IgG Antibodies to Cyclic Citrullinated Peptides Exhibit Profiles Specific in Terms of IgG Subclasses, Fc-Glycans and a Fab-Peptide Sequence

• DOI: 10.1371/journal.pone.0113924
• Publication Date: 2014-11-26T22:54:36Z
• Authors: Susanna L. Lundström; Cátia Fernandes-C...; A. Jimmy Ytterberg; Elena Ossipova; Aase H. Hensvold; Per-Johan Jakobsson; Vivianne Malmström; Anca I. Catrina; Lars Klareskog; Karin Lundberg; Roman A. Zubarev
• Keywords: Fragment crystallizable region; Subclass; Immunoglobulin Fc Fragments; Glycoproteomics

The Fc-glycan profile of IgG1 anti-citrullinated peptide antibodies (ACPA) in rheumatoid arthritis (RA) patients has recently been reported to be different from non-ACPA IgG1, a phenomenon which likely plays role RA pathogenesis. Herein we investigate the Fc-glycosylation pattern all ACPA-IgG isotypes and simultaneously detail IgG protein-chain sequence repertoire. serum or plasma (S/P, n = 14) synovial fluid (SF, 4) 18 ACPA-positive RA-patients was enriched using Protein G columns followed by ACPA-purification on cyclic citrullinated peptide-2 (CCP2)-coupled columns. Paired ACPA (anti-CCP2 eluted IgG) flow through (FT) fractions were analyzed LC-MS/MS-proteomics. peptides, corresponding Fc-glycopeptides quantified interrogated uni- multivariate statistics. Fc-glycans IgG4 EEQFNSTYR validated protein A column purification. Relative FT-IgG4, ACPA-IgG4 Fc-glycan-profile contained lower amounts (p 0.002) agalacto asialylated core-fucosylated biantennary form (FA2) higher content 0.001) sialylated glycans. Novel differences ACPA-IgG1 compared FT-IgG1 observed distribution bisected forms (n 5, p 0.0001, decrease) mono-antennnary 3, 0.02, increase). Our study also confirmed abundance FA2 afucosylated 4, relative as well IgG2 0.0000001) elevated 0.004) FT. One λ-variable significantly increased 0.0001). In conclusion, both are distinct. Given that have Fc-receptor complement binding affinities, this affects effector- immune-regulatory functions an isotype-specific manner. These findings further highlight importance antibody characterization relation functional vivo vitro studies.