MPO and granulomatosis with polyangiitis: AAV is divided into three distinct clinical-pathological phenotypes including granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA), and are associated with proteinase 3 (PR3) and myeloperoxidase (MPO) antibodies.