Poly-γ-glutamic acid (γ-PGA) is an anionic polypeptide synthesized and secreted by Bacillus species. In γ-PGA, d- and/or l-glutamate is polymerized via γ-amide linkages formed between the α-amino and γ-carboxylic acid functional groups23. We had previously reported the activation of TLR4 signaling pathway by γ-PGA, leading to the production of type I interferon (IFN) (α and β)6. In vitro, γ-PGA displays antiviral activity against severe acute respiratory syndrome coronavirus and hepatitis C virus6. In norovirus-infected cells, IFN-α/β production is initiated by the sensing of viral RNA genome via the cytoplasmic PRR MDA5 (melanoma differentiation-associated gene 5) and TLR3, followed by phosphorylation of IFN regulatory factor 3 (IRF-3) through two independent pathways24. This type I IFN signaling plays a major role in clearing mouse norovirus24–26 and HuNoV27,28.