Generation of the primary antibody repertoire in rabbits: expression of a diverse set of Igk-V genes may compensate for limited combinatorial diversity at the heavy chain locus.

In mouse and human, generation of combinatorial diversity through use of different heavy and light chain variable region genes in immunoglobulin rearrangements can be a major contributor to the primary antibody repertoire. In rabbits, the contribution of the combinatorial mechanism to heavy chain diversity is minimal, as only a few Igh-V genes are rearranged and expressed. To investigate the contribution of combinatorial diversity toward generation of the rabbit V(kappa) repertoire, we constructed five genomic libraries from rabbit kidney DNA and 1 cDNA library from the bone marrow of a 1-day-old rabbit using a series of polymerase chain reaction-based strategies. Our analyses indicate that most of the sequences that we recovered from our libraries belong to a single family and some are extremely similar. The actual number of germline Igk-V genes is potentially greater than our conservative estimate of at least 39, 28 of which we found expressed as mRNA. The germline Igk-V genes display different lengths of the coding region 3' of Cys 88 ranging from 7 to 12 amino acids, resulting in CDR3 length heterogeneity among functional V(kappa)J(kappa) sequences ranging from 8 to 15 amino acids. Some of the V(kappa)J(kappa) junctions had N and P nucleotide additions. Thus, in contrast to limited combinatorial diversity of its heavy chain, the rabbit can draw upon a diverse set of germline Igk-V genes. The kappa light chain has the potential to be a major contributor toward generation of the antibody specificities of the rabbit pre-immune repertoire.