Background/Purpose: ANCA-associated vasculitis (AAV) and systemic lupus erythematosus (SLE) both cause glomerulonephritis with pauci-immune and full-house immunofluorescence patterns, respectively. Although AAV and SLE are clinically divergent autoimmune diseases, neutrophil extracellular traps (NETs) are postulated to be involved in both diseases. NETs are immunogenic, extracellular DNA structures harbouring relevant AAV- and SLE-autoantigens. The aim of this study was to dissect AAV- and SLE-induced NET formation and study their pathogenic role in the pathophysiology of these autoimmune diseases.

Methods: Ex vivo NET formation was quantified by a novel, highly-sensitive NET-quantification assay using 3D-confocal microscopy for 82 AAV patients, 56 SLE patients and 10 healthy controls (HC). Morphology and kinetics of AAV- and SLE-induced NET formation was studied through live-cell imaging. Qualitative characteristics of NETs were investigated by immunofluorescence microscopy that detected co-localisation of NET-related proteins, including citrullinated histon-3 (CitH3) and high mobility group box-1 (HMGB1). Also, the presence of IgG, IgM or IgA autoantibodies on AAV- and SLE-induced NETs was studied through immunofluorescence. Autoantibodies as trigger of NET formation were investigated by depleting serum from IgG and NET inhibition assays were performed using peptidylarginine deiminase-4 (PAD4) and NADPH inhibitors.

Results: Ex vivo NET formation was higher for AAV compared to SLE, which was triggered by immune complexes (ICx) in SLE but not in AAV. In AAV, lytic NET formation was induced involving NADPH oxidase and PAD enzymes resulting in a lytic expulsion of citrullinated NETs within a timeframe of hours. In SLE, non-lytic NET formation with clustering of NET-ting neutrophils is induced within minutes. SLE-induced NETs have immunogenic properties including enrichment for HMGB1, oxidized mtDNA and immune complex formation which was not the case for AAV-induced NETs.

Conclusion: This study demonstrates that excessive NET formation in AAV is intrinsically different to NET formation in SLE, identifying suicidal NET formation and vital NET formation, respectively, which closely associated with the respective, typical features of “pauci-immune”, histone-mediated crescentic glomerulonephritis in AAV and immune-complex mediated “full-house” lupus nephritis in SLE.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/excessive-formation-of-neutrophil-extracellular-traps-different-role-in-the-pathogenesis-of-anca-associated-vasculitis-and-systemic-lupus-erythematosus/