Rationale: Allergic asthma is linked to impaired bronchial epithelial secretion of IFNs, which may be causally linked to the increased risk of viral exacerbations. We have previously shown that allergen immunotherapy (AIT) effectively reduces asthma exacerbations and prevents respiratory infections requiring antibiotics; however, whether AIT alters antiviral immunity is still unknown. Objectives: To investigate the effect of house dust mite sublingual AIT (HDM-SLIT) on bronchial epithelial antiviral and inflammatory responses in patients with allergic asthma. Methods: In this double-blind, randomized controlled trial (VITAL [The Effect of Allergen Immunotherapy on Anti-viral Immunity in Patients with Allergic Asthma]), adult patients with HDM allergic asthma received HDM-SLIT 12-SQ or placebo for 24 weeks. Bronchoscopy was performed at baseline and at Week 24, which included sampling for human bronchial epithelial cells. Human bronchial epithelial cells were cultured at baseline and at Week 24 and stimulated with the viral mimic polyinosinic:polycytidylic acid (poly(I:C)). mRNA expression was quantified using qRT-PCR, and protein concentrations were measured using multiplex ELISA. Measurements and Main Results: Thirty-nine patients were randomized to HDM-SLIT (n = 20) or placebo (n = 19). HDM-SLIT resulted in increased polyinosinic:polycytidylic acid–induced expression of IFN-β at both the gene (P = 0.009) and protein (P = 0.02) levels. IFN-λ gene expression was also increased (P = 0.03), whereas IL-33 tended to be decreased (P = 0.09). On the other hand, proinflammatory cytokines IL-6 (P = 0.009) and TNF-α (tumor necrosis factor-α) (P = 0.08) increased compared with baseline in the HDM-SLIT group. There were no significant changes in TSLP (thymic stromal lymphopoietin), IL-4, IL-13, and IL-10. Conclusions: HDM-SLIT improves bronchial epithelial antiviral resistance to viral infection. These results potentially explain the efficacy of HDM-SLIT in reducing exacerbations in allergic asthma. Clinical trial registered with www.clinicaltrials.gov (NCT 04100902).

Background: Asthma is characterised by an aggravated immune response to respiratory viral infections. This phenomenon is a clinically well-recognised driver of acute exacerbations, but how different phenotypes of asthma respond immunologically to viruses is unclear.Objectives: To describe the association between different phenotypes and severity of asthma and bronchial epithelial immune responses to viral stimulation.Methods: In the Immunoreact study, healthy subjects (n=10) and 50 patients with asthma were included; 30 (60%) were atopic, and 34 (68%) were eosinophilic; 14 (28%) had severe asthma. All participants underwent bronchoscopy with collection of bronchial brushings. Bronchial epithelial cells (BECs) were expanded and stimulated with the viral replication mimic poly (I:C) (Toll-like receptor (TLR)3 agonist)in vitro. The expression of TLR3-induced pro-inflammatory and antiviral responses of BECs were analysed using reverse transcriptase quantitative PCR and multiplex ELISA and compared across asthma phenotypes and severity of disease.Results: Patients with atopic asthma had increased induction of interleukin (IL)-4, interferon (IFN)-β, IL-6, tumour necrosis factor-α, and IL-1β after poly (I:C) stimulation compared to non-atopic patients, whereas in patients with eosinophilic asthma only IL-6 and IL-8 induction was higher than in non-eosinophilic asthma. Patients with severe asthma displayed a decreased antiviral IFN-β, and increased expression of IL-8, most pronounced in atopic and eosinophilic asthmatics. Furthermore, induction of IL-33 in response to poly (I:C) was increased in severe atopic and in severe eosinophilic asthma, but thymic stromal lymphopoietin only in severe eosinophilic asthma.Conclusions: The bronchial epithelial immune response to a viral mimic stimulation differs between asthma phenotypes and severities, which may be important to consider when targeting novel asthma treatments.

Introduction: Allergen exposure worsens viral‐triggered asthma exacerbations and could predispose the host to secondary bacterial infections. We have previously demonstrated that exposure to house dust mite (HDM) reduced TLR‐3‐induced IFN‐β in human bronchial epithelial cells (HBECs) from healthy donors. We hypothesize that HDM sensitization in different ways may be involved in both viral and bacterial resistance of HBECs in asthma. In this study, the role of HDM sensitization and effects of HDM exposure on viral stimulus‐challenged HBECs from asthmatic donors have been explored with regard to expression and release of molecules involved in anti‐viral and anti‐bacterial responses, respectively.Methods: HBECs from HDM‐sensitized (HDM+) and unsensitized (HDM‐) patients with asthma were used. HBECs were exposed to HDM or heat inactivated (hi)‐HDM (20 μg/ml) for 24 h prior to stimulation with the viral infection mimic, Poly(I:C), for 3 or 24 h. Samples were analyzed with ELISA and RT‐qPCR for β‐defensin‐2, IFN‐β, TSLP, and neutrophil‐recruiting mediators: IL‐8 and TNF‐⍺. NFκB signaling proteins p105, p65, and IκB‐⍺ were analyzed by Western blot.Results: Poly(I:C)‐induced IFN‐β expression was reduced in HBECs from HDM + compared to HDM‐ patients (p = 0.05). In vitro exposure of HBECs to HDM furthermore reduced anti‐microbial responses to Poly(I:C) including β‐defensin‐2, IL‐8, and TNF‐⍺, along with reduced NFκB activity. This was observed in HBECs from asthma patients sensitized to HDM, as well as in non‐sensitized patients. By contrast, Poly (I:C)‐induced release of TSLP, a driver of T2 inflammation, was not reduced with exposure to HDM.Conclusion: Using HBECs challenged with viral infection mimic, Poly(I:C), we demonstrated that allergic sensitization to HDM was associated with impaired anti‐viral immunity and that HDM exposure reduced anti‐viral and anti‐bacterial defense molecules, but not TSLP, across non‐allergic as well as allergic asthma. These data suggest a role of HDM in the pathogenesis of asthma exacerbations evoked by viral infections including sequential viral‐bacterial and viral‐viral infections.