Upregulation of ICAM-1 expression in bronchial epithelial cells by airway secretions in bronchiectasis

The airway epithelium participates in chronic airway inflammation by expressing adhesion molecules that mediate the transmigration of neutrophils into the inflamed airways. We hypothesize that, in patients with bronchiectasis, cytokines in their bronchial secretions enhance the expression of intercellular cell adhesion molecule (ICAM-1) in the bronchial epithelium and thus contribute to sustained recruitment of neutrophils into the inflamed airways. In the present study, we investigated the effect of bronchial secretions on the regulation of ICAM-1 in bronchial epithelial cells, and its modulation by pharmacologic agents. The expression of ICAM-1 mRNA and protein in human bronchial epithelial cells upon exposure to sputum sol from subjects with bronchiectasis were evaluated by reverse transcription-polymerase chain reaction (RT-PCR) and ELISA, respectively. Modulating effects of dexamethasone, ibuprofen, MK-663 or triptolide on ICAM-1 regulation were investigated in vitro. We demonstrated that changes in ICAM-1 expression correlated with levels of TNF-alpha in the sputum sol, and treatment of sol samples with TNF-alpha antibodies attenuated both the increase in ICAM-1 mRNA and protein. The role of TNF-alpha was further demonstrated when TNF-alpha elicited dose dependent increase in ICAM-1 expression. The sputum effect could also be suppressed dose-dependently by pre-incubation of bronchial epithelial cells with dexamethasone, ibuprofen, MK-663 or triptolide. Evidence is thus provided for the upregulation of bronchial epithelial ICAM-1 expression by airway secretions in bronchiectasis and a specific role for TNF-alpha in the secretions. The success of drug attenuation of this upregulation provides insight into possible therapeutic paradigms in the management of the disease.