The protective efficacy of chimeric SO7/IL-2 DNA vaccine against coccidiosis in chickens

The protective efficacy of recombinant vaccines encoding an Eimeria refractile body antigen SO7 was assessed in broiler chickens following oral infection with Eimeria tenella. The SO7 and chicken IL-2 genes were cloned into the expression vector pVAX1 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 μg of plasmids pVAX-SO7 or pVAX-SO7-IL-2, or 200 μg 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 5 × 104 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 containing the SO7 gene and the recombinant SO7 protein could obviously alleviate body weight loss and cecal lesions compared with unvaccinated and challenged control. These findings also suggested that chicken IL-2 could effectively enhance the immunity of SO7 against E. tenella challenge compared with vaccination using pVAX-SO7 alone.