CD24分子调节急性肝损伤的免疫机理研究

Immunological regulation of acute liver injury is one of the major topics of today's immunology and liver disease research areas. In recent studies, CD24, also known as the heat-stable antigen (HSA), is expressed as a glycosyl-phosphatidyl-inositol (GPI)-anchored molecule, however, what the kinds of immunological cells in liver can express CD24 and how the CD24 regulates the inflammation remain unresolved. More recently, we found administration of anti-CD24 antibody caused rapid death of wild-type (WT) mice-induced by pertussis toxin (PTX) within 12 hours, which is accompanied by increasing amounts of serum alanine transaminase (ALT), aspartate aminotransferase (AST) and liver hemorrhage, meanwhile, we detected a massive increase in the inflammtory cytokines tumor necrosis factor-alpha (TNF-a) after PTX and anti-CD24 antibody treatment. Furthermore,using CD24-/- mice，we also got similar results. To test whether the absence of T and B cells can affect these results, we repeated these experiments using Rag-/- mice, and found all of these indicative of liver damage keeping the similar results,this suggests that CD24 regulating the mouse model of PTX-induced acute liver injury may be mainly related to liver innate immune.On the basis of these discoveries, we hypothesize that CD24 may serve as an important negative regulator for acute liver injury, which expresses on the surface of one or several kinds of the innate immunological cells in the liver, inhibits immune response and inflammation, and protects the host against attack of foreign pathogens and its derivatives. Therefore, we will try to explore the following key scientific questions: 1) what is the role of CD24 in acute liver injury? 2) How dose CD24 distribute in liver? 3) what is the molecular mechanisms of CD24 regulating acute liver injury? Our proposed studies will not only contribute to clarify the immunological mechanisms of CD24 in the regulation of acute liver injury, but also deepen the understanding of pathogen or damage-induced inflammatory response in the liver of host, furthermore, and to uncover new drug targets for the clinical treatment on liver diseases.

CD24分子是一种具有免疫调节作用的糖基化磷脂酰肌醇锚定分子，其免疫调节机制尚不清楚。我们发现：anti-CD24中和抗体能加重野生型小鼠肝损伤，表现为小鼠死亡率升高、肝出血、谷丙转氨酶等肝功能指标以及血清中TNF-α明显增加，利用CD24-/-小鼠进一步证实了该结果。利用Rag1-/-小鼠，重复上述实验发现小鼠的各项指标无明显改变。我们假设：CD24分子可能是急性肝损伤的一个重要负反馈调节分子，在肝脏中某种或几种固有免疫细胞上表达，通过调节固有免疫反应抑制肝内炎症反应和肝损伤的发生。本研究中我们试图解决如下几个关键的科学问题：1）肝内CD24表达与急性肝损伤的关系；2）CD24在肝内的细胞学分布；3）CD24分子调节急性肝损伤的细胞学基础和相关分子机理。本研究有助于系统阐明CD24分子调控急性肝损伤的免疫学机制，加深病原体在宿主肝内炎症反应调节机制的理解，为肝病治疗寻找新的药物。

肝脏损伤是所有肝脏疾病的基础，免疫介导的肝损伤一直是肝病研究领域的重点问题。近年来的研究成果正在揭示各种肝脏疾病的肝内免疫反应和免疫抑制平衡调节的精细机制，但肝内炎症反应的负向调节机制尚待进一步阐明。CD24分子，即热稳定抗原（HSA），是一种糖基化磷脂酰肌醇（GPI）锚定分子，最新的研究成果正在揭示CD24分子在免疫反应中的负反馈调节作用。我们在前期实验的基础上提出以下假设：CD24分子可能是机体内急性肝损伤的一个重要负反馈调节分子，在肝脏中某种或多种固有免疫细胞上表达，通过调节Kupffer等肝内固有免疫细胞保护肝脏免于百日咳毒素等病原体及衍生物的攻击。本课题的主要研究内容包括：1.观察CD24分子对百日咳毒素（PTX)诱导急性肝损伤的调节作用，CD24分子在肝脏中的表达和细胞分布； 2.解析CD24分子表达对急性肝损伤中固有免疫，尤其是对肝内kupffer细胞的免疫调节；3.揭示CD24分子保护百日咳毒素诱导肝损伤的分子机理。本研究中通过建立Con A和LPS诱导的小鼠急性肝损伤模型证实了CD24分子在急性肝损伤中的调节作用；观察到了CD24分子在小鼠急性肝损伤的肝内巨噬细胞和NKT细胞表达变化相对较高，而中性粒细胞、树突状细胞和NK细胞较低；解析了CD24分子调节小鼠急性损伤作用与肝内巨噬细胞及其亚型的关系，国际上首次发现了CD24分子主要通过肝内M1型巨噬细胞调节小鼠的急性肝损伤；发现了CD24分子对小鼠的急性肝损伤调节与肝内HMGB1表达呈正相关，证实了HMGB1的表达与Siglects家族中的Siglect-G的表达相关，提出了HMGB1-CD24-Siglect-G可能是CD24分子调节小鼠急性肝损伤的主要信号传导通路。上述结论基本完成了我们预定的研究目标，在此基础上我们还开展了CD24分子对肝内NKT细胞调节作用、对肝纤维化的调节作用及其相关机制以及由基础研究到临床转化方面的研究工作。本课题研究揭示了CD24分子在急性肝损伤的免疫调节机理，对肝脏免疫损伤的天然免疫识别机制及天然免疫调控机制提出了新的解释，有助于对肝炎等重大传染性疾病的机理提出重要见解，并可能提供潜在的诊治靶点。