MPO and granulomatosis with polyangiitis: Granulomatosis with polyangiitis (GPA), also referred to as Wegener's granulomatosis, microscopic polyangiitis (MPA), and eosinophilic GPA (EGPA), commonly known as Churg-Strauss syndrome, are characterized by a lack of tolerance to neutrophil granule proteins like PR3 or MPO [5].