Fatal influenza A virus (IAV) infections in humans, such as those resulting from spill over of from birds, are associated with excessive inflammation. The emergence of novel avian IAV in humans has highlighted the need to identify the molecular mechanisms that drive hyperinflammation and to identifying new therapeutic interventions. The NLRP3 inflammasome is a protein complex which is activated during infection resulting in the secretion of the potent pro-inflammatory cytokine IL-1β. Studies have demonstrated that mice lacking components of the NLRP3 inflammasome are more susceptible to IAV infection. However, fatal infections in humans are associated with the production of high levels of IL-1β in the airways.
We identified the virulence factor PB1-F2 in the avian H7N9 IAV as a potent activator of the NLRP3 inflammasome. H7N9 PB1-F2 peptide induced IL-1β secretion in vitro in a NLRP3/caspase-1-dependent manner. Importantly, PB1-F2 peptides from seasonal strains of IAV were not found to activate NLRP3. Intranasal treatment of mice with H7N9 PB1-F2 peptide induced leukocyte infiltration and IL-1β secretion, which could be therapeutically blunted with the NLRP3 inhibitor MCC950.
We have investigated the role of NLRP3 in modulating disease during IAV infection. Using the NLRP3 inhibitor MCC950, we revealed that the 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 production. We are extending our study to examine the therapeutic potential of other inhibitors which could be repurposed to modulate NLRP3 responses during IAV infections.
Overall, H7N9 PB1-F2 is as a novel inflammasome activator which drives hyperinflammation. Our data provides evidence that therapeutically targeting the NLRP3 inflammasome may be a clinical option for reducing inflammation associated with severe IAV infections.