Cells in stress and cancer cells downregulate MHC class I expression and disengage the inhibitory KIRs, or upregulate stress-induced molecules, such MICA/MICB (MHC class I chain-related protein A/B), to engage activating KIRs that tilts the activation of NK cells to kill target cells [81, 82] Fig. 3. The gene discussed is MICA; the disease is cancer.