Fig. 1

The pathogenetic model of PF. Aging-associated changes, environmental factors and genetic susceptibility result in damage to alveolar epithelial cells. The injured epithelium secretes a plethora of mediators that induce the activation and proliferation of fibroblasts and myofibroblasts, which are resistant to apoptosis and persistently secrete ECM. The ECM also serves as a reservoir of mediators and continuously induces myofibroblast differentiation and ECM secretion in a positive feedback loop, leading to the inexorable progression of PF. By Figdraw (www.figdraw.com)