Tea polyphenol (TPP) restrains the infection and replication of porcine reproductive and respiratory syndrome virus (PRRSV) in Marc-145 cells. (A) The cytotoxicity of TPP was measured by the alamarBlue® assay. Marc-145 cells were treated with TPP at indicated concentrations for 48 h, and a cell viability assay was performed. (B) Marc-145 cells were infected with PRRSV-EGFP (MOI = 0.6) in the presence of different concentrations of TPP for 36 h and then were harvested for fluorescence microscope examination. Scale bar, 100 μm. (C) Marc-145 cells were infected with PRRSV-CHR6 (MOI = 0.6) in the presence of different concentrations of TPP for 36 h. The mRNA expression of viral ORF7 (PRRSV N) was detected by qRT-PCR. (D,E) Marc-145 cells were infected with PRRSV-CHR6 (MOI = 0.6) in the presence or absence of TPP for different time points, the mRNA level of viral ORF7 (PRRSV N) was detected by qRT-PCR (D), and PRRSV N protein was determined by Western blot (E). (F,G) Marc-145 cells were infected with PRRSV-CHR6 at different MOIs in the presence or absence of TPP for 36 h, and the expression of viral ORF7 (PRRSV N) was detected by qRT-PCR (F) and N protein was determined by Western blot (G). (H) Marc-145 cells were infected with JXA1, TJM-92, and VR-2332 strains (MOI = 0.6) in the presence or absence of TPP for 36 h, and the viral N protein was determined by Western blot. Data are representative of the results of three independent experiments (means ± SE). Significant differences compared to the control group are denoted by ** p < 0.01, and *** p < 0.001.