Abstract: 【Abstract】 Objective To clone and express bradyzoite antigen 1（BAG1） gene of T. gondii，and analyze the immunoreactivity of the recombinant product. Methods The differentiation of T. gondii RH strain tachyzoites into bradyzoites was induced in vitro，and the coding sequence of BAG1 was amplified from bradyzoites by RT-PCR. The PCR product was analyzed by sequencing. The BAG1 coding sequence was further subcloned into the plasmid pET32a(+). The plasmid pET32a(+)-BAG1 was then transformed into BL21(DE3) to express after IPTG induction. The expression product was purified with Ni-NTA agarose and the purified BAG1 was further analyzed by Western blotting and ELISA. Results BAG1 cDNA was amplified from bradyzoites. After IPTG induction，BAG1 was expressed in a fusional form in E. coli. Western blotting showed that the purified recombinant protein could be specifically recognized by sera from mice chronically infected by T. gondii B36 strain. ELISA showed that the positive rate of T. gondii IgG antibodies of 350 human sera detected by the recombinant BAG1(17.4%) was higher than by recombinant SAG1 (12.6%)（P＜0.05）. Conclusion　 The expressed recombinant BAG1 shows a specific immunoreactivity.

Key words: Toxoplasma gondii, Bradyzoite antigen 1(BAG1), Gene expression, Immunoreactivity