Figure 1: Overview of the structurally characterized activating and inhibitory human NK receptors and their ligands. The upper panel displays the chief activating receptors found on human NK cells including the homodimer NKG2D, the natural cytotoxicity receptors, NKp46, NKp44, and NKp30, the c-type lectin heterodimer CD94 : NKG2C, the Fc receptor CD16, and also the KIR activating receptors. The associated cytoplasmic signaling molecules for these activating receptors which include DAP12, DAP10, and CD3ζ/FcεRIγ and the specific transmembrane residues which facilitate the interaction are also shown. The lower panel illustrates the structurally characterized inhibitory receptors found on NK cells. These include the KIR receptors KIR 2DL1 and KIR 2DL2 which have been characterized in complex with peptide bound MHC class I molecules, the heterodimeric CD94 : NKG2A which binds to peptide bound HLA-E. The C-type lectin receptor KLRG-1 which binds to cadherin and the NK cell receptor LAIR-1 molecule which binds to collagen are also shown. The known ligands for both the activating and inhibitory receptors are illustrated above their respective NK cell receptor.