Chang Sooghee, Yang Liu, Moon Young Mee, Cho Young Gyu, Min So Youn, Kim Tae Joo, Kim Young Joo, Patrick Wilson, Kim Ho-Youn, Mohan Chandra
Department of Internal Medicine, University of Texas Southwestern Medical School, Dallas, TX 75390, USA.
Mol Immunol. 2009 Oct;46(16):3420-6. doi: 10.1016/j.molimm.2009.07.014. Epub 2009 Aug 21.
When monoclonal ANAs and non-ANAs generated from a genetically simplified mouse model of lupus, B6.Sle1, were recently compared, the ANAs exhibited three sequence motifs in their immunoglobulin heavy chains, including increased cationicity in CDR3 ("motif A"), reduced anionicity in CDR2 ("motif B") and increased aspartate at H50 ("motif C"). The present study was designed to elucidate the extent to which these ANA-associated sequence motifs might be hard-wired into the primary B-cell repertoire in lupus. The immunoglobulin heavy chain sequence of total splenic B-cells, follicular B-cells and marginal zone B-cells from B6.Sle1 congenic mice and C57BL/6 controls were amplified by single-cell PCR and compared. Analysis of the primary immunoglobulin heavy chain repertoire indicated that the first two sequence motifs "A" and "B" were already encoded in the naïve repertoire of B6.Sle1(z) mice, whereas the third motif "C" was introduced in part by somatic mutation. Site-directed mutagenesis confirmed that non-anionic CDR2 and cationic CDR3 residues in the immunoglobulin heavy chain facilitated nuclear antigen binding in concert, whereas aspartate at H50 strongly vetoed DNA-binding, while preserving nucleosome reactivity. Hence, anti-nuclear antibodies appear to arise as a consequence of two distinct processes-genetically programmed selection of specific CDR charge motifs into the primary immunoglobulin repertoire, with secondary contribution from somatic mutation. Polymorphisms in the lupus susceptibility gene Ly108 that impair central B-cell tolerance may be mechanistically responsible for these early repertoire differences in lupus.
最近，当对源自狼疮基因简化小鼠模型B6.Sle1产生的单克隆抗核抗体（ANA）和非抗核抗体进行比较时，抗核抗体在其免疫球蛋白重链中表现出三种序列基序，包括互补决定区3（CDR3）中阳离子性增加（“基序A”）、CDR2中阴离子性降低（“基序B”）以及重链50位（H50）天冬氨酸增加（“基序C”）。本研究旨在阐明这些与抗核抗体相关的序列基序在狼疮原发性B细胞库中可能被预先设定的程度。通过单细胞聚合酶链反应（PCR）扩增并比较了B6.Sle1同源基因小鼠和C57BL/6对照小鼠的脾总B细胞、滤泡B细胞和边缘区B细胞的免疫球蛋白重链序列。对原发性免疫球蛋白重链库的分析表明，前两个序列基序“A”和“B”已编码在B6.Sle1（z）小鼠的初始库中，而第三个基序“C”部分是由体细胞突变引入的。定点诱变证实，免疫球蛋白重链中不带阴离子的CDR2和带阳离子的CDR3残基协同促进核抗原结合，而H50位的天冬氨酸强烈抑制DNA结合，同时保留核小体反应性。因此，抗核抗体似乎是两个不同过程的结果——特定CDR电荷基序通过基因编程选择进入原发性免疫球蛋白库，并由体细胞突变产生次要影响。狼疮易感基因Ly108中的多态性损害中枢B细胞耐受性，可能是狼疮这些早期库差异的机制原因。
