Department of Pediatrics, University of Alabama at Birmingham, Birmingham, AL 35294, USA.
J Immunol. 2010 Nov 15;185(10):6075-84. doi: 10.4049/jimmunol.1001419. Epub 2010 Oct 18.
Compared with adult bone marrow (BM), the composition of the perinatal liver CDR-3 of the Ig H chain (CDR-H3) repertoire is marked by a paucity of N nucleotides and by enrichment for use of J(H) proximal DQ52 and D(H) proximal V(H) and J(H) gene segments. To test the extent to which these differences reflect limited perinatal TdT activity versus differences in the fetal/adult environment, we used the Hardy scheme to sort fractions B-F B lineage cells from TdT-deficient BALB/c adult BM. V(H)7183-containing VDJCμ transcripts from these cells were amplified, cloned, sequenced, and compared with transcripts from wild-type perinatal liver and adult BM. The pattern of V(H)DJ(H) usage in TdT-deficient BM largely matched that of TdT-sufficient adult cells. What minor differences were detected in the pro-B cell stage tended to diminish with B cell maturation, suggesting strong environmental or Ag-driven pressure to achieve a specific range of V(H)DJ(H) usage regardless of the extent of N nucleotide addition. However, although the patterns of V(H)DJ(H) usage in the TdT-deficient B lineage cells paralleled that of wild-type adult cells, the length distribution, global amino acid composition, and charge distribution of the CDR-H3 repertoire proved to be a close, although not exact, homologue of the CDR-H3 repertoire first expressed by late pre-B cells in the TdT-insufficient perinatal liver. Thus, although differing in V(H) content, TdT-deficient mice appear to represent a good, although not perfect, model for testing the role of perinatal CDR-H3 limitations on late B cell development and Ab responses.
与成人骨髓（BM）相比，围产期肝脏 CDR-3 的 Ig H 链（CDR-H3）组成特征在于缺乏 N 核苷酸，并且富含使用 J(H)近端 DQ52 和 D(H)近端 V(H)和 J(H)基因片段。为了测试这些差异在多大程度上反映了围产期 TdT 活性的有限性与胎儿/成人环境的差异，我们使用 Hardy 方案从 TdT 缺陷的 BALB/c 成年 BM 中分离出 B 谱系细胞的分数 B-F。从这些细胞中扩增、克隆、测序 V(H)7183 包含的 VDJCμ 转录本，并与野生型围产期肝脏和成人 BM 的转录本进行比较。TdT 缺陷 BM 中的 V(H)DJ(H)使用模式在很大程度上与 TdT 充足的成年细胞相匹配。在 Pro-B 细胞阶段检测到的较小差异往往随着 B 细胞成熟而减少，这表明存在强烈的环境或 Ag 驱动压力，以实现特定范围的 V(H)DJ(H)使用，而不管 N 核苷酸添加的程度如何。然而，尽管 TdT 缺陷的 B 谱系细胞中的 V(H)DJ(H)使用模式与野生型成年细胞相似，但 CDR-H3 库的长度分布、整体氨基酸组成和电荷分布被证明是与 TdT 不足的围产期肝脏中晚期前 B 细胞首次表达的 CDR-H3 库非常相似但不精确的同源物。因此，尽管在 V(H)含量上存在差异，但 TdT 缺陷小鼠似乎是一个很好的模型，尽管不是完美的模型，可用于测试围产期 CDR-H3 限制对晚期 B 细胞发育和 Ab 反应的作用。
