ARTHRITIS & RHEUMATISM Vol. 63, No. 7, July 2011, pp 2105–2115 DOI 10.1002/art.30362 © 2011, American College of Rheumatology Sialylation Levels of Anti–Proteinase 3 Antibodies Are Associated With the Activity of Granulomatosis With Polyangiitis (Wegener’s) Ce ´cile Espy, 1 Willy Morelle, 2 Niloufar Kavian, 1 Philippe Grange, 1 Claire Goulvestre, 1 Vivian Viallon, 1 Christiane Che ´reau, 1 Christian Pagnoux, 1 Jean-Claude Michalski, 2 Loı ¨c Guillevin, 1 Bernard Weill, 1 Fre ´de ´ric Batteux, 1 and Philippe Guilpain 1 Objective. To investigate whether the glycosyla- tion 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 immunosor- bent assay, and their levels of glycosylation and sialyla- tion 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 gly- cans, 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 character- istic curve for the sialylation ratio of anti-PR3 antibod- ies, 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 dHex 1 Hex 3 HexNAc 4 (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. Granulomatosis with polyangiitis (Wegener’s) (GPA) is a small-sized vessel necrotizing vasculitis asso- ciated with giant cell granulomas and necrosis. GPA usually affects the upper respiratory tracts, lungs, and kidneys, but any organ may be involved, including the skin, peripheral nerve, gastrointestinal tract, heart, and central nervous system. Antineutrophil cytoplasmic autoantibodies (ANCAs) (1–3) exhibiting a classic cyto- plasmic (cANCA) pattern of fluorescence and specific for proteinase 3 (PR3) are detected in 85–90% of patients with GPA. Anti-PR3 antibodies are considered to play a pathogenic role through the induction of the oxidative burst of neutrophils (4), but the measurement of anti-PR3 antibody levels as a tool to monitor disease activity remains controversial. Their levels are usually not correlated with disease activity and clinical outcome (5–7), although some authors found a clear association 1 Ce ´cile Espy, PharmD, Niloufar Kavian, PharmD, PhD, Philippe Grange, PhD, Claire Goulvestre, PharmD, PhD, Vivian Viallon, PhD, Christiane Che ´reau, PharmD, Christian Pagnoux, MD, PhD, Loı ¨c Guillevin, MD, Bernard Weill, MD, PhD, Fre ´de ´ric Batteux, MD, PhD, PharmD, Philippe Guilpain, MD, PhD: Universite ´ Paris Descartes and Ho ˆpital Cochin, Assistance Publique Ho ˆpitaux de Paris, Paris, France; 2 Willy Morelle, PhD, Jean-Claude Michalski, PhD: UMR 8576, Universite ´ des Sciences et Technologies de Lille, Ville- neuve D’Ascq, France. Drs. Batteux and Guilpain contributed equally to this work. Address correspondence to Fre ´de ´ric Batteux, MD, PhD, PharmD, Laboratoire d’Immunologie, UPRES EA 1833, 24 Rue du Faubourg St. Jacques, 75679 Paris Cedex 14, France. E-mail: frederic.batteux@cch.aphp.fr. Submitted for publication November 30, 2009; accepted in revised form March 15, 2011. 2105