Idiotypes of anti-myoglobin antibodies: shared idiotypes among monoclonal antibodies to distinct determinants of sperm whale myoglobin

Guinea pig anti-idiotypic antibodies against monoclonal antibodies to Mb were raised, and the resulting antisera were extensively absorbed with normal mouse Ig. The monoclonal antibodies (all IgG1, κ) bind to different sites on Mb based on their distinct cross-reactivity patterns on a large panel of related myoglobins of known amino acid sequence. Moreover, antibodies from clones 1, 2, 3, or 4 can bind simultaneously with clone 5 antibody to monomeric Mb. Therefore, antibodies from clones 1, 2, 3, and 4 must bind to sites on the antigen molecule distant from those recognized by clone 5. These antibodies would be expected to have distinct idiotypes. Surprisingly, by competitive binding studies, anti-idiotypic antiserum (1004) to clone 4 inhibited Mb binding by antibodies of clone 1 as well as clone 4 but not clone 5, 6, or A.SW anti-Mb. Anti-idiotypic antiserum (1382) to clone 5 also inhibited Mb binding by antibodies of clones 1 and 4 as well as clone 5 but not clone 6 or A.SW anti-Mb. Therefore, despite having different combining sites specific for different antigenic determinants, antibodies from clone 5 share idiotope(s) with clone 1 and clone 4 antibodies; likewise, antibodies from clone 4 share some idiotope(s) with clone 1 antibodies, although in the latter case we cannot exclude the possibility that the determinants recognized might overlap slightly, even though the data weigh against this. Mb inhibited the binding of anticlone 4 idiotypic antiserum (1004) to antibodies of clones 1 and 4. Therefore, anti-idiotypic antiserum (1004) interacts with variable region residues within, or very close to, the antigen combining site of clones 1 and 4. The sharing of idiotopes within otherwise distinct antibody combining sites may reflect the action of idiotope-specific regulatory T cells in the animal from which these clones were derived.