Growth dynamics of parental and reassortant viruses in swine nasal epithelium cells (SNE), swine tracheal epithelium cells (STE), human alveolar basal epithelial cells (A549), chicken embryo fibroblasts (DF-1), and Madin-Darby canine kidney (MDCK) cells.

Cells were infected at a multiplicity of infection of 0.001 TCID50/cell with the indicated parental or reassortant viruses. The nasal wash fluids (N) and tissue sections of the testing genotypes of the reassortant viruses are shown (U, upper respiratory tract; M, middle respiratory tract; L, lower respiratory tract). The origin of each segment for indicated viruses are shown at the top of the columns; red indicates segments from swine H3N2 virus, and blue indicates segments from avian H1N1 virus. Infected cells were incubated at 33°C, 37°C, or 39°C. Growth curves were determined by using the viral titers in the supernatants of infected cells obtained at 12, 24, 48, and 72 h post-inoculation. Data shown represent the mean titers ± standard errors (n = 3 cultures). Significance is noted (*PPP<0.001) where virus titers obtained for a virus at 33°C or 39°C were statistically different from those obtained at 37°C at the same time point.