Because of their major role in tissue inflammation and damage in ANCA-associated vasculitis, the products of neutrophil degranulation, namely MPO, PR3, but also other serine proteases (elastases, cathepsin G, etc.), are already the subject of scientific studies [21, 22]; these promising concepts are reinforced by our clinical data. This evidence concerns the gene MPO and anti-neutrophil cytoplasmic antibody-associated vasculitis.