沙门氏菌感染过程中AIM2的免疫调控作用及其机制研究

The interplay between pathogen virulence factor and host innate immune system largely determines the outcome of infection. The innate immune system is essential for limiting microbial replication and spread through the recognition of pathogen-associated molecular patterns (PAMPs) by pattern recognition receptors (PRRs), and critically involved in the activation of adaptive immune responses. Most recently, AIM2 (Absent in Melanoma 2) has been identified as a new cytoplasmic PRR, which is known to initiate innate immune response by assembling as an inflammasome complex. However, our understanding of AIM2 in host immune function remains much poor. Based on our preliminary data we hypothesize that some pathogens subvert AIM2 inflammasome signaling for immune escape, and that AIM2 may exert important roles in innate and adaptive immunity beyond inflammasome. Salmonella is the bacterial agent most frequently posing huge threat to public and animal health. S. Typhimurium also has been proven to be a useful model organism for the study of host-intracellular pathogen interaction. To define the interplay between AIM2 and Salmonella, we will try to uncover the molecular mechanism by which Salmonella hampers AIM2 inflammasome activation, to determine AIM2-initiated signal transduction, and to clarify how AIM2 regulates TLR signaling and T cell activation. Further investigation will be carried out to evaluate whether AIM2 signaling is required for vaccine-induced protective immunity. These studies are aimed at gaining a better understanding of the mechanism of immune escape used by Salmonella, and unveiling the novel roles of AIM2 in innate and adaptive immunity, which will lead to the rational design of vaccines against Salmonella infection and cancer.

病原感染的结局很大程度上取决于致病因子与天然免疫系统的相互作用。天然免疫系统通过模式识别受体识别病原相关分子模式，限制病原增殖扩散，并诱导适应性免疫反应。AIM2是新发现的胞内模式识别受体，能以炎性体的形式参与天然免疫反应，但目前对其认识有限。本项目预实验提示，干扰AIM2炎性体信号可能是一些胞内病原菌的免疫逃逸机制，并且AIM2可能以非炎性体形式在天然免疫和适应性免疫反应中起重要作用。沙门氏菌是严重危害家畜和人类健康的病原菌，也是探讨胞内病原感染机制的模式菌。本项目紧密围绕国家畜牧业发展和人类健康需求，以沙门氏菌与AIM2的相互作用为研究主线，以AIM2炎性体的调控、AIM2信号转导、AIM2对TLR信号和T细胞活化的调节、AIM2在疫苗免疫保护中的作用为主要研究内容，着眼于揭示AIM2的新功能和沙门氏菌免疫逃逸机制，为研制靶向AIM2信号的新型疫苗，控制沙门氏菌感染和治疗肿瘤奠定基础。

沙门菌感染性肠炎危及各种动物和人类，是全球重要的公共卫生问题。研究沙门菌毒力机制和宿主天然免疫防御作用，是有效防治沙门菌感染的前提。肠上皮屏障的完整性在防御肠道病原微生物侵入中起重要作用，但调节胃肠道上皮屏障功能的机制仍不清楚。本项目研究发现，DNA受体AIM2介导宿主抗沙门菌黏膜感染，却不影响沙门菌全身性感染。AIM2以非炎性体依赖形式促进肠黏膜屏障完整，并且AIM2通过调节AKT活化，促进肠上皮细胞紧密衔接蛋白表达，从而降低上皮通透性，限制沙门菌经细胞旁途径易位。我们也发现沙门菌效应因子sifA和sopB调节沙门菌诱导的巨噬细胞炎性体活化。借助其磷酸酶活性，sopB促进AKT信号活化，从而抑制NLRC4而非AIM2、NLRP3、IFI16炎性体依赖的细胞因子释放和细胞焦亡。我们进一步研究了sopB在沙门菌黏膜感染中的作用和机制，发现沙门菌侵入肠上皮杯状细胞后，适应性下调sopB表达，从而增强杯状细胞MLKL依赖的坏死性凋亡，损害肠黏膜屏障功能，逃避宿主黏液防御。我们对AIM2和细胞焦亡执行分子GSDMD在疾病防治中的可行性进行了探索，构建了AIM2和GSDMD-N表达载体，转入减毒沙门菌SL7207疫苗株，发现外源表达GSDMD-N的重组沙门菌体体内外明显抑制金葡菌的增殖及金葡菌诱导性乳腺炎，并具较好安全性。总之，这些研究揭示了沙门菌与宿主天然免疫反应之间的互作关系，为研发有效防治方法，控制细菌感染提供了重要数据。在该项目的资助下，部分研究结果已发表于Mucosal Immunology、Frontier Immunology和Molecular Immunology等杂志。