Reduced NK cell-mediated cytotoxicity in PRRSV infected pigs. Percent NK-specific cytotoxicity was measured in pig PBMC (effectors). (A) Day 0 pre-infection and (B) day 2 post-infection against K-562 target cells. Effectors and targets at indicated E:T ratios were co-cultured and the supernatant harvested after 24 h was analyzed spectrophotometrically (OD490 nm) for released LDH from the lysed cells using a LDH substrate. Each line corresponds to NK cell-specific lysis from one pig at the four different E:T ratios. Statistical analysis was performed using a paired t-test by comparing the percent specific NK cell lysis between day 0 and day 2 post-infection at respective E:T ratios: P = 0.0115 at 1:100; P = 0.0001 at 1:50; P = 0.0007 at 1:25; P = 0.0069 at 1:12.5.