目的:对人源程序性死亡因子1配体2(PD-L2)的B细胞表位进行预测及其与PD-1结合的三维结构分析。方法:采用生物信息学分析软件及服务器上的在线分析系统预测人类PD-L2蛋白的二级结构,柔性区域,Hopp&Woods亲水性、Zimmerman极性参数和Jameson-Wolf抗原指数以及Emini表面可及性方案等,预测结果被用以对PD-L2的优势B细胞表位区段进行多方面分析。运用抗原指数分析,预测PD-L2的B细胞表位。使用BLAST分析人源PD-L2与小鼠PD-L2的同源性,将人源PD-L2的B表位与小鼠PD-L2的序列进行匹配。将与人源PD-L2表位匹配的序列在小鼠PD-1与小鼠PD-L2的结合模型上定位,对其立体结构进行模拟,进一步直观地分析B细胞表位与蛋白结合位点的关系。结果:PD-L2的全长氨基酸序列共含有273个氨基酸,相对分子质量为31 k Da的可溶性蛋白;经综合分析,其B细胞优势表位可能为氨基酸序列N端的60~72、93~97、133~139、164~171区段。模拟立体结构分析显示表位60~72区段"QKVENDTSPHRER"位于PD-1与PDL2的结合区域内。结论:利用生物信息学预测发现PD-L2的优势B细胞表位中,60~72、93~97、133~139、164~171区段为PD-L2的B细胞表位,其中表位60~72区段"QKVENDTSPHRER"位于PD-1与PD-L2的结合区域内。可为PD-L2抗体设计和研究提供理论基础。
Epstein-Barr virus （EBV） is prevalent throughout the world and is associated with several malignant diseases in humans. Latent membrane protein 2 （LMP2） of EBV plays a crucial role in the pathogenesis of EBV-associated tumors; therefore, LMP2 has been considered to be a potential immunodiagnostic and immunotherapeutic target. A multi-epitope-based antigen is a promising option for therapeutic vaccines and diagnoses of such malignancies. In this study, we systematically screened cytotoxic T lymphocyte （CTL）, helper T cell （Th） and B-cell epitopes within EBV-LMP2 using bioinformatics. Based on the screen, two peptides rich in overlapping epitopes of both T cells and B cells were selected to construct a plasmid containing the sequence for a chimeric multi-epitope protein referred to as EBV-LMP2m, which is composed of LMP2aa195-232 and LMP2aa419-436. The EBV-LMP2m protein was expressed in E. coil BL21 （DE3） after prokaryotic codon optimization. Inoculation of the purified chimeric antigen in BALB/c mice induced not only high levels of specific IgG in the serum and secretory IgA in the vaginal mucus but also a specific CTL response. By using purified EBV-LMP2m as an antigen, the presence of specific IgG in the serum specimens of 202 nasopharyngeal carcinoma （NPC） patients was effectively detected with 52.84% sensitivity and 95.40% specificity, which represents an improvement over the traditional detection method based on VCA-IgA （60.53% sensitivity and 76.86% specificity）. The above results indicate that EBV-LMP2m may be used not only as a potential target antigen for EBV-associated tumors but also a diagnostic agent for NPC patients.
