CD72在原发免疫性血小板减少症B细胞中的表达及调控研究

CD72 is one of co-receptors of B cells，which is involved in immune reaction of B cells, and plays an important role in autoimmune diseases. Our preliminary study showed that CD72 mRNA levels of expression of peripheral mononuclear cells in primary immune thrombocytopenia (ITP) patients were significantly decreased. The proportion of B cells in lymphocytes was higher in patients with active ITP. In addition, CD72 expression was increased on B cells and CD19+CD27+ memory B cells in ITP patients with active diseases, which was correlated significantly with the platelet counts. These data suggested that CD72 may be involved in the regulation of B cellular immunity in ITP. In this project we will evaluate the CD72 expression on B cell subsets of the ITP patients, and explore the role of CD72 in ITP on B cell proliferation, apoptosis, differentiation, antibody formation, the role of CD72 on the function of the B regulatory cell, the role of CD72 on the respond of B cell induced by B cell activating factor via in vitro and in vivo animal model. Understanding the mechanism of CD72 regulation of B cell function in ITP will provide the theoretical basis for the target of the treatment.

CD72是B细胞共受体之一，参与B细胞的免疫反应，在自身免疫性疾病中起到重要作用。我们前期研究结果显示原发免疫性血小板减少症（ITP）患者外周血单个核细胞CD72 mRNA表达显著减低。ITP活动期患者B细胞在淋巴细胞中的比例增高。CD72在B细胞及CD19+CD27+记忆B细胞表达增高，并与血小板计数呈负性相关。这些结果提示ITP患者CD72可能参与B细胞免疫调控。本项目中我们拟通过体外和体内小鼠模型实验检测B细胞不同亚群CD72表达情况，研究CD72在ITP患者B细胞增殖、凋亡、分化、抗体形成中的作用，CD72对B调节细胞功能的影响，以及CD72对B细胞激活因子介导B细胞反应的影响，探讨CD72调控B细胞功能参与ITP发病的作用机制，为CD72作为靶点治疗提供理论依据。

CD72是广泛表达在B细胞表面的共受体，是决定B细胞抗原受体（BCR）信号阈值的关键分子，通过与BCR交联，调控BCR信号传导，因而CD72在I型糖尿病、自身免疫性血管炎等自身免疫性疾病中起到重要作用。我们课题组前期研究发现CD72第8内含子重复序列多态性与ITP患者初次发病年龄显著相关，且活动期患者外周血单个核细胞的CD72mRNA表达与血浆炎症因子IL-2水平呈正相关，综上所述，我们推测CD72可能通过调控B细胞功能，参与ITP的发生与进展。研究发现：（1）ITP患者CD19+B细胞比例、CD19+CD27+记忆B细胞比例明显高于正常对照组及缓解组，而CD19+CD27-B细胞比例明显低于正常对照组及缓解组。ITP患者各B细胞亚群表面CD72的平均荧光强度（MFI）明显高于正常对照组和缓解组，且与血小板计数及是否携带抗血小板自身抗体相关。（2）体外实验证实，CD40L诱导CD72在CD19+CD27+B细胞上表达；而IL-21抑制CD40L对CD72的诱导作用。活动期ITP患者CD4+T细胞CD40L表达与对照组比较明显升高，且与CD19+CD27+B细胞上CD72表达呈正相关。（3）ITP患者B细胞表面CD40活化能上调其表面CD72的表达，CD72的上调进一步促进B细胞表面CD80/86的表达、B细胞增殖、浆细胞分化及抗体产生，同时抑制B细胞凋亡，最终进一步促进自身抗体的产生，加速疾病进程。（4）体外实验显示加入anti-CD72阻断B细胞表面CD72信号通路后，能明显逆转自身免疫反应。本研究的进行进一步拓宽了我们对ITP发病机制的认识，同时也为将来以CD72为靶点的治疗提供理论依据。该项目共发表文章15篇，其中SCI文章9篇。培养博士毕业生4名。