A/HK/218449/06 (H3N2) influenza virus induces greater ERK phosphorylation leading to higher virus titers. (A) MDCK cells were infected with either virus at m.o.i. = 1. After Western blot analysis, ERK activation was analyzed with a mAb specific for the phosphorylated kinase (P-ERK). Subsequently, loading was controlled with a mAb against ERK2. Respective bands of three independent experiments were quantified, and relative ERK activation was calculated and normalized to the loading control (mock-infected, white bar). Virus types and the time of analysis post infection (p.i.) are indicated. (B) MDCK cells were infected with either virus at m.o.i. = 1, and the supernatant was harvested at 9 h p.i. to determine the virus titers. The mean virus titers are given as plaque forming units/ml. The error bars were derived from three independent experiments.