Figure 3
Plaque morphologies of the live-attenuated viruses in CEK cell at different temperatures. Confluent CEK cells in six-well plates were infected with 2mH7N2:6WF10att or 2H7N2:6WF10att. The numbers 10-6, 10-5, and 10-3 on the plaque pictures indicate the virus dilution used to infect cells at the indicated temperature. The cells incubated at 37°C, 39°C, or 41°C, respectively, for 4 days post infection and then fixed and the viral antigen was visualized by immunostaining as described in Materials and Methods. The plaques sizes were observed and the plaque numbers were counted and calculated as the log10 PFU/ml, as indicated below the individual plaque picture. A titer of <3.0 log10 PFU/ml indicates that no virus was detected at 10-3 dilution.