Department of Immunopathology, Sanquin Research and Landsteiner Laboratory, Amsterdam UMC, University of Amsterdam, Amsterdam, the Netherlands.
Department of Experimental Immunohematology, Sanquin Research, Amsterdam, the Netherlands.
J Immunol. 2023 Dec 1;211(11):1725-1735. doi: 10.4049/jimmunol.2300307.
Complement activation via the classical pathway is initiated when oligomeric Igs on target surfaces are recognized by C1 of the complement cascade. The strength of this interaction and activation of the complement system are influenced by structural variation of the Ab, including Ab isotype, subclass, and glycosylation profile. Polymorphic variants of IgG have also been described to influence Fc-dependent effector functions. Therefore, we assessed complement binding, deposition, and complement-dependent cytotoxicity (CDC) of 27 known IgG allotypes with anti-trinitrophenyl specificity. Differences between allotypes within subclasses were minor for IgG1, IgG3, and IgG4 allotypes, and more substantial for IgG2. Allelic variant IGHG2*06, containing a unique serine at position 378 in the CH3 domain, showed less efficient complement activation and CDC compared with other IgG2 polymorphisms. We also observed variable cell lysis between IgG1 and IgG3, with IgG3 being superior in lysis of human RBCs and Ramos cells, and IgG1 being superior in lysis of Raji and Wien133 cells, demonstrating that a long-standing conundrum in the literature depends on cellular context. Furthermore, we compared IgG1 and IgG3 under different circumstances, showing that Ag density and Ab hinge length, but not complement regulators, define the context dependency of Ab-mediated CDC activity. Our results point toward a variation in the capacity of IgG subclasses to activate complement due to single amino acid changes and hinge length differences of allotypes to activate complement, which might give new insights on susceptibility to infectious, alloimmune, or autoimmune diseases and aid the design of Ab-based therapeutics.
补体经典途径的激活是通过识别靶表面的寡聚 Ig 来启动的，这些寡聚 Ig 被补体级联中的 C1 识别。这种相互作用的强度和补体系统的激活受 Ab 的结构变异的影响，包括 Ab 的同种型、亚类和糖基化谱。已经描述了 IgG 的多态变体影响 Fc 依赖性效应功能。因此，我们评估了 27 种具有抗三硝基苯特异性的已知 IgG 同种型的补体结合、沉积和补体依赖性细胞毒性 (CDC)。在 IgG1、IgG3 和 IgG4 同种型中，同种型内的差异较小，而在 IgG2 中则更为显著。等位基因变体 IGHG2*06 在 CH3 结构域的位置 378 处含有一个独特的丝氨酸，与其他 IgG2 多态性相比，其补体激活和 CDC 效率较低。我们还观察到 IgG1 和 IgG3 之间的细胞裂解存在差异，IgG3 在裂解人 RBC 和 Ramos 细胞方面更优越，而 IgG1 在裂解 Raji 和 Wien133 细胞方面更优越，这表明文献中长期存在的难题取决于细胞环境。此外，我们在不同情况下比较了 IgG1 和 IgG3，结果表明 Ag 密度和 Ab 铰链长度，但不是补体调节剂，定义了 Ab 介导的 CDC 活性的上下文依赖性。我们的研究结果表明，由于同种型的单个氨基酸变化和铰链长度差异，IgG 亚类激活补体的能力存在差异，这可能为易感性提供新的见解传染病、同种免疫或自身免疫性疾病，并有助于基于 Ab 的治疗药物的设计。
