Genetic polymorphism of rabbit immunoglobulins: description of b98, a ninth allele at the kappa b-locus

Organization and structure of wild rabbit kappa2 genes: implications for regulation of kappa expression

In domestic populations, the rabbit kappa light chains are known to be encoded by two loci which are unequally expressed. The kappa1 chains account for the majority of total serum kappa chains, and display an unusual complex polymorphism. In order to study the evolution and the putative correlations between the expression, the organization and the structure of the kappa genes, we analysed the kappa loci in wild rabbit populations. The kappa genes of b95, b97 and b98 allotypes are organized in two loci similar to that of domestic rabbits. The structure of the constant region of the kappa2 locus was determined from a wild rabbit which expresses b95 allotype kappa1 chains. The Ckappa2bas2 of b95 displays a single silent mutation when compared to Ckappa2bas2 associated with b4 and one amino acid change relative to Ckappa2bas1 chain. Therefore, in contrast to the kappa1 locus, the constant regions of the kappa2 locus display strong conservation during evolution. A model based on conformation of the kappa chains is discussed to explain the evolution and expression of the two kappa loci.

Characterization of the b99 allotype of rabbit immunoglobulin kappa 1 light chain

A previously undetected allotypic specificity, A99, was found in a wild rabbit (Oryctolagus cuniculus) population in Portugal. The A99 allotype cross-reacted with anti-b6 and anti-b96 sera, but carried its own antigenic determinants and was therefore distinct from the known allotypes of the b series. The A99 determinants were located on the kappa 1 light chain of IgG molecules and were inherited as allotypic determinants of the b series. Taken together, these data provide evidence that A99 is encoded by an allele at the b locus, tentatively designated b99. The great similarity between the b6, b96 and b99 allotypes suggests that they derived from a common ancestor.

Mouse monoclonal antibodies against rabbit b6 allotype and their use for characterization of light-chain subpopulations

Mouse anti-allotypic hybridomas directed against different antigenic determinants of the b6 rabbit allotype have been raised. The fine specificity of these monoclonal antibodies (mAbs) was determined by radioimmunoassay and it was possible to classify them into three groups, each directed against distinct epitopes of the b6 allotype. Hare "b6" IgG were tested with anti-b6 mAb and no reaction was found indicating that the number of allotopes present on b6 molecules is greater than the three detected by the mAb. Comparative analysis by precipitation in gel of IgG from homozygous b6/b6 rabbits using mouse mAb and rabbit anti-b6 antibodies suggested that at least two categories of molecules can be discriminated. The observation of b6 subpopulations was confirmed by isolation of a minor subpopulation of IgG on a mouse monoclonal immunoadsorbent.

Monoclonal antibodies specific for the b5 allotype of rabbit kappa light chains

The mouse monoclonal antibodies (mAb), 3B5 and 4B5, which recognize rabbit kappa light chains bearing the b5 allotype, were produced from separate fusions. The specificity of the mAbs was determined by solid-phase inhibition radioimmunoassay. Nonimmune sera of 15 b5b5 rabbits of various heavy chain haplotypes inhibited the binding of both mAbs to b5 IgG, whereas 20 sera from rabbits not expressing the b5 allotype were not inhibitory. In addition, the binding of both mAbs was inhibited by purified b5 light chains, but not by b4 light chains. The b5 epitope recognized by the mAbs was shown by sequential precipitation to be present on all b5-bearing molecules that are defined by an alloantiserum produced in a b4b4 rabbit. Antibody 4B5 forms strong precipitin bands with b5 serum and Ig in gel diffusion assays. An anomalous reaction of nonidentity was observed when mAb was compared to rabbit anti-b5 antiserum and a hypothesis to explain this phenomenon is proposed.

A second rabbit kappa isotype

Immunoglobulin G (IgG) from the rabbit strain Basilea was previously shown to contain two distinct populations of molecules one with light chain belonging to the known lambda isotype and the others to a new kappa-like L chain type. Alloantisera prepared against the Basilea IgG are directed against the kappa-like light chain (anti-bas antisera). All Basilea rabbits express kappa-like chains recognized by anti-bas sera, but IgG from other domestic rabbits did not react with these antisera. Genetic studies of wild rabbits belonging to different populations show that the bas+ phenotype could be found in heterozygous rabbits as well as those homozygous at the b locus. The gene encoding the bas+ light chain is closely linked to the b locus. Moreover, antigenic determinants recognized by anti-bas antibodies and antigenic determinants recognized by antibodies directed against allotypic determinants of the b series are located on distinct IgG molecules. These results show that there are two rabbit kappa isotypes: the kappa 1 isotype, bearing allotypic determinants of the b series, and the kappa 2 isotype, for which bas+ chain is one of the allotypic forms. The kappa 1 and kappa 2 isotypes are controlled by closely linked genes.