idiotypic antiserum. This indicated that the region of the hapten-binding site is a major idiotypic determinant. The myeloma protein is thus similar to rabbit antibenzoate antibody in this respect. These results, considered in conjunction with other data in the literature, indicate that an anti-idiotypic antiserum prepared in an isologous or heterologous species can recognize the same determinant, in this case the region comprising the ligand-binding site. Quantitative aspects of the data indicate that there is competition between the hapten and antiidiotypic antibodies for the site.