FIGURE 2 Proposed model of the involvement of epithelial cell-derived extracellular vesicles (EVs) in injury-repair responses in the lung. Intrinsic (e.g., ageing, genetics, mitochondria function, immunological signalling, mechanical stress) and extrinsic (e.g., cigarette smoke, infection, microaspiration, radiation, drug) sources of injury can cause epithelial cell death or cellular senescence, leading to dysfunction of resident epithelial stem cells. In the absence of injury, epithelial stem cell-derived EVs maintain lung quiescence. Under injury, epithelial stem cell-derived EVs can preserve lung homeostasis (repair). However, if these are unsuccessful, the EVs can also help to regenerate lung tissue. On the contrary, pathogenic EVs derived from damaged epithelial stem cells (e.g., senescent cells) develop a remodelling, which can be involved in lung pathogenesis such as idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD).