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This paper was about the study on the mechanism of Microtus fortis against Schistosoma japonicum. Firstly,we confirmed that Microtus fortis came from epidemic region (Dongting Lake beaches) and non-epidemic region (Qingtong Gorge in Ningxia province) were both resistant to Schistosoma japonicum infection after re-infection tests for several times. It seemed that their resistant ability was inheritable rather than acquired. Secondly, it was demonstrated by in vivo check-up and in vitro killing assay that there were some native antibodies of IgG3 subclass specifically to the schistosomula and adult worm of Schistosoma japonicum in Microtus fortis, which probably played an important role in resisting Schistosoma japonicum associated with complement. It was shown that macrophages and eosinophils in abdominal cavity of Microtus fortis had native ability of adhering to the schistosomula of Schistosoma japonicum. Then, the adult worm cDNA library of Schistosoma japonicum was screened with sera from Microtus fortis. Five positive clones were obtained, four of which were identified as new genes. Full-length cDNA of the two new genes were isolated by RACE. DNA vaccine was constructed with one named EST-mfs-3. After the Kunming mice immunized with this vaccine, the worm reduction rate and the egg reduction rate were 28.4% and 21.73% compared with that in control group respectively. This kind of DNA-based EST-mfs-3 vaccine was highly expressed in E. coli and induecd strong immune response in challenged group.Finally, two groups of cDNA probes prepared from liver and lung of Microtusfortis with or without Schistosoma japonicum infection were hybridized to the eDNA chip prepared from rat respectively. 156 and 332 genes revealed differential expression in infectious group compared with normal group. In conclusion, there would be many factors contribute to the mechanism of Microtusfortis against Schistosoma japonicum. We should stress the essentials and make further research on how to take advantage of them to defend us from Schistosoma japonicum infection.