Schneiderman R D, Lint T F, Knight K L
Department of Microbiology and Immunology, University of Illinois, Chicago 60680.
J Immunol. 1990 Jul 1;145(1):233-7.
Previous experiments have resulted in the identification and cloning of 13 nonallelic genes encoding the constant region of rabbit IgA H chains. The genes, C alpha 1 to C alpha 13, were each cloned into an expression vector containing the VDJ gene of a dansyl (DNS)-binding murine hybridoma and the constructs were then transfected into SP2/0 cells that were producing murine kappa-L chains from the DNS-binding hybridoma. Of the 13 resulting transfectomas, 12 were shown, by ELISA, to secrete DNS-binding chimeric rabbit-mouse IgA molecules. These transfectoma antibodies, representing 12 different isotypes, are of high affinity and provide a unique source of Ag-specific IgA for comparison of the functions of the multiple IgA isotypes. One such function for antibodies is activation of C by either the classical or alternative pathway. We have used the DNS-binding IgA transfectoma antibodies in C assays based on binding of rabbit C3 to IgA-Ag complexes in an ELISA. The results demonstrated that all 12 IgA isotypes are capable of activating C by the alternative pathway but that none can activate C by the classical pathway. Control experiments demonstrated that activation was hapten dependent and was not caused by endotoxin contamination. These data demonstrate that Ag-specific IgA molecules, unmodified by heat or chemical aggregation, activate C by the alternative pathway but not by the classical pathway.
先前的实验已鉴定并克隆出13个非等位基因，这些基因编码兔IgA重链的恒定区。基因Cα1至Cα13分别被克隆到一个表达载体中，该载体包含一个丹磺酰（DNS）结合型小鼠杂交瘤的VDJ基因，然后将构建体转染到从DNS结合型杂交瘤产生小鼠κ轻链的SP2/0细胞中。在产生的13个转染瘤中，通过ELISA显示有12个分泌DNS结合型嵌合兔-小鼠IgA分子。这些代表12种不同同种型的转染瘤抗体具有高亲和力，为比较多种IgA同种型的功能提供了独特的抗原特异性IgA来源。抗体的一个这样的功能是通过经典途径或替代途径激活补体（C）。我们已在基于ELISA中兔C3与IgA-抗原复合物结合的补体检测中使用了DNS结合型IgA转染瘤抗体。结果表明，所有12种IgA同种型都能够通过替代途径激活补体，但没有一种能通过经典途径激活补体。对照实验表明，激活是半抗原依赖性的，不是由内毒素污染引起的。这些数据表明，未经加热或化学聚集修饰的抗原特异性IgA分子通过替代途径激活补体，但不通过经典途径激活补体。
