Decrease of virus yield in BHK-21 cells treated with siRNA-expressing plasmids. Cells transiently transfected with either control plasmids or specific siRNA-expressing plasmids were infected with 100 TCID₅₀ of FMDV HKN/2002 (A), FMDV CHA/99 (B), FMDV YNBS/58 (C) and FMDV Jiangsu/2005 (D) per 0.1 mL. Culture supernatants were collected at different times, and the virus titer (TCID₅₀) was determined three times on BHK-21 cells. Error bars indicate standard deviations.