Figure 1.

Alveolar Cell Lineages Involved in Lung Repair and Regeneration

(A) The human distal airways connect with the alveolar niche through a transitional respiratory airway (also called the respiratory bronchiole or RB) region. The RB is lined with a simple but poorly characterized cuboidal epithelium while the more intermediate airways exhibit a pseudostratified epithelium containing secretory, goblet, and ciliated cells that may exhibit as yet distinct heterogeneity. Of note, basal cells are found in human intermediate and respiratory airways.

(B) Mice do not have respiratory bronchioles and transition from the intermediate airways, which exhibit a pseudostratified nature but lack basal cells, into the alveolar region. The distal BADJ region in the mouse lung, which is not found in the human lung, contains the BASC population. The architecture and cell lineages found in both the mouse and human lungs are very similar and contain both AT1 and AT2 epithelial lineages as well as various mesenchymal lineages and vascular endothelial cells.

(C) The various cell types found in the distal airways and alveolus of the human and mouse lung.