MPO and microscopic polyangiitis: In ANCA-associated vasculitis, pANCA, mainly directed against myeloperoxidase (MPO-ANCA), is a well-established and very specific marker for microscopic polyangiitis, whereas proteinase 3 (PR3)-ANCA is the “classical” cANCA antigen and specific for granulomatosis with polyangiitis also known as Wegener's granulomatosis [10].