Both PR3-ANCA and MPO-ANCA are highly sensitive and specific markers for the ANCA-associated vasculitides (AAV), in particular granulomatosis with polyangiitis and microscopic polyangiitis. This close association suggests a pathogenic role of the autoantibodies. In vitro and in vivo experimental data strongly support such a role, particularly for MPO-ANCA. As pathogenic autoantibodies ANCA could serve as biomarkers for AAV. Longitudinal observations indeed prove that MPO-ANCA could serve as a biomarker for AAV although being not perfect. For PR3- ANCA, data are less convincing as some studies found a fair correlation between changes in levels of PR3-ANCA and disease activity of the AAV, but others found not. This could be due to methodological shortcomings but also to inherent differences in pathogenicity between MPO-ANCA and PR3-ANCA. More studies are needed to solve this question.
Keywords: PR3-ANCA, MPO-ANCA, granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA), proteinase 3, ANCA-associated vasculitides, Idiopathic crescentic glomerulonephritis, c-ANCA, P-ANCA
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