Evaluation of the immune protective efficacy afforded by a telomerase interacting protein OTU in Eimeria tenella

Chicken coccidiosis threatens the development of the poultry industry. The protective antigen genes applied to genetically engineered vaccines against Eimeria tenella ( E. tenella ) include TA4, SO7, 3-1E and MIC etc, while their immunoprotective effects are unsatisfactory. So selecting a novel antigen is very important to design genetically engineered vaccines. Ovarian tumor proteases (OTU) is a telomerase-interacting protein in E. tenella , but its immunoprotective effect on E. tenella infection has not been reported. Recombinant prokaryotic expression plasmid pET32a-EtOTU was constructed, and the recombinant E. tenella OTU (rEtOTU) protein was expressed and checked through immunoblot. The localization of the OTU protein within sporozoites was examined using indirect immunofluorescence techniques. The immunoprotective efficacy of rEtOTU was evaluated through the anticoccidial index (ACI), while levels of IgY/IgG, IFN-γ, IL-10, and IL-2 were quantified using ELISA. Histopathological assessment was performed via hematoxylin and eosin (HE) staining. The findings revealed that the OTU protein predominantly localized in the cytoplasm of E. tenella sporozoites. The recombinant OTU protein (rEtOTU) displayed better reactogenicity and the ACI of rEtOTU immunization group was 168.65. Meanwhile, the rEtOTU protein stimulated higher levels of IgY/IgG, enhanced the proliferation of splenic T lymphocytes, and elevated the productions of IL-2 and IFN-γ. HE staining results further verified that obvious histopathological changes were not observed in the tissues and organs of rEtOTU-immunized chickens after E. tenella infection. In conclusion, this study demonstrates that the rEtOTU protein can effectively induce immune protection against E. tenella infection and may serve as a promising candidate antigen for the development of genetically engineered vaccines against chicken coccidiosis.