Effects of Simulated Weightlessness on Human NK Cell Cytotoxicity

Objective To determine the effect of simulated weightlessness on cytotoxicity of human NK cells and to explore the mechanism of its changes on activating receptors,inhibitory receptors and perforin in cytolytic activity primarily. Methods Pure human NK cells obtained from’NK ex vivo expansion system’ were incubated in clinostat to simulate weightlessness. The cytotoxicity of human NK cells were tested after 48 h and 72 h simulated weightlessness. The expression levels of NKG2D,NKG2A and perforin genes were determined on mRNA level with real-time RT-PCR. Results The cytotoxicity of human NK cells decreased 16% ( P0.05) and 26% ( P0.05) respectively,after simulated weightlessness treatment for 48 h and 72 h. For the group of 72 h,the gene expression level of activating receptor NKG2D was down-regulated with quantitative analysis of NK cell mRNA,while inhibitory receptor NKG2A up-regulated. However,there was no significant change for the expression of perforin. The NK cytotoxicity recovered from the effect of simulated weightlessness after 6 d cultured in normal condition. Conclusion Cytotoxicity of human NK cells can decrease significantly after simulated weightlessness. Altered expression levels of NKG2D and NKG2A probably contribute to decrease cytotoxicity.