Glycan profiling of anti-citrullinated protein antibodies isolated from human serum and synovial fluid.
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.
Scherer
Hans U
HU
Leiden University Medical Center, Leiden, The Netherlands.
van der Woude
Diane
D
Ioan-Facsinay
Andreea
A
el Bannoudi
Hanane
H
Trouw
Leendert A
LA
Wang
Jun
J
Häupl
Thomas
T
Burmester
Gerd-R
GR
Deelder
André M
AM
Huizinga
Tom W J
TW
Wuhrer
Manfred
M
Toes
René E M
RE
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
D001323:Autoantibodies; D007074:Immunoglobulin G; D010456:Peptides, Cyclic; C487763:cyclic citrullinated peptide