Immunoglobulin G galactosylation and sialylation are associated with pregnancy-induced improvement of rheumatoid arthritis and the postpartum flare: results from a large prospective cohort study

Abstract

Introduction: Improvement of rheumatoid arthritis (RA) during pregnancy has been causatively associated with increased galactosylation of immunoglobulin G (IgG) N-glycans. Since previous studies were small, did not include the postpartum flare and did not study sialylation, these issues were addressed in the present study.

Methods: Serum from 148 RA cases and 32 healthy controls was collected at several time points before, during and after pregnancy. Improvement during pregnancy and postpartum flare were determined according to the European League Against Rheumatism (EULAR) response criteria. Galactosylation and sialylation of Immunoglobulin G (IgG) and the presence of bisecting N-acetylglucosamine (GlcNAc) were analyzed by matrix-assisted laser desorption/ionization - time of flight - mass spectrometry (MALDI-TOF-MS).

Results: IgG1 and IgG2 galactosylation of the cases and controls increased during pregnancy with a maximum in the third trimester. Galactosylation decreased directly postpartum. IgG galactosylation of controls was at a higher level than cases (P < 0.001 at all time points) and a similar pattern was observed for sialylation. Moreover, there was a good association between galactosylation and sialylation. The increase in galactosylation was significantly more pronounced for cases with improvement than cases without improvement during pregnancy. The reverse was true for deteriorators and non-deteriorators postpartum. The presence of bisecting GlcNAc was not significantly influenced by pregnancy or postpartum for cases and controls.

Conclusions: This large cohort study demonstrates the association of changes in galactosylation with both pregnancy-induced improvement and postpartum flare in RA-patients, suggesting a role for changes in glycosylation in the pregnancy-induced improvement of RA.

Figure 1

MALDI-TOF-MS analysis of tryptic glycopeptides of IgG1 and IgG2. A representative sample of an RA-patient before pregnancy (a) and in the third trimester (b) is shown. Glycopeptides derived from IgG1 and IgG2 were analyzed for galactosylation and sialylation in the reflectron positive mode. Glycopeptides of IgG 1 are indicated by continued arrows, while glycopeptides of IgG2 are indicated by striated arrows. Three glycoforms of IgG1 have been found to be below the detection limit of the MALDI-TOF-MS method in this sample as well as in several other samples.

Figure 2

Mean galactosylation of IgG1 and IgG2 in cases and controls during pregnancy and postpartum. IgG1 (a) and IgG2 (b) galactosylation levels (in percentages) increase during pregnancy and decline postpartum. IgG1 and IgG2 galactosylation profiles of controls are at a significantly higher level than cases (P < 0.001, Linear Mixed Model at all timepoints). The vertical bars illustrate the 95% confidence intervals. Abbreviations: trim = trimester of pregnancy; wk = weeks; PP = postpartum; mon = months.

Figure 3

Mean IgG1 galactosylation levels in relation to rheumatoid arthritis disease activity levels. For this purpose at every timepoint all cases were divided in two categories; that is, those with a DAS28>3.2 or DAS28<2.6. Please note that each timepoint may include different RA-cases. For comparison controls are added to the graph. The IgG1 galactosylation level which is associated with disease remission (DAS28 <2.6) is dependent on the timepoint of measurement. Similar data were observed for IgG2 (data not shown). The vertical bars illustrate the 95% confidence intervals. Abbreviations: DAS28 = disease activity score; trim = trimester of pregnancy; wk = weeks; PP = postpartum; mon = months.

Figure 4

Mean change in IgG1 and IgG2 galactosylation during pregnancy and early or late postpartum. (a) Mean change in IgG1 and IgG2 galactosylation (×100%) during pregnancy in (good and moderate) responders according to the EULAR response criteria (cases that improved during pregnancy, n = 37) and non-responders (cases that did not improve during pregnancy, n = 38). The change in IgG galactosylation was significantly different between responders and non-responders for IgG1 (P < 0.02), whereas for IgG2 a trend towards significance could be observed (P = 0.11). (b) Mean change in IgG1 and IgG2 galactosylation (×100%) in the postpartum period in cases with an early flare between six weeks and three months postpartum (deterioration, n = 35) and cases without an early flare (no deterioration, n = 106). The change in galactosylation was significantly different between early flare and no early flare for IgG1 and IgG2 (P < 0.004). (c) Mean change in IgG1 and IgG2 galactosylation (×100%) in the postpartum period in cases with a late flare from three to six months postpartum (deterioration, n = 29) and cases without a late flare (no deterioration, n = 112). The change in galactosylation was significantly different between late flare and no late flare for IgG1 and IgG2 (P < 0.0001 and P < 0.0004, respectively). The vertical bars illustrate the 95% confidence intervals.