MHC II类分子在NK细胞功能发育中的作用机制

NK cells are a critical cell population in innate immunity. The defect or over-activation of NK cells function will results in the disorders of immune system. According to the “licensing model”, NK cells from MHC I-deficient mice and humans are defective in IFN-γ secretion and cytotoxicity. So far, there is no investigation about the direct relationship between MHC class II molecules and the development of NK cell function. However, our preliminary experiments indicated that the function of NK cells from MHC II-deficient (MHC II-/-) mice were enhanced obviously. Thus, we hypothesize that the MHC class II and I molecules involve together in maintaining the balance of development of NK cell function. The aim of this project is to confirm whether MHC class II molecules involve in development of NK cell function. Then the precise NK cell subsets regulated directly by MHC class II molecules and the underlying mechanism will be explored. Firstly, we will detect the number, phenotype and the stage of development of NK cells and then evaluate the alteration of NK cells function in MHC II-/- mice. Furthermore, the precise NK cell subsets and the immunological mechanisms regulated directly by MHC class II molecules will be investigated by using gene chip and bone marrow transfer.

NK细胞免疫功能缺陷或过度活化都将导致机体免疫系统的紊乱。“Licensing”学说证实了MHC I类分子缺陷后NK细胞分泌IFN-γ和杀伤功能均显著减弱，严重影响其功能发育；然而MHC II类分子与NK细胞功能发育之间的相互关系迄今尚未有研究报道。我们的实验发现MHC II类分子缺陷后NK细胞分泌IFN-γ和杀伤功能明显增强，推测MHC II类分子和MHC I类分子可能共同对NK细胞功能的发育起着协调平衡作用。本课题希望明确MHC II类分子是否参与NK细胞功能的正常发育，并探寻受MHC II类分子调控的特定NK细胞亚群以及调控机制。利用MHC II缺陷鼠检测NK细胞的表型并分析NK细胞的的功能变化；采用基因芯片和骨髓转输来寻找MHC II缺陷鼠中NK细胞功能显著变化的特定亚群并探索MHC II类分子调控NK细胞功能发育的免疫学机制。

MHCⅠ类分子在NK的功能发育以及免疫识别中发挥重要的作用，然而其同源物MHC Ⅱ类分子与NK细胞的功能发育有无联系暂时未见报道。项目受资助后，以MHC Ⅱ类分子基因缺陷小鼠为研究模型，对MHC Ⅱ类分子是否参与调控NK细胞功能的正常发育问题进行了全面的实验论证。首先观察MHC Ⅱ类分子缺失后各脏器中NK细胞的比例、NK细胞的发育阶段有无变化、受体表达情况；进一步对比分析NK细胞在anti-NK1.1抗体、Yac-1肿瘤细胞等不同体系刺激下的活化状态、分泌细胞因子能力以及杀伤作用。经过大量重复的实验，得到明确的结论——MHC Ⅱ类分子缺失后NK细胞表型为更易活化的的功能状态，说明NK细胞在正常发育过程中依赖MHC Ⅱ类分子的存在。此外，我们探讨了临床患者发生急性脊髓损伤后早期阶段外周血中NK细胞的免疫功能。患者24小时内外周血标本结果显示NK细胞分子CD69、HLA-DR（人MHC Ⅱ类分子）、NKG2D和NKp30表达显著上调。同时，脑源型神经营养因子（BDNF）的血浆含量在患者中也显著上升，且与NK细胞比例呈显著的正相关。进一步体外实验证实，BDNF与NK细胞培养24小时后可以促进NK细胞表面分子CD69、NKG2D和NKp30的表达增加，与体内结果一致。该结果首次提出急性脊髓损伤后24小时内NK细胞受BDNF调节的机制。