FIG 1.

Growth characteristics of YN200 and DR13 with or without trypsin. (A) Vero cells were infected with YN200 or DR13 at an MOI of 0.01 in the presence or absence of trypsin. Infected cells were fixed at 12 h or 24 h postinfection and were then detected by immunofluorescence staining against the nucleocapsid protein (green). Nuclei were stained with DAPI (blue). Bars, 200 μm. (B) The numbers of nuclei per syncytium were determined and are displayed in the scatter plot. Statistical significance was assessed by an unpaired one-tailed Student t test. (C) Cells were stained with hematoxylin and eosin at 18 h postinfection. Bars, 20 μm. (D and E) Growth kinetics of YN200 (D) and DR13 (E) in Vero cells at an MOI of 0.01. The supernatant was harvested at 6, 12, 18, 24, 36, 48, 60, and 72 h postinfection and was titrated on Vero cells. Three replicates were performed. Error bars represent means ± standard deviations. Asterisks indicate significant differences (*, P < 0.05; ***, P < 0.001); ns, not significant.