Multiplex Detection of Immunoglobulins Uncovers Intrathecal IgA Elevation in Multiple Sclerosis

Abstract Background: Intrathecal IgG synthesis is a well-established hallmark of multiple sclerosis (MS), yet the roles of other immunoglobulin isotypes remain underinvestigated. This study aimed to comprehensively profile immunoglobulin distributions in cerebrospinal fluid (CSF) and plasma from MS patients and neurological controls. Methods: Paired CSF and plasma samples from 20 MS patients and 20 neurological controls were analyzed using a multiplex Luminex-based immunoassay targeting IgG1–4, IgA, and IgM. The findings were validated using commercial ELISA kits and Western blot analysis. Results: Multiplex analysis revealed a striking intrathecal enrichment of IgA and IgM in MS CSF, with significantly higher levels compared to both matched plasma and control CSF. IgG1 was modestly elevated in MS CSF by ELISA but not by multiplex assay. Western blotting confirmed a robust elevation of IgA in MS CSF, supporting localized synthesis. Conclusion: These findings uncover previously underappreciated dominance of IgA and IgM in the MS CNS compartment, challenging the traditional IgG-centric view of MS immunopathology. The results suggest alternative antibody-mediated mechanisms in MS and highlight the importance of assay selection in biomarker discovery. IgA may represent a novel target for future diagnostic and therapeutic strategies.