Figure 4.

Proposed model to explain cytolytic activity of licensed and unlicensed NK cells against normal-self (top), missing-self (medium) and increasing-self (bottom) targets. Our hypothesis sustains that licensed NK cells (left) responding through activating receptors (aRec) can kill missing-self and increasing-self tumors expressing ligands for aRec (aLig), but not normal cells. By contrast, unlicensed NK cells (right) would kill missing-self tumors,⁴¹ but not normal tissue or increasing-self tumors with a mild expression of aLig such as myeloma.