Innate immunity plays an important role during NTHI and RV sequential infection

Abstract

Background: Approximate 10% of people with asthma have a neutrophilic disease, characterized by severe symptoms and poor responsiveness to corticosteroids. Non-typeable Haemophilus influenzae (NTHI) is the most common lower respiratory tract bacterial pathogen in neutrophilic asthma, whilst rhinoviruses (RV) are the predominant precipitant of acute exacerbations. Long-term azithromycin (AZM) reduces exacerbations and improves the quality of life in uncontrolled severe asthma, but the mechanisms are still uncertain. In this study, we established a sequential infection model to mimic this situation in patients in vitro.

Objective: To elucidate underlying mechanisms of AZM during bacterial-viral co-infection.

Methods: BEAS-2B cells were infected with NTHI398 (AZM-sensitive strain) and NTHI398/T34 (AZM-resistant strain) for several hours, then treated with AZM, before introducing co-infection with RV16 and RV1B. Bacterial loads were determined by using CFU counting assay, and viral loads were measured by TCID50 assay and qPCR.

Results: 1. Eradication of NTHI398 by Azithromycin was dose-dependent. A higher concentration of AZM significantly reduced the abundance of the resistant strain NTHi398/T34. 2. NTHI398 and NTHI398/T34 promoted RV16 and RV1B infection. 3. Higher concentration of AZM inhibited RV replication irrespective of NTHi infection. 4. NTHI infection significantly reduced epithelial cell ifn-β mRNA expression compared to uninfected cells and AZM can restore the level of ifn-β mRNA expression.

Conclusion: NTHI infection suppressed innate epithelial cell immunity, which enhances susceptibility to RV infection in vitro. The antiviral immunomodulatory role of AZM in airway epithelium was identified.