Decades of studies on antibody structure led to the tenet that the V region binds antigens while the C region interacts with immune effectors. In some antibodies, however, the C region affects affinity and/or specificity for the antigen. One such case is that of the 3E5 antibodies, a family of monoclonal murine IgGs in which the mIgG3 isotype has different fine specificity to the Cryptococcus neoformans capsule polysaccharide than the other mIgG isotypes. Our group serendipitously found another pair of mIgG1/mIgG3 antibodies based on the 2H1 hybridoma to the C. neoformans capsule that recapitulated the differences observed with 3E5. In this work, we report the molecular basis of the constant domain effects on antigen binding using recombinant antibodies. As with 3E5, immunofluorescence experiments show a punctate pattern for 2H1-mIgG3 and an annular pattern for 2H1-mIgG1. Also as observed with 3E5, 2H1-mIgG3 bound on ELISA to both acetylated and non-acetylated capsular polysaccharide, whereas 2H1-mIgG1 only bound well to the acetylated form, consistent with differences in fine specificity. In engineering hybrid mIgG1/mIgG3 antibodies, we found that switching the 2H1-mIgG3 hinge for its mIgG1 counterpart changed the immunofluorescence pattern to annular, but a 2H1-mIgG1 antibody with a mIgG3 hinge still had an annular pattern. The hinge is thus necessary but not sufficient for these changes in binding to the antigen. This important role for the constant region in binding of antibodies to the antigen could affect the design of therapeutic antibodies and our understanding of their function in immunity.

中文翻译：

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铰链影响小鼠IgG与新型隐球菌胶囊的结合。

抗体结构的数十年研究得出这样的信条：V区结合抗原，而C区与免疫效应物相互作用。然而，在某些抗体中，C区影响对抗原的亲和力和/或特异性。一种这样的情况是3E5抗体，这是一种单克隆鼠科IgG家族，其中mIgG3同种型对新型隐球菌胶囊多糖的精细特异性与其他mIgG同种型不同。我们组偶然发现基于所述2H1杂交瘤对另一对mIgG1的改变/ mIgG3抗体的新生隐球菌胶囊概括了3E5观察到的差异。在这项工作中，我们报告了使用重组抗体对抗原结合的恒定域作用的分子基础。与3E5一样，免疫荧光实验显示2H1-mIgG3为点状，而2H1-mIgG1为环形。同样用3E5观察到，2H1-mIgG1在ELISA上与乙酰化和非乙酰化荚膜多糖都结合，而2H1-mIgG1仅与乙酰化形式结合得很好，这与精细特异性的差异一致。在工程杂合mIgG1 / mIgG3抗体中，我们发现将2H1-mIgG3铰链切换为其mIgG1对应物可将免疫荧光模式更改为环形，但具有mIgG3铰链的2H1-mIgG1抗体仍具有环形模式。因此，对于这些与抗原结合的变化，铰链是必需的，但不足以实现。恒定区在抗体与抗原结合中的重要作用可能会影响治疗性抗体的设计以及我们对其免疫功能的理解。