Abstract: Objective To express the recombinant antigen B（rAgB）of Echinococcus granulosus（Eg）and investigate its immunoreactivity. Methods The rAgB gene fragments were inserted into pET41a（+）prokaryotic vector. The recombinant plasmid was transformed into E. coli BL21（DE3）and followed by expression of the protein induced by isopropyl β-D-1-thiogalactopyranoside（IPTG）. The protein was purified with sepharose 4B by affinity chromatography, and tested by SDS-PAGE electrophoresis. Its immunoreactivity was examined by Western blotting, and a rapid diagnosis kit for human echinococcosis was used as control. Results The constructed recombinant plasmid pET41a-rAgB was identified by PCR, digestion with restriction enzyme and sequencing. The recombinant rAgB-GST was about Mr 40 800 with a purity of 78.4%. Western blotting showed that the positive rate of rAgB-GST reacting with sera of cystic echinococcosis（CE）, alveolar echinococcosis（AE）, paragonimiasis westermani and clonorchiasis sinensis patients, and healthy persons is 79.2%（95/120）, 51.1%（23/45）, 0（0/32）, 0（0/20）, and 0（0/24）, respectively. Its overall sensitivity and specificity were 79.2%（95/120） and 81.0%（98/121）, respectively, slightly higher than the sensitivity（72.8%, 75/103） and specificity （76.9%, 30/39）of the rapid diagnosis kit for human echinococcosis. Conclusion The rAgB-GST recombinant protein is recognized by the sera of CE and AE patients, showing a proper immunoreactivity.

Key words: Echinococcus granulosus, Recombinant antigen B, Immunodiagnosis