a) HNEpC (Human Nasal Epithelial Cells) are isolated from nasal mucosa
b) HTEpC (Human Tracheal Epithelial Cells) from the surface epithelium of trachea
c) HBEpC from the surface epithelium of bronchie, and
d) HSAEpC (Human Small Airway Epithelial Cells) from the distal portion of the respiratory tract in the 1 mm bronchiole area
(comprising the cells from bronchioli and alveoli).