MPO and granulomatosis with polyangiitis: Anti-neutrophil cytoplasmic autoantibodies (ANCA) are found in primary vasculitic syndromes, granulomatosis and polyangiitis (GPA) and microscopic polyangiitis (MPA) exhibit specificity for azurophilic granular proteins proteinase 3 (PR3) and myeloperoxidase (MPO) [[63], [64], [65], [66]].