Therapeutic potential of sialylated Pemphigoid Disease autoantibodies

近年来，已积累的证据表明，IgG抗体（Ab）可以具有促或促效应子功能，并且这些潜力关键取决于其双触角Fc N-糖苷链的末端糖部分，该双触角Fc N-糖苷链与两条重链的Asp 297偶联。在本文中，抗炎IgG Ab的Fc N-糖苷链含有末端半乳糖基和另外的唾液酸部分，并且分别被分类为半乳糖基化和唾液酸化IgG Ab。没有这些末端糖残基的IgG Ab被称为无半乳糖基化的，并执行促炎作用，如类风湿性关节炎中的IgG自身抗体（AAb）。由这些不同的末端糖部分制定的分子机制在很大程度上仍然难以捉摸。在本文中，差异糖基化的IgG Ab不仅靶向经典Fc γ受体，而且靶向C型凝集素受体（Fcy）家族的成员。例如，已经表明激活Fc γ受体和甘露糖受体介导无半乳糖基化IgG Ab、Dectin-1和IgG抑制性受体Fc γ RIIB的作用，半乳糖基化IgG Ab和唾液酸化IgG Ab的那些可主要独立于Fc γ RIIB通过SIGN-R1（DC-SIGN）和DCIR起作用。由于无半乳糖基化和半乳糖基化/唾液酸化IgG Ab的相反作用，假设其在抗原特异性IgG Ab池中的相对频率可决定是否发生促炎性免疫应答，并可作为表征抗原特异性免疫应答的最有价值的诊断标志物。根据这一观点，我们发现初步证据表明，在活动性BP患者中，无半乳糖基化IgG Ab在抗XVII型胶原IgG AAb中占主导地位。同时，使用我们的被动AAb转移EBA小鼠模型，我们已经发现无半乳糖基化和半乳糖基化IgG Ab在疾病的效应期分别具有促炎和抗炎作用的证据。因此，从其他致病性抗VII型胶原IgG AAb中去除糖苷链完全消除了皮肤炎症。相反，应用含有半乳糖基化IgG Ab的免疫复合物通过包括Dectin-1与中性粒细胞上的Fc？RIIB交联的机制抑制皮肤炎症。相比之下，唾液酸化IgG Ab在PD皮肤炎症效应期的额外作用尚未得到解决。项目4的主要目的是分别研究无半乳糖基化、半乳糖基化和唾液酸化IgG AAb在PD及其受体（尤其是中性粒细胞）效应期的激活或抑制潜力。这些研究对于了解PD皮肤炎症的出现至关重要，也将阐明唾液酸化IgG AAb是否可用于以自身抗原特异性方式治疗PD患者。我们的研究旨在为PD患者开发一种新的治疗策略，其中患者自身衍生，体外唾液酸化和重新应用IgG AAb。

In recent years, evidence has accumulated that IgG antibodies (Abs) can have pro- or antiinflammatory effector functions and that these potentials critically depend on the terminal sugar moieties of their biantennary Fc N-glycoside chains coupled to Asp297 of both heavy chains. Herein, the Fc N-glycoside chains of anti-inflammatory IgG Abs contain terminal galactosyl and additional sialyl moieties and are categorized into galactosylated and sialylated IgG Abs, respectively. IgG Abs without these terminal sugar residues are referred to as agalactosylated and execute proinflammatory actions such as IgG autoantibodies (AAbs) in rheumatoid arthritis. The molecular mechanisms enacted by these differential terminal sugar moieties are still largely elusive. Herein, differentially glycosylated IgG Abs not only target the classical Fcy receptors, but also members of the C-type lectin receptor (CLR) family. Activating Fcy receptors and the mannose receptor, for instance, have been suggested to mediate effects of agalactosylated IgG Abs, Dectin-1 and the IgG inhibitory receptor FcyRIIB those of galactosylated IgG Abs, and sialylated IgG Abs can act primarily independent of FcyRIIB through SIGN-R1 (DC-SIGN) and DCIR. Due to the opposite effects of agalactosylated and galactosylated/sialylated IgG Abs, their relative frequencies in the pool of antigen-specific IgG Abs is hypothesized to decide whether a proinflammatory immune response is mounted and may serve as most valuable diagnostic marker to characterize an antigen-specific immune response. In line with this notion, we have found preliminary evidence that agalactosylated IgG Abs are dominant among anti-type XVII collagen IgG AAbs in patients with active BP. In parallel, using our passive AAb transfer EBA mouse model, we have found evidence for both proinflammatory and antiinflammatory effects of agalactosylated and galactosylated IgG Abs, respectively, in the effector phase of the disease. Thus, removal of the glycoside chains from otherwise pathogenic anti-type VII collagen IgG AAbs completely abrogated skin inflammation. Conversely, application of immune complexes containing galactosylated IgG Abs suppressed skin inflammation by a mechanism including crosslinking of Dectin-1 with Fc¿RIIB on neutrophils. In contrast, the additional actions of sialylated IgG Abs in the effector phase of PD skin inflammation have not been addressed. The main aim of Project 4 is to investigate the activating or inhibitory potential of agalactosylated, galactosylated and sialylated IgG AAbs, respectively, in the effector phase of PD and their receptors, especially on neutrophils. These studies will be essential to understand the emergence of PD skin inflammation and will also clarify whether sialylated IgG AAbs can be used to treat PD patients in an autoantigen-specific manner. Our research aims to develop a new therapeutic strategy for PD patients with patient self-derived, ex vivo sialylated and re-applied IgG AAbs.