Barreto V, Meo T, Cumano A
Unité du Développement des Lymphocytes, Institut Pasteur, Paris, France.
J Immunol. 2001 May 1;166(9):5638-45. doi: 10.4049/jimmunol.166.9.5638.
V(H)DJ(H) recombination has been extensively studied in mice carrying an Ig heavy chain rearranged transgene. In most models, inhibition of endogenous Ig rearrangement occurs, consistently with the feedback model of IgH recombination. Nonetheless, an incomplete IgH allelic exclusion is a recurrent observation in these animals. Furthermore, transgene expression in ontogeny is likely to start before somatic recombination, thus limiting the use of Ig-transgenic mice to access the dynamics of V(H)DJ(H) recombination. As an alternative approach, we challenged the regulation of somatic recombination with the introduction of an extra IgH locus in germline configuration. This was achieved by reconstitution of RAG2(-/-) mice with fetal liver cells trisomic for chromosome 12 (Ts12). We found that all three alleles can recombine and that the ratio of Ig allotype-expressing B cells follows the allotypic ratio in trisomic cells. Although these cells are able to rearrange the three alleles, the levels of Ig phenotypic allelic exclusion are not altered when compared with euploid cells. Likewise, we find that most VDJ rearrangements of the silenced allele are unable to encode a functional mu-chain, indicating that the majority of these cells are also genetically excluded. These results provide additional support for the feedback model of allelic exclusion.
V(H)DJ(H)重排在携带免疫球蛋白重链重排转基因的小鼠中已得到广泛研究。在大多数模型中，内源性免疫球蛋白重排受到抑制，这与免疫球蛋白重链（IgH）重排的反馈模型一致。尽管如此，在这些动物中反复观察到不完全的IgH等位基因排斥现象。此外，转基因在个体发育中的表达可能在体细胞重排之前就开始了，因此限制了使用Ig转基因小鼠来研究V(H)DJ(H)重排的动力学。作为一种替代方法，我们通过引入处于种系构型的额外IgH基因座来挑战体细胞重排的调控。这是通过用12号染色体三体的胎肝细胞重建RAG2(-/-)小鼠来实现的。我们发现所有三个等位基因都能重排，并且表达免疫球蛋白同种异型的B细胞比例遵循三体细胞中的同种异型比例。尽管这些细胞能够重排三个等位基因，但与整倍体细胞相比，免疫球蛋白表型等位基因排斥的水平并未改变。同样，我们发现沉默等位基因的大多数VDJ重排无法编码功能性的μ链，这表明这些细胞中的大多数在基因上也被排斥。这些结果为等位基因排斥的反馈模型提供了额外的支持。
