Late response of bronchial epithelium to rhinovirus in severe asthma

Introduction

Alteration of bronchial epithelium is one of the main features of severe asthma. Bronchial epithelial cells (BEC) promote airway inflammation and remodeling leading to chronic symptoms and airway hyperresponsiveness and obstruction. Moreover, BEC are the first line in viral infections, which are the major contributor to asthma exacerbation. However, the consequences of the persisting long-term responses to viral infection of BEC in severe asthma are not fully understood. The aim of our study was to investigate the morphological and functional responses of bronchial epithelium induced by human rhinovirus in acute and late phase post-infection in severe asthma in an ALI culture model.

Methods

Primary human bronchial epithelial cells (HBECs) from control (C) (n = 3) and severe asthmatic (SA) (n = 4), cultured in air–liquid interface (ALI), were infected with Rhinovirus A16 (RV-A16) at the apical pole. The virus was removed four hours after infection. Differences in term of viral replication, cytotoxicity (measured by LDH activity), epithelium cohesion (TEER measurement) and antiviral response was assessed at the acute phase (until 4 days) and at the late phase (until 14 days) post-infection (dpi).

Results

RV-A16 replication increased during the acute phase then decreased during the late phase, without difference between control and severe asthmatic. Cytotoxicity was slightly induced by RV-A16 infection only in the acute phase with no difference observed between control and severe asthmatic (fold induction compared to MOCK: 10.4 and 11.7 for C and SA respectively at 4 dpi). Epithelium cohesion is damaged by RV-A16 in severe asthmatics at the late phase whereas it is strengthened in controls (Fold induction compared to MOCK: 1.12 and 0.62 for C and SA respectively at 14 dpi). RV-A16 induced secretion of several antiviral defense peptides (IFNλ2-3, IFNλ1, IFNβ, IFNα2) and inflammatory mediators (CCL5, CXCL10, IL 33, TSLP) over the first week post-infection, with different kinetic and intensities between control and severe asthmatic. IL-33 and TSLP secretion is significantly more induced in severe asthmatic than in control (P < 0.05). Antiviral and proinflammatory mediator's secretion returns to baseline at 14 dpi in both severe asthmatics and controls, but declines more rapidly in severe asthmatics.

Conclusion

The antiviral response is different in terms of profile and intensity between control and severe asthmatic, both in the acute and late phases. The virus induces alteration of epithelium cohesion in severe asthmatics, suggesting a defect in cellular events normally induced by injury. Then, an altered response of HBECs in severe asthma, illustrated by the increased secretion of epithelial alarmins IL-33 and TSLP, could contribute to increased disease susceptibility and an enhanced inflammatory response to rhinovirus infection.