(B) YTS KIR2DL1 cells were transfected with either N.S siRNA (blue curve) or with SHP-1 and Cbls siRNA (red curve). After 48 hours, cells were loaded with calcium-sensitive Fluo-3-AM and analyzed for basal intracellular calcium levels for 1 min. The NK cells were then mixed with 721.221 Cw4 target cells at 37°C and monitoring of calcium levels was continued. The data shown are representative of three independent experiments. 