Lactobacillus salivarius HHuMin-U Activates Innate Immune Defense against Norovirus Infection through TBK1-IRF3 and NF-κB Signaling Pathways

The composition of commensal bacteria plays a critical role in controlling immune responses in the intestine. Studies have shown that specific bacterial strains may have the capacity to enhance host immune defense against gastrointestinal viral infections. While norovirus is known to be the most common cause of gastroenteritis, leading to an estimated 200,000 deaths every year, identification of bacterial strains with protective effects against norovirus infection remains elusive. Here, we discovered Lactobacillus salivarius HHuMin-U (HHuMin-U) as a potent antiviral strain against norovirus infection. HHuMin-U significantly suppressed murine norovirus replication and lowered viral RNA titers in macrophages. The transcriptome sequencing (RNA sequencing) analysis revealed that HHuMin-U markedly enhanced the expression level of antiviral interferon-stimulated genes compared to mock treatment. HHuMin-U treatment dose-dependently induced type I interferons (IFN-α and IFN-β) and tumor necrosis factor-α production in mouse and human macrophages, promoting antiviral innate responses against norovirus infection. Investigation on the molecular mechanism demonstrated that HHuMin-U can activate nuclear factor κB and TANK-binding kinase 1 (TBK1)–interferon regulatory factor 3 signaling pathways, leading to the phosphorylation of signal transducer and activator of transcription 1 and signal transducer and activator of transcription 2, the key mediators of interferon-stimulated genes. Finally, oral administration of HHuMin-U increased IFN-β levels in the ileum of mice and altered the gut microbiome profile. These results suggest the species/strain-specific importance of gut microbial composition for antiviral immune responses and the potential use of HHuMin-U as a probiotic agent.