Non-typeable Haemophilus influenzae directly and through TNF-α production enhances polymorphonuclear leukocytes adherence to bronchial epithelial cells and activation
Rationale. Non-typeable Haemophilus influenzae (NTHi), the leading cause of localized upper respiratory tract infection in children, can be the causative agents of lower respiratory tract disorders and chronic lung disorder exacerbations. Infection of bronchial epithelial cells by NTHi is characterized by a sustained neutrophilic inflammation that is thought to play a key pathogenetic role in lung parenchyma damage. Methods. To characterize the mechanisms involved in BEC activation in response to NTHi, a human cell line (BEAS-2B) was stimulated with NTHi lysates. The production of TNF-α, and the expression of TLR2, the microbial ligand that recognizes NTHi molecular patterns, and of ICAM-1, an adhesion molecule required for neutrophil adhesion, were evaluated. The respective role of TNF-α and ICAM-1 in neutrophil adhesion to BEAS-2B cells was then evaluated by inhibition of their activity by specific monoclonal antibodies (mAbs). Results. A time- and dose-dependent induction of TNF-α synthesis and release by BEAS-2B cells was detected after 24-hour exposure to NTHi lysates (0.4 to 1.6 mg/ml). TNF-α, but also directly NTHi lysates, significantly amplified ICAM-1 and TLR2 expression and synthesis by BEAS-2B cells. Stimulation of BEAS-2B cells with NTHi lysates or with TNF-α induced a dose-dependent increase neutrophil adhesion, stronger after NTHi lysates exposure, associated with MPO production. Finally, the NTHi lysates-induced neutrophil adhesion to BEAS-2B cells was significantly inhibited by anti-TNF-α and anti-ICAM-1 mAbs. Conclusion. Exposure to NTHi lysates induced functional and structural changes in BEAS-2B cells leading to neutrophil recruitment, adhesion, and activation. The observation that all these BEAS-2B cell changes were also induced by TNF-α can at least partially explain the sustained inflammation seen in NTHi infections.