Arnold L W, Grdina T A, Whitmore A C, Haughton G
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill 27514.
J Immunol. 1988 Jun 15;140(12):4355-63.
We have selected and cloned variant cells from the murine B cell lymphoma, CH12, that produce a variety of other Ig isotypes in addition to or in place of the original IgM and IgD. Variants were selected by flow cytometry and automated cloning and isotype production was analyzed by membrane immunofluorescence and ELISA of culture fluids. Variants have been isolated that produce the single isotypes IgA, IgG2b, and IgG3, as well as variants that produce more than one isotype simultaneously, i.e., IgM, IgD, and IgA; IgG2b and IgA; IgG3 and IgA. All isotypes have been seen as cell surface proteins and all except IgD have been found in culture supernatants. All isotypes display the same idiotype and Ag-binding specificity for phosphatidyl choline as the original IgM and all are translated from the same VDJH and VJ kappa gene assemblies. Production of more than one isotype by a variant clone is due to simultaneous production of all the isotypes by each cell within the clone. The finding that the variants producing more than one isotype are all tetraploid suggests the interesting possibility that each isotype is derived from an independently switching chromosome. All isotype variants can be stimulated by LPS to secrete the appropriate Ig isotype at an increased rate similar to the IgM expressing parent. The variants differ in stability; some have remained stable for more than 9 months in culture, whereas other have undergone further isotype switching. The facts that some isotypes have not been seen, that multistep switching has occurred, and that many variants produce IgA in addition to another isotype are discussed in relation to current notions of isotype switching mechanisms.
我们从鼠B细胞淋巴瘤CH12中筛选并克隆了变异细胞，这些细胞除了产生原始的IgM和IgD之外，还能产生多种其他Ig同种型，或者替代它们产生其他Ig同种型。通过流式细胞术筛选变异细胞，并进行自动克隆，通过膜免疫荧光和培养液的酶联免疫吸附测定（ELISA）分析同种型的产生情况。已分离出产生单一同种型IgA、IgG2b和IgG3的变异细胞，以及同时产生不止一种同种型的变异细胞，即IgM、IgD和IgA；IgG2b和IgA；IgG3和IgA。所有同种型均已在细胞表面蛋白中检测到，除IgD外，所有同种型均在培养上清液中被发现。所有同种型均显示与原始IgM相同的独特型和对磷脂酰胆碱的抗原结合特异性，并且所有同种型均由相同的VDJH和VJκ基因组合翻译而来。变异克隆产生不止一种同种型是由于克隆内每个细胞同时产生所有同种型。产生不止一种同种型的变异细胞均为四倍体，这一发现提示了一种有趣的可能性，即每种同种型均源自一条独立发生类别转换的染色体。所有同种型变异细胞均可被脂多糖（LPS）刺激，以与表达IgM的亲本相似的增加速率分泌相应的Ig同种型。这些变异细胞在稳定性方面存在差异；一些在培养中保持稳定超过9个月，而另一些则发生了进一步的同种型转换。结合当前关于同种型转换机制的观点，讨论了某些同种型未被发现、发生多步转换以及许多变异细胞除了产生另一种同种型外还产生IgA的事实。
