Anti-citrullinated protein antibodies acquire a pro-inflammatory Fc glycosylation phenotype prior to the onset of rheumatoid arthritis

Abstract

ObjectiveTo determine whether anticitrullinated protein antibodies (ACPA) exhibit specific changes in Fc glycosylation prior to the onset of arthritis.MethodsSerum samples of patients with ACPA-positive arthralgia (n=183) were collected at baseline and at various time points of follow-up. 105 patients developed arthritis after a median of 12 months (IQR 6–24) and were classified as having either rheumatoid arthritis (RA, n=48) or undifferentiated arthritis (UA, n=57) based on the 1987 American College of Rheumatology (ACR) criteria. ACPA and total serum IgG were isolated by affinity purification and cleaved by trypsin. ACPA-IgG1 Fc-glycopeptides were subsequently analysed by nano-liquid chromatography mass spectrometry and compared to those of total IgG1.ResultsAt baseline, ACPA-IgG1 and total IgG1 from arthralgia patients displayed similar Fc glycosylation patterns. By contrast, at the onset of arthritis, ACPA exhibited a decrease in galactose residues in RA patients, but not in UA patients. This decrease occurred around 3 months prior to diagnosis and was paralleled by an increase in systemic inflammation (erythrocyte sedimentation rate). Galactosylation of total IgG1 was also decreased in RA, but this did not precede the onset of arthritis. Interestingly, we additionally noted a higher degree of ACPA-IgG1 Fc core fucosylation at baseline as compared with total IgG1, which further increased prior to diagnosis.ConclusionsACPA display significant changes in Fc galactosylation and fucosylation prior to the onset of RA. These changes towards a more pro-inflammatory phenotype could be involved in driving the disease process.

Structural Analysis of Variable Domain Glycosylation of Anti-Citrullinated Protein Antibodies in Rheumatoid Arthritis Reveals the Presence of Highly Sialylated Glycans

“…Earlier, we and others reported that the galactosylation and sialylation levels of Fc-glycans from ACPA-IgG is lower compared with control IgG, and this is more pronounced in ACPA-IgG isolated from SF (28,29). In addition, we observed that the changes of ACPA-IgG Fcglycosylation already occur a few months before of the diagnosis of RA (23).…”

“…As expected, control IgG was characterized by two electrophoretic bands corresponding to the heavy and light chains (HC and LC), whereas ACPA-IgG showed several HC and LC bands with higher molecular weights as described previously (13). Released N-glycans from both the HC of IgG and the HC1 of ACPA-IgG displayed a typical Fc-linked glycan profile in UHPLC (23,26), whereas no N-glycans were detected in the LC of IgG and the LC1 of ACPA-IgG (Fig. 2B).…”

“…Part of the Fc-linked Nglycans also contained a bisecting GlcNAc. Of note, a relatively high proportion of agalactosylated glycans (G 0 ) was observed as previously described (23). The N-glycans released from (ACPA)-IgG F(abЈ) 2 fragments consisted of highly galactosylated and sialylated diantennary glycoforms, that may carry bisecting GlcNAc and/or a core fucose ( Fig.…”

“…An internal calibration was performed with m/z values indicated in supplemental Table S4. Finally, to analyze the Fc-linked glycosylation of (ACPA)-IgG at the glycopeptide level, antibodies were digested with trypsin and analyzed by LC-MS as described (23,24). Processing and analysis of the LC-MS data were performed as previously described (23).…”

“…The Fab-linked Glycosylation Pattern of ACPA-IgG Differs from the Pattern on "Conventional" IgG-We have previously shown that Fc-linked N-glycans of ACPA-IgG isolated from patients present a more pronounced reduction in the level of galactosylation and sialylation but an increased degree of core fucosylation than those of other IgG molecules (23,26 Table S7, S8, and S9). In addition, our data revealed important differences between the Fablinked N-glycan profile of ACPA-IgG and that of control IgG (Fig.…”