关键词: 细粒棘球蚴, AgB抗原亚单位, 多表位重组抗原, 血清学分析

Abstract: Objective  To evaluate the diagnostic value of six recombinant multi-epitope antigens and three AgB subunit antigens from antigen B subunit of Echinococcus granulosus.  Methods  A linker sequence was inserted into the sequence of MEA-26 to make it an MEA-49. I-TASSER on-line server was used to analyze protein structure. The reactivity of two multi-epitope recombinant antigens with the same target sequence but in different tertiary structure was compared. The reactivity of six multi-epitope antigens（MEA-8, MEA-20, MEA-26, MEA-36, MEA-49, and MEA-52）, 3 subunit antigens （AgB1, AgB2, and AgB4）, and 2 control antigens （Trx and linker） was determined by indirect ELISA. The assays were performed on 232 serum samples separated as follows: 112 sera from patients with cystic echinococcosis, 35 sera from individuals with alveolar echinococcosis, 43 sera from patients with cysticercosis and 42 sera from healthy individuals. Their diagnostic performance was assessed by receiver operating characteristic （ROC） curve analysis.  Results  Tertiary structure prediction showed that the epitope regions of MEA-26 were closer to each other and aligned in parallel, while that in MEA-49 were farther apart from each other and formed two independent domains. Serological analysis revealed that the mean P/N value （2.88±2.02）, sensitivity （92%） and diagnostic efficiency （89%） of MEA-49 were higher than that of MEA-26 （2.54±2.02, 78% and 82%）. MEA-20　（2.24±1.31）, MEA-26 （2.54±2.02）, MEA-36 （2.44±1.51）, MEA-49（2.88±2.02） and MEA-52（2.50±1.37） showed a high reactivity to the sera from patients with cystic echinococcosis, which was superior to that of AgB1（2.15±1.26）. There was no significant difference in the reactivity to sera from individuals with alveolar echinococcosis between multi-epitope antigens and AgB1（P>0.05）. MEA-52 showed a high diagnostic sensitivity in cysticercosis cases（1.27±0.70）, superior to that of AgB1 （0.95±0.13） （P<0.01）. The reactivity of MEA-8 （1.04±0.15） to sera from healthy individuals was significantly higher than that of AgB1 （0.89±0.07） （P<0.01）. ROC analysis showed in the cases of cystic echinococcosis, the diagnostic sensitivity accomplished with AgB1, AgB2, and AgB4 was 77%, 55%, and 66%, respectively; the multi-epitope antigens of MEA-49（92%）, MEA-36（92%）, MEA-52 （87%）, and MEA-26（78%） revealed a higher sensitivity than AgB1.  Conclusion  The reactivity of multi-epitope antigens is superior to that of AgB subunit antigens. The reactivity of MEA-49 is higher than that of MEA-26 which has the same target sequence but in different tertiary structure.

Key words: Echinococcus granulosus, Antigen B subunit, Multi-epitope antigen, Serological analysis