Summary

 Background: Anti-neutrophil cytoplasm antibodies in necrotizing vasculitides need to be distinguished from ANCAs¹  in other inflammatory conditions to avoid clinical misinterpretation.

Objectives: To help clinicians and laboratory scientists recognize and utilize vasculitis-related ANCAs as an aid in diagnostic workup and patient follow-up, and be aware that ANCAs with different characteristics are commonly found in other chronic inflammatory conditions that persistently engage neutrophils in the inflammatory process.

Methods: Indirect immunofluorescence and enzyme immunoassay methods were used to detect ANCAs with both known and unknown neutrophil autoantigenic targets.

Results: Primary necrotizing small vessel vasculitides such as Wegener’s granulomatosis, Churg-Strauss syndrome, microscopic polyangiitis, and renal-limited rapidly progressive necrotizing glomerulonephritis target either the serine protease proteinase 3 or myeloperoxidase  in azurophilic granules. In ulcerative colitis and rheumatoid arthritis, we found multiple ANCA targets contained in azurophilic and specific granules, the cytosol and the nucleus, whereas PR3² and MPO³ were not, or only weakly, recognized.

Conclusions: ANCAs typically found in active SVV⁴ are demonstrable both by indirect immunofluorescence and antigen-specific enzyme immunoassay, and strong reactivity to either PR3 or MPO is characteristic. Strong ANCA with MPO reactivity is also found in some patients with drug-induced syndromes (lupus, vasculitis). Intermediate to strong perinuclear ANCAs are found in a substantial proportion of patients with UC⁵ (40–60%) and RA⁶ (30–70%), but in these conditions the ANCAs have many antigen targets that are only weakly recognized.

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¹ ANCA = anti-neutrophil cytoplasm antibody

² PR3 = protease proteinase 3

³ MPO = myeloperoxidase

⁴ SVV = small vessel vasculitides

⁵ UC = ulcerative colitis

⁶ RA = rheumatoid arthritis