FIG 1.

Replication of wild-type and mutant H18N11 viruses in MDCK II, MDCK, and Calu-3 cells in the presence or absence of exogenous sialidase. MDCK II (A), MDCK (B), and Calu-3 (C) cells were infected with wild-type and mutant H18N11 viruses at an MOI of 0.01 for 1 h at 37°C. The cells were then washed with PBS twice and incubated with Opti-MEM medium with 0.5 μg/ml TPCK-trypsin in the presence or absence of sialidase from Clostridium perfringens (20 mU/ml). Supernatant was collected at 12, 24, 48, 72, and 96 h for virus titration by use of TCID₅₀ assays in MDCK II cells. Virus-infected cells were identified by IFA with an antibody to HA. The data shown are mean values from three independent experiments with standard deviations. P values were calculated by use of the R statistical package (www.r-project.org), the lme4 package (47), and the EMMeans package (48), followed by Holm’s method (*, P < 0.05).