Replication of H1 and H3 viruses in nocodazole-treated cells. MDCK (A) and A549 (B) cells were infected with A/WSN/1933 (H1N1), A/CA/O7/2009 (H1N1), and A/Perth/16/2009 (H3N2) viruses at an MOI of 0.01. Cells were treated with DMSO or nocodazole (5 μg/ml) at 4 hpi, and supernatants were harvested at 6, 24, 48, and 72 hpi for titration on MDCK cells. (C) Single-cycle growth curves of A/CA/O7/2009 (H1N1) in MDCK cells determined at different MOIs as indicated. Cells were treated with DMSO or nocodazole (5 μg/ml) at 4 hpi, and supernatants were harvested at 6, 8, 12, and 24 hpi for titration on MDCK cells. Virus titers were determined by the endpoint method. Values presented are means from three independent experiments, and standard deviations are represented by error bars. A two-way analysis of variance with multiple comparisons was used to define statistically significant differences (marked by asterisks). The dashed line denotes the limit of detection for the titration assay.