Airway epithelial cells as regulators of airway inflammation (Review).

Airway epithelial cells (AEC) are known to play an integral role in the airway defense mechanism via mucociliary system as well as mechanical barriers. Recent studies further indicate that AEC can produce and release biologically active compounds including lipid mediators, growth factors, endothelin and a variety of cytokines/chemokines important in the pathogenesis of airway disorders. Human bronchial epithelial cells were isolated from normal and diseased states, and purely cultured in hormonally defined, serum-free medium. Culture supernatants of AEC contained detectable amounts of cytokines such as IL-1, IL-6, IL-8, G-CSF and GM-CSF. Proinflammatory cytokines IL-1 and TNFalpha generally upregulated expression and release of these cytokines. Moreover, human bronchial epithelial cells from patients with airway diseases such as asthma showed increased levels of mRNA for the cytokines. AEC are considered to interact with immune and inflammatory cells by direct adhesion as well as by humoral factors including cytokines. For example, eosinophil adhesion to AEC may be an important signal for the activation and degranulation of eosinophils. AEC is also believed to take part in the airway mucosal immunity by interacting with lymphocytes. Finally, AEC may play a crucial role in the processes of airway remodelling found in chronic airway inflammatory diseases. These findings strongly suggest that AEC are actively involved as regulators of airway inflammatory responses playing an important role in the pathogenesis of airway disorders, and become a target for therapeutic intervention.