Figure 1.

Sschematic of proposed lung epithelial candidate stem or progenitor cells and their niches in the proximal conducting airways and distal alveoli. Cells whose localization or existence is not clear or accepted are indicated with dashed boxes and/or question marks. AEC2 = type 2 alveolar epithelial cell; BADJ = bronchoalveolar duct junction; Gland = submucosal gland duct; NEB = neuroepithelial body. Marker abbreviations used for each cell subtype include the following: CCSP = Club cell secretory protein; CGFP = calcitonin gene–related peptide; Itg = integrin; K = cytokeratin; SPC = surfactant protein C. Adapted by permission from Reference 20.