Effect of each SNP on the transcriptional activity of the CXCL13 promoter. A Eight SNPs discovered in the critical promoter region of porcine CXCL13. B Luciferase activities of pGL3-CXCL13YL and site-directed mutants of pGL3-CXCL13YL in PK15 cells at 48 h post-transfection. C–G Luciferase activities of each site-directed mutant of pGL3-CXCL13YL in PK15 cells with and without PCV2 infection. PCV2-infected groups (pGL3-(−3065T)-i, pGL3-(−2991G)-i, pGL3-(−1014G)-i, pGL3-(−712T)-i, and pGL3-(−604C)-i) were inoculated with PCV2 at an MOI of 0.1 TCID50, and PCV2-uninfected groups (pGL3-(−3065T)-u, pGL3-(−2991G)-u, pGL3-(−1014G)-u, pGL3-(−712T)-u, and pGL3-(−604C)-u) were treated with equivalent PK15 cell lysate at 6 h post-transfection. Luciferase activity was detected at 0, 12, 24, 36, and 48 hpi. Each bar represents the mean value ± SE of three experiments. *, **, and *** indicate significance at the P value threshold levels of 0.05, 0.01, and 0.001, respectively.