ANCA-associated vasculitis (AAV) represents a group of systemic autoimmune diseases characterized by necrotizing inflammation of small to medium-size blood vessels without immune-complex deposition, and by the presence in the serum of anti-neutrophil cytoplasmic antibodies (ANCA), especially anti-proteinase 3 (PR3) and anti-myeloperoxidase (MPO). Here, MPO is linked to anti-neutrophil cytoplasmic antibody-associated vasculitis.