Figure 1.

Alveolar progenitor cells. Various epithelial cells in the distal airways of lungs can generate alveolar type 2 (AT2) cells. These bipotent progenitor cells include club cells, ciliated cells, tuft cells, pulmonary neuroendocrine cells (PNECs), basal cells, and respiratory airway secretory cell (RAS)/alveolar type 0 (AT0) cells. Except for basal cells, which are found in human and not mouse airways, these distal airway progenitor epithelial cells are found in human and mouse lungs, and some can self-renew. AT2 cells in the alveolar compartment can self-renew and differentiate into AT1 cells via a transitional cell type. (Created with BioRender.com with permission).