Abstract
Acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is an acute-onset neutrophil-dominant inflammatory lung disease caused by or associated with various illness and injuries. The mortality rate related to this disorder can be as high as 40%. In contrast, idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP) is a chronic progressive inflammatory lung disease of unknown etiology, with a mean survival of five years. There are no established treatments for either disease and novel therapies are eagerly desired. Lung epithelial cells were initially discovered to be derived from bone marrow stem cells and progenitor cells. As a result of progress made in regenerative medicine, several types of tissue stem cells and progenitor cells have been identified in the lungs, each of which is involved in tissue repair and regeneration at different levels of the bronchial tree. In terminal bronchioles and alveoli, where lung cells are specifically vulnerable to injuries caused by inflammatory cells, Clara cell-specific protein-positive epithelial cells, including bronchioalveolar stem cells, and a subgroup of alveolar epithelial type II cells, have been identified as lung tissue stem cell and progenitor cell candidates. Intratracheal administration of alveolar epithelial type II cells or epithelial progenitor cells has been shown to be effective in animal models of ALI/ARDS and IPF/UIP. As a novel strategy based on regenerative medicine, this could be a promising approach to treat inflammatory lung diseases.