Among many pathological and radiological subtypes of pulmonary fibrosis, one of typical pathological types is usual interstitial pneumonia (UIP), followed by nonspecific interstitial pneumonia and organizing pneumonia. These subtypes are related to treatment responses to corticosteroids and/or immunosuppressants. Pathologically, proliferation of fibroblasts and abnormal deposition of extracellular matrix (ECM) are mainly distributed in the margins of pulmonary lobules, destroying the normal alveolar structure in pulmonary fibrosis. In UIP, scattered fibroblastic foci with immature fibroblasts with abnormal cuboidal epithelial cells covering the surface of fibroblast foci are assumed to be the forefront of the process of pulmonary fibrosis, and alterations in which the alveolar epithelium of alveolar walls and small airways is replaced by metaplastic bronchiolar epithelium are also observed. Mild inflammatory cell infiltration is often seen at fibrotic sites.
Among antifibrotic agents in treating pulmonary fibrosis, nintedanib is a PDGF/VEGF/FGF receptor tyrosine kinase inhibitor that suppresses ECM production from fibroblasts induced by TGF-β stimulation, and pirfenidone inhibits ECM production and growth of fibroblasts by TGF-β stimulation, and suppresses reactive oxygen species. The crosstalk between bronchial and alveolar epithelium and fibroblasts may be involved in the pathogenesis of pulmonary fibrosis, and blocking these molecular pathways in the crosstalk can be the potential therapeutic target of pulmonary fibrosis.