Effect of Haemophilus influenzae endotoxin on the synthesis of IL-6, IL-8, TNF-alpha and expression of ICAM-1 in cultured human bronchial epithelial cells

Abstract

Although studies of infective lung diseases have demonstrated that Haemophilus influenzae is a major pathogen, the mechanisms underlying pathogenesis by this organism are not clear. We have cultured human bronchial epithelial cells (HBEC) to confluency and have investigated the effect of H. influenzae endotoxin (HIE) on: 1) epithelial permeability, by movement of 14C-bovine serum albumin (14C-BSA) across HBEC and measurement of electrical resistance of HBEC; 2) release of interleukin-6 (IL-6), interleukin-8 (IL-8) and tumour necrosis factor-alpha (TNF-alpha) into the supernatant, by enzyme-linked immunosorbent assay (ELISA); and 3) expression of intercellular adhesion molecule-1 (ICAM-1), by immunofluorescence staining. HIE did not significantly increase the movement of 14C-BSA across HBEC. In contrast, HIE progressively increased the electrical resistance of HBEC, such that this was significant after 24 h. Compared with untreated cells, 10-100 micrograms.ml-1 HIE-treated cells released significantly greater amounts of IL-6, IL-8 and TNF-alpha, after 24 h, which was blocked by 10(-5) M hydrocortisone. Similarly, incubation of HBEC with 10-100 micrograms.ml-1 HIE, significantly increased the total number of ICAM-1 positive cells, which were significantly decreased on incubation of the cells in the presence 10(-5) M hydrocortisone. Conditioned medium from HIE-exposed HBEC lead to significant increase in neutrophil chemotaxis and adhesion to endothelial cells in vitro. These results suggest that HIE may affect epithelial cell function and influence inflammation of the airway mucosa via induction of proinflammatory mediators.