The reported germline repertoire of human immunoglobulin kappa chain genes is relatively complete and accurate.

We describe a bioinformatic analysis of germline and rearranged immunoglobulin kappa chain (IGK) gene sequences, performed in order to assess the completeness and reliability of the reported IGK repertoire. In contrast to the reported heavy-chain gene repertoire, which includes many dubious sequences, only five IGK variable gene (IGKV) alleles appear to have been reported in error. There was, however, insufficient evidence to justify removing these IGKV genes from the germline repertoire. Bioinformatic analysis of apparent mismatches between reported germline genes and 1,863 expressed IGK sequences suggested the existence of two unreported IGKV polymorphisms. Genomic screening of 12 individuals led to the confirmation of both of these polymorphisms, IGKV1-16*02 and IGKV2-30*02. We also show that in contrast to the heavy chain, the IGK repertoire is dominated by sequences that use just a handful of kappa variable (IGKV) and junction (IGKJ) gene pairs. There is also little modification of IGKV and IGKJ genes by the processes of exonuclease removal and N nucleotide addition. The expressed IGK repertoire therefore lacks diversity and the junction region is particularly constrained. Remarkably, the analysis of a dataset of 435 relatively unmutated rearranged kappa genes showed that ten amino acid sequences account for almost 10% of the rearrangements, with identical sequences being derived from as many as seven independent sources. Such dominant sequences are likely to have important roles in the operation of the humoral immune response.