Changes in N-glycans of IgG4 and its relationship with the existence of hypocomplementemia and individual organ involvement in patients with IgG4-related disease

BackgroundAlthough increased serum IgG4 level and tissue infiltration of IgG4-positive cells are key events in IgG4-related disease (IgG4RD), and nearly half of IgG4RD patients show hypocomplementemia, the role of IgG4 in the pathogenesis of IgG4RD remains unclear. Many reports show that altered IgG glycosylation, especially IgG with agalactosylated N-linked glycan (G0 N-glycan), have proinflammatory roles including complement activation, implicated in the pathogenesis of various inflammatory diseases. This study determined the concentration of N-linked glycans (N-glycan) released from serum IgG4 in IgG4RD patients and compared the difference of glycosylation changes to those in healthy controls. We also compared the concentration of each IgG4 glycoform between patients with and without hypocomplementemia and individual organ involvement (kidney, pancreas, lymph node) in IgG4RD.MethodsWe collected sera from 12 IgG4RD patients and 8 healthy controls. IgG4 was isolated from sera via Melon™ Gel IgG Spin Purification Kit followed by Capture Select IgG4 (Hu) Affinity Matrix. IgG4 N-glycans were analyzed by S-BIO GlycanMap® Xpress methodology.ResultsSignificant increases of IgG4 G0 N-glycan and IgG4 fucosylated N-glycan (F1 N-glycan) concentrations were observed in IgG4RD compared with healthy controls. Although we observed decreased levels of IgG4 F0 glycan in IgG4RD with hypocomplementemia, there were no significant differences in the galactosylation and sialyation of IgG4 N-glycans. Furthermore, there were no significant differences in the glycosylation of IgG4 N-glycans between patients with and without individual organ involvement of IgG4RD.ConclusionsAlthough IgG4 has anti-inflammatory properties, IgG4 G0 and F1 glycans were increased in patients with IgG4RD. Our results suggest that decreased galactosylation of IgG4 is not related to complement activation and the differences of individual organ involvement in IgG4RD. IgG4 fucosylation change may be related to complement activation in IgG4RD. Further investigation is needed to clarify the role of IgG4 in IgG4RD.

背景：尽管血清IgG4水平升高以及IgG4阳性细胞组织浸润是IgG4相关疾病（IgG4-related disease, IgG4RD）的核心特征，且近半数IgG4RD患者表现为低补体血症，但IgG4在IgG4RD发病机制中的作用仍未明确。多项研究表明，IgG糖基化异常——尤其是带有无半乳糖基化N连接聚糖（agalactosylated N-linked glycan, G0 N-聚糖）的IgG——具有促炎作用，包括补体激活，这与多种炎症性疾病的发病机制相关。本研究测定了IgG4RD患者血清IgG4释放的N连接聚糖（N-glycan）浓度，并将其糖基化变化与健康对照人群进行比较。此外，本研究还对比了伴与不伴低补体血症的IgG4RD患者，以及存在单个器官受累（肾脏、胰腺、淋巴结）的IgG4RD患者之间，各IgG4糖型的浓度差异。
方法：本研究收集了12例IgG4RD患者与8例健康对照者的血清样本。通过Melon™ Gel IgG Spin Purification Kit，再经Capture Select IgG4 (Hu) Affinity Matrix亲和层析柱，从血清中分离纯化IgG4。采用S-BIO GlycanMap® Xpress技术分析IgG4的N连接聚糖。
结果：与健康对照相比，IgG4RD患者的IgG4 G0 N-聚糖以及IgG4岩藻糖基化N连接聚糖（F1 N-聚糖）浓度显著升高。尽管在伴低补体血症的IgG4RD患者中观察到IgG4 F0糖型水平降低，但IgG4 N连接聚糖的半乳糖基化与唾液酸化水平并无显著差异。此外，伴与不伴单个器官受累的IgG4RD患者之间，其IgG4 N连接聚糖的糖基化水平也无显著差异。
结论：尽管IgG4本身具有抗炎特性，但IgG4RD患者体内的IgG4 G0与F1聚糖水平升高。本研究结果提示，IgG4的半乳糖基化水平降低与补体激活以及IgG4RD的单个器官受累差异均无关联。IgG4的岩藻糖基化变化可能与IgG4RD中的补体激活相关。未来仍需进一步研究以阐明IgG4在IgG4RD中的作用机制。