The outer capsid spike protein Vp55 of grass carp reovirus interacts with host toll-like receptor 2 to modulate the Nf-κb-Tnfα antiviral signaling pathway.

Grass carp reovirus (GCRV) causes hemorrhagic disease and poses a serious threat to the grass carp aquaculture industry in China. The outer capsid spike protein Vp55 of the GCRV-104 strain, similar to its counterparts in other orthoreovirus, is supposed to be involved in viral attachment and cell entry. Here, we identified a peptide that specifically interacts with prokaryotically expressed rVp55 through phage display screening. Bioinformatics analysis indicated that the peptide sequence corresponds to a segment of grass carp Tlr2, a membrane surface receptor that primes proinflammatory cytokine expression upon sensing pathogen-associated molecular patterns. Protein-protein interaction and co-localization assays demonstrated a physical association between Vp55 and Tlr2. Cytokine expression analysis indicated that rVp55 alone is sufficient to suppress the Tlr2/Nf-κb/Tnfα pathway, which is consistent with the downregulated tlr2 signaling observed during the early phase of GCRV-104 infection in GCO cells. Overexpression of tlr2 resulted in reduced viral replication, and a synthesized Vp55-interacting peptide could attenuate the Vp55-Tlr2 interaction through competitive binding, thereby effectively impairing GCRV-104 infection efficiency and inhibiting viral immune evasion. Thus, our study reveals that Vp55 of GCRV-104 acts as an antagonist of the Tlr2-dependent antiviral immune response by targeting Tlr2, suggesting that Tlr2 might serve as a novel host-directed target for developing antivirals against GCRV via blocking the Vp55-Tlr2 interaction.