Fifty-million-year-old polymorphism at an immunoglobulin variable region gene locus in the rabbit evolutionary lineage

B cell development and repertoire diversification vary significantly among species. Diversification of the Ig repertoire occurs through the combinatorial joining of multiple V, D, and J gene segments for the Ig heavy and light chains through VDJ Rearrangement, followed by somatic mutagenesis upon subsequent B-cell encounter with foreign antigen (Somatic Hypermutation). Compared to humans and mice, which use a diverse assortment of germline VH gene segments during VDJ rearrangement of the heavy chain, the rabbit IgH repertoire displays highly restricted VH gene segment usage.

The rabbit and chicken immune system generates antibody diversity and optimizes affinity by mechanisms that are more efficient than those of mice and other rodents. Other than the common Somatic Hypermutation, Rabbit and chicken B cells also employed a mechanism called Gene Conversion, which involves the non-reciprocal homologous recombination of upstream pseudo V gene loci into the recombined VDJ (and VJ) locus. The gene conversion with the approximate of 300 pseudo V-genes dramatically enhanced the diversity of its antibody repertoire and increased the possibility of generating functional antibody clones.

Reference:

Fifty-million-year-old polymorphism at an immunoglobulin variable region gene locus in the rabbit evolutionary lineage Proc. Natl. Acad. Sci. USA 1999 96:9710-9715

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC22275/\

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