KIR and NKG2A receptor expression by alloreactive NK-cell clones. Immunofluorescence analyses of 2 representative alloreactive NK clones are shown. Such clones express, as their only inhibitory receptor for self, the KIR for which there is no class I ligand in the recipient. (A) An NK clone from HLA-C1–positive donor detected in HLA-C1–negative recipient is KIR2DL2/3/S2⁺ and KIR2DL1/3DL1/NKG2A⁻. (B) An NK clone from HLA-C2–positive donor detected in HLA-C2–negative recipient is KIR2DL1⁺ and KIR2DL2/3/S2/3DL1/NKG2A⁻. These 2 clones are representative of 20 tested that exhibited the same phenotype.