Institute of Cell Biology (Cancer Research), Medical School, University of Duisburg-Essen, Virchowstrasse 173, 45122 Essen, Germany.
Int Immunol. 2010 Apr;22(4):289-98. doi: 10.1093/intimm/dxq007. Epub 2010 Feb 5.
It is controversially discussed whether human IgM(+)IgD(+)CD27(+) B cells, which carry somatically mutated Ig variable region (IgV) genes, are derived from germinal centres (GC) B cells or originate from another developmental pathway. GC composed of IgM(+)IgD(+) B cells, which co-express the CD70 surface marker, have been described in approximately 10% of tonsils. As IgM(+)IgD(+)CD27(+) B cells might be generated in such GC, we characterized IgD(+) tonsillar GC cells. GC dominated by IgD(+) B cells were present in 10 of 67 tonsils analyzed. Three GC were additionally positive for CD70. Detailed analysis of one such GC by microdissection and single-cell DNA PCR revealed IgD(+) GC B cells undergoing somatic hypermutation during clonal expansion. However, further analysis of this GC as well as five additional microdissected GC by reverse transcription (RT)-PCR for clonally related Igmu and Igdelta transcripts indicated that the B-cell clones in five of these six IgD(+) GC belong to the IgD-only B cell subset, which has deleted the Cmu gene, and that only one GC harboured a large IgM(+)IgD(+) B-cell clone. Hence, most IgD(+) GC consist of IgD-only B cells and fully developed IgM(+)IgD(+)(CD70(+)) GC are very rare. This indicates that the rare IgM(+)IgD(+) GC B-cell clones from IgD(+) GC contribute little to the large population of IgM(+)IgD(+)CD27(+) B cells. Finally, an RT-PCR analysis with clone-specific primers for two IgD(+) GC B-cell clones showed an absence of IgG or IgA class-switched clone members, indicating strict regulation of class switching and a selective production of IgD(+) B cells from such clones.
人们对于携带体细胞突变免疫球蛋白可变区（IgV）基因的人 IgM(+)IgD(+)CD27(+)B 细胞是源自生发中心（GC）B 细胞还是起源于另一种发育途径存在争议。大约 10%的扁桃体中存在由同时表达 CD70 表面标记的 IgM(+)IgD(+)B 细胞组成的 GC。由于 IgM(+)IgD(+)CD27(+)B 细胞可能在这种 GC 中产生，因此我们对 IgD(+)扁桃体 GC 细胞进行了特征描述。在分析的 67 个扁桃体中，有 10 个存在 GC 主导的 IgD(+)B 细胞。其中 3 个 GC 还为 CD70 阳性。通过显微切割和单细胞 DNA PCR 对其中一个 GC 进行详细分析显示，在克隆扩增过程中 IgD(+)GC B 细胞发生体细胞超突变。然而，对该 GC 以及通过逆转录（RT）-PCR 对另外五个微切割 GC 进行的克隆相关 Igmu 和 Igdelta 转录本分析表明，这六个 IgD(+)GC 中的五个 GC 中的 B 细胞克隆属于 IgD 仅 B 细胞亚群，该亚群已删除 Cmu 基因，只有一个 GC 含有一个大的 IgM(+)IgD(+)B 细胞克隆。因此，大多数 IgD(+)GC 由 IgD 仅 B 细胞组成，完全成熟的 IgM(+)IgD(+)(CD70(+))GC 非常罕见。这表明，来自 IgD(+)GC 的罕见 IgM(+)IgD(+)GC B 细胞克隆对大量 IgM(+)IgD(+)CD27(+)B 细胞的贡献很小。最后，用针对两个 IgD(+)GC B 细胞克隆的克隆特异性引物进行 RT-PCR 分析显示缺乏 IgG 或 IgA 类别转换克隆成员，表明类别转换受到严格调控，并且此类克隆选择性地产生 IgD(+)B 细胞。
