No substantial differences in the plaque sizes and morphologies were detected among ZH501, rZH501-M847-G and rZH501-M847-A in both Vero cells and MRC-5 cells (data not shown). ZH501, rZH501-M847-G and rZH501-M847-A showed similar replication kinetics in VeroE6 cells, mouse 3T3 cells and mouse macrophage-derived J774.1 cells (Fig. 2) , while titers of rZH501-M847-G were roughly 10 times higher than those of rZH501-M847-A in human lung fibroblast MRC-5 cells from 24 h to 72 h p.i. (Fig. 2) . Also there was a trend that CPE induced by rZH501-M847-A was less prominent CPE than that induced by rZH501-M847-G or ZH501 at a given time in all four cell lines (Fig. 2) . Unpaired-t-tests of three independent experiments examining the replication kinetics of rZH501-M847-G and rZH501-M847-A in MRC-5 cells from 0 h to 72 h p.i. revealed that the titer of rZH501-M847-G was a significantly higher (P,0.01) than that of rZH501-M847-A at 72 h p.i. (Fig. S1 ).