Protein composition of apical surface fluid from the human airway cell line Calu-3: effect of ion transport mediators

Background: Analysis of the protein components of airway secretions is a potential means of detecting and characterizing biochemical alterations associated with airway diseases. Methods: We evaluated airway protein secretions using the airway epithelial cell line Calu-3 grown at an air–liquid interface. To observe changes in apically secreted proteins, we analyzed the protein content of apical surface fluid (ASF) washings of Calu-3 monolayers treated with ion transport mediators. Results: Immunoassay screening for antibacterial and inflammatory proteins indicated the presence of measurable levels of lysozyme and IL-8 in Calu-3 ASF. RT-PCR and immunoassay studies indicated that Calu-3 cells do not produce clara cell 10 kDa protein (CC10). The total protein secretion of Calu-3 was not altered by bradykinin, but amiloride and adenosine significantly increased Calu-3 protein secretion. Lysozyme secretion was not altered by bradykinin, but amiloride and adenosine significantly reduced lysozyme secretion. IL-8 secretion was not altered by bradykinin or adenosine, but amiloride significantly decreased IL-8 secretion. Conclusion: Our results demonstrate the presence of antibacterial protein lysozyme and the pro-inflammatory cytokine IL-8 in Calu-3 ASF and that ion transport mediators such as bradykinin, amiloride and adenosine influence the secretion of Calu-3 ASF proteins.