A common idiotypic specificity of rabbit antibodies to the a2 allotype of the immunoglobulin heavy chain variable region.

Anti-idiotype antibody to anti-a2 VH-allotype antibody was induced in a1a1 homozygous rabbits with a purified antibody preparation isolated from three a1a1 rabbits. By immunodiffusion assay, the anti-idiotype antibody reacted to give a line of identity with all 15 anti-a2 VH-allotype antisera from our serum bank and with isolated anti-a2 antibody or Faby fragments thereof, but did not react with the preimmune sera. By radioimmunoassay, essentially all of the anti-a2 antibody molecules having the anti-a2 activity also had the common idiotypic specificity and vice versa. By an inhibition assay, the common idiotypic specificity on each of the anti-a2 antibody populations was very similar if not identical. This common idiotypic specificity was not dependent on the expression of a VH or light chain allotype, since the anti-a2 antibodies were obtained from rabbits with different a locus (VH region) or b locus (K-chain) allotypes. Also, this common idiotypic specificity was not limited to our colonies of rabbits, since one of the 15 rabbits tested was from The Jackson Laboratory, Bar Harbor, Maine. The expression of a common idiotypic specificity on anti-allotype antibodies of the same specificity is in sharp contrast to the findings for other antibodies and may indicate that the number of VH region genes coding for anti-allotype antibody are limited. Our results are similar to those found independently by Roland and Cazenave regarding a common idiotypic specificity of anti-b4 (K-chain allotype) antibodies. Common idiotypic specificities among anti-allotype antibodies may have an important role in the regulation of Ig synthesis.