Influenza A virus (IAV) continues to pose a significant global health threat, causing severe respiratory infections that result in substantial annual morbidity and mortality. Recent research highlights the pivotal role of innate immunity, cell death, and inflammation in exacerbating the severity of respiratory viral diseases. One key molecule in this process is ZBP1, a well-recognized innate immune sensor for IAV infection. Upon activation, ZBP1 triggers the formation of a PANoptosome complex containing ASC, caspase-8, and RIPK3, among other molecules, leading to inflammatory cell death, PANoptosis, and NLRP3 inflammasome activation for the maturation of IL-1β and IL-18. However, the role for other molecules in this process requires further evaluation. In this study, we investigated the role of MLKL in regulating IAV-induced cell death and NLRP3 inflammasome activation. Our data indicate IAV induced inflammatory cell death through the ZBP1-PANoptosome, where caspases and RIPKs serve as core components. However, IAV-induced lytic cell death was only partially dependent on RIPK3 at later timepoints and was fully independent of MLKL throughout all timepoints tested. Additionally, NLRP3 inflammasome activation was unaffected in MLKL-deficient cells, establishing that MLKL and MLKL-dependent necroptosis do not act upstream of NLRP3 inflammasome activation, IL-1β maturation, and lytic cell death during IAV infection.
Keywords: IAV; MLKL; NLRP3; PANoptosis; RIPK3; apoptosis; caspase; cell death; executioner; gasdermin; inflammasome; necroptosis; pyroptosis.