The report presents the cellular structure of the respiratory system as well as the history of club cells (Clara cells), their ultrastructure, and location in the airways and human organs. The authors discuss the biochemical structure of proteins secreted by these cells and their importance for the integrity and regeneration of the airway epithelium. Their role as progenitor cells for the airway epithelium and their involvement in the bio­transformation of toxic xenobiotics introduced into the lungs during breathing is emphasized.

This is followed by a discussion of the clinical aspects associated with club cells, demonstrating that tracking the serum concentration of club cell-secreted proteins is helpful in the diagnosis of a number of lung tissue diseases. Finally, suggestions are provided regarding the possible use of proteins secreted by club cells in the treatment of serious respiratory conditions.