Antibody repertoire development in fetal and neonatal pigs. VII. Characterization of the preimmune κ light chain repertoire

Combinatorial diversity is highly restricted in the preimmune porcine H chain repertoire compared with that in humans and mice. This raised the question of whether similar restriction characterized the preimmune L chain repertoire. In this study we present evidence that >90% of all expressed Vκ genes in the porcine preimmune repertoire belong to three subfamilies of Vκ genes that share 87% sequence similarity with human IGKV2. This porcine Vκ family also shares sequence similarity with some, but not all, Vκ genes from sheep. Hybridization with sperm DNA and sequence analyses of polynucleotides from overlapping bacterial artificial chromosome clones suggest swine possess ∼60 IGVK2 genes. The latter method also revealed that certain IGKV2 subfamilies are not expressed in the preimmune repertoire. Six members of an IGVK1 family were also expressed as part of the preimmune repertoire, and these shared 87% sequence similarity with human IGVK1. Five Jκ segments, complete with recombination signal sequences and separated by ∼300 nt, were identified ∼3 kb upstream of a single Cκ. Surprisingly, Jκ2 accounted for >90% of all framework region 4 sequences in the preimmune repertoire. These findings show that swine use ∼10 IGVK2 genes from three of six subfamilies and preferentially one Jκ segment to generate their preimmune κ repertoire. These studies, like those of porcine Ig constant regions and MHC genes, also indicate unexpected high sequence similarity with their human counterparts despite differences in phylogeny and the mechanism of repertoire diversification.