PD-1/PD-L1：负性调控脓毒症炎性因子过度分泌的重要通路

One of the major strategies of immunotherapy of sepsis is tempering "cytokine storm" which is induced by over-activation of innate immune response. Recent studies revealed that T lymphocytes could dampen cytokine secretion by innate immune cells in a cell-cell contact manner. However, the mechanisms remain unclear. PD-1 (programmed death-1), a co-inhibitory molecule was well recognized as a key regulator of adaptive immune response. Our previous study found that neutralizing antibodies of PD-1 and PD-L1 could reverse the inhibitory effect of T cells on cytokine secretion by innate immune cells. Meanwhile, an increase of both PD-1 and PD-L1 expression was noted on innate immune cells after infection. Thus, we suppose that PD-1/PD-L1 might play a key role in inhibiting innate immune response during sepsis. To test this hypothesis, we intend to perform in vitro and in vivo experiments to investigate the role of PD-1/PD-L1 in negative regulation of innate immunity, either by T cells or self feedback regulation of innate immunity. Moreover, we will clarify the downstream signalling pathways of PD-1/PD-L1 in innate immune cells. Our study would expand our knowledge about PD-1/PD-L1 from adaptive immune response to innate immune response, and promote clinic immune therapy research for sepsis.

抑制天然免疫系统过度活化导致的"细胞因子风暴"，是脓毒症免疫治疗研究的重点。最近发现：T淋巴细胞可通过细胞直接接触抑制天然免疫细胞过度分泌细胞因子，但机制不清。既往认为共抑制分子PD-1主要调控获得性免疫应答。申请人前期工作发现：抗PD-1抗体和抗PD-L1抗体可逆转T 细胞对天然免疫细胞分泌细胞因子的抑制作用，并且感染可迅速上调PD-1及其配体PD-L1在天然免疫细胞的表达水平，由此提出："PD-1/PD-L1是脓毒症时抑制天然免疫应答的重要信号通路"。我们拟采用体外和体内实验，证实PD-1/PD-L1通过 1）参与T 淋巴细胞抑制天然免疫应答；2）参与天然免疫自身负反馈调控，抑制天然免疫细胞分泌炎性细胞因子；阐明天然免疫细胞内PD-1/PD-L1的下游信号通路，将PD-1/PD-L1这一重要免疫调节通路的关注点，由获得性免疫应答延伸到天然免疫应答领域，推动脓毒症的临床免疫治疗研究。

细胞因子的产生和吞噬是天然免疫系统的两个主要效应。脓毒症时，细胞因子风暴和吞噬作用减弱导致组织损伤和病原体播散，因此必须精确控制先天免疫反应。近年来研究表明，非调节性T细胞通过抑制骨髓细胞过度产生炎性细胞因子而保护宿主免受病毒感染引起的死亡。早期研究集中于细胞内部自身的信号改变，如TLR负性信号等。新近研究发现，周围环境或其他邻近细胞可以通过负性调控信号来调控天然免疫细胞反应。然而，何种表面分子介导了适应性免疫细胞和先天免疫细胞之间的抑制性信号传导仍然不清楚。.我们研究发现，T细胞通过程序化死亡配体1（PD-L1）与天然免疫细胞表面的受体PD-1之间的相互作用，抑制天然免疫细胞产生细胞因子和发挥吞噬效应。体内注射抗PD-L1与PD-1抗体进行阻断，可以增强宿主对病毒或toll样受体配体诱导的脓毒性休克的敏感性，但又同时可保护小鼠避免死于多种微生物感染。特定细胞因子导致感染过程中T细胞表面PD-L1和天然免疫细胞表面PD-1和PD-L1的快速上调。PD-L1/PD-1在髓系细胞通过SHP1/2磷酸化调控下游信号通路，抑制Akt-mTOR信号级联和增强PTEN的表达来调节先天免疫应答。我们的研究结果表明PD-1通过骨髓细胞和T细胞之间的相互干扰以及骨髓细胞之间的负反馈回路，影响宿主对病毒和细菌感染的不同反应。