Influenza virus M2 and PB1-F2 proteins have been proposed to activate the Nodlike receptor family, pyrin domain-containing 3 (NLRP3) inflammasome in macrophages by altering intracellular ionic balance or mitochondrial reactive oxygen species (ROS) production. However, the precise mechanism by which these viral proteins trigger the NLRP3 inflammasome activation remains unclear. Here we show that influenza virus stimulates oxidized DNA release from macrophages. Ion channel activity of the M2 protein or mitochondrial localization of the PB1-F2 protein was required for oxidized DNA release. The oxidized DNA enhanced influenza virus-induced IL-1b secretion, whereas inhibition of mitochondrial ROS production by antioxidant Mito-TEMPO decreased the virus-induced IL-1b secretion. In addition, we show that influenza virus stimulates IL-1b secretion from macrophages in an AIM2-dependent manner. These results provide a missing link between influenza viral proteins and the NLRP3 inflammasome activation and reveal the importance of influenza virus-induced oxidized DNA in inflammasomes activation.Recently, we demonstrated that the ion channel activity of influenza virus M2 protein is essential for mitochondrial DNA (mtDNA) release into the cytosol (Moriyama et al., 2019). In addition, recent studies

Intranasal vaccination induces the nasal IgA antibody which is protective against respiratory viruses, such as influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Therefore, understanding how mucosal immune responses are elicited following viral infection is important for developing better vaccines.

Fever is a common symptom of influenza and coronavirus disease 2019 (COVID-19), yet its physiological role in host resistance to viral infection remains less clear. Here, we demonstrate that exposure of mice to the high ambient temperature of 36 °C increases host resistance to viral pathogens including influenza virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). High heat-exposed mice increase basal body temperature over 38 °C to enable more bile acids production in a gut microbiota-dependent manner. The gut microbiota-derived deoxycholic acid (DCA) and its plasma membrane-bound receptor Takeda G-protein-coupled receptor 5 (TGR5) signaling increase host resistance to influenza virus infection by suppressing virus replication and neutrophil-dependent tissue damage. Furthermore, the DCA and its nuclear farnesoid X receptor (FXR) agonist protect Syrian hamsters from lethal SARS-CoV-2 infection. Moreover, we demonstrate that certain bile acids are reduced in the plasma of COVID-19 patients who develop moderate I/II disease compared with the minor severity of illness group. These findings implicate a mechanism by which virus-induced high fever increases host resistance to influenza virus and SARS-CoV-2 in a gut microbiota-dependent manner.