Clara cells are specialised cells which populate the epithelium of the respiratory tree from the level of terminal bronchiole to alveolar duct.
They are polyhedral in shape and unlike surrounding epithelial cells, they do not possess cilia. Their cytoplasm is filled with the biosynthetic organelles and their apical cytoplasm stains for a proteinaceous substance.
Clara cells are purported to have a role in:
- surfactant production; their product is not the same as that produced by the type II pneumocytes, but it may form one constituent of surfactant
- detoxification; the number of Clara cells increases in response to increased exposure to pollutants e.g. chronic cigarette inhalation