Gangliosides, Ab1 and Ab2 antibodies. I. Towards a molecular dissection of an idiotype-anti-idiotype system

This report is focused on the molecular basis for the interaction of a monoclonal antibody (mAb) and its anti-idiotypic mAb. P3 mAb (Ab1) recognizes N-glycolyl-gangliosides, and 1E10 mAb is one of its anti-idiotypic mAbs (Ab2). Chimeric versions of both antibodies retained their specificity. Charged residues in their H-CDRs, particularly H-CDR3, were considered to play a major role in their binding and immunogenic properties. P3 mAb has the unusual property of generating a strong antibody response in syngeneic mice, even when it is administered in saline. We selected phagotopes from a 12mer peptide library displayed on filamentous phage to characterize amino acid motifs recognized by these antibodies. The peptides were enriched in charged amino acids similar to those present in P3 and 1E10 mAb H-CDR3. We also report the construction of four mutants of the P3 antibody, where arginine residues in the heavy chain CDRs were substituted by serine residues, and the characterization of their interaction with 1E10 mAb and GM3(NeuGc) ganglioside, as well as their immunogenic properties in Balb/c mice. H-CDR1 R₃₁ residue appears to have a central role in P3 mAb reactivity and antigenicity. H-CDR3 R_100a residue seems to be more involved in the immunogenicity of the P3 idiotype.