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Elevated N-linked glycosylation of IgG variable regions in myasthenia gravis disease subtypes

ABSTRACT: Elevated N-linked glycosylation of immunoglobulin G variable regions (IgG-VN-Glyc) is an emerging molecular phenotype associated with autoimmune disorders. To test the broader specificity of elevated IgG-VN-Glyc, we studied patients with distinct subtypes of myasthenia gravis (MG), a B cell-mediated autoimmune disease. Our experimental design included adaptive immune receptor repertoire sequencing to quantify and characterize N-glycosylation sites in the global B cell receptor repertoire, proteomics to examine glycosylation patterns of the circulating IgG, and production of human-derived recombinant autoantibodies, which were studied with mass spectrometry and antigen binding assays to confirm occupation of glycosylation sites and determine whether they alter binding. We found that the frequency of IgG-VN-Glyc motifs was increased in the B cell repertoire of MG patients when compared to healthy donors. Motifs were introduced by both biased V gene segment usage and somatic hypermutation. IgG-VN-Glyc could be observed in the circulating IgG in a subset of MG patients. Autoantigen binding, by patient-derived MG autoantigen-specific monoclonal antibodies with experimentally confirmed presence of IgG-VN-Glyc, was not altered by the glycosylation. Our findings extend prior work on patterns of variable region N-linked glycosylation in autoimmunity to MG subtypes. Although occupied IgG-VN-Glyc motifs are found on MG autoantigen-specific monoclonal antibodies, they are not required for binding to the autoantigen in this disease.

ORGANISM(S): Homo sapiens

PROVIDER: GSE182038 | GEO | 2021/08/13

REPOSITORIES: GEO

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Project description:The discovery of hepatitis C virus (HCV) in 1989 revealed the virus as the etiology of 40%-90% of the “essential” mixed cryoglobulinemia, where immune complex forms deposit called cryoprecipitate at temperatures below 37 °C. Cryoprecipitate constitutes monoclonal IgM and polyclonal IgG, some of which has reactivity against HCV core and NS3 epitopes. Resultant immune complex is considered entrapped on microvascular endothelium via C1q receptor, leading to complement activation and organ injury presenting predominantly as dermopathy, peripheral neuropathy and nephropathy. However, currently little is known on whether auto-reactive, cold-precipitating IgG components enriched in cryoprecipitate may play some role on the deposition of immune complex and subsequent complement-mediated injury of specific organs. Recently, with the advent of high-throughput immune repertoire sequencing and mass spectrometry, technical feasibility is growing to delineate antibodies of interest and their sequences directly from serum. To date, vast majority of studies actually utilized the antigen column for affinity purification of antibodies of interest, although this strategy is not applicable to disease entity with unknown antigen involvement. In such cases, disease-specific and organ-specific immune deposits may be a good alternative source of etiological antibodies. Herein, targeting HCV cryoglobulinemic vasculitis as a model, we conducted a proof-of-concept study aiming at characterizing the IgG components most prone to cryoprecipitation. To this end, we longitudinally studied one patient with cryoglobulinemic vasculitis with chronic HCV infection. After obtaining informed consent, cryoprecipitate and supernatant were separated from peripheral blood sample. Fab fragments from Protein G-purified IgG were recovered after papain digestion for isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomics. Simultaneously, total RNA was isolated from peripheral blood, and immunoglobulin heavy chain variable region (IGHV) was PCR-amplified with unique molecular identifier (UMI) strategy to construct a personal IGHV sequence library of immunoglobulin variable region. Sequencing output from MiSeq was bioinformatically converted into mass spectrometry database. Search was performed using MaxQuant software.

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Elevated N-linked glycosylation of IgG variable regions in myasthenia gravis disease subtypes

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