Immunogenetic analysis of variable regions encoding ab1 and γ-type AB2 antibodies from the NeuGC-containing ganglioside family

The variable regions from P3, a murine monoclonal antibody (MAb) against NeuGc-containing gangliosides, and two anti-idiotype MAbs directed to P3 MAb were cloned and sequenced. Comparisons with previously reported sequences showed that P3 is a germline antibody encoded by genes from the V_HQ52 and V_k19 families. Analysis of nucleotides at the heavy chain CDR3 (H-CDR3) showed the presence of an extensive 3′ N region that contains almost 50% of the nucleotides of this CDR. In addition, amino acid sequence analysis of the H-CDRs of this MAb revealed the presence of three arginines, two of which are present in the H-CDR3, that could be involved in the interaction of P3 MAb with its electronegative epitope on gangliosides. Anti-idiotype 1E10, which seems to define a "regulatory" idiotope on P3 MAb (it induces Id₊ Ab3), represents a germline Ab2 that belongs to the V_HJ558 and V_k10 gene families. By contrary, the anti-idiotype 3B11 is an extensively mutated antibody that belongs to the V_H3660 and V_k4/5 gene families, defining a "private" idiotope on P3 MAb. Even when different V genes contribute to the variable regions of 1E10 and 3B11 MAbs, they share an acidic motif E/D-D-Y/D-Y-D in H-CDR3, suggesting that both Ab2s recognize paratope positive residues on the Ab1. Therefore, complementary electrostatic interactions involving H-CDR3 from both Ab1 and Ab2, might provide a clue to understand the molecular basis for the generation of γ-type anti-idiotype antibodies to V regions recognizing glycolylated ganglioside antigens.