MPO and interstitial lung disease: Because repeated episodes of alveolar hemorrhage due to pulmonary capillaritis could be the pathogenesis of progressive pulmonary fibrosis, and MPO-ANCA may play a direct role in the pathogenesis of progressive pulmonary fibrosis [23–25], to sum up, we might see non-MPA-ILD (indeterminate for UIP pattern) patients experiencing a sequence of events (i.e., pre-stage) that lead to MPA-ILD (progressive stage: UIP).