CNS-compartmentalized IgG aggregates and glycosylation in multiple sclerosis contribute to oligoclonal bands and neuronal cytotoxicity.

Background: Oligoclonal bands (OCBs) are a hallmark of multiple sclerosis (MS), yet their molecular characteristics and pathogenic relevance remain incompletely understood. Recent evidence suggests that immunoglobulin G (IgG) aggregates and glycosylation may contribute to neuroinflammation and neuronal injury in MS. Methods: We analyzed paired cerebrospinal fluid (CSF) and plasma samples from MS patients and other neurological controls using transmission electron microscopy, protein aggregation assays, proteomics, isoelectric focusing immunoblotting, and Western blots. Neuronal cytotoxicity was assessed using human iPSC-derived neurons and SH-SY5Y cells. IgG glycosylation was evaluated by enzymatic deglycosylation and lectin-based detection. Results: We identified large IgG aggregates (> 100 nm) in MS CSF, which were absent in controls and induced complement-dependent neuronal apoptosis. These aggregates were enriched in OCBs and were disrupted by urea or glycine-HCl, resulting in the loss of OCBs. Proteomic analysis revealed enrichment of IgG subclasses and complement components in MS CSF. In addition, MS CSF contained significantly elevated levels of galactosylated and sialylated IgG compared to paired plasma. Enzymatic removal of glycans reduced both OCB intensity and neuronal cytotoxicity. Conclusions: Our findings demonstrate that CNS-compartmentalized IgG aggregates and glycosylation contribute to the formation of OCBs and neuronal cytotoxicity in MS. These results provide new insights into the molecular basis of OCBs and suggest that targeting IgG glycosylation or aggregation may offer novel therapeutic strategies for MS.