Non-typeable Haemophilus influenzae directly and through TNF-α production enhances polymorphonuclear leukocytes adherence to bronchial epithelial cells and activation

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. 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 the Tumor Necrosis Factor-α (TNF-α), and the expression of the Toll-like Receptor2 (TLR2), the microbial ligand that recognizes NTHi molecular patterns, and of the Intercellular Adhesion Molecule-1 (ICAM-1), an adhesion molecule required for neutrophil adhesion, were evaluated.
The respective role of TNF-α and ICAM-1 in neutrophil adhesion to BE- AS-2B cells was then evaluated by inhibition of their activity by specific monoclonal antibodies (mAbs). 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 myeloperoxidase (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. 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.

What is already known about this topic? Non-typeable Haemophilus influenzae (NTHi) airway infection is characterized by a sustained neutrophilic inflammation leading to parenchymal lung damage. Bronchial epithelial cells exposed to NTHi lysate promoted a powerful neutrophil recruitment and activation with a positive feedback loop. What does this article add to our knowledge? This in vitro study evaluates the mechanisms leading to the powerful neutrophil recruitment and activation and to the promotion, through a feedback loop, of a vicious circle with detriments results. How does this study impact current management guidelines? To prevent this vicious circle, in clinical practice, NTHi infections should be treated with a high dosage antibiotic to which NTHi is susceptible and for a suitable period.


Received: Nov 23, 2023
Accepted: Jan 23, 2024
Published: June 1, 2024

Table of Contents: Vol. 2, n. 2, June 2024

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