KLRG1 expression is positively associated with apoptosis of NK cells following HCV infection. (A) PBMCs from HCV-infected patients and HS were stimulated with 10 ng/ml rhIL-12 for 18 h, followed by 1 μg/ml brefeldin A 4 h prior to harvest of the cells (to block cytokine secretion). PBMCs were immunostained and then analyzed for Annexin V expression on total CD3 − CD56 + and CD3 − CD56 bright and CD3 − CD56 dim NK cells by flow cytometry. Representative dot plots for Annexin V expression on KLRG1 + and KLRG1 − NK cells, including CD3 − CD56 + and the CD3 − CD56 bright and CD3 − CD56 dim subsets from an HCV-infected patient and HS are shown. (B) Average percentage of Annexin V expression from the KLRG1 + versus KLRG1 − cell fraction of total CD3 − CD56 + NK cells and the CD3 − CD56 bright and CD3 − CD56 dim subsets. Results are expressed as means ± SD of the percentages of Annexin V expression by NK cells from 24 HCV-infected patients versus 8 HS. *, P