Original study
For inclusion in the study, we selected patients with newly diagnosed or relapsing AAV, who had a Birmingham Vasculitis Activity Score version 3 (BVAS v. 3) of ≥3. Diagnosis of granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) was established according to the American College of Rheumatology criteria [11], EMA algorithm [12] and the Chapel Hill Conference Consensus definition [13]. Healthy control subjects were recruited at Tareev Clinic of Internal Disease (Moscow) and Vladimir Regional Clinical Hospital. All subjects provided written informed consent approved by the local ethics committee of the Sechenov University. The study was in compliance with the Declaration of Helsinki Principles.
Plasma concentrations of human complement components were determined by enzyme-linked immunosorbent assay, including MAC (HK328-02, Hycult Biotech, the Netherlands), C5a (HK349-01, Hycult Biotech, the Netherlands), C3a (HK354-01, Hycult Biotech, the Netherlands), factor B (EF7001-1, ASSAYPRO, USA), and properdin (factor P; SEA783Hu, Cloud-Clone Corporation, USA). All the complement components were assayed according to the manufacturer’s instructions. Upper reference limits (the 97.5th percentile) for each complement component were defined from the values in the control group after log transformation of the primary data.
Renal biopsies were evaluated according to a standardized protocol [14]. ANCA-associated glomerulonephritis class was established according to the Berden classification [15]. The percentage of glomeruli with crescents and global sclerosis was calculated as the percentage of the total number of glomeruli in a biopsy. Interstitial fibrosis and tubular atrophy are given as the percentage of the tubulointerstitial compartment affected. Deposition of IgA, IgG, IgM, C3, kappa and lambda light chains was scored semi-quantitatively by immunofluorescence staining.