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Background Asthma was identified as the most common comorbidity in hospitalized patients during the 2009 H1N1 influenza pandemic. We determined using a murine model of allergic asthma whether these mice experienced increased morbidity from pandemic H1N1 (pH1N1) viral infection and whether blockade of interleukin-4 receptor α (IL-4Rα), a critical mediator of Th2 signalling, improved their outcomes. Methods Male BALB/c mice were intranasally sensitized with house dust mite antigen (Der p 1) for 2 weeks; the mice were then inoculated intranasally with a single dose of pandemic H1N1 (pH1N1). The mice were administered intraperitoneally anti-IL-4Rα through either a prophylactic or a therapeutic treatment strategy. Results Infection with pH1N1 of mice sensitized to house dust mite (HDM) led to a 24% loss in weight by day 7 of infection (versus 14% in non-sensitized mice; p Conclusion Together, these data implicate allergic asthma as a significant risk factor for H1N1-related morbidity and reveal a potential therapeutic role for IL-4Rα signalling blockade in reducing the severity of influenza infection in those with allergic airway disease.

Additional file 1: Table E1. Primers used for qPCR assays. Figure E1. Lung Tissue Sectioning. The left lung was cut in a transverse manner to create a superior and an inferior segment. The inferior segment was embedded into paraffin, while the superior segment was further cut in a sagittal manner and embedded. Figure E2. House dust mite (HDM) sensitization delays viral clearance. Phosphate-buffered saline (PBS)-exposed or HDM-sensitized mice were infected with pandemic H1N1 (pH1N1) and sacrificed on days 0, 2, 4, 6, and 8 post-infection. (A) IFN-β protein expression was determined using ELISA on the supernatant of bronchoalveolar lavage fluid (BALF). (B) qPCR was performed on RNA from homogenized lung tissue to determine the number of viral RNA copies, and results were compared using a two-tailed Student’s t-test. Data (n=5 per group per day) were compared using a two-way ANOVA with Sidak’s multiple comparison’s test and are expressed as mean ± SEM. *P