Production of BALB/c anti-idiotypic antibodies against the BALB/c myeloma protein 315 does not require an intact ligand-binding site.

To determine whether the ligand-binding site of the BALB/c myeloma protein 315 is essential for the anti-idiotypic response in syngeneic animals, 17 BALB/c mice were immunized with M315 that had been affinity-labeled with bromo-acetyl-DNP-L-lysine (BADL). Essentially all the active sites of M315 were blocked by the affinity label. Fourteen mice produced antibodies that reacted with an idiotypic determinant localized in the Fv fragment of M315, but this idiotype was not part of the DNP-lysine-binding site, and it was absent from L315 and H315 chains. Two groups of BALB/c mice were immunized with nonaffinity-labeled M315, to determine whether the same idiotype was recognized with this immunogen. All animals in the group that received the most prolonged immunization produced antibodies that could be divided in two populations: about 75% were directed against the site-associated idiotype, and the rest reacted with the nonsite idiotype. The other group produced antibodies exclusively specific for the site. Thus, the site-associated idiotype of M315 is not essential for the antibody response of BALB/c mice against M315, and M315 carries at least two different idiotypes that can be recognized by B cells of syngeneic animals.