Measuring Circulating Complement Activation Products in Myeloperoxidase– and Proteinase 3–Antineutrophil Cytoplasmic Antibody–Associated Vasculitis

Abstract

Objective There is accumulating evidence that complement activation is important in antineutrophil cytoplasmic antibody (ANCA)–associated vasculitis (AAV) pathogenesis. This study was undertaken to investigate complement activation in AAV with myeloperoxidase (MPO) positivity and AAV with proteinase 3 (PR3) positivity after determining optimal methods for measuring activated complement factors in circulation. Methods Participants included 98 patients with AAV (45 MPO‐ANCA positive, 53 PR3‐ANCA positive) and 35 healthy controls. Plasma was obtained from blood collected using EDTA tubes, with or without 100 μg/ml Futhan. Levels of Bb, C3a, C5a, soluble C5b–9 (sC5b–9), properdin, and C4d were measured by enzyme‐linked immunosorbent assay. Group comparisons were made using Wilcoxon's 2‐sample test. Paired data were analyzed using a matched pairs signed rank test. Results Compared to healthy controls, certain complement analyte levels were high in patients with active AAV with MPO positivity, including C3a (P < 0.0001), C5a (P = 0.0004), and sC5b–9 (P = 0.0007). During remission, levels of Bb (P = 0.001), C3a (P < 0.0001), and sC5b–9 (P = 0.003) were higher. Compared to healthy controls, C3a (P < 0.0001), C5a (P = 0.002), sC5b–9 (P = 0.0001), and C4d (P = 0.005) levels were higher in patients with active AAV with PR3 positivity; levels of C3a (P < 0.0001) and C4d (P = 0.007) were also higher duriing remission. There were no significant differences in any complement analyte for either ANCA serotype between patients with active disease and those with disease in remission. Among patients with paired samples, sC5‐9 levels were significantly lower during disease remission compared to active disease. C5a was significantly lower among patients with disease in long‐term remission who were not receiving therapy. For Bb, C5a, and sC5b–9, median levels and individual values were considerably higher in control and patient samples processed without Futhan compared to those processed with Futhan. Conclusion Complement activation occurs in both MPO‐positive AAV and PR3‐positive AAV. The complement activation profile differs according to disease activity and possibly ANCA serotype. Futhan reduces in vitro complement activation and provides a more accurate measurement.

Management of ANCA associated vasculitis

“…Neutrophil extracellular traps (NETs) have been recently recognized as important in the pathogenesis 53. Moreover, although immunoglobulins and complement are infrequently observed in biopsy specimens, the alternative pathway is now considered pathogenically important, and complement inhibitors (such as anti-C5a) may have efficacy in AAV 5455…”

The alternative complement pathway in ANCA-associated vasculitis: further evidence and a meta-analysis

“…After reviewing titles and abstracts, 19 studies were selected for full-text reading. Of these, 14 were excluded (one study was not available for the raw data) to finally include four eligible articles by 12 December 2019 [11][12][13]20]. Among these, Gou et al measured the levels of complement pathway factors twice at different time-points, to which we refer as 'Gou, sequential' .…”

Personalized Medicine in ANCA-Associated Vasculitis ANCA Specificity as the Guide?

“…The lack of immunoglobulin and complement in the renal lesions of AAV, for example, contrasts strikingly with the glomerular lesions observed in systemic lupus erythematosus, for example. However, mounting evidence suggests that activation of the alternative pathway is important to the pathogenesis of MPO-ANCA+ and, more recently, PR3-ANCA+ AAV (18, 19). A recent study by Wu et al suggested that the classical or lectin complement pathways are activated in PR3-ANCA+ but not MPO-ANCA+ AAV (18).…”

“…However, mounting evidence suggests that activation of the alternative pathway is important to the pathogenesis of MPO-ANCA+ and, more recently, PR3-ANCA+ AAV (18, 19). A recent study by Wu et al suggested that the classical or lectin complement pathways are activated in PR3-ANCA+ but not MPO-ANCA+ AAV (18). Moreover, avacopan, a C5a receptor inhibitor, was found in early phase trials to have efficacy in AAV and have a potential role as a glucocorticoid-sparing drug in remission induction (20).…”