MPO and microscopic polyangiitis: Three major subgroups are granulomatosis with polyangiitis (GPA), known as Wegener’s granulomatosis), microscopic polyangiitis (MPA), and eosinophilic GPA (EGPA; also known as Churg–Strauss syndrome), which is characterized as a lack of tolerance to the main proteins of neutrophil granule, including proteinase 3 (PR3) or myeloperoxidase (MPO) [1].