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The protective efficacy of recombinant vaccines encoding an Eimeria refractilebodyantigen SO7 was assessed in broiler chickens following oral infection with Eimeria tenella.The SO7 and chicken IL:2 geneswere cloned into the expression vector pVAX 1 consecutively to construct DNA vaccines pVAX:SO7 and pVAX:SO7:IL:2.Expression of SO7 and IL:2 gene transcripts and proteins encoded by the plasmid DNAs in vivo was detected by reverse transcription:polymerase chain reaction and Western blot.Chickens were inoculated with 100 1g ofplasmids pVAX:SO7 or pVAX:SO7:IL:2,or 200 ug of recombinant SO7 protein or chicken IL:2 protein by leg intramuscular injection.At 28 days of age,all chickens except the unchallenged control group were challenged orally with 5104 sporulated oocysts of E.tenella.All chickens were euthanized to determine the effects of immunization on the 7th day post:challenge.The results showed that both DNA vaccines containingthe SO7gene and the recombinant SO7protein could obviously alleviate body weight loss andcecal lesions comparedwith unvaccinated and challenged control.These findings also suggested that chicken IL:2could effectively enhance the immunity of SO7 against E.tenella challenge compared with vaccination using pVAX:SO7 alone.