Endogenous nitric oxide inhibits neutrophil adherence to lung epithelial cells to modulate interleukin-8 release

To investigate the effect of neutrophil adherence to epithelial cells on the release of interleukin 8 (IL-8), we measured neutrophil adherence in the presence or absence of IFN-γ+TNF-α+IL-1β (cytomix) stimulation on cultured A549 epithelial cells. The extent of neutrophil adherence to A549 epithelial cells was measured and the concomitant production of IL-8 and nitrite were assayed. The roles of adhesion molecules and nitrite in modulation of neutrophil adherence were examined by pretreatment with oversaturating ICAM-1 blocking antibody and L-NAME (1mM), respectively. There was a time-dependent spontaneous and cytomix-induced release of IL-8 from epithelial cells, as well as a time-dependent increase in the magnitude of neutrophil adherence to epithelial cells. Stimulation of epithelial cells with cytomix induced a further increase in neutrophil adherence. Pretreatment with oversaturated ICAM-1 monoclonal antibody inhibited neutrophil adherence with or without cytomix stimulation. The inhibition of neutrophil adherence to epithelial cells with ICAM-1 monoclonal antibody or a semipermeable membrane downregulated the release of IL-8 with or without cytomix stimulation. Stimulation with cytomix decreased nitrite production. Both neutrophil adherence and L-NAME pretreatment significantly inhibited the production of nitrite. The inhibition of neutrophil adherence to epithelial cells with ICAM-1 monoclonal antibody or a semipermeable membrane upregulated nitrite production. Pretreatment with L-NAME failed to modify the spontaneous release of IL-8, but significantly enhanced the response to adherence and cytomix. In conclusion, endogenous nitric oxide may play a role in preventing neutrophil adherence to lung epithelial cells, thus modulating concomitant IL-8 release.