Growth properties of A/HK/218847/06 (H1N1) and A/HK/218449/06 (H3N2) influenza viruses. (A) MDCK cells were infected with either H1N1 virus (blue line) or H2N3 virus (red line) at m.o.i. = 2. The growth curve is based on virus titers at the indicated time points after infection. The mean virus titers are given as log10 plaque forming units/ml. The error bars were derived from three independent experiments. (B) Plaque formation after virus titration on MDCK cells. The virus-containing supernatant from cells infected at m.o.i. = 1 was harvested 9 h after infection. (C) MDCK cells were infected with either virus at m.o.i. = 1. The percentage of NP-expressing cells was measured by flow cytometry (FACS) using anti-NP mAb. The error bars were derived from three independent experiments.