Identification of NK subpopulations expressing the activating form of KIRs. Double fluorescence (A-C) and reverse-antibody dependent cellular cytotoxicity (R-ADCC) analyses (D-F) were performed using NK cell populations derived from the following informative donors: no. 20 (A,D) and no. 4 (B,E and C,F). Dot plots identify the subset expressing the activating KIR in the upper left quadrant with the percentage of cells included. For staining, the following mAb were used in combination: #143211-FITC (anti-KIR2DL1) and EB6B-PE (anti-KIR2DL1/S1) (A); ECM41 (anti-KIR2DL3) and GL-183 (anti-KIR2DL2/L3/S2) followed by isotype-specific PE- and FITC-conjugated, respectively, second reagents (B); DX9-FITC (anti-KIR3DL1) and Z27-PE (anti-KIR3DL1/S1) (C). For R-ADCC, ⁵¹Cr-labeled P815 were incubated with polyclonal NK cell populations in the absence (□) or presence (■) of the indicated mAb. Effector to target (E:T) ratio of 4:1 was used. The results are representative of 3 independent experiments; the SD of the mean of the triplicates was less than 5%.