FIG. 1.
Growth properties of recombinant influenza viruses expressing core proteins derived from the avian MZ or human P908 influenza virus isolate in the WSN background. (A) Growth curves of the parental P908 and reassortant P908-WSN viruses on MDCK cells. Cell monolayers were infected at an MOI of 0.001 and incubated for 72 h at 37, 35, or 33°C. At the indicated time points, the supernatants were harvested, and virus titers were determined by plaque assays on MDCK cells. (B) Growth curves of the parental MZ and reassortant MZ-WSN viruses on MDCK cells. Experimental conditions were as described in panel A, except that virus titers were determined on QT6 cells. (C to F) Plaque phenotype of the P908 and reassortant P908-WSN viruses (C and E) or MZ and reassortant MZ-WSN viruses (D and F) assayed on MDCK or QT6 cells, as described in Materials and Methods. Cell monolayers were stained with crystal violet after 72 h of incubation at 37 or 33°C. Representative data are shown. The dilutions of the viral stock used for infection are indicated.