MLKL-independent RIPK3 signaling alters adaptive immune responses to IAV pneumonia

Abstract

Abstract Necroptosis, a programmed form of lytic cell death, is initiated by various viral and bacterial pathogens as result of irreparable ion dysregulation and energy depletion. This cellular damage results in the activation of the kinases RIPK1 and RIPK3, then the activation and membrane targeting of MLKL, resulting in cell lysis. We demonstrated that necroptosis of airway epithelial cells (AECs) is key in the development of the adaptive immune response to the bacterial pathogen, Streptococcus pneumoniae. Here we examined the role of necroptosis in the generation of an adaptive immune response to influenza A virus (IAV), a pathogen also shown to induce necroptosis of AECs. Wildtype (WT), RIPK3 KO, and MLKL KO mice were challenged intranasally with IAV strain A/Puerto Rico/8/1934 (i.e. PR8). Weight loss was monitored as a measure of disease severity. Compared to WT and MLKL KO, RIPK3 KO mice experienced the most severe weight loss, independent of viral titers, as they were equivalent. The lungs of RIPK3 KO mice showed a significant increase in IAV-specific CD8+ T cells compared to those of WT and MLKL KO. In vitro we observed increased IL-8 production by IAV-infected RIPK3 deficient AECs. IAV-specific germinal center B cells in RIPK3 KO and MLKL KO mice were decreased compared to WT. No differences were observed in IAV specific lymph node and lung regulatory, follicular helper, central, effector, or tissue resident memory T cells. These results suggest fundamental differences in the roles of RIPK3 and MLKL in the development of adaptive immunity against IAV infection. Ongoing studies are focused on determining the contribution of MLKL-independent RIPK3 responses in AECs and immune cells in IAV infection and pathology.