FIG 2.

Syncytium formation assay at different temperatures. Vero/hSLAM cells were transfected with expression plasmids encoding the wild-type (wt) or mutant F protein with T461I or triple substitutions (S103I/N462S/N465S), together with that encoding the wt H protein. The cells were incubated at 37°C or 25°C. At 24 h (37°C) or 48 h (25°C) posttransfection, the cells were stained with a Giemsa solution and observed under a light microscope. Scale bar, 200 μm. To show the syncytia better, the central rectangle area enclosed in the upper panel is shown below in the lower panel after 3-fold enlargement. –, No syncytium formation; +, syncytium formation.