GP5 induced IL-10 mRNA and protein expression. (a) PAMs were transfected with PRRSV structural and non-structural proteins (2 μg) or stimulated with LPS (1 μg ml-1) as positive control. IL-10 mRNA expression at 24 h post transfection was evaluated by real-time PCR. (b) Cell supernatants collected from viral structural protein transfected PAMs were analyzed for IL-10 production by ELISA. (c) CRL-2843 cells were cotransfected with a mixture of pIL-10-luc plasmid, pRL-TK plasmid, and viral structural protein-encoding plasmids or empty vector. At 24 h post transfection, luciferase activities were measured with the Dual-Luciferase Reporter Assay System. (d) Increasing amounts (0.1, 0.5 and 2 μg) of GP5-encoding plasmid were transfected into PAMs. IL-10 mRNA expression at 24 h post transfection was examined by real-time PCR. The results represent means ± SD of three independent transfections. * Significant difference (P < 0.05) from empty vector control using Student’s t-test.