Paradoxical modulation of influenza by intranasal administration of non-replicating adenovirus particles

Respiratory mucosal infection by airborne microbes is a common event that occurs every day. We report here that intranasal administration of non-replicating adenovirus (Ad) particles to mice could either confer rapid protection against influenza virus (IFV) challenge independent of adaptive immunity, or exacerbate influenza by triggering rapid death. The life-or-death outcome hinges on the time interval between Ad administration and IFV challenge in conjunction with specific mouse/IFV strains. Intranasal instillation of Ad particles 1–47 days prior to IFV challenge conferred rapid protection against influenza in Balb/c mice whereas exposure to Ad 39 days prior to challenge with a specific IFV strain or 1 day post-challenge with that IFV strain induced rapid death in C57BL/6 mice. Notably, consecutive administrations of Ad prior to IFV challenge conferred a synergy in triggering a potent anti-influenza state; even a detrimental Ad exposure 39 days before challenge with the deadly IFV strain was reversed to a beneficial one by subsequent Ad boosts. Results revealed an intricate relationship between infection and innate immunity that is a linchpin around which effects revolve from protective immunity to collateral damage. It is urgent to repeat the experiments with an expanded scope for characterizing the status that defines susceptibility or resistance to IFV infection and subsequently reveal the underlying mechanisms. Whether broad heterologous protective effects induced by AdE and adaptive immunity elicited by vaccination could confer synergy during mitigation of a pandemic remains to be seen.