A genomic gene encoding the b5 rabbit immunoglobulin kappa constant region: implications for latent allotype...

We previously reported that domestic rabbits of five immunoglobulin kappa allotype strains (b4v, b4, b5, b6, and b9) harbor at least two DNA sequences that hybridize strongly to kappa constant region probes in Southern blots. One of these sequences ("type A") has been identified as encoding the constant region of the kappa 2 isotype, an immunoglobulin chain that most rabbits express only at low levels, if at all. We identified the second sequence--for rabbits of the b4 allotype--as encoding the nominal b4 kappa chain (or kappa 1 isotype), but for rabbits of other allotypes no definite identification for this "type B" sequence could be made. Here we suggest that the type B sequence in rabbits of the other domestic allotypes also encodes the nominal kappa 1 immunoglobulin chain. We show this directly for the b5 allotype; a type B sequence cloned from b5 DNA has been found to contain an apparently functional gene encoding the b5 constant region sequence. Indirect arguments suggest the corresponding conclusion for the b4v, b6, and b9 allotypes. We have considered the implications of these results for the phenomenon of "latent allotype" expression.