Giachino C, Padovan E, Lanzavecchia A
Basel Institute for Immunology, Switzerland.
J Exp Med. 1995 Mar 1;181(3):1245-50. doi: 10.1084/jem.181.3.1245.
It is a common notion that mature B lymphocytes express either kappa or lambda light (L) chains, although the mechanism that leads to such isotypic exclusion is still debated. We have investigated the extent of L chain isotypic exclusion in normal human peripheral blood B lymphocytes. By three-color staining with anti-CD19, anti-kappa, and anti-lambda antibodies we could estimate that 0.2-0.5% of peripheral blood B cells from healthy adults express both kappa and lambda on the cell surface. The kappa+lambda+ cells were sorted, immortalized by Epstein-Barr virus, and five independent clones were characterized in detail. All clones express both kappa and lambda on the cell surface and produce immunoglobulin M that contain both kappa and lambda chains in the same molecule, i.e., hybrid antibodies. Sequencing of the L chains revealed in three out of five clones evidence for somatic mutations. It is interesting to note that among a panel of single receptor B cell clones we identified two lambda+ clones that carried a productively rearranged kappa, which was inactivated by a stop codon generated by somatic mutation. These findings indicate that dual receptor B lymphocytes can be found among mature antigen-selected B cells and suggest that somatic mutation can contribute to increase the degree of isotypic exclusion by inactivating a passenger, nonselected L chain.
一种普遍的观点认为，成熟的B淋巴细胞表达κ或λ轻（L）链，尽管导致这种同种型排斥的机制仍存在争议。我们研究了正常人外周血B淋巴细胞中L链同种型排斥的程度。通过用抗CD19、抗κ和抗λ抗体进行三色染色，我们估计健康成年人外周血B细胞中有0.2 - 0.5%在细胞表面同时表达κ和λ。对κ + λ + 细胞进行分选，用爱泼斯坦 - 巴尔病毒使其永生化，并对五个独立克隆进行了详细表征。所有克隆在细胞表面均表达κ和λ，并产生在同一分子中同时含有κ和λ链的免疫球蛋白M，即杂交抗体。L链测序显示，五个克隆中有三个存在体细胞突变的证据。有趣的是，在一组单受体B细胞克隆中，我们鉴定出两个λ + 克隆，它们携带一个经重排且有功能的κ，但该κ因体细胞突变产生的终止密码子而失活。这些发现表明，在成熟的抗原选择B细胞中可以发现双受体B淋巴细胞，并提示体细胞突变可通过使非选择的过客L链失活来促进同种型排斥程度的增加。
