Scherer Hans U, van der Woude Diane, Ioan-Facsinay Andreea, el Bannoudi Hanane, Trouw Leendert A, Wang Jun, Häupl Thomas, Burmester Gerd-R, Deelder André M, Huizinga Tom W J, Wuhrer Manfred, Toes René E M
Leiden University Medical Center, Leiden, The Netherlands.
Arthritis Rheum. 2010 Jun;62(6):1620-9. doi: 10.1002/art.27414.
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.
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.
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.
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.
抗瓜氨酸化蛋白抗体（ACPA）对类风湿关节炎具有独特的特异性。然而，ACPA是否以及如何促成疾病发病机制尚未完全明确。人IgG的Fc部分带有2个N - 连接聚糖部分，这对抗体的结构稳定性至关重要，并且调节其与Fcγ受体的结合亲和力及其激活补体的能力。我们开展本研究以分析血清和滑液（SF）中IgG1 ACPA的Fc糖基化，以便进一步明确对瓜氨酸化抗原的免疫反应特征。
使用环瓜氨酸化肽作为抗原，通过亲和纯化分离ACPA。采用质谱分析法分析IgG1 Fc糖基化。将ACPA IgG1聚糖谱与从85例特征明确的患者获得的总血清IgG1聚糖谱进行比较。另外11例患者可获得配对的SF和血清样本的聚糖谱。
与血清IgG1库相比，ACPA IgG1缺乏末端唾液酸残基。在SF中，ACPA高度去半乳糖基化且缺乏唾液酸残基，这一特征在总SF IgG1中未检测到。此外，在类风湿因子（RF）阳性和RF阴性患者中检测到不同的ACPA聚糖谱。
ACPA IgG1呈现出一种与总血清IgG1不同的特定Fc连接聚糖谱。此外，ACPA的Fc糖基化在SF和血清之间存在显著差异。由于Fc糖基化直接影响Fc介导的效应机制的募集，这些数据可能有助于我们进一步理解ACPA对疾病发病机制的作用。
