The idiotypy of the MOPC 173 (IgG2a) mouse myeloma protein: characterization of syngeneic, allogeneic and xenogeneic anti-idiotypic antibodies. Contribution of the H and L chains to the idiotypic determinants.

Anti-idiotypic antibodies were raised against the mouse (γ_2a, κ) myeloma protein MOPC 173 in syngeneic, allogeneic and xenogeneic conditions. Syngeneic immunization resulted in individual hemagglutination titers ranging from 1:40 to 1:160000 with about 30% of nonresponders, whereas upon allogeneic immunization (in A/J mice) almost all animals responded, with titers ranging from 1:1250 to 1:320000. Anti-idiotypic antisera were also obtained in the rabbit. Inhibition of a radioimmunoassay using ¹²⁵I-labeled MOPC 173 Fab fragments as the reference antigen indicated that the native Ig and the Fab competed on a similar molar basis. No inhibition was observed with the Fc or with other mouse monoclonal Ig, of the same or different classes or subclasses. Standard BALB/c serum did not inhibit either. Whatever the anti-idiotypic antiserum used, idiotypic determinants were not found on isolated heavy (H) and light (L) chains provided they were carefully purified. Reoccurrence of idiotypic determinants was obtained in high yield whenever Ig molecules were reformed from the homologous H and L chains, whereas no potentiation of the low inhibition of isolated chains was observed when hybrid molecules were formed using heterologous complementary chains isolated from the MOPC 21A (γl, ?) or the LPC 1 (γ_2a, ?) protein. These results suggest that MOPC 173 idiotypic determinants rely on the specific H-L interaction and that they must be largely conformational in nature. Heterogeneity of the anti-idiotypic antibodies was analyzed by isoelectric focusing. A major pattern was observed for the A/J antisera, whereas, in the case of BALB/c, expression of a few clones, characteristic of each “high responder” animal, was strongly suggested, superimposed to faint production of antibodies by clones that were common to all mice.