Sialylation levels of anti-proteinase 3 antibodies are associated with the activity of granulomatosis with polyangiitis (Wegener's).

Objective: To investigate whether the glycosylation and sialylation levels of anti-proteinase 3 (anti-PR3) antibodies could affect their pathogenicity, and whether these levels could be correlated with the activity of granulomatosis with polyangiitis (Wegener's) (GPA).

Methods: Forty-two serum samples positive for anti-PR3 antibodies from 42 patients with active or weakly active/inactive GPA were included. Anti-PR3 antibodies were assayed by enzyme-linked immunosorbent assay, and their levels of glycosylation and sialylation were assessed by enzyme-linked lectin assay. The glycosylation and sialylation levels of IgG purified from the serum of healthy donors and patients with active, remitted, or weakly active disease were assessed by permethylation and mass spectrometry analysis of glycans, following neuraminidase digestion. The neutrophil oxidative burst induced by purified IgG was assayed by spectrofluorimetry.

Results: The mean sialylation ratio of anti-PR3 antibodies was significantly lower in patients with active disease than in patients with weakly active or inactive disease, and this was inversely correlated with the Birmingham Vasculitis Activity Score (BVAS) (P < 0.0001). Similar results were obtained using the BVAS/GPA. The area under the receiver operating characteristic curve for the sialylation ratio of anti-PR3 antibodies, as a test to determine the activity of GPA, was 0.82 (P = 0.0006). The characterization of N-glycans showed a decrease in 2,6-linked sialylated N-glycans and an increase in dHex₁ Hex₃ HexNAc₄ (mass/charge 1,836) agalactosylated structures in purified IgG from patients with active disease compared with controls. The anti-PR3 antibody-induced oxidative burst of neutrophils was inversely correlated with the sialylation levels of anti-PR3 IgG.

Conclusion: The sialylation level of anti-PR3 antibodies contributes to the clinical activity of GPA, by modulating the oxidative burst of neutrophils induced by these autoantibodies.