2.4. Virus Yield Reduction Assay

Anti-IBV activity was evaluated by cytopathogenic effect (CPE) and MTT assays. Confluent monolayers of MDCK cells in 96-well plates were inoculated with virus (0.01 MOI). After 2 h, the inoculums were replaced with test medium containing a series of concentrations of LQ or DMSO (less than 1%) with 1 μg/ml tosyl-phenylalanine chloromethyl-ketone (TPCK) treated trypsin (Sigma), 100 U/ml penicillin, and 100 μg/ml streptomycin (Gibco). The plate was incubated at 34°C, 5% CO₂, for 72 h. The inhibition rates were measured via MTT assay. Three independent tests were conducted, and the 50% inhibition concentration (IC₅₀) was obtained via the Reed-Muench method [16].