流感病毒、呼吸道合胞体病毒以及冠状病毒等是常见的呼吸道病毒，感染后可导致严重的肺部损伤。2019年末出现的新型冠状病毒SARS-CoV-2更是在世界范围内引起大规模流行。建立一种理想的动物模型以测试可能的治疗和预防策略的有效性必不可缺。小鼠是最常用于构建病毒性肺炎动物模型的模式实验动物。利用小鼠来模拟人类病毒性肺炎是研究疾病发病机制、评估候选疫苗、开发抗病毒药物的重要步骤。小鼠肺炎病毒(Pneumonia virus of mice, PVM)作为一种包膜单链RNA的病毒，是啮齿动物体内的一种自然病原体，是能够模仿人类呼吸道合胞病毒(Respiratory syncytial virus, RSV)病原体临床和病理特征的替代病原体，用于探索急性呼吸道病毒感染。

病毒感染引起的免疫反应可以抑制病原体的增殖；然而，免疫反应同时也可造成严重病理损害。固有免疫系统在机体抵御病毒感染时发挥重要作用。固有免疫细胞，如巨噬细胞大量存在于肺微环境中，可极化为M1和M2表型巨噬细胞，分别在宿主防御中发挥促炎作用和抗炎反应及组织重塑作用。越来越多的证据表明，巨噬细胞的极化受细胞因子、趋化因子和转录因子的调控。而巨噬细胞的极化调控与病毒性肺炎疾病的发生发展密切相关，对其进行精确的调节可能是病毒性肺炎的一种潜在治疗方案。固有免疫分子，如警报素HMGB1等，在病毒性肺炎中发挥着启动和调节固有免疫反应及适应性免疫反应的作用。已有研究发现，病毒感染可促进支气管肺泡灌洗液中HMGB1及其他细胞因子的分泌而HMGB1能诱导炎症反应并通过旁分泌机制促进感染过程中的组织损伤。

我们还注意到外界病原刺激除了对组织的直接或间接炎症损伤外，对机体的免疫系统存在一定的影响。2012年，有研究报道了固有免疫系统存在记忆能力。固有免疫细胞在一次刺激后发生代谢重编程和表观遗传修饰，再次接受刺激后表现出高效、快速的应答称为训练免疫（trained immunity），或者产生沉默。这一现象最先报道于卡介苗、β-葡聚糖等含细菌、真菌成分的训练免疫诱导剂中。有研究报道称，部分COVID-19患者在病愈后对其它非冠状病毒病原易感性增加。

综上，我们提出了以下几个问题：病毒性肺炎的发生发展过程中固有免疫系统发挥了怎样的作用？病毒感染后是否存在固有免疫的记忆，若存在，固有免疫记忆建立的机制是什么？关键固有免疫因子HMGB1是否发生改变？这些改变是否可以进行调节，调节是否会引起疾病转归的变化？

为了探索以上问题，我们应用小鼠肝炎病毒（Mouse Hepatitis Virus, MHV）感染小鼠，待病毒清除后，再次感染支原体和PVM，建立继发感染动物模型，进行了固有免疫记忆的研究；应用RAW264.7细胞，接种感染MHV，建立了巨噬细胞病毒感染细胞模型，通过转录组学分析验证其作为巨噬细胞感染体外研究模型的价值,并初步筛选可能与固有免疫记忆建立有关的核心基因；应用PVM感染BALB/c小鼠，建立了病毒性肺炎动物模型，在此模型的基础上，针对HMGB1警报素分子开展固有免疫干预调节的研究。

通过继发感染动物实验，我们发现相比于初次感染的动物，继发感染其他类病原体的动物在肺部病理损伤减轻、肺组织内免疫细胞群体比列改变，同时肺组织细胞中与基因转录后翻译、糖代谢、氧化磷酸化有关的基因表达水平发生改变；在MHV感染小鼠巨噬细胞的实验中，我们发现巨噬细胞在感染MHV后炎症有关基因和代谢有关基因在不同时间的表达水平变化，同时巨噬细胞的极化表型随时间变化，此外我们筛选出部分可能与巨噬细胞极化和固有免疫记忆有关的关键基因；通过病毒性肺炎小鼠给药抑制警报素HMGB1的生成和位移，有效的改善了感染小鼠肺炎时的临床表现，其肺组织病理损伤减轻、炎症因子水平明显下降。

通过本论文的研究工作，我们发现了HMGB1可以作为调节病毒性肺炎固有免疫应答的节点，并验证了甘草酸在病毒性肺炎中的药效作用；发现MHV冠状病毒感染对于小鼠，其固有免疫存在训练免疫的状态,这与文献中报道的人类感染新冠病毒后对其他病原体的免疫力降低并不一致。在MHV感染巨噬细胞的转录组研究中，验证了细胞模型在一定程度上可以验证固有免疫应答的过程，而且可以反应出其免疫记忆的过程，在此基础上我们初步筛选出的可能与建立固有免疫记忆的关键基因。

