Elevated Fab glycosylation of autoantibodies maintained during B cell depletion therapy

Abstract

Several chronic autoimmune diseases are characterized by elevated autoantibody Fab glycosylation. Whether Fab glycans link to disease state or development remains unclear, yet may serve as a marker thereof. Many autoimmune diseases are treated with B cell depletion therapies that particularly result in a decline of autoantibodies. The question arises whether B cell depletion therapy may have an impact on Fab glycosylation. Here, we investigated the longitudinal effects of B cell depletion therapy on Fab glycosylation of total IgG and IgG autoantibodies in rheumatoid arthritis (RA), pemphigus vulgaris (PV), ANCA-associated vasculitis (AAV), and multiple sclerosis (MS). Baseline Fab glycosylation was compared to 6-12 months into therapy by lectin affinity chromatography, determining Fab sialylation as an estimate of Fab glycosylation. We observed a modest decrease in Fab glycosylation of total IgG for RA (median 13.8%[IQR 11.7-16.3] - 9.1%[IQR8-11]) and PV (16.4%[IQR14.9-17.5] - 13.01%[IQR10.8-15.5]) after 6 months, whereas for AAV Fab glycosylation slightly increased (11.6%[IQR7.4-15] - 14.9%[IQR11.4-19.3]), and no changes were found for MS. Autoantibody titers (anti-CCP, anti-PR3, anti-Dsg3) had declined following B cell depletion therapy, yet their elevated Fab glycosylation levels were maintained. Taken together, Fab glycosylation levels of autoantibodies do not decrease upon B cell depletion therapy, thereby retaining their predictive potential as biomarker.

Keywords: B cell depletion therapy; Changes in Fab glycosylation of total IgG compartment upon B cell depletion therapy in autoantibody-mediated chronic autoimmune diseases; Chronic autoimmunity; Fab glycosylation autoantibodies; High Fab glycosylation of autoantibodies maintained during B cell depletion therapy.

Fig. 1

Total IgM and IgG titers following B cell depletion therapy. Longitudinal antibody titers are shown for RA (red), PV (yellow), AAV (green), and MS (pink). A Total IgM levels (g/L) at 0, 6, and 12 months after initiation of B cell depletion therapy. Connected dots represent a patient. Grey area indicates normal range: 0.4–2.3 g/L IgM. B. Total IgG (g/L) as measured at 0, 6, and 12 months after start B cell depletion therapy. Grey area indicates normal range: 7–16 g/L. Statistical differences were determined using a Wilcoxon matched-pairs signed rank test. *p < 0.05, **p < 0.01, ***p < 0.001, ****p < 0.0001.

Fig. 2

Auto-antibody titers following B cell depletion therapy. Longitudinal auto-antibody IgG titers are shown for RA; anti-CCP (red), PV; anti-Dsg3 (yellow), and AAV; anti-PR3 (green) in arbitrary units (AU)/mL. Connected dots represent a single patient. Statistical differences were determined using a Wilcoxon matched-pairs signed rank test. *p < 0.05, **p < 0.01, ***p < 0.001.

Fig. 3

Fab sialylation level of total IgG and auto-antibodies following B cell depletion therapy. A Percentage of total IgG that is Fab sialylated at 0, 6, and 12 months after start of B cell depletion therapy. In RA (red), PV (yellow), AAV (green), and MS (pink). Connected dots represent a patient. B Percentage of auto-antibodies that is Fab sialylated at 0, 6, and 12 months following B cell depletion therapy. For RA; anti-CCP (red), PV; anti-Dsg3 (yellow), and AAV; anti-PR3 (green). Statistical differences were determined using a Wilcoxon matched-pairs signed rank test. *p < 0.05, **p < 0.01, ***p < 0.001.