Objective: To investigate the regulatory effect of IFN-gamma on recognition of target cells by human natural killer (NK) cells.
Methods: The cytotoxic activity of human NK cell lines (NK92, NKL) was detected by MTT method. Expression of NK cell receptors (NKG2D, NKG2A/B, KIR2DL1 and KIR2DS1) and MICA on target cells (the ligand of NKG2D) was measured by RT-PCR.
Results: Both NK92 and NKL cells exerted higher cytotoxicity to tumor cells with MICA expression, while tumors without MICA expression could resist NK cell lysis. IFN-gamma (> 1000 U/ml) inhibited NK lysis of tumor cells with MICA expression through down-regulating the expression of NKG2D, but up-regulating the expression of NKG2A/B and KIR2DL1.
Conclusion: IFN-gamma has a negative effect on activation and cytotoxicity of human NK cells by altering the balance between the expression of activating and inhibitory receptors on NK cells in favor of inhibition. This may serve to limit NK cell over-activation in vivo.