Klotz E L, Storb U
Committee on Immunology, University of Chicago, IL 60637, USA.
J Immunol. 1996 Nov 15;157(10):4458-63.
Previous experiments have suggested an important role for the Ig enhancers and transcription in targeting somatic hypermutation. To determine whether the requirement of the enhancers is Ig chain specific, we analyzed two lambda 2 light chain transgenes under the control of different enhancers, either the lambda 2-4 enhancer or the heavy chain intron enhancer. The transgenes were amplified and cloned from B220+PNAhigh B cells from either Peyer's patches (PP) or SRBC-immunized spleen. The lambda 2 transgene under the control of the lambda 2-4 enhancer underwent mutation in both the PP and splenic B cell populations, but at a frequency lower than endogenous light chain genes. This requirement for the lambda 2-4 enhancer could be replaced by the heavy chain intron enhancer. Interestingly, the heavy chain intron enhancer-driven lambda 2 construct showed evidence of statistically significant mutation in the PP B cell population, but not the spleen-derived population. This difference in somatic hypermutation suggests that a lower mutation frequency can be more readily detected in B220+PNAhigh B cells isolated from the PP. The ability of the heavy chain intron enhancer to replace the lambda 2-4 enhancer shows that the requirement for the Ig enhancers in somatic hypermutation is not Ig locus specific. Given that these Ig enhancers have very few elements in common, our results further suggest that the Ig enhancers are primarily important in the timing of transcription in the mutating B cell population.
先前的实验表明，免疫球蛋白增强子和转录在靶向体细胞高频突变中起重要作用。为了确定增强子的需求是否具有免疫球蛋白链特异性，我们分析了在不同增强子（λ2-4增强子或重链内含子增强子）控制下的两个λ2轻链转基因。这些转基因是从派尔集合淋巴结（PP）或经绵羊红细胞免疫的脾脏中分离出的B220+PNA高的B细胞中扩增并克隆得到的。在λ2-4增强子控制下的λ2转基因在PP和脾脏B细胞群体中均发生了突变，但频率低于内源性轻链基因。对λ2-4增强子的这种需求可以被重链内含子增强子替代。有趣的是，重链内含子增强子驱动的λ2构建体在PP B细胞群体中显示出统计学上显著的突变证据，但在脾脏来源的群体中则没有。体细胞高频突变的这种差异表明，从PP分离出的B220+PNA高的B细胞中较低的突变频率更容易被检测到。重链内含子增强子替代λ2-4增强子的能力表明，体细胞高频突变中对免疫球蛋白增强子的需求并非免疫球蛋白基因座特异性的。鉴于这些免疫球蛋白增强子几乎没有共同的元件，我们的结果进一步表明，免疫球蛋白增强子在发生突变的B细胞群体转录的时间方面至关重要。
