RNA is an Adjuvanticity Mediator for the Lipid-Based Mucosal Adjuvant, Endocine

Natural infections with respiratory viruses such as influenza virus strongly elicit systemic and mucosal immune responses, and these immune responses prevent re-infection. The secretory IgA mucosal antibody in particular has been shown to possess neutralization activity against hetero-subtype viral strains and prevent viral entry into host cells by neutralizing invading viruses at their port of entry1,2. However, parenteral vaccination barely induces a mucosal immune response. Therefore, to improve a vaccine’s ability to prevent viral entry and improve vaccine cross-reactivity by eliciting mucosal immunity, various nasal vaccines have been developed and tested in preclinical or clinical studies3,4, but the exact mechanism of action for most of them (except TLR ligands) is still unknown. Most adjuvants target pathogen recognition receptors (PRRs) such as Toll-like receptors (TLRs), RIG-like receptors, Nod-like receptors (NLRs), C-type lectin receptors (CLRs), AIM2-like receptors (ALRs) or cytoplasmic DNA sensors, and PRR engagement triggers expression of co-stimulatory molecules on antigen presenting cells, inflammatory cytokines and type I interferon (IFN) production via downstream molecules5,6. Furthermore, it has been reported that some adjuvants cause cell damage at the administration site and indirectly activate innate immunity via the damage-associated molecular pattern (DAMP) molecules released from damaged cells. Thus far, various molecules, such as the high-mobility group box 1 (HMGB1), nucleic acids or ATP, have been identified as DAMPs7. Among these DAMPs, ATP and DNA are key molecules for the adjuvanticity of MF59 and alum, respectively8,9. Endocine, a novel mucosal adjuvant consisting of oleic acid and mono-olein, has developed for nasal vaccines and has been shown in animal studies and clinical trials to be robustly immunogenic with the tolerability10,11. However, the mechanism of action of Endocine remains unknown. In this study, we found that DAMPs are likely to be required for the adjuvanticity of Endocine.