血吸虫感染小鼠早期诊断抗原的研究

Evaluation of early diagnostic value of 6 antigens from Schistosoma japonicum in mice

目的对已知的6种日本血吸虫抗原的早期诊断价值进行评价,为研制用于哨鼠早期诊断的免疫试剂提供候选抗原。方法用日本血吸虫尾蚴感染小鼠,收集感染前及感染后不同时间的小鼠血清。采用重组日本血吸虫中国大陆株23kDa膜蛋白大亲水性肽段与谷胱甘肽的融合表达蛋白(GST-HD)、可溶性虫卵抗原(SEA)、血吸虫四跨膜蛋白第二亲水基团(TSP2HD)、血吸虫虫卵蛋白(IPSE)、日本血吸虫虫卵毛蚴抗原(SjMP-10)及日本血吸虫信号蛋白(Sj14-3-3)作为诊断抗原,采用酶联免疫吸附试验检测感染血吸虫后不同时间小鼠血清中特异性抗体IgM和IgG水平,通过分析感染后不同时间点抗原特异性抗体水平变化及阳性率,筛选具有血吸虫感染早期诊断价值的抗原分子。采用免疫印迹试验进一步验证其对血吸虫急性感染早期诊断的价值。结果感染后第18、21、28天,抗GST-HD抗体IgM阳性率分别为60%、70%、100%,特异性IgG阳性率分别为40%、60%、90%;抗SEA抗体IgM阳性率为50%、60%、90%,特异性IgG阳性率为20%、50%、70%;抗TSP2HD抗体IgM阳性率为30%、40%、50%,特异性IgG阳性率为20%、30%、70%;抗IPSE抗体IgM阳性率为20%、30%、50%,特异性IgG阳性率为20%、30%、60%;抗SjMP-10抗体IgM阳性率为10%、20%、20%,特异性IgG阳性率为10%、20%、30%;抗Sj14-3-3抗体IgM阳性率为0、10%、20%,特异性IgG阳性率为0、10%、30%。以GST-HD融合蛋白和SEA为抗原,检测小鼠早期感染血吸虫的敏感性高于Sj14-3-3、IPSE、TSP、MP-10,检测IgM的敏感性高于IgG。免疫印迹试验结果显示,SEA中分子量在73kDa左右的蛋白条带可被感染后1周小鼠血清所识别,并随着时间推移反应加强。GST-HD最早出现反应的血清是感染后第10天小鼠血清,反应强度在感染后第5周达到最强。结论重组GST-HD融合蛋白与SEA中分子量约73kDa的蛋白分子具有血吸虫感染早期诊断价值,免疫印迹试验的敏感性比酶联免疫吸附试验高。

Objective To find out the candidate antigen for immunoreagent, which could be used to diagnose Schistosoma japonicum infection early in mice. Methods The mice were infected with cereariae of S. japonicum Chinese mainland strain. The sera of mice before and after infection at different time were collected. The recombinant fusion protein （GST-HD） of the large hydrophilic domain （HD） of 23 kDa membrane protein of S. japonicum with the Glutathione-S-transferase （GST） of S. japonicum, soluble eggs antigen （SEA）, TSP2 hydrophilic domain of S. japonicum （TSP2HD）, IL4-inducing principle of S. mansoni eggs （IPSE）, fusion protein GST-SjMP10 （SjMP-10）, and recombinant S. japonicum （Chinese strain） signaling protein 14-3-3 （Sj14-3-3） were used as diagnostic antigens, the specific IgG and IgM antibodies were measured respectively by enzyme linked immunosorbent assay （ELISA）. The antigens with the value of diagnosing schistosomiasis early were screened by analyzing the changes of the levels of specific IgG （or IgM） antibodies and the positive rates of specific antibodies in the sera of mice before and post infection at different time. Moreover, the antigen’s value of early diagnosis was further validated by Immunoblot. Results On the 18th, 21st and 28th day post infection, the positive rates of specific antibody IgM against GST-HD were 60%, 70% and 100%, respectively; the positive rates of specific antibody IgG against GST-HD were 40%, 60% and 90%, respectively. The positive rates of antibody IgM against SEA were 50%, 60% and 90%, respectively; the positive rates of antibody IgG against SEA were 20%, 50% and 70%, respectively. The positive rates of IgM against TSP2HD were 30%, 40% and 50%, respectively; the rates of IgG against TSP2HD were 20%, 30% and 70%, respectively. The positive rates of IgM against IPSE were 20%, 30% and 50%, respectively; the positive rates of IgG against IPSE were 20%, 30% and 60%, respectively. The positive rates of IgM against SjMP-10 were 10%, 20% and 20%, respectively; the rates of IgG against SjMP-10 were 10%, 20% and 30%, respectively. The positive rates of IgM against Sj14-3-3 were 0, 10% and 20%, respectively; the rates of IgG against Sj14-3-3 were 0, 10% and 30%, respectively. The sensitivities of GST-HD and SEA for diagnosing schistosome infection early in mice were significantly higher than those of Sj14-3-3, IPSE, TSP, and MP-10. The sensitivity of IgM was higher than that of IgG. In Western blotting, the about 73 kDa protein band of SEA was recognized by sera of mice one week post infection and showed stronger reaction as the infected time went on. Moreover, the bands （33 kDa） of GST-HD were earliest recognized by the mouse sera on the 10th day post-infection, the bands showed strong reaction with the mouse sera of 5-week post-infection. Conclusions The GST-HD fusion protein and the protein of which molecular weight is about 73 kDa of SEA have the early diagnostic value for schistosomiasis, and the sensitivity of Immunoblot is higher than that of ELISA.