Efficient Induction of Ig Gene Hypermutation in Ex Vivo-Activated Primary B Cells
Efficient Induction of Ig Gene Hypermutation in Ex Vivo-Activated Primary B Cells
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在离体激活的原代 B 细胞中有效诱导 Ig 基因超突变
DOI：
10.4049/jimmunol.1700868
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发表时间：
2017-11-01
影响因子：
4.4
通讯作者：
Wang, Ji-Yang
中科院分区：
文献类型：
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作者：
Liu, Jun;Xiong, Ermeng;Wang, Ji-Yang
激活诱导型胞苷脱氨酶(AID)同时启动Ig基因的体细胞超突变(SHM)和类切换重组(CSR)。AID是如何靶向免疫球蛋白V基因和转换区来触发SHM和CSR的，目前仍不清楚。CD40L+IL-4或LPS+IL-4刺激的原代B细胞发生了有效的CSR，但很难在这些细胞中诱导SHM。在本研究中，我们使用携带VH186.2DFL16.1JH2抗体基因的B1-8hi小鼠的B细胞，在体外培养条件下研究了SHM的诱导。CD40L+IL-4或LPS+IL-4刺激的B1-8hi脾B细胞对IgG1有较强的CSR反应，但不能产生VH186.2基因的SHM。值得注意的是，异位表达AID的B1-8hi B细胞诱导有效的SHM的速度与生发中心B细胞接近。我们进一步建立了AID缺乏的CH12B淋巴瘤细胞系，发现AID在突变株中的异位表达，而在AID充足的CH12细胞中不表达，诱导了V基因的有效点突变和缺失。这些结果表明，体外激活的原代B和B淋巴瘤细胞中的内源性AID不仅不能诱导SHM，而且能抑制外源性AID诱导的SHM。我们的结果进一步表明，AID的时空分布和/或翻译后修饰强烈影响体外激活的原代B细胞SHM的诱导。
Activation-induced cytidine deaminase (AID) initiates both somatic hypermutation (SHM) and class switch recombination (CSR) of Ig genes. How AID is targeted to the Ig V gene and switch region to trigger SHM and CSR remains elusive. Primary B cells stimulated with CD40L plus IL-4 or LPS plus IL-4 undergo efficient CSR, but it has been difficult to induce SHM in these cells. In the current study, we used B cells from B1-8hi mice carrying a prerecombined VH186.2DFL16.1JH2 Ab gene to investigate the induction of SHM under in vitro culture conditions. B1-8hi splenic B cells stimulated with CD40L plus IL-4 or LPS plus IL-4 underwent robust CSR to IgG1, but failed to generate SHM in the VH186.2 gene. Remarkably, ectopic expression of AID in AID-deficient, but not wild-type, B1-8hi B cells induced efficient SHM at a rate close to that observed in germinal center B cells. We further established an AID-deficient CH12 B lymphoma line and found that ectopic expression of AID in the mutant line, but not in AID-sufficient CH12 cells, induced efficient point mutations and deletions in the V gene. These results demonstrate that the endogenous AID in ex vivo–activated primary B and B lymphoma cells not only cannot induce SHM but also inhibit the induction of SHM by the exogenous AID. Our results further suggest that the spatiotemporal distribution and/or posttranslational modification of AID strongly affects the induction of SHM in ex vivo–activated primary B cells.