Abstract: Objective To induce protective effect of co-immunization with S.japonicum triose-phosphate isomerase fused to heat shock protein 70 （SjCTPI-Hsp70） plasmid and interleukin-12 （IL-12） DNA vaccines against Schistosoma japonicum （Chinese strain） infection in water buffalo. Methods Forty-five 8-10 months-old water buffalo from a non-endemic area were divided into three treatment groups each with fifteen buffalo: experimental group A （SjCTPI-Hsp70+IL-12， 300 μg）， experimental group B （SjCTPI+IL-12， 300 μg）， and control group C （pVAX+IL-12， 300 μg）. All buffalo were immunized with a series of 3 intramuscular injections administered once every four weeks. Twenty-eight days post-vaccination， water buffalo were percutaneously challenged with 1 000 S.japonicum cercariae. Fecal examinations were con-ducted two days prior， one day prior， and on perfusion day， and the number of hatching miracidia and eggs per gram feces were recorded. Fifty-six days post-infection， the buffalo were sacrificed and perfused via the descending aorta. The recovered adult worms and eggs in liver tissue were counted. Results Groups A and B showed a worm reduction rate of 51.2% and 41.5% （χ²=1.89，P＞0.05））， female worm reduction of 48.9% and 44.7%（χ²=0.35，P＞0.05）， fecal egg reduction of 52.1% and 38.3%（χ²=3.84，P＜0.05）， a reduction of miracidia-hatching rate by 52.1% and 33.2% （χ²=7.30，P＜0.01）， and liver egg reduction of 61.5% and 42.0% （χ2=7.61，P＜0.01）， respectively. Conclusion Co-immunization with SjCTPI-Hsp70 and IL-12 DNA vaccines induces protective immunity against S.japonicum in water buffalo.

Key words: Schistosoma japonicum, SjCTPI-Hsp70, DNA vaccine, IL-12, Co-immunization, Water buffalo, Protective immunity