Exposure to common respiratory bacteria alters the airway epithelial response to subsequent viral infection

Background

Colonization of the airways with potential pathogenic bacteria is observed in a number of chronic respiratory diseases, such as COPD or cystic fibrosis. Infections with respiratory viruses are known triggers of exacerbations of these diseases. We here investigated if pre-exposure to bacteria alters the response of lung epithelial cells to subsequent viral infection.

Methods

Bronchial epithelial cells (BEAS-2B cells and primary bronchial epithelial cells) were exposed to heat-inactivated Haemophilus influenzae, Pseudomonas aeruginosa or Streptococcus pneumoniae and subsequently infected with respiratory syncytial virus (RSV), type 2 human adenovirus or influenza B. Levels of pro-inflammatory cytokines, viral replication and expression of pattern recognition receptors were determined in culture supernatants and/or cell lysates.

Results

Exposure of BEAS-2B cells to H. influenzae before and during RSV-infection synergistically increased the release of IL-6 (increase above calculated additive effect at 72 h: 56 % ± 3 %, mean ± SEM) and IL-8 (53 % ± 12 %). This effect was sustained even when bacteria were washed away before viral infection and was neither associated with enhanced viral replication, nor linked to increased expression of key pattern recognition receptors. P. aeruginosa enhanced the release of inflammatory cytokines to a similar extent, yet only if bacteria were also present during viral infection. S. pneumoniae did not enhance RSV-induced cytokine release. Surprisingly, adenovirus infection significantly reduced IL-6 release in cells exposed to either of the three tested bacterial strains by on average more than 50 %. Infection with influenza B on the other hand did not affect cytokine production in BEAS-2B cells exposed to the different bacterial strains.

Conclusion

Pre-exposure of epithelial cells to bacteria alters the response to subsequent viral infection depending on the types of pathogen involved. These findings highlight the complexity of microbiome interactions in the airways, possibly contributing to the susceptibility to exacerbations and the natural course of airway diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0382-z) contains supplementary material, which is available to authorized users.

Advances in the prevention, management, and treatment of community-acquired pneumonia

Community-acquired pneumonia (CAP) is the infectious disease with the highest number of deaths worldwide. Nevertheless, its importance is often underestimated. Large cohorts of patients with CAP have been established worldwide and improved our knowledge about CAP by far. Therefore, current guidelines are much more evidence-based than ever before. This article discusses recent major studies and concepts on CAP such as the role of biomarkers, appropriate risk stratification to identify patients in need of hospitalisation or intensive care, appropriate empiric antibiotic therapy (including the impact of macrolide combination therapy and antibiotic stewardship), and CAP prevention with novel influenza and pneumococcal vaccines.

Efficacy of IFN-λ1 to protect human airway epithelial cells against human rhinovirus 1B infection

Impaired interferon (IFN) production has been observed in various obstructive respiratory diseases. This contributes to enhanced sensitivity towards viral infections triggering acute exacerbations. To compensate for this impaired host IFN response, there is need to explore new therapeutic strategies, like exogenous administration of IFNs as prophylactic treatment. In the present study, we examined the protective potential of IFN-λ1 and compared it with the previously established protecting effect of IFN-β. A549 cells and human primary bronchial epithelial cells were first treated with either IFN-β (500 IU/ml) or IFN-λ1 (500 ng/ml) for 18 h. For infection, two approaches were adopted: i) Continuous scenario: after pre-treatment, cells were infected immediately for 24 h with human rhinovirus 1B (HRV1B) in IFN-containing medium, or were cultured for another 72 h in IFN-containing medium, and then infected for 24 h with HRV1B, ii) Pre-treatment scenario: IFN-containing medium was replaced after 18 h and cells were infected for 4 h either immediately after pre-treatment or after additional culturing for 72 h in IFN-free medium. The protective effect was evaluated in terms of reduction in the number of viral copies/infectious progeny, and enhanced expression of IFN-stimulated genes (ISGs). In both cell types and in both approaches, IFN-λ1 and IFN-β treatment resulted in pronounced and long-lasting antiviral effects exemplified by significantly reduced viral copy numbers and diminished infectious progeny. This was associated with strong up-regulation of multiple ISGs. However, in contrast to the IFN-β induced expression of ISGs, which decreased over time, expression of ISGs induced by IFN-λ1 was sustained or even increased over time. Here we demonstrate that the protective potential of IFN-λ1 is comparable to IFN-β. Yet, the long-lasting induction of ISGs by IFN-λ1 and most likely less incitement of side effects due to more localized expression of its receptors could make it an even more promising candidate for prophylactic treatment than IFN-β.

The host immune response contributes to Haemophilus influenzae virulence

BACKGROUND

There is compelling evidence that infections with non-typeable Haemophilus influenzae (NTHi) are associated with exacerbations in COPD patients. However, NTHi has also been isolated frequently during clinically stable disease. In this study we tested the hypothesis that genetically distinct NTHi isolates obtained from COPD patients differ in virulence which could account for dissimilarities in the final outcome of an infection (stable vs. exacerbation).

RESULTS

NTHi isolates (n = 32) were obtained from stable COPD patients, or during exacerbations. Genetically divergent NTHi isolates were selected and induction of inflammation was assessed as an indicator of virulence using different in vitro models. Despite marked genomic differences among NTHi isolates, in vitro studies could not distinguish between NTHi isolates based on their inflammatory capacities. Alternatively, when using a whole blood assay results demonstrated marked inter-, but not intra-individual differences in cytokine release between healthy volunteers irrespective of the origin of the NTHi isolate used.

CONCLUSION

Results suggest that the individual immune reactivity might be an important predictor for the clinical outcome (exacerbation vs. no exacerbation) following NTHi infection.