Zhang M, Majid A, Bardwell P, Vee C, Davidson A
Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
J Immunol. 1998 Sep 1;161(5):2284-9.
Rheumatoid factors (RF) recognize conformational determinants located within the Fc portion of IgG. By analyzing a panel of monoclonal rheumatoid arthritis (RA)-derived RFs, we previously demonstrated that the somatically generated light chain complementarity-determining region 3 (CDR3) contributes to RF specificity. We have now generated a panel of heavy chain mutants of the B'20 Ab, a high affinity RA-derived IgM RF. B'20 also binds avidly to protein A and weakly to ssDNA and tetanus toxoid. B9601, a RF negative Ab that is highly homologous to B'20 but does not bind any of the Ags tested, and RC1, a low affinity polyreactive RF, were used to generate heavy chain mutants with framework (FR) and CDR switches. The mutated heavy chains were cotransfected into a myeloma cell line with the germline counterpart of the B'20 light chain, and the expressed Ig tested for antigenic specificity. We show that both RF specificity and polyreactivity of B'20 is dependent on its unique heavy chain CDR3 region. Replacement with a B9601 CDR3 shortened to the same length as the B'20 CDR3, and with only 5 amino acid differences, did not restore Fc binding. Conversely, absence of protein A binding of B9601 is due to the presence of a serine residue at position 82a in the B9601 heavy chain FR3 region. Together, our data suggest that Ig gene recombination events can generate B cells with autoantibody specificities in the preimmune repertoire. Abnormal release, activation, expansion, or mutation of such cells might all contribute to the generation of a high titer RF response in patients with RA.
类风湿因子（RF）可识别位于IgG Fc部分的构象决定簇。通过分析一组源自类风湿关节炎（RA）的单克隆RF，我们先前证明体细胞产生的轻链互补决定区3（CDR3）有助于RF的特异性。我们现在构建了一组B'20抗体的重链突变体，B'20是一种源自RA的高亲和力IgM RF。B'20还能与蛋白A紧密结合，与单链DNA和破伤风类毒素结合较弱。B9601是一种与B'20高度同源但不结合任何测试抗原的RF阴性抗体，RC1是一种低亲和力多反应性RF，用于产生具有框架（FR）和CDR转换的重链突变体。将突变的重链与B'20轻链的种系对应物共转染到骨髓瘤细胞系中，并检测表达的Ig的抗原特异性。我们表明，B'20的RF特异性和多反应性均取决于其独特的重链CDR3区域。用缩短至与B'20 CDR3相同长度且仅有5个氨基酸差异的B9601 CDR3进行替换，未能恢复Fc结合。相反，B9601不与蛋白A结合是由于B9601重链FR3区域第82a位存在丝氨酸残基。总之，我们的数据表明Ig基因重组事件可在免疫前库中产生具有自身抗体特异性的B细胞。此类细胞的异常释放、激活、扩增或突变可能都有助于RA患者产生高滴度的RF反应。
