Myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA)-associated vasculitis is a systemic condition affecting the small vessels with production of MPO-ANCA in serum. It has been suggested that the formation of neutrophil extracellular traps (NETs) induced by MPO-ANCA is a driver of pathogenesis, with involvement of neutrophil elastase (NE), which in turn is activated by the enzyme cathepsin C.