Functions of proteins and lipids in airway secretions.

Proteins and lipids synthesized by airway secretory cells or transudated are active components in the protection of respiratory epithelium. Proteins and ions are involved in the control of mucus hydration. Secretory proteins, such as secretory immunoglobulin A (IgA), transferrin and lysozyme, participate in the airway antibacterial defence. Other biochemical components found in secretions, such as anti-inflammatory and antioxidant agents as well as antiproteases, contribute significantly to the protection of the underlying epithelium.