Abstract: Objective   To analyze reactive epitope of three subunit antigens AgB1，AgB2 and AgB4 of Echinococcus granulosus by using synthetic peptides.  Methods   Five synthetic peptides，KK36，RK30，B4-1，B4-2，and B4-3，derived from the sequences of AgB1，AgB2，and AgB4 subunit of E. granulosus，and the three recombinant subunits were used for the detection of serum antibodies by ELISA. A panel of 209 serum samples from patients with cystic echinococcosis （115），alveolar echinococcosis （54），cysticercosis （22），and healthy persons （18） was used in the study. The diagnostic efficiency of the recombinant subunits and peptides for serum detection was estimated and compared using receiver-operating characteristics （ROC） curve.  Results   The sensitivity and specificity of peptides KK36 and RK30 in patients with cystic echinococcosis were 89.2% and 62.5%，85.0% and 59.4%，respectively. Their diagnostic efficiency （84.8% and 80.4%） was similar to AgB1 and AgB2 antigen （84.5% and 81.2%）. The ROC curves of peptides KK36 and RK30 were well fitted by that of recombinant subunit AgB1 and AgB2. For the three peptides derived from AgB4 subunit，serum detection indicated that the diagnostic efficiency of B4-1，B4-2 and B4-3 were 49.4%，57.9%，and 77.4%，respectively. Peptides B4-3 showed best reactivity and B4-2 also showed certain reactivity to the sera from patients with cystic echinococcosis.   Conclusion   Peptides KK36 and RK30 contain the reactive epitope region of AgB1 and AgB2 subunits. B4-2 and B4-3 contain partial region of the reactive epitope of AgB4. The epitope region of AgB4 may be in the central and back part.

Key words: Echinococcus granulosus, AgB gene family, Antigen subunit, Synthetic peptide, Epitope analysis