Furthermore, treatment with 100 nM γ-PGA resulted in a 98% decrease in plaque titer and significantly reduced the level of VP1, a viral structural protein (Fig. 1d). The antiviral potency of 2,000-kDa γ-PGA was comparable to that of 17-DMAG (Supplementary Fig. 1, mean 50% effective concentration of 17-DMAG: 35 nM), an Hsp90 inhibitor that has been recently shown to be effective in controlling MNV infection32. The antiviral activity of 2,000-kDa γ-PGA was not attenuated by co-treatment with 500-kDa γ-PGA at 100 nM or 500 nM, suggesting the importance of molecular mass or a specific structure formed by 2,000-kDa γ-PGA for the activation of TLR4 signaling.