Contrastingly, GGOs represent an acute inflammation process in MPO-ANCA positive MPA-ILD, and correspond to alveolar hemorrhage, interstitial chronic inflammation in the alveolar septa, and vasculitis in small-sized arteries with infiltration of lymphocytes in the pathologic findings of MPO-ANCA-positive AAV-ILD24,25. This evidence concerns the gene MPO and microscopic polyangiitis.