Lung stem cells.

The identity of putative stem cells in tracheobronchial, bronchiolar and alveolar compartments is reviewed. Their developmental appearance is described, as is the experimental evidence for their ability to repopulate areas of damage caused by noxious agents such as ozone, mineral fibres, chemicals and mechanical or enzymatic removal. Factors affecting pulmonary cell proliferation and differentiation are considered. The role played by these cells in carcinogenesis is also discussed, with consideration of the position of neuroendocrine cells in this process.