*3.3. The Anti-PRRSV Ability of Rg1 Treatment Was E*ff*ective in Marc-145 Cells and PAMs Infected with the HP-PRRSV, NADC30-Like and Classical Strains*

In view of the high genetic variation among strains of type 2 PRRSV, we tested whether Rg1 possesses antiviral activity against broad lineages of strains. The antiviral effects of Rg1 against PRRSV strains, including JXA1 (HP-PRRSV; lineage 8.7), XH-GD (HP-PRRSV; lineage 8.7), VR2332 (classical strain; lineage 5.1) and HNLY (NADC30-like strain, lineage 1), in Marc-145 cells were examined by IFA and EC50. As shown in Figure 3A, the four lineages of PRRSV infection in Marc-145 cells were significantly inhibited by Rg1 in a dose-dependent manner. Therefore, EC50 of Rg1 against JXA1, XH-GD, HNLY and VR2332 infection in Marc-145 cells was calculated respectively. Results indicate that the values vary significantly, ranging from 55.05 to 94.21 μM among the four PRRSV strains by analyzing infection rate from IFA images (Table 2). To evaluate the inhibition effect of Rg1 on virus replication of four PRRSV, the growth curves of these strains were generated in Marc-145 cells. The results indicate that the inhibitory effect of Rg1 on the production of progeny virus is mainly seen at the plateau phase, and the antiviral activity is most obvious at 50 μM in all four PRRSV strains (Figure 3B). Moreover, the growth curves of the four PRRSV strains treated with Rg1 was further determined in PAMs, and the results display a similar decreasing trend (Figure 3C). These data indicate that Rg1 possesses an inhibitory effect on PRRSV infection and that this effect is observed in a broad range of PRRSV lineages.



<sup>a</sup> the concentration required to protect 50% cells from PRRSV infection by counting cells from IFA images.
