Abstract: 【Objective】 The aim of the experiment is to screen and clone antigen genes of Schistosoma japonicum specific to the sera of Microtus fortis and study the protective efficiency. 【Method】A cDNA library of Schistosoma japonicum adult worm was immunologically screened with the sera from Microtus fortis infected with the schistosome. Then mice were immuned with DNA vaccine of SjPP to evaluate the immunological protective efficiency. 【Result】(1) Five positive clones, mfs-1, mfs-2, mfs-3, mfs-4 and mfs-5, were obtained and their sequences were deposited with GenBank under accession No. BE974942, BE974943, BE974944, BE974945, BE974946 respectively. (2) A full length cDNA fragment containing a complete open reading frame coding 302 amino acid sequences (Mr=34.7kD, pI=5.51) was amplified. Sequence analyses revealed that it was a novel gene which deduced amino acid sequence contain a conserve sequence (LRGNHE) of serine/threonine specific protein phosphatases, as well as a binding site (SAPNYC) of the phosphatase's specific inhibitor okadaic acid. The gene was showed high homology to other protein phosphatases such as human PP6 (72%), PP4C (59%), rat PPV (71%), fruit fly PPV (70%), fission yeast ppe1 (63%), budding yeast sit4p (61%) and was named as SjPP. (3) Compared with those of the blank control group, 23.91% reduction in mean hapetic tissue egg count and 31.91% reduction in mean faecal egg count were recovered in the mice injected with the recombinant plasmid pCMV-Script/SjPP. 【Conclusion】(1) A novel antigen gene of Schistosoma japonicum, SjPP, was cloned and identified. (2) The partial protection was obtained in the mice vaccinated with the DNA vaccine pCMV-Script/SjPP.

Key words: Schistosoma japonicum, Microtus fortis, serine/threonine specific protein phosphatase, nucleic acid vaccine, immunity