FIG 4.

Growth kinetics of viruses in MDCK cells. Growth curves of CK/1180, CK/1214, and CK/1180-1214HA in MDCK cells infected at multiplicities of infection (MOI) of 0.001 (A) and 5 (B) are shown. Viruses were inoculated into MDCK cells. At the indicated times after infection, virus titers in the supernatant were determined by means of plaque assays. The reported values are means ± SD from two independent experiments. **, P < 0.01 (multiple t tests in GraphPad Prism 6). (C) Viruses were inoculated into MDCK cells at an MOI of 0.001. At the indicated times after infection, the cells were fixed with 4% paraformaldehyde in PBS and then analyzed with an anti-HA antibody in an immunofluorescence assay. (D) Plaque diameters of CK/1180, CK/1214, and CK/1180-1214HA viruses in MDCK cells. Plaque assays were produced under standard conditions and stained with 0.1% crystal violet. The diameters of 50 random plaques were measured for each virus. ***, P < 0.001 (Student's t test).