Anti-idiotypic antibodies against anti-vitamin A transporting protein react with prealbumin

Abstract

IDIOTYPIC determinants on antibodies are those antigenic determinants in one antibody population which are not present in another antibody population from the same animal¹. The restriction of a set of idiotypic determinants to antibodies directed against a single antigen suggests that the idiotypic determinants may reside in the antibody combining site. In fact, amino acid sequence determinations of antibodies sharing the same idiotype have shown that the variable portions of light chains as well as heavy chains of the various antibodies are very similar if not identical (see ref. 2 for review). These and similar observations have suggested that antibodies against the idiotypic determinants (anti-idiotypic antibodies) recognise only a clonotype, that is, antibodies with a given set of variable regions. This seems well founded in as much as antibodies raised in two species against a single antigen only infrequently seem to share idiotypic determinants. Since the antibody system is degenerate then some antibodies raised against a protein antigen, called A, which forms part of the protein–protein complex AB, may recognise protein A in a fashion similar to that of the normally interacting protein B. Consequently, the idiotypic determinants of some of the antibodies against protein A may have structures in common with protein B. If so, antibodies raised against such idiotypic determinants should bind to protein B. To test this assumption we explored the situation with regard to the retinol-binding protein (RBP)–prealbumin protein complex^3–6. The data presented here show that it is possible to raise anti-idiotypic antibodies against anti-RBP and that such antibodies interact with prealbumin.