Background:
Fatal influenza A virus (IAV) infections in humans, such as those resulting from spill over of from birds, are associated with excessive production of cytokines, including IL-1β. The emergence of novel avian IAV in humans has highlighted the need to identify the molecular mechanisms that drive these excessive immune responses and to identifying new therapeutic interventions. Studies have demonstrated that mice lacking components of the NLRP3 inflammasome are more susceptible to IAV infection, suggesting that it plays a protective role.
Methods:
We utilised the NLRP3 inhibitor MCC950 and a preclinical mouse model of IAV infection. IAV PB1-F2 peptides were also delivered into the lungs of mice.
Results:
We identified the virulence factor PB1-F2 in the avian H7N9 IAV as a potent activator of the NLRP3 inflammasome. H7N9 PB1-F2 peptide derived from H7N9 was a potent inducer of IL-1b secretion. Importantly, IL-1b secretion by macrophages deficient in inflammasome components ASC, Caspase-1 and NLRP3 was ablated. In addition, intranasal treatment of mice with H7N9 PB1-F2 peptide induced leukocyte infiltration and IL-1b secretion into the lung airspaces, which could be therapeutically blunted with MCC950 treatment.
We investigated the role of NLRP3 in modulating disease during IAV infection of mice. Using the NLRP3 inhibitor MCC950, we reveal for the first time that NLRP3 plays a biphasic role in modulating disease. Early intranasal MCC950 treatment rendered mice more susceptible to IAV infection; however, late inhibition of NLRP3 reduced local and systemic inflammation and protected against severe disease. Late treatment was associated with significantly reduced pro-inflammatory cytokines including IL-1β.
Conclusions:
We have identified H7N9 PB1-F2 as a novel inflammasome activator. Our data provides the first evidence that temporally therapeutically targeting the NLRP3 inflammasome may be a clinical option for reducing inflammation associated with pandemic IAV infections.