(B) YTS KIR2DL1 cells were incubated with SHP-1 and Cbls siRNAs-loaded NPs (red curve), with NS siRNA loaded NPs (green curve) or with empty NPs (blue 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. 