Pulmonary epithelial stem cells

Abstract

Classically, the stem/progenitor cells of the pulmonary epithelium are considered to be the basal and mucous cells of the proximal airways, Clara cells in the bronchioles and type II pneumocytes in the alveoli. Recent data suggest that there is a variant of Clara cells, lying in pulmonary neuroendocrine bodies, that meets several stem cell criteria and that type II pneumocytes exist in at least two populations, one of which is more resistant to injury. However, a complete revision of our understanding of pulmonary stem cell biology is underway as a result of the discovery of pulmonary epithelium derived from blood-borne cells. In addition, the existence in the lung of a 'universal' pluripotent cell has long been speculated upon and now some initial evidence has emerged with the identification of a spore-like cell that can differentiate in vitro to bronchiolar tissue.

Figure 1

Progenitor cells freshly isolated from the epithelium of human fetal lung (gestational age 12 weeks). The epithelial phenotype is shown by immunostaining for cytokeratin (red). These cells were maintained in vitro and, after two weeks, were found to express surfactant protein C, a specific marker of type II pneumocytes (nuclei counterstained blue with DAPI). Photograph courtesy of Dr HM Romanska.