title: Glycan profiling of anti-citrullinated protein antibodies isolated from human serum and synovial fluid.
abstract: OBJECTIVE
  Anti-citrullinated protein antibodies (ACPA) exhibit unique specificity for rheumatoid arthritis. However, it is incompletely understood whether and how ACPA contribute to disease pathogenesis. The Fc part of human IgG carries 2 N-linked glycan moieties that are crucial for the structural stability of the antibody and that modulate both its binding affinity to Fcgamma receptors and its ability to activate complement. We undertook this study to analyze Fc glycosylation of IgG1 ACPA in serum and synovial fluid (SF) in order to further characterize the immune response to citrullinated antigens.
  
  
  METHODS
  ACPA were isolated by affinity purification using cyclic citrullinated peptides as antigen. IgG1 Fc glycosylation was analyzed by mass spectrometry. ACPA IgG1 glycan profiles were compared with glycan profiles of total serum IgG1 obtained from 85 well-characterized patients. Glycan profiles of paired SF and serum samples were available from 11 additional patients.
  
  
  RESULTS
  Compared with the pool of serum IgG1, ACPA IgG1 lacked terminal sialic acid residues. In SF, ACPA were highly agalactosylated and lacked sialic acid residues, a feature that was not detected for total SF IgG1. Moreover, differential ACPA glycan profiles were detected in rheumatoid factor (RF)-positive and RF-negative patients.
  
  
  CONCLUSIONS
  ACPA IgG1 exhibit a specific Fc-linked glycan profile that is distinct from that of total serum IgG1. Moreover, Fc glycosylation of ACPA differs markedly between SF and serum. Since Fc glycosylation directly affects the recruitment of Fc-mediated effector mechanisms, these data could further our understanding of the contribution of ACPA to disease pathogenesis.
authors.affiliation: Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Hans U
authors.initials: HU
authors.lastname: Scherer
authors.forename: Diane
authors.initials: D
authors.lastname: van der Woude
authors.forename: Andreea
authors.initials: A
authors.lastname: Ioan-Facsinay
authors.forename: Hanane
authors.initials: H
authors.lastname: el Bannoudi
authors.forename: Leendert A
authors.initials: LA
authors.lastname: Trouw
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.forename: Thomas
authors.initials: T
authors.lastname: Häupl
authors.forename: Gerd-R
authors.initials: GR
authors.lastname: Burmester
authors.forename: André M
authors.initials: AM
authors.lastname: Deelder
authors.forename: Tom W J
authors.initials: TW
authors.lastname: Huizinga
authors.forename: Manfred
authors.initials: M
authors.lastname: Wuhrer
authors.forename: René E M
authors.initials: RE
authors.lastname: Toes
mesh_terms: D000328:Adult; D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism; D001323:Autoantibodies / Q000032:analysis / Q000276:immunology* / Q000378:metabolism; D006031:Glycosylation; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis / Q000276:immunology* / Q000378:metabolism; D013058:Mass Spectrometry; D010456:Peptides, Cyclic / Q000032:analysis / Q000276:immunology* / Q000378:metabolism; D018709:Statistics, Nonparametric; D013582:Synovial Fluid / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism
chemical_list: D001323:Autoantibodies; D007074:Immunoglobulin G; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide