1. The biology of natural killer cells in cancer, infection, and pregnancy 
Jeffrey S Miller 
Experimental Hematology 
Volume 29, Issue 10, Pages (October 2001)
DOI: /S X(01)

2. Figure 1
NK cells function through a diverse repertoire of activating and inhibitory receptors. Activating receptor ligation triggers the cytotoxic mechanism while inhibitory receptors protect from NK cell lysis. Since multiple receptors are involved between NK cells and their targets, the decision of whether or not to kill a target is the net sum of all receptor interactions and inhibitory receptor signaling is dominant. Both classical and nonclassical class I MHC (left side, upper panel) and non-MHC ligands (right side, upper panel) are known for many NK cell receptors. In contrast to T cells, which require class I MHC to kill their targets, inhibitory KIR have exactly the opposite effect (lower panel)
Experimental Hematology  , DOI: ( /S X(01) )