They are generally divided into proteinase-3 (PR3), specific for Granulomatosis with Polyangiitis (GPA); Myeloperoxidase (MPO), more specific for Microscopic Polyangiitis (MPA) and Eosinophilic Granulomatosis with Polyangiitis (EGPA); and atypical ANCA [87]. Here, MPO is linked to granulomatosis with polyangiitis.