补体C3抑制巨噬细胞自噬促进胞内病原体存活的机制研究

Macrophage plays an important role in anti-intracellular pathogen infection. The ability of phagocytosis and killing by macrophage controls the survival and proliferation of the intracellular pathogen. It has been found that autophagy is one of the key mechanisms of intracellular pathogen killing by macrophage. Surprisingly, we found that during the early Listeria Monocytogenes infection period, complement C3 deficient mice showed much lower bacterial titer when compared with the wild type mice. Then, we found that the complement C3 deficient macrophage showed increased level of autophagy. These results suggest that C3 inhibits autophagy of macrophage and promotes the survival of the intracellular pathogen. In this project, we try to explore the mechanism through analysis of complement fragments, detection of cellular surface receptor and transduction signaling pathway by using related gene knockout mice, specific blocker or inhibitor and bone marrow reconstitution. This study not only helps clarify the interrelation between innate immune molecule (complement C3) and innate immune cells (macrophage), but also guide the design and screening of novel anti-intracellular pathogen.

巨噬细胞在抗胞内病原体感染中发挥重要作用，其对胞内病原体的吞噬杀伤能力，直接决定了被其吞噬的胞内病原体的存活与繁殖速率。近年发现，自噬是巨噬细胞杀灭胞内病原体的关键机制之一。在完成上一基金过程中，我们意外发现胞内菌Listeria Monocytogenes感染早期，与野生型小鼠相比，天然免疫分子补体C3敲除小鼠细菌滴度显著下降，随后发现补体C3缺失的巨噬细胞自噬功能显著增强并伴随细菌滴度下降，提示巨噬细胞表达补体C3会显著抑制其自噬功能并促进胞内病原体的存活。本项目拟从探讨补体功能片段、细胞表面受体、信号途径等几个方面，利用相关基因敲除小鼠、特异性阻断剂、骨髓重建实验等从不同角度论证补体C3抑制巨噬细胞自噬，促进胞内病原体存活的机制。本项目的结果不但有利于理解天然免疫分子（补体）和天然免疫细胞（巨噬细胞）的相互作用，而且对于设计筛选新型抗胞内病原体靶标药物有指导意义。

巨噬细胞和补体分别属于天然免疫中的细胞和体液免疫成分，在抗感染免疫和维持免疫自稳中均发挥重要作用。在完成上一基金过程中，我们意外发现胞内菌Listeria Monocytogenes感染早期，补体C3敲除小鼠与野生型小鼠相比，细菌滴度显著下降，随后发现补体C3抑制巨噬细胞功能，促进胞内病原体的存活；补体C3敲降的肿瘤细胞荷瘤小鼠，肿瘤相关巨噬细胞的免疫抑制功能显著低于野生型肿瘤细胞荷瘤小鼠的巨噬细胞，肿瘤生长也显著慢。本项目从探讨补体活性功能片段、巨噬细胞表面受体、胞内信号通路等几个方面出发，利用相关基因敲除小鼠、特异性阻断剂等从不同角度论证补体C3调节巨噬细胞功能的机制。结果发现：补体C3活化片段C3a与巨噬细胞表面的C3aR结合，活化PI3K-AKT通路，促进巨噬细胞的抑制功能，在抗肿瘤免疫中促进肿瘤生长，在抗胞内病原体中促进病原体的繁殖。本项目的结果不但有利于理解天然免疫分子（补体）和天然免疫细胞（巨噬细胞）的相互作用，而且对于设计筛选新型抗胞内病原体靶标药物及抗肿瘤药物有指导意义。