Extracellular Vesicles Containing MDP Derived from <i>Lactobacillus rhamnosus</i> GG Inhibit HSV‐2 Infection by Activating the NOD2‐IFN‐I Signalling Pathway

The immune evasion strategies and lifelong latency of herpes simplex virus type 2 (HSV-2) present significant challenges for effective treatment. Recent studies have demonstrated that the commensal microbiota plays an important role in regulating immunity against viral infections. We previously reported that Lactobacillus rhamnosus GG (LGG) activates the expression of type I interferons (IFN-I) to inhibit HSV-2 infection. However, the specific molecular mechanisms remain unclear. Bacterial extracellular vesicles (EVs) are small lipid bilayer-bound particles secreted by bacteria, which can serve as intercellular communication vehicles between the host and pathogens, functioning as immunomodulatory vectors defending against viral infections. In this study, we confirmed that LGG-EVs activate the nucleotide-binding oligomerisation domain-containing protein 2 (NOD2)-IFN-I signalling pathway, inducing the expression of interferon-stimulated genes (ISGs) to combat HSV-2 infection both in vivo and in vitro. Furthermore, we explored the specific components within LGG-EVs and identified the presence of muramyl dipeptide (MDP). We demonstrated that MDP-enriched LGG-EVs effectively inhibit HSV-2 infection via activation of the NOD2-IFN-I pathway. These findings suggest that LGG-EVs could serve as a novel therapeutic strategy for HSV-2 and provide a mechanistic foundation for future antiviral research.