Complement activation is involved in renal damage in human antineutrophil cytoplasmic autoantibody associated pauci-immune vasculitis.

Objective: This study was to investigate the evidence for complement activation in renal biopsy specimens of patients with myeloperoxidase (MPO)-antineutrophil cytoplasmic autoantibody (ANCA)-associated pauci-immune vasculitis.

Methods: Renal biopsy specimens from seven patients with MPO-ANCA positive pauci-immune necrotizing crescentic glomerulonephritis (NCGN) were used to detect the staining of membrane attack complex (MAC), C3d, C4d, mannose-binding lectin (MBL), factor B and factor P using immunohistochemistry and immunofluorescence. Renal tissue from seven patients with minimal change disease (MCD) and two normal renal tissue were used as controls.

Results: MAC, C3d, factor B and factor P could be detected in glomeruli and small blood vessels with active vasculitis of patients with pauci-immune AAV, but not or scarcely in patients with MCD and in normal renal tissue. C3d and factor B co-localized with MAC, factor P colocalized with C3d. MBL and C4d were not detected in patients with AAV.

Conclusion: The alternative pathway of the complement system is involved in renal damage of human pauci-immune AAV.