MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis: Anti-neutrophil cytoplasmic autoantibody (ANCA)-associated vasculitis (AAV) constitute a group of autoimmune diseases characterized by pauci-immune necrotizing small-vessel inflammation and by the production autoantibodies against proteinase 3 (PR3-ANCA) and myeloperoxidase (MPO-ANCA) (18).