Neil Jean, Fenaille François, Bruneel Arnaud, Stojkovic Tanya, Cholet Sophie, Delmont Emilien, Ober Pauline, Raynor Alexandre, Amiot Quentin, Dorgham Karim, Viala Karine, Ghillani-Dalbin Pascale, Gorochov Guy, Sterlin Delphine
Département d'Immunologie, Assistance Publique Hôpitaux de Paris (AP-HP), Hôpital La Pitié-Salpêtrière, Sorbonne Université, France.
Inserm, CNRS, Centre d'Immunologie et des Maladies Infectieuses (CIMI-Paris), Sorbonne Université, France.
Neurol Neuroimmunol Neuroinflamm. 2025 Sep;12(5):e200440. doi: 10.1212/NXI.0000000000200440. Epub 2025 Jul 31.
Anti-myelin-associated glycoprotein (anti-MAG) neuropathy is a chronic demyelinating neuropathy with deposits of IgM and sural nerve fiber demyelination. While growing evidence supports the critical role of IgG glycosylation in autoimmune diseases, IgM glycosylation profiles markedly differ from those of IgG but are largely neglected. The aim of this study was to characterize IgM N-glycosylation in patients with anti-MAG neuropathy and its involvement in anti-MAG pathogenicity.
IgM antibodies were isolated from patients with anti-MAG neuropathy (n = 17), asymptomatic patients with monoclonal gammopathy of undetermined significance (n = 8), and healthy donors ([HDs], n = 6). N-glycan analysis was performed using mass spectrometry. Binding to myelin-associated glycoprotein (MAG), complement (C1q), and IgM Fc receptors (Fcα/μR and DC-SIGN) was compared using ELISA between anti-MAG and MGUS IgM, before and after N-deglycosylation/desialylation. Finally, we assessed how IgM N-glycosylation influences cytokine production by monocyte-derived macrophages by measuring cytokine levels in culture supernatants.
Anti-MAG IgM exhibited a unique glycosylation pattern, dominated by fucosylated, monosialylated N-glycan with a bisecting N-acetyl glucosamine (N-glycan 12), representing 48.5% of the total N-glycan pool, compared with 27.3% in MGUS IgM and 35.6% in HD IgM. We showed that deglycosylation and desialylation significantly reduced anti-MAG activity and C1q binding (average % of decrease 58.3 ± 18.8, < 0.01, and 40.0 ± 19.9%, < 0.05, respectively). Furthermore, anti-MAG IgM binding to C1q was significantly higher than that of MGUS IgM and HD IgM ( < 0.0001 and < 0.001, respectively). Compared with MGUS IgM, anti-MAG IgM also significantly increased the production of proinflammatory cytokines IL-1, IL-6, IL-8, TNF-α, and IFN-Υ by macrophages, in a glycan-dependent manner ( < 0.01 to < 0.001), with IL-8 being particularly elevated. Finally, we found that anti-MAG IgM bound more strongly Fcα/μ receptor and DC-SIGN compared with MGUS IgM ( < 0.05 and = 0.06).
This study uncovered a unique N-glycosylation pattern of anti-MAG IgM, crucial for its interaction with MAG and binding to C1q. Moreover, anti-MAG IgM increased the macrophage cytokine production, driven by their glycosylation. The increased IL-8 expression and anti-MAG IgM binding to C1q might open 2 potential therapeutic avenues: inhibiting IL-8 activity or targeting the complement pathway. In addition, the glycosylation and C1q binding of anti-MAG IgM could serve as biomarkers for monitoring this neuropathy.
抗髓鞘相关糖蛋白（anti-MAG）神经病是一种慢性脱髓鞘性神经病，伴有IgM沉积和腓肠神经纤维脱髓鞘。虽然越来越多的证据支持IgG糖基化在自身免疫性疾病中的关键作用，但IgM糖基化谱与IgG明显不同，却在很大程度上被忽视。本研究的目的是表征anti-MAG神经病患者的IgM N-糖基化及其在anti-MAG致病性中的作用。
从anti-MAG神经病患者（n = 17）、意义未明的单克隆丙种球蛋白病无症状患者（n = 8）和健康供者（HDs，n = 6）中分离IgM抗体。使用质谱法进行N-聚糖分析。在N-去糖基化/去唾液酸化前后，通过ELISA比较anti-MAG和MGUS IgM与髓鞘相关糖蛋白（MAG）、补体（C1q）和IgM Fc受体（Fcα/μR和DC-SIGN）的结合情况。最后，我们通过测量培养上清液中的细胞因子水平，评估IgM N-糖基化如何影响单核细胞衍生巨噬细胞产生细胞因子。
anti-MAG IgM表现出独特的糖基化模式，以岩藻糖基化、单唾液酸化的N-聚糖为主，带有一个平分型N-乙酰葡糖胺（N-聚糖12），占总N-聚糖池的48.5%，而MGUS IgM中为27.3%，HD IgM中为35.6%。我们发现去糖基化和去唾液酸化显著降低了anti-MAG活性和C1q结合（平均降低百分比分别为58.3±18.8，P<0.01，和40.0±19.9%，P<0.05）。此外，anti-MAG IgM与C1q的结合显著高于MGUS IgM和HD IgM（分别为P<0.0001和P<0.001）。与MGUS IgM相比，anti-MAG IgM还以糖基依赖的方式显著增加了巨噬细胞促炎细胞因子IL-1、IL-6、IL-8、TNF-α和IFN-Υ的产生（P<0.01至P<0.001），其中IL-8升高尤为明显。最后，我们发现与MGUS IgM相比，anti-MAG IgM与Fcα/μ受体和DC-SIGN的结合更强（P<0.05和P = 0.06）。
本研究揭示了anti-MAG IgM独特的N-糖基化模式，这对其与MAG的相互作用和与C1q的结合至关重要。此外，anti-MAG IgM通过其糖基化增加了巨噬细胞细胞因子的产生。IL-8表达增加和anti-MAG IgM与C1q结合可能开辟两条潜在的治疗途径：抑制IL-8活性或靶向补体途径。此外，anti-MAG IgM的糖基化和与C1q的结合可作为监测这种神经病的生物标志物。
