Systems Immunology Lab, Department of Biology, Institute for Theoretical Biology, Humboldt University, Invalidenstrasse 43, 10115 Berlin, Germany.
Int Immunol. 2011 May;23(5):345-56. doi: 10.1093/intimm/dxr018.
Affinity maturation of B lymphocytes within germinal centers involves both diversification of their B-cell receptors (BCRs) by somatic hypermutation (SHM) and a crucial receptor-mediated selection step. However, in contrast to recent advances in revealing the molecular mechanism of SHM, the fundamentals of the selection process are still poorly understood, i.e. it is often not clear how and how many mutations contribute to improving a BCR during the response against a given antigen. A general drawback in assessing the mutations relevant to the selection process is the difficult task of rating the relative contributions of selection and intrinsic biases to the experimentally observed mutation patterns of BCRs. The approach proposed here is premised on statistical comparison of the frequency distributions of nucleotide substitutions as observed in datasets of hypermutated BCRs against their frequency distribution expected under the null hypothesis of no selection. Thereby, we show that the spectrum of mutations relevant to maturation of canonical anti-(4-hydroxy-3-nitrophenyl)acetyl BCRs is much broader than previously acknowledged, going beyond the scope of single key mutations. Moreover, our results suggest that maturation not only involves selection by means of affinity but likewise expression and stabilization of BCRs.
生发中心内 B 细胞的亲和力成熟既涉及 B 细胞受体 (BCR) 的体细胞高频突变 (SHM) 多样化，也涉及关键的受体介导选择步骤。然而，与最近揭示 SHM 分子机制的进展相比，选择过程的基础仍知之甚少，即通常不清楚在针对给定抗原的反应中，有多少和哪些突变有助于改善 BCR。评估与选择过程相关的突变的一个普遍缺点是，评估选择和内在偏差对 BCR 实验观察到的突变模式的相对贡献的任务非常困难。这里提出的方法基于对高频突变为 BCR 观察到的核苷酸取代频率分布与无选择假设下预期的频率分布进行统计比较。由此，我们表明，与经典抗-（4-羟基-3-硝基苯）乙酰 BCR 成熟相关的突变谱比以前认为的要广泛得多，超出了单个关键突变的范围。此外，我们的结果表明，成熟不仅涉及通过亲和力进行选择，还涉及 BCR 的表达和稳定。
