Involvement of different activating and inhibitory NK receptors in the lysis of MSCs. Results of 2 mAb-mediated blocking experiments. ⁵¹Cr-labeled MSCs were used as target cells, and activated polyclonal NK cells were used as effectors. NK cells were preincubated with saturating amounts of mAb to the indicated receptors, washed, and added to the cytolytic assay. To mask HLA class I molecules, MSCs were preincubated with saturating amounts of anti-HLA class I A6136 mAb before addition to the assay. (A) Cytolytic assay in which effector NK cells were tested against allogeneic MSCs. (B) Experiment performed using autologous target MSCs. Data are expressed as percentage of lysis. The E/T ratio used was 10:1.