IFA of Lpro during FMDV infection. LF-BK cells were infected at an MOI of 10 with FMDV A12-WT (panels 1, 4, 7, and 10), A12-LLV2 (panels 2, 5, 8, and 11), or double SAP mutant A12#49 (panels 3, 6, 9, and 12) and were fixed at different times postinfection. Viral protein Lpro was detected using a rabbit polyclonal Ab and an Alexa Fluor 488-conjugated secondary Ab. Viral protein VP1 was detected using mouse MAb 6HC4 and an Alexa Fluor 594-conjugated secondary Ab.