NK-cell reactivity is determined by the balance between activating and inhibitory signals. Activating receptors such as the natural cytotoxicity receptors (NKp30, NKp44, and NKp46), NKG2D, and DNAM-1 interact with ligands on target cells and direct the NK cell toward cytotoxicity. Inhibitory receptors such as inhibitory KIRs, leukocyte Ig-like receptor (LIR), and CD94/NKG2A interact with MHC class I molecules and protect autologous targets from NK cytotoxicity. Adapted from Stagg et al. Drug News Perspect. 2007;20(3):155-163. Copyright © 2007 Prous Science, SA. All rights reserved.