Basal cells (BCs) are relatively undifferentiated. In the mouse trachea, the basal cells are long-term progenitor/stem cells that give rise to Clara and ciliated cells both in steady state and after epithelial injury. Well-defined basal cells are not seen in the mouse trachea until around the time of birth.
Like basal cells in other epithelial tissues, such as the skin and esophagus, lung basal cells are characterized by the expression of Trp63 (p63) and cytokeratins 5 and 14 (Krt5/14). Subsets of Keratin-14 (K-14)-expressing BCs in the trachea can restore differentiated epithelium after injury and are distinct from bronchial BCs.