They do this by secreting a small variety of products, including club cell secretory protein uteroglobin, and a solution similar in composition to pulmonary surfactant.
These play an important defensive role, and they also contribute to the degradation of the mucus produced by the upper airways.
The heterogeneous nature of the dense granules within the club cell's cytoplasm suggests that they may not all have a secretory function.
Some of them may contain lysosomal enzymes, which carry out a digestive role, either in defense: Club cells engulf airborne toxins and break them down via their cytochrome P-450 enzymes (particularly CYP4B1, which is only present in the club cells) present in their smooth endoplasmic reticulum; or in the recycling of secretory products.
Club cells contain tryptase, which is believed to be responsible for cleaving the hemagglutinin surface protein of influenza A virus, thereby activating it and causing the symptoms of flu.
[7] In May 2012, the editorial boards of most of the major respiratory journals (including the journals of the American Thoracic Society, the European Respiratory Society and the American College of Chest Physicians) concluded that the continued use of Clara's eponym would be equivalent to honoring him; they therefore introduced a name-change policy, which went into effect beginning January 1, 2013.