Xu L, Gorham B, Li S C, Bottaro A, Alt F W, Rothman P
Department of Microbiology and Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032.
Proc Natl Acad Sci U S A. 1993 Apr 15;90(8):3705-9. doi: 10.1073/pnas.90.8.3705.
Recent work has shown that the ability of cytokines to direct immunoglobulin heavy chain class-switch recombination to particular heavy chain constant (C) region (CH) genes correlates with the induction of specific germ-line CH transcripts. To test the role of germ-line transcripts in class switching, we have used homologous recombination to mutate the immunoglobulin heavy chain locus of the 18.81A20 murine pre-B-cell line. In the parent cell line, the combination of interleukin-4 (IL-4) and lipopolysaccharide (LPS) induces germ-line epsilon locus transcription prior to class switching to epsilon. The heavy chain locus of the mutated cell line contains the immunoglobulin heavy chain enhancer and variable region gene promoter in place of the LPS/IL-4-responsive germ-line epsilon promoter. The mutant cell line constitutively transcribes the epsilon locus in the absence of IL-4. Strikingly, the mutant cell line also switches to epsilon in the absence of IL-4. This result demonstrates that, at least in the 18.81A20 cell line, germ-line epsilon transcription plays a direct role in class switching to the epsilon locus. In addition, the ability to change the pattern of class switching by altering transcriptional activity indicates that transcription of germ-line CH is mechanistically important in regulation of class switching.
近期研究表明，细胞因子引导免疫球蛋白重链类别转换重组至特定重链恒定（C）区（CH）基因的能力与特定种系CH转录本的诱导相关。为了测试种系转录本在类别转换中的作用，我们利用同源重组对18.81A20小鼠前B细胞系的免疫球蛋白重链基因座进行了突变。在亲本细胞系中，白细胞介素-4（IL-4）和脂多糖（LPS）的组合在类别转换至ε之前诱导种系ε基因座转录。突变细胞系的重链基因座包含免疫球蛋白重链增强子和可变区基因启动子，取代了LPS/IL-4应答性种系ε启动子。突变细胞系在无IL-4的情况下组成性转录ε基因座。引人注目的是，突变细胞系在无IL-4的情况下也转换至ε。这一结果表明，至少在18.81A20细胞系中，种系ε转录在类别转换至ε基因座中起直接作用。此外，通过改变转录活性来改变类别转换模式的能力表明，种系CH转录在类别转换调控中具有重要的机制意义。
