AIM2炎性体通路启动和调控抗巨细胞病毒免疫应答与对感染结局的影响

The pathogenicity of CMV and the prognosis of CMV diseases are closely related to the host immune status. CMV dsDNA was recognized by innate immune cells, which induced the change of innate immunity was the first "switch" affecting the outcome of the CMV infections. Our previous studies found that HCMV could activate the AIM2 inflammasome of the microphages as the same way as poly (dA:dT). We so supposed that AIM2 inflammasome pathway which recognizes the exogenous dsDNA in innate immune cells plays a key role of linking between the innate and acquired immune against CMV. This project means to: (1) in HCMV infected macrophage model, study the role and regulatory mechanisms of AIM2 inflammasome pathway in the anti-HCMV immune responses, and find reversely out the key target component of AIM2 inflammasome pathway affected by HCMV using selective siRNA interfering and specific inhibitor techniques in vitro; (2) by means of the MCMV acute (C57BL/6) and chronic (BALB/c) infected gene-knock-out (AIM2-/- or caspase-1-/-) mice models and bone marrow reconstitution techniques, investigate the role and mechanisms of AIM2 inflammasome pathway on triggering and regulating the innate and acquired immunity against CMV by assessing the responses of anti-MCMV immunity and the outcome of infections in vivo; (3) further explore the related protein of HCMV restraining the AIM2 inflammasome pathway and its mechanisms in vitro. All of these will contribute to comprehensively elucidate the mechanisms of immune pathogenesis, immune escape and chronicity of CMV infection.

CMV致病性及疾病转归与宿主免疫状态密切相关。CMV dsDNA被免疫识别并诱导的天然免疫变化是影响感染结局的第一个"道闸"。我们前期研究发现HCMV以poly(dA:dT)相同方式激活巨噬细胞的AIM2炎性体，提出天然免疫细胞内能识别外源性dsDNA的AIM2炎性体通路是"桥接"抗CMV天然免疫和获得性免疫的关键环节。本项目将在细胞水平研究AIM2炎性体通路在抗HCMV免疫应答中的作用与调控机制，通过选择性阻断技术反向寻找其关键作用位点；借助MCMV急性感染(C57BL/6)和慢性感染(BALB/c)的基因敲除小鼠模型和骨髓重建技术，整体研究AIM2炎性体通路启动和调控抗CMV天然与获得性免疫应答的作用与机制及其对抗病毒效应与感染结局的影响；进一步体外研究HCMV抑制AIM2炎性体通路而实现免疫逃逸的相关蛋白分子及其作用机制，将有助于全面阐明CMV免疫致病机制和免疫逃逸与感染慢性化机制。

本课题在细胞水平和整体水平证实，CMV可被天然免疫细胞内AIM2识别进而激活AIM2炎性体，后者参与抗病毒天然免疫应答，抑制细胞内病毒基因转录；并激活下游IL-1β和IL-18表达，协同活化树突状细胞在感染后7天启动特异性免疫应答；活化NK细胞和Th1/Tc1优势应答有助于急性期病毒清除，但渐被抑制，导致感染慢性化。急性后期IL-17A+细胞选择性高表达于脾和唾液腺，参与其病理损伤，还可能与病毒潜伏相关。进入慢性期，Treg细胞应答逐渐增强，是维持慢性感染的主要机制。上述结果部分阐明AIM2炎性体在启动抗CMV天然免疫和“桥接”适应性免疫应答的时机与关键作用，明确特异性细胞免疫动态变化及感染慢性化或潜伏机制。与BALB/c小鼠相比，对MCMV具天然抗性的C57小鼠主要脏器病变较轻且恢复快，其NK细胞活性，产IFN-γ NK细胞比率以及表面受体Ly49表达更高。进一步研究肺组织免疫应答发现，C57首先诱导更强和更持久的NK反应，继而诱导更为强烈的特异性CTL细胞应答；其表面活化受体NKp46表达显著降低，可能是NK应答差异的另一原因；二者NK细胞表面CD11c表达谱差异明显亦可能与NK细胞调节功能相关。本课题还发现在感染早期HCMV pUL83与AIM2蛋白在胞质中结合；导致AIM2炎性体蛋白丰度降低及活化减少，证实CMV免疫逃逸的又一重要机制和作用位点。