髓系源性抑制细胞在IgG4相关硬化性胆管炎发病机制中的作用及其调控机制

Immunoglobulin G4-related sclerosing cholangitis (IgG4-SC) is an autoimmune liver disease characterized by IgG4-positive lymphoplasmacytic infiltration of bile ducts and that causes biliary strictures. Th2 cells are implicated in the disease pathogenesis. Myeloid-derived suppressor cells (MDSCs) play vital roles in the hepatic immune microenvironment, but we have not yet seen MDSCs and IgG4-SC related research published. In our present studies, we investigated the dramatic increase of receptor activator of nuclear factor-κB ligand (RANKL) expression in IgG4-SC, which was mainly produced by B cells (especially plasmablast cells) in the liver. Then, we found that MDSCs, especially monocytic MDSCs expressed RANKL receptor RANK. We will utilize a series of in vivo and vitro experiments, such as the expansion of RANKL stimulated MDSCs through RANKL/RANK/NF-κB pathway, in order to answer the following scientific questions: ①What is the correlation between RANKL levels and the number of MDSCs with the severity of IgG4-SC and the clinical outcome? ②How do MDSCs regulate the differentiation and secretion of helper T cells in the intrahepatic microenvironment, thereby affecting the balance of Th1-Th2 and B cells/plasmablast, participating in the progression of the disease? Our study may elucidate the role of myeloid-derived suppressor cells in the pathogenesis of IgG4-related sclerosing cholangitis, and explore the promising immunotherapy strategy.

IgG4相关硬化性胆管炎（IgG4-SC）是以胆管周围大量IgG4阳性浆细胞浸润为特征的自身免疫性肝病，发病机制中以Th2细胞的免疫反应占主导。髓系源性抑制细胞（MDSCs）在肝内微环境中具有重要免疫调控作用，但尚未见其在该疾病中的相关研究。我们前期在IgG4-SC患者中观察到肝组织内B细胞（尤其是浆母细胞）表达活化NF-κB受体配体（RANKL）以及MDSCs表达RANK的有趣现象，拟通过针对RANKL/RANK/NF-κB途径刺激诱导MDSCs扩增等体内外实验回答下列科学问题：①RANKL和MDSCs是否与IgG4-SC的严重程度、临床预后相关？②MDSCs是如何参与调节Th细胞的分化与分泌功能，从而影响肝内Th1-Th2平衡，与B细胞/浆母细胞共同参与疾病的进展？本课题旨在通过研究IgG4-SC 时RANKL调控MDSCs的生物学行为机制，为探索更有效的免疫治疗策略提供理论依据。

IgG4相关性疾病是以血清IgG4水平升高、胆管周围大量IgG4阳性浆细胞浸润为特征，可累及全身几乎所有器官的自身免疫性疾病。当累及肝脏胆管时，命名为IgG4相关硬化性胆管炎，若不及时治疗或疗效不佳，患者可进展至肝硬化、肝衰竭进而危及生命。阐明IgG4-SC发病机制，并在此基础上寻找敏感性和特异性兼具的早期诊断新标志物和特异性治疗靶点，是我们所面临的刻不容缓的科学问题之一。MDSC由于其强大的免疫抑制功能受到我们的关注。探索RANKL-RANK信号通路对MDSC的扩增和活化的调控机制，及其在IgG4相关硬化性胆管炎发病机制中的作用。采用流式细胞术、免疫组化、免疫荧光共聚焦技术分析IgG4-SC患者及对照组的外周血及肝脏MDSC表达和功能特征，并利用体外实验探究诱导IgG4-SC患者MDSC扩增的可能机制。IgG4-SC患者外周血和肝脏MDSC显著扩增，且具有免疫抑制功能。IgG4-SC患者成熟B细胞可分泌高水平的RANKL，作用于MDSC细胞表面的RANK，激活下游NF-kB通路，从而促使MDSC扩增与活化。RANKL可诱导MDSC高表达NO，促使CD4+ T细胞向Th2型分化，促进IgG4-SC纤维化的进展。IgG4-SC患者扩增活化的MDSC可促进肝内免疫向Th2型过度活化，加重IgG4-SC纤维化的发生。RANKL诱导的MDSC信号途径可能作为未来治疗IgG4-SC的免疫治疗靶点。