MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (AAV) is an autoimmune disease characterized by serum-positive ANCA which mainly recognizes myeloperoxidase (MPO) or proteinase 3 (PR3) and the rapidly progressive glomerulonephritis which shows pauci-immune complex deposition in pathogenic biopsy [1].