期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：5
页码：E458-E466
DOI：10.1073/pnas.1418001112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe recombinatorial process of V(D)J rearrangement generates a vast antibody repertoire from a limited number of genes. The joints generated in the course of V(D)J recombination are imprecise thus yielding greater diversity but also resulting in frequent generation of nonproductive VDJ rearrangements. We have previously shown that B cells with two nonproductive IgH rearrangements can be efficiently rescued by a form of secondary V(D)J recombination called VH replacement. We now demonstrate that VH replacement also contributes to the diversity of the immune repertoire by modifying productive IgH rearrangements. Results presented herein suggest that VH replacement occurs exclusively during early stages of B-cell development and therefore does not contribute to the editing of self-reactive antibodies. The genes encoding the variable (V) region of the B-cell antigen receptor (BCR) are assembled from V, D (diversity), and J (joining) elements through a RAG-mediated recombination process that relies on the recognition of recombination signal sequences (RSSs) flanking the individual elements. Secondary V(D)J rearrangement modifies the original Ig rearrangement if a nonproductive original joint is formed, as a response to inappropriate signaling from a self-reactive BCR, or as part of a stochastic mechanism to further diversify the Ig repertoire. VH replacement represents a RAG-mediated secondary rearrangement in which an upstream VH element recombines with a rearranged VHDHJH joint to generate a new BCR specificity. The rearrangement occurs between the cryptic RSS of the original VH element and the conventional RSS of the invading VH gene, leaving behind a footprint of up to five base pairs (bps) of the original VH gene that is often further obscured by exonuclease activity and N-nucleotide addition. We have previously demonstrated that VH replacement can efficiently rescue the development of B cells that have acquired two nonproductive heavy chain (IgH) rearrangements. Here we describe a novel knock-in mouse model in which the prerearranged IgH locus resembles an endogenously rearranged productive VHDHJH allele. Using this mouse model, we characterized the role of VH replacement in the diversification of the primary Ig repertoire through the modification of productive VHDHJH rearrangements. Our results indicate that VH replacement occurs before Ig light chain rearrangement and thus is not involved in the editing of self-reactive antibodies.
