Molecular interactions in the "GAT" idiotypic network: an approach using synthetic peptides

In order to approach some of the dominant epitopes which are recognized in the GAT (Glu60 Ala30Tyr10)n random terpolymer, a variety of peptides containing 7 to 14 residues were synthesized using glutamic acid and tyrosine as building blocks, and thus were able to mimic determinants common to GAT and GT (Glu50Tyr50)n. One decapeptide and on dodecapeptide were found to inhibit GT-mAb1 (or mAb1') binding to the same extent as GAT. Antibodies were also raised against synthetic peptides which reproduced the sequence of the 6 CDR of the germline anti-GAT Ab1 antibody. Antibodies were obtained against all peptides except L1, and were shown to recognize the native Ab1-Fab. Surprisingly, some of these antibodies also recognized GAT, i.e. anti-L2, anti-H2 and anti-H3, an observation which speaks in favour of a triggering of the idiotypic network at the Ab3 level. Finally, a monoclonal antibody derived from an immunization with an Ab2-D region synthetic peptide was found to be of the Ag+Id- type. Sequence data indicate that the light chain at least is completely different from that the of Ab1/Ab1', which uses only a very precise pair of V germline genes.