Protective immunity against Eimeria necatrix infection in Chickens induced by immunization with the recombinant gametocyte antigen EnGAM22

Macrogametocyte stage antigens reportedly provide protective immunity against coccidiosis in poultry. This study was designed to evaluate the ability of a purified recombinant protein from Eimeria necatrix gametocytes (rEnGAM22) to stimulate immunity against experimental infection with sporulated E. necatrix oocysts. The immunogenicity of the recombinant protein was studied in chickens by subcutaneous injection of 25, 50, or 75 µg of the protein with Freund’s adjuvant. Vaccine efficacy was assessed after oral parasite challenge by fecal oocyst output, lesion scores, body weight gain, serum antibodies, and cytokine responses. Chickens vaccinated with 50 µg of rEnGAM22 and challenged with sporulated E. necatrix oocysts showed reduced fecal oocyst shedding and lesion scores compared with other immunized groups and the infected control group, with the exception of the live oocyst group. There was no difference in body weight between the immunized groups and the infected control group. Furthermore, rEnGAM22 also stimulated higher production of anti-rEnGAM22 serum antibodies 7 days after secondary immunization, especially with 50 µg of rEnGAM22. Serum levels of interleukin (IL)-2, IL-4, IL10, and interferon (IFN)-γ also showed the greatest immune response from 50 µg of rEnGAM22, and IL-2 and IL-4 responses were greater than those of IL-10 and IFN-γ. These results indicated that rEnGAM22 protected against E. necatrix infection to some degree and may potentially be used to develop a recombinant subunit vaccine against coccidiosis.