Background: Recurrent human rhinovirus infection in early life is associated with asthma development. We hypothesized that repetitive HRV infection increases susceptibility to asthma by inducing an aberrantly amplified innate immune response in airway epithelial cells.

Methods: Primary normal human bronchial epithelial cells were cultured at the air?liquid interface. They were infected with HRV-16 three times, twice or once, and then exposed to IL-13. At the end of the experiment, inflammatory factors were measured at gene and protein levels by RT-PCR and MSD U-PLEX Platform, respectively. Genome-wide DNA methylation was quantified using Illumina MethylationEPIC BeadChip.

Results: Pre-infected cells (three-times/twice/once) had an enhanced expression of RIG-1 and IL-8 genes in response to IL-13 exposure, in comparison with non-infected ones. IL-13 exposure significantly enhanced IL-4 expression by ~2.5 fold in non-infected and pre-infected cells, compared to controls (p<0.05-0.01). In line with this, pre-infected cells (especially three-times infection) released more inflammatory mediators including IL-4 (p<0.05), IL-5 (p<0.01-0.001), IFN-?1, IL-8 and IP-10 following IL-13 exposure, in comparison with non-infected ones. Additionally, preliminary methylation results indicate distinctive methylation patterns between the groups, that is, IL-13 exposure compared to co-stimulation of IL-13 and viral infection (three-times/twice/once).

Conclusion: The results indicate that recurrent HRV-16 infection of airway epithelium could pave the way to exacerbate IL-13-induced inflammation; whether DNA methylation plays a role requires further investigation.