Background: Viruses play an important role in asthma exacerbations and are detected by Toll-like receptors (TLRs). Better characterization of mucosal innate immunity to viral triggers may help understand dysregulated host responses in asthma.

Aims & Objectives: A synthetic analogue of single-stranded RNA (ssRNA) and TLR7/8 agonist resiquimod (R848) was administered in vivo to study the effect of allergy and asthma on nasal mucosal innate immune responses.

Methods: Nasal spray with saline and R848 was administered to healthy non-allergic (n=12), allergic rhinitis (n=12) and allergic asthma (n=11) participants. Immune mediators from nasal and blood samples, nasal mucosal gene expression and peripheral differential cell counts were measured.

Results: R848 was well tolerated with no evidence of systemic immune activation. R848 significantly induced nasal mucosal IFN-a2a, IFN-?, pro-inflammatory cytokines (TNF-a, IL-2, IL-12p70) and chemokines (CXCL10, CCL2, CCL3, CCL4 and CCL13) compared to saline. Participants with allergic rhinitis and asthma had increased IFN-a2a, CCL3 and CCL13 relative to healthy participants, whilst those with asthma alone had increased gene expression of interferon stimulated genes DDX58, MX1 and IFIT3. Nasal R848 administration was associated with a decrease in blood eosinophils at 4h and decrease in peripheral lymphocytes at 24h, a finding restricted to participants with allergic rhinitis and asthma.

Conclusions: These results confirm the suitability of nasal delivery of R848 as a non-invasive tool to assess mucosal innate immunity and highlights a key role for asthma in determining host responses to viral RNA analogues.