Effect of interleukin-6 on IgG antibody glycosylation

IL-6不仅对T细胞依赖性(TD)免疫球蛋白抗体(Ab)的保护性应答起着至关重要的作用，而且对免疫球蛋白介导的自身免疫病理的发展也是至关重要的。IL-6在免疫应答的不同阶段发挥作用，包括树突状细胞和CD4+T细胞之间的相互作用，以及在抗体亲和力成熟和产生免疫球蛋白亚类记忆B细胞(PC)的生发中心(GC)反应中。然而，越来越多的证据表明，不仅是免疫球蛋白亚类，而且连接在抗体Fc结构域上的N-连接的糖链结构也调节了免疫球蛋白的效应功能。非(A)半乳糖化的免疫球蛋白抗体与炎症反应有关，例如在类风湿关节炎(RA)患者中，而半乳糖化的和末端唾液酸化的免疫球蛋白抗体具有降低炎症潜能和抑制免疫反应的作用。我们最近在小鼠中表明，炎症环境通过编程调节免疫球蛋白+GC B细胞和PC中相应糖基转移酶的表达水平的CD4+T滤泡辅助细胞反应来决定GC反应中抗原特异性的免疫球蛋白糖基化的类型。然而，目前尚不清楚什么细胞因子环境对于设定免疫球蛋白糖基化模式的GC环境是必要的。初步数据表明，IL-6缺陷小鼠不能在强烈的炎性免疫反应中诱导无半乳糖化的Ig G抗体，因此我们假设IL-6在GC反应之前和/或期间的细胞相互作用中发挥重要作用，以设定炎性Ig G的糖基化模式。然而，IL-6如何影响Ig G糖基化尚不清楚，这也是因为IL-6可以通过三条信号途径起作用：i)经典信号描述了IL-6与膜结合的IL-6R然后结合到同一细胞上的膜结合的信号亚单位gp130。ii)反式信号描述了IL-6与可溶性IL-6R的结合，允许激活只表达gp130的细胞。3)最近描述的反式递呈描述了由树突状细胞产生的IL-6与同一细胞上的IL-6R结合，从而激活另一细胞上的gp130(例如，CD_4+T细胞)。在这个项目中，我们将探索IL-6是通过什么细胞和信号途径(S)调节Ig G糖基化的。我们将利用一组条件基因敲除和转基因小鼠，研究IL-6对TD免疫后产生的免疫球蛋白G+GC B细胞和PC中T滤泡辅助细胞分化和糖基转移酶表达的影响。最后，我们将研究IL-6干扰通过阻断IL-6信号通路对自身免疫小鼠模型和RA患者的免疫球蛋白糖基化的治疗作用。我们期望这项研究将提供更好的理解在GC依赖反应中免疫球蛋白糖基化差异编程背后的机制，并确定调节IL-6信号以重编致病免疫球蛋白糖基化以治疗自身免疫性疾病的治疗潜力。

IL-6 is crucial for mounting protective T cell-dependent (TD) IgG antibody (Ab) responses but also for development of IgG-mediated autoimmune pathologies. IL-6 acts at various stages of an immune response, including the interaction between dendritic cells and CD4+ T cells and later in the germinal center (GC) reaction during Ab affinity maturation and generation of IgG subclass memory B cells and plasma cells (PCs).However, accumulating evidence suggest that not only the IgG subclass but also the structure of an N-linked glycan attached to the Fc domain of IgG Abs modulates IgG effector functions. Non-(a)galactosylated IgG Abs are associated with inflammatory actions e.g. in rheumatoid arthritis (RA) patients, whereas galactosylated plus terminal sialylated IgG Abs have reduced inflammatory potential and may suppress immune reactions.We recently showed in mice that the inflammatory environment determines the type of antigen-specific IgG glycosylation during the GC reaction by programming the CD4+ T follicular helper cell response that regulates the expression level of the corresponding glycosyltransferases in IgG+ GC B cells and PCs.However, it remains unclear what cytokine milieu is necessary for setting the GC environment for setting the IgG glycosylation pattern. Preliminary data suggest that IL-6 deficient mice fail to induce agalactosylated IgG Abs in response to strong inflammatory immunizations.We therefore hypothesise that IL-6 plays an essential role during cellular interactions prior to, and/or during, the GC reaction to set the inflammatory IgG glycosylation pattern. However, how IL-6 influences IgG glycosylation is unclear, also because IL-6 can act via three signaling routes:I) Classical-signaling describes binding of IL-6 to membrane-bound IL-6R and then to the membrane-bound signaling subunit gp130 on the same cell.II) Trans-signaling describes binding of IL-6 to soluble IL-6R, which allows activation of cells that only express gp130.III) The recently described trans-presentation describes binding of IL-6 produced e.g. by dendritic cells to IL-6R on the same cell for activating gp130 on another cell (e.g. CD4+ T cell).In this project, we will explore through which cells and signaling route(s) IL-6 modulates IgG glycosylation. We will study the effect of IL-6 on T follicular helper cell differentiation and glycosyltransferases expression in IgG+ GC B cells and PCs generated upon TD immunization by using an array of conditional knockout and transgenic mice. Finally, we will study a therapeutic effect of IL-6 interference on IgG glycosylation by blocking IL-6 signaling in autoimmune mouse models and RA patients.Together, we expect that this study would provide better understanding of the mechanisms behind differential programming of IgG glycosylation during GC-dependent responses and define a therapeutic potential of modulating IL-6 signaling to reprogram pathogenic IgG glycosylation for treating autoimmune disorders.