14 - Antineutrophil cytoplasmic autoantibodies with specificity for proteinase 3

Abstract

Antineutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) are a sensitive and specific marker for ANCA-associated systemic vasculitis and, in particular, for Wegener's granulomatosis (WG). Using indirect immunofluorescence (IIF) on ethanol-fixed neutrophils, antibodies to PR3 give a cytoplasmic staining (CANCA). They are usually detected by Enzyme-linked immunosorbent assay (ELISA) using purified PR3 as substrate (direct ELISA). An alternative and promising method is constituted by a capture ELISA, where a monoclonal antibody to PR3 is used as capturing ligand. The best diagnostic performance is obtained when IIF is combined with PR3-specific ELISA. PR3-ANCA are present in about 65% of patients with WG and in a much lower percentage of patients with microscopic polyangiitis (and Churg–Strauss syndrome). Their prevalence is influenced by disease activity/extent and by the methodology used. PR3-ANCA levels are useful to monitor disease activity but should not be used by themselves to guide treatment. A significant increase in ANCA titres, or the reappearance of ANCA, should alert the clinicians and lead to a stricter patient control. There is increasing, mainly indirect, evidence that ANCA may have a pathogenic role.