Natural cytotoxicity receptors that trigger human NK-cell-mediated cytolysis

Natural killer (NK) cells can detect whether cells have undergone tumor tra nsformation or viral infection. The discovery of specific inhibitory recept ors for major histocompatibility complex class I molecules clarified the ba sis of this discrimination. However, the receptors responsible for NK-cell triggering in the process of natural cytotoxicity remained elusive until re cently. Here, Alessandro Moretta and colleagues describe the identification and characterization of several such receptors.