Stimulation of both human bronchial epithelium and neutrophils is needed for maximal interactive adhesion

It has become clear that the bronchial epithelium is not just a passive barrier but plays an active role in inflammation. It can produce several inflammatory mediators and does express cell adhesion molecules of which intercellular adhesion molecule (ICAM)-1 can be upregulated by cytokines like interferon (IFN)-γ. In the present study, we analyzed in detail the interaction of neutrophils with human bronchial epithelial cells, both primary cultured cells and the bronchial epithelial cell line BEAS-2B. Confluent monolayers of epithelial cells were incubated with freshly isolated51Cr-labeled neutrophils for 30 min at 37°C; then the nonadherent cells were removed by washing gently. Stimulation of the epithelial cells with IFN- γ or the combination of IFN-γ and tumor necrosis factor-α (TNF-α) (which doubles the ICAM-1 expression) increased neutrophil adhesion. Activation of the neutrophils themselves with N-formylmethionyl-leucyl-phenylalanine (fMLP), platelet-activating factor, or TNF-α also caused a profound enhancement of the adhesion. A significant additional increase was found when the epithelial cells had been exposed to IFN-γ and the neutrophils were stimulated with fMLP simultaneously. This effect was even more pronounced with epithelium preincubated with IFN-γ and TNF-α. With the use of monoclonal antibodies against CD18 and ICAM-1, it was demonstrated that the increased adhesion was mainly mediated by the ICAM-1/β2-integrin interaction. This study highlights that both the activation state of the bronchial epithelial cells and the activation state of the neutrophils are critical for their interactive adhesion.