Figure 1. NK cell education: adaption of the responsiveness depending on inhibitory receptor - ligand interactions.

(a) In normal major histocompatibility complex (MHC) class I-sufficient individuals (humans and mice), NK cells expressing inhibitory receptors recognizing those MHC class I molecules become educated. Those cells are responsive to activating receptor stimulation. The subset of NK cells that lacks inhibitory receptors for self MHC class I are non-educated and hyporesponsive when triggered through activating receptor stimulation. Under certain conditions, such as infections or cytokine stimulation, this subset can become responsive.

(b) In MHC class I-deficient individuals, NK cells are non-educated and hyporesponsive due to the lack of inhibitory ligands. After transfer to a new MHC class I-sufficient host, NK cells can become “re-educated” and responsive if they express the matching inhibitory receptors.

KIR, killer cell immunoglobulin-like receptor.