Influenza viruses, respiratory syncytial viruses, and coronaviruses are common respiratory viruses that can cause severe lung damage when infected. The emergence of the novel coronavirus SARS-CoV-2 in late 2019 has caused a large-scale epidemic worldwide. It is essential to establish an ideal animal model to test the effectiveness of possible treatment and prevention strategies. Mice are the model laboratory animals most commonly used to construct animal models of viral pneumonia. Using mice to mimic human viral pneumonia is an important step in studying disease pathogenesis, evaluating vaccine candidates, and developing antiviral drugs. As an enveloped single-stranded RNA virus, mouse pneumonia virus (PVM) is a natural pathogen in rodents and an alternative pathogen that can mimic the clinical and pathological characteristics of human respiratory syncytial virus (RSV) pathogens for the exploration of acute respiratory virus sensation.

The immune response caused by viral infection can inhibit the proliferation of pathogens; However, the immune response can also cause severe pathological damage. The innate immune system plays an important role in the body's fight against viral infections. Innate immune cells, such as macrophages, are abundant in the lung microenvironment and can be polarized into M1 and M2 phenotypic macrophages, which play a pro-inflammatory and anti-inflammatory response and tissue remodeling role in host defense, respectively. Accumulating evidence suggests that macrophage polarization is regulated by cytokines, chemokines, and transcription factors. The polarization regulation of macrophages is closely related to the occurrence and development of viral pneumonia, and precise regulation of macrophages may be a potential treatment option for viral pneumonia. Innate immune molecules, such as the alarm hormone HMGB1, play a role in initiating and regulating innate immune responses and adaptive immune responses in viral pneumonia. Viral infection has been shown to promote the secretion of HMGB1 and other cytokines in bronchoalveolar lavage fluid, and HMGB1 can induce inflammatory responses and promote tissue damage during infection through paracrine mechanisms.

We also noticed that external pathogenic stimuli have a certain impact on the body's immune system, in addition to direct or indirect inflammatory damage to tissues. A 2012 study reported that the innate immune system has memory capacity. Innate immune cells undergo metabolic reprogramming and epigenetic modification after a single stimulation, and exhibit an efficient and rapid response after receiving another stimulation, which is called trained immunity, or silencing. This phenomenon was first reported in training immune inducers containing bacterial and fungal components, such as BCG and β-glucan. Studies have reported that some COVID-19 patients have an increased susceptibility to other non-coronavirus pathogens after recovery.

We ask the following questions: What role does the innate immune system play in the occurrence and development of viral pneumonia? Is there an innate immune memory after viral infection, and if so, what is the mechanism by which the innate immune memory is established? Is the key innate immune factor HMGB1 altered? Can these changes be moderated, and do they cause changes in disease prognosis?

In order to explore the above questions, we used MHV to infect mice, and after the virus was cleared, they were re-infected with mycoplasma and PVM, and an animal model of secondary infection was established, and innate immune memory was studied. A cell model of macrophage virus infection was established by inoculating RAW264.7 cells infected with MHV, and its value as an in vitro research model of macrophage infection was verified by transcriptomic analysis, and the core genes that may be related to the establishment of innate immune memory were preliminarily screened. An animal model of viral pneumonia was established by using PVM to infect BALB/c mice, and on the basis of this model, innate immune intervention and regulation of alarm hormone molecules such as HMGB1 were studied.

Through experiments on secondary infection animals, we found that compared with the animals with primary infection, the pathological damage of other pathogens was reduced, the proportion of immune cells in lung tissue was changed, and the expression levels of genes related to gene post-transcriptional translation, glucose metabolism and oxidative phosphorylation were changed in lung tissue cells. In the experiment of MHV infection of mouse macrophages, we found that the expression levels of inflammation-related genes and metabolism-related genes of macrophages changed at different times after MHV infection, and the polarization phenotype of macrophages changed with time. The inhibition of the production and displacement of the alarm hormone HMGB1 by administration of viral pneumonia mice effectively improved the clinical manifestations of pneumonia in infected mice, and the pathological damage of lung tissue was reduced and the level of inflammatory factors was significantly reduced.

Through the research work in this paper, we found that HMGB1 can be used as a node to regulate the innate immune response of viral pneumonia, and verified the pharmacodynamic effect of glycyrrhizic acid in viral pneumonia. It was found that the innate immunity of mice infected with MHV coronavirus was in a state of trained immunity, which was inconsistent with the reduced immunity of humans to other pathogens after infection with the novel coronavirus reported in the literature. In the transcriptome study of MHV-infected macrophages, the inflamed cell model can verify the process of innate immune response to a certain extent, and can reflect the process of immune memory.