The opposite effect of mMICA and rMICA on the expression of NKG2D and the influence on NK cell receptor repertoire
Objective To observe the effect of mMICA and rsMICA on the expression of NK cell receptors and investigate the anti-tumor mechanisms of NK cells and the significance of MICA expression on tumor cells. Methods The cytotoxicity of human NK cells (NK92) was detected by MTT method. The expression of NK cell receptors (NKG2D, NKG2A/B, KIR2DL1 and KIR2DS1) and MICA (the ligand of NKG2D) were measured by RT-PCR or by FACS. Results The membrane MICA (mMICA) on surface of tumor cells can up-regulate the expression of NKG2D, but down-regulate the expression of inhibitory receptor NKG2A/B and KIR2DL1. The soluble MICA (sMICA) exerts negative effect on the expression of NKG2D, NKG2A/B and KIR2DL1. Conclusion mMICA can enhance the cytotoxicity of NK cells against tumor through up-regulating the expression of NKG2D. While sMICA down-regulate the immune response of NK cells by reducing the expression of NKG2D, which may promote tumor immune evasion.