Importance of NKG2D-NKG2D ligands interaction for cytolytic activity of natural killer cell.

In this study, we investigate the relationship between natural killer (NK) cell susceptibility and the surface markers of cancer cells. Through phenotypic analysis, we found evidence that more susceptible cancer cell lines (K562 and Jurkat) express more NKG2D ligands. Major histocompatibility complex (MHC) class I chain-related A/B (MIC-A/B) and UL16 binding protein (ULBP) 1-5 molecules are typical ligands of NKG2D. The high killing activity of NK cells against K562 was abolished through the addition of a NKG2D blocking antibody. Upon in vitro stimulation with quercetin, low susceptible cancer cells increased NKG2D ligand expression, leading to enhancement of NK cell cytolytic activity. These results suggested that the anti-cancer activity of NK cells is not dependent on the origin and growth style of the target cells, but is dependent on the surface markers of the target cells.