MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Eosinophilic granulomatosis with polyangiitis (EGPA), Granulomatosis with polyangiitis (GPA), and microscopic polyangiitis (MPA), are the major categories of AAV, and proteinase 3 (PR3) and myeloperoxidase (MPO) are two major antigens of ANCA2.