IPF is an irreversible, fatal interstitial lung disease with death occurring in most patients within 5 years of diagnosis. Impaired regeneration of injured alveolar epithelium has been observed in fibrotic interstitial lung diseases, including idiopathic pulmonary fibrosis (IPF).

2 Importantly, a subset of surfactant protein C-positive (SPC +) AEC-II cells serve as regional progenitors in the alveoli and differentiate into AEC-I cells, playing a crucial role in replenishing the alveolar epithelial barrier during both homeostasis and repair after injury. They are multifunctional cells that produce, secrete, and recycle pulmonary surfactants regulate alveolar fluid balance and synthesize and secrete a number of immune-modulatory proteins involved in host defense. 1 In contrast, AEC-II cells are small cuboidal cells located in the corners of alveoli that cover only 5% of the alveolar surface. It is generally thought that the squamous AEC-I cells are terminally differentiated cells that interface with pulmonary capillaries and cover >90% of the alveolar surface where the exchange of CO 2/O 2 takes place. In the normal adult lung, the alveolar epithelium is composed of two major cell types, the alveolar epithelial type I (AEC-I) and alveolar epithelial type II (AEC-II) cells.

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