λ-Carrageenan regulates antiviral responses by targeting classical NF-κB and IRF3-mediated signaling pathways

λ-Carrageenan (λ-CGN) has attracted attention for its biological activities, such as anticoagulant, antitumor, and pro-inflammatory effects. Here, we explored the function of λ-CGN in modulating innate immune responses. Our study showed that λ-CGN inhibited the infection by various viruses. Mechanistically, λ-CGN mediated inflammatory responses by activating classical NF-κB signaling. Importantly, λ-CGN attenuated K48 ubiquitination of IRF3, thereby promoting IRF3 protein stability and activating IRF3-mediated type I IFN responses. Furthermore, orally administered λ-CGN attenuated the pathogenicity of PRV and VSV in mice. These results demonstrate a novel mechanism by which λ-CGN modulates immune responses and support λ-CGN as a potential antiviral drug.