Fig 3.

Deficiency in EndoU activity did not impair TGEV propagation. (A–C) Viral titer determination for WT- and EnUmt-TGEV in PK-15, IPI-2I, and ST cells. Cell culture supernatants [infection dose, multiplicity of infection (MOI) = 0.1] were collected at the indicated hours post-infection (hpi). The titer of infectious virus was determined using a 50% tissue culture infectious dose (TCID₅₀) assay performed in triplicate, and the results are shown as the mean ± SD. Data sets at the same time point were analyzed with an unpaired t-test. (D) TGEV dose-dependently triggers activation of the IFN-β signaling pathway. PK-15 cells were cotransfected with pRL-TK and IFN-β-Luc, followed by infection with increasing doses of TGEV (MOI = 0.01, 0.1, and 1) at 12 h post-transfection. At 24 h after the initial transfection, the cells were infected with SeV. The cell lysates were collected for dual luciferase assays at 24 hpi. (E and F) WT- and EnUmt-TGEV infection induces a consistent type I IFN response. At 12 h and 24 h after TGEV infection (MOI = 0.1), cells were lysed to collect total RNA for cDNA synthesis, and quantitative PCR was used to measure the relative expression levels of the indicated mRNAs for IFN-β (E) and ISG15 (F). The representative data sets of three independent experiments are shown. Values are presented as the mean ± SD and were analyzed by unpaired t-test. The significant differences are indicated as follows: *P < 0.05 and **P < 0.01.