Brown M, Stenzel-Poore M, Stevens S, Kondoleon S K, Ng J, Bächinger H P, Rittenberg M B
Department of Microbiology and Immunology, Oregon Health Sciences University, Portland 97201.
J Immunol. 1992 Jan 15;148(2):339-46.
Anti-phosphocholine (PC)-keyhole limpet hemacyanin hybridomas representative of a memory response that express the lambda 1 L chain isotype have a high reactivity to PC-protein. A common feature of these hybridomas possessing high affinity for PC-protein is the occurrence of somatic mutations resulting in replacement changes in three CDR2 positions of the lambda 1 L chain. The influence of each of these three positions on the Ag binding properties of these antibodies was examined by site-specific mutagenesis and expression of recombinant antibody molecules by transfected cells. Affinity measurements and fine specificity profile determinations demonstrated the importance of the three lambda 1 CDR2 positions in Ag binding. Compared to antibodies expressing germline lambda 1, including one with an additional junctional serine that is not encoded by V or J, those antibodies possessing critical changes in CDR2 would have a strong selective advantage based on affinity differences for Ag. Sequence analysis of a group of clonally related hybridomas expressing mutated lambda 1 genes allowed construction of a hypothetical genealogic tree that suggests selection based on changes in CDR2 of lambda 1 in the absence of H chain mutations. The results are consistent with stepwise acquisition of mutations and selection based on affinity constraints.
表达λ1轻链同种型、代表记忆反应的抗磷酸胆碱（PC）-钥孔戚血蓝蛋白杂交瘤对PC-蛋白具有高反应性。这些对PC-蛋白具有高亲和力的杂交瘤的一个共同特征是发生体细胞突变，导致λ1轻链的三个互补决定区2（CDR2）位置发生替换变化。通过定点诱变和转染细胞表达重组抗体分子，研究了这三个位置中的每一个对这些抗体的抗原结合特性的影响。亲和力测量和精细特异性谱测定证明了λ1 CDR2的三个位置在抗原结合中的重要性。与表达种系λ1的抗体相比，包括一种具有额外连接丝氨酸（该丝氨酸不是由V或J编码的）的抗体，那些在CDR2中具有关键变化的抗体基于对抗原的亲和力差异将具有强大的选择优势。对一组表达突变λ1基因的克隆相关杂交瘤进行序列分析，构建了一个假设的谱系树，该谱系树表明在没有重链突变的情况下，基于λ1的CDR2变化进行选择。结果与基于亲和力限制的突变逐步获得和选择一致。
