Interferon-λ1 and viral wheeze in asthma: a Gothic duality?

The Role of Interferons in Driving Susceptibility to Asthma Following Bronchiolitis: Controversies and Research Gaps

Bronchiolitis is the most common cause of hospitalization in infancy and is associated with a higher risk for the development of childhood asthma. However, not all children hospitalized with bronchiolitis will develop asthma. The mechanisms underlying asthma development following bronchiolitis hospitalization are complex. Immune responses to respiratory viruses may underlie both bronchiolitis severity and long-term sequela (such as asthma). Interferons (IFNs) are important components of innate immune responses to respiratory viruses and could influence both asthma development and asthma exacerbations. However, the nature of the relationship between interferon production and wheezing illnesses is controversial. For example, low peripheral blood IFN responses at birth have been linked with recurrent wheeze and asthma development. In contrast, there is evidence that severe illnesses (e.g., hospitalization for bronchiolitis) are associated with increased IFN responses during acute infection (bronchiolitis hospitalization) and a higher risk for subsequent asthma diagnosis. Furthermore, mechanistic studies suggest that bronchial epithelial cells from asthmatic children have impaired IFN responses to respiratory viruses, which may enable increased viral replication followed by exaggerated secondary IFN responses. This review aims to discuss controversies around the role of IFNs as drivers of susceptibility to asthma development following bronchiolitis hospitalization. Past evidence from both mechanistic and cohort studies are discussed. We will highlight knowledge gaps that can inform future research study design.

Virus/Allergen Interaction in Asthma Exacerbation

Allergy and viral respiratory infections have long been recognized as two of the most important risk factors for exacerbations of asthma. These observations have raised questions regarding potential interactions between these two important risk factors. For example, does allergy diminish the antiviral response, thereby promoting exacerbations of asthma? Alternately, do viral respiratory infections potentiate ongoing allergic inflammation in the airway? The answers to these questions are likely to have implications regarding the prevention and treatment of exacerbations of asthma. This article reviews that clinical evidence linking viral infections and allergy to exacerbations of asthma, reviews potential interactions between these two risk factors, and discusses possible application of new insights in virus/allergen interactions to the prevention and treatment of exacerbations of asthma.

Effects of rhinovirus species on viral replication and cytokine production

BACKGROUND

Epidemiologic studies provide evidence of differential virulence of rhinovirus species (RV). We recently reported that RV-A and RV-C induced more severe illnesses than RV-B, which suggests that the biology of RV-B might be different from RV-A or RV-C.

OBJECTIVE

To test the hypothesis that RV-B has lower replication and induces lesser cytokine responses than RV-A or RV-C.

METHODS

We cloned full-length cDNA of RV-A16, A36, B52, B72, C2, C15, and C41 from clinical samples and grew clinical isolates of RV-A7 and RV-B6 in cultured cells. Sinus epithelial cells were differentiated at the air-liquid interface. We tested for differences in viral replication in epithelial cells after infection with purified viruses (10(8) RNA copies) and measured virus load by quantitative RT-PCR. We measured lactate dehydrogenase (LDH) concentration as a marker of cellular cytotoxicity, and cytokine and/or chemokine secretion by multiplex ELISA.

RESULTS

At 24 hours after infection, the virus load of RV-B (RV-B52, RV-B72, or RV-B6) in adherent cells was lower than that of RV-A or RV-C. The growth kinetics of infection indicated that RV-B types replicate more slowly. Furthermore, RV-B released less LDH than RV-A or RV-C, and induced lower levels of cytokines and chemokines such as CXCL10, even after correction for viral replication. RV-B replicates to lower levels also in primary bronchial epithelial cells.

CONCLUSIONS

Our results indicate that RV-B types have lower and slower replication, and lower cellular cytotoxicity and cytokine and/or chemokine production compared with RV-A or RV-C. These characteristics may contribute to reduced severity of illnesses that has been observed with RV-B infections.

Rhinovirus and dsRNA induce RIG-I-like receptors and expression of interferon β and λ1 in human bronchial smooth muscle cells

Rhinovirus (RV) infections cause exacerbations and development of severe asthma highlighting the importance of antiviral interferon (IFN) defence by airway cells. Little is known about bronchial smooth muscle cell (BSMC) production of IFNs and whether BSMCs have dsRNA-sensing receptors besides TLR3. dsRNA is a rhinoviral replication intermediate and necrotic cell effect mimic that mediates innate immune responses in bronchial epithelial cells. We have explored dsRNA-evoked IFN-β and IFN-λ1 production in human BSMCs and potential involvement of TLR3 and RIG-I-like receptors (RLRs). Primary BSMCs were stimulated with 0.1-10 µg/ml dsRNA, 0.1-1 µg/ml dsRNA in complex with the transfection agent LyoVec (dsRNA/LyoVec; selectively activating cytosolic RLRs) or infected with 0.05-0.5 MOI RV1B. Both dsRNA stimuli evoked early (3 h), concentration-dependent IFN-β and IFN-λ1 mRNA expression, which with dsRNA/LyoVec was much greater, and with dsRNA was much less, after 24 h. The effects were inhibited by dexamethasone. Further, dsRNA and dsRNA/LyoVec concentration-dependently upregulated RIG-I and MDA5 mRNA and protein. dsRNA and particularly dsRNA/LyoVec caused IFN-β and IFN-λ1 protein production (24 h). dsRNA- but not dsRNA/LyoVec-induced IFN expression was partly inhibited by chloroquine that suppresses endosomal TLR3 activation. RV1B dose-dependently increased BSMC expression of RIG-I, MDA5, IFN-β, and IFN-λ1 mRNA. We suggest that BSMCs express functional RLRs and that both RLRs and TLR3 are involved in viral stimulus-induced BSMC expression of IFN-β and IFN-λ1.