Positive role of KIR2DS1 in allorecognition. (A) 721.221 cells transfected with HLA-Cw6 (C2) or -Cw7 (C1) were stained with either W6/32 anti-HLA class I mAb followed by PE-conjugated isotype-specific goat anti–mouse mAb or with KIR2DL1-Fc or KIR2DS1-Fc soluble receptors followed by PE-conjugated goat anti–human second reagents. Empty profiles indicate staining with second reagent only. Numbers within histograms indicate MRFI. The representative 5R-13 (KIR2DS1⁺/L2⁺; B,C) and 5R-4 (KIR2DS1⁺/NKG2A⁺; D,E) clones, derived from recipient no. 5, 6 months after transplantation were tested against patient leukemia blasts (B,D), BOB (C; see Figure 2 legend for HLA-I genotypes) and LM expressing HLA-A*3,*29, -B*44,*35 (Bw4/Bw6), -Cw*4,*5 (C2/C2) (E) B-EBV cell lines. The cytolytic activity was evaluated in the absence (□) and in the presence (■) of mAb to the indicated molecules, such as 11PB6 (KIR2DS1), GL-183 (KIR2DL2), Y9 (CD94/NKG2A), and A6-136 (HLA-class I). Similar data were obtained also with HP-3E4 (KIR2DS1) and CH-L (KIR2DL2) mAb. The E:T ratio used was 10:1. The results are representative of 2 independent experiments; the standard deviation of the mean of the triplicates was less than 5%.