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Table 1 Why the distinction between PR3- versus MPO-ANCA-positive (and versus ANCA-negative) vasculitides may be better than that based on the clinical diagnosis (GPA, MPA or EGPA)

From: Linking classification and therapeutic management of vasculitides

The reported frequencies of ANCA in GPA, MPA and EGPA and their specificities differ: for example, in non-Asian populations, GPA is mainly associated with PR3-ANCA (c-ANCA), and MPA and EGPA with MPO-ANCA (p-ANCA)
The pathogenic role of MPO-ANCA is supported by in vitro experiments, animal models, and one (isolated) mother-to-inborn case report. The possible pathogenic role of PR3-ANCA is much less established yet
The monitoring of PR3-ANCA is not a reliable marker of disease activity or predictor of flare, unless, perhaps, in those patients with renal involvement
Genetic studies demonstrated that the associations with the SNPs of HLA-DP, SERPINA1 and PRTN3 with PR3-ANCA status and HLA-DQ alleles with MPO-ANCA status were stronger than with the diagnosis of GPA or MPA, respectively
The outcomes of PR3- and MPO-ANCA-positive patients differ and the statistical associations between the ANCA type and renal outcome, mortality or relapse rates are stronger than with the diagnosis (GPA versus MPA)
The exact place of EGPA in the ANCA-associated vasculitis group is unclear: the most common manifestations of EGPA (asthma, eosinophilia) are very different from those of GPA and MPA; less than 40 % of EGPA patients are ANCA-positive, mainly with MPO-ANCA (p-ANCA). None of the reported animal models of MPO-ANCA-associated vasculitis showed eosinophilic infiltrates as observed in EGPA
  1. See text for detail and references. ANCA antineutrophil cytoplasm antibodies (c-ANCA refers to ANCA with a cytoplasmic labeling pattern in immunofluorescence, p-ANCA to ANCA with a perinuclear labeling pattern in immunofluorescence), EGPA eosinophilic granulomatosis with polyangiitis, GPA granulomatosis with polyangiitis, HLA human leukocyte antigen/histocompatibility antigens (DP and DQ are HLA class II antigen), MPA microscopic polyangiitis, MPO myeloperoxidase, PR3 proteinase 3, PRTN3 proteinase 3 gene, SERPINA1 ‘serpin peptidase inhibitor, clade A, member 1’ coding for alpha-1 antitrypsin gene, SNP single nucleotide polymorphism