IgG4-related disease (IgG4-RD) is characterized by intense infiltration of IgG4-positive plasma cells in affected organs. However, the mechanisms acting in the immune responses in IgG4-RD are not fully understood. The aim of this study was to dissect the mechanism underlying the immunoglobulin class switch in IgG4-RD by addressing the crosstalk between IL-35-producing and Th9 cells. The expression level of IL-35 was examined in plasma samples from patients with hepatobiliary and/or pancreatic manifestations of IgG4-RD. Our data demonstrate that IgG4-RD patients exhibit significantly high-level productions of IL-35 as compared to disease and healthy controls. We detected the two subunits of IL-35, EBI3 and IL-12p35, in the two major affected organs, liver and pancreatic tissue, from IgG4-RD. The EBI3- and IL-12p35-positive cells were significantly higher in affected organs in IgG4-RD as compared to disease controls. The colocalization of EBI3 with CD19 and CD38, markers for B cells, suggest the presence of IL-35-producing B cells in affected organs in IgG4-RD. The effects of IL-35 in Th9 differentiation and IL-9 in production of immunoglobulin were then assessed. Surprisingly, IL-35 treatment promoted naïve CD4 T cell differentiating towards Th9 cells through IRF4 signaling. As a consequence, IL-9 secreted by Th9 cells promoted the differentiation of plasma cells and production of IgG1 and IgG4, predominantly IgG4. In conclusion, our data demonstrate that IL-35 actively participates in the process of inflammation and plays an important role in Th9 differentiation resulting in an immunoglobulin class switch towards IgG4.

IgG4 相关疾病 (IgG4-RD) 的特征是受累器官中 IgG4 阳性浆细胞的强烈浸润。然而，在 IgG4-RD 中作用于免疫反应的机制尚不完全清楚。本研究的目的是通过解决产生 IL-35 和 Th9 细胞之间的串扰来剖析 IgG4-RD 中免疫球蛋白类别转换的潜在机制。在来自具有 IgG4-RD 肝胆和/或胰腺表现的患者的血浆样品中检查了 IL-35 的表达水平。我们的数据表明，与疾病和健康对照相比，IgG4-RD 患者表现出显着高水平的 IL-35 产生。我们从 IgG4-RD 中检测到 IL-35 的两个亚基，EBI3 和 IL-12p35，在两个主要受影响的器官，肝脏和胰腺组织中。与疾病对照相比，IgG4-RD 中受影响器官中的 EBI3 和 IL-12p35 阳性细胞显着更高。EBI3 与 CD19 和 CD38（B 细胞标志物）的共定位表明 IgG4-RD 中受影响器官中存在产生 IL-35 的 B 细胞。然后评估了 IL-35 在 Th9 分化中的作用和 IL-9 在免疫球蛋白产生中的作用。令人惊讶的是，IL-35 治疗通过 IRF4 信号促进了幼稚 CD4 T 细胞向 Th9 细胞分化。因此，Th9 细胞分泌的 IL-9 促进了浆细胞的分化和 IgG1 和 IgG4（主要是 IgG4）的产生。总之，我们的数据表明 IL-35 积极参与炎症过程并在 Th9 分化中发挥重要作用，导致免疫球蛋白类别向 IgG4 转变。