Rhomboid Protein 2 of Eimeria Maxima Provided Partial Protection Against Infection by Homologous Species

Abstract

Background: Rhomboid-like proteases (ROMs) are considered as a new candidate antigen for developing new-generation vaccine due to their important role involved in the invasion of apicomplexan protozoa. In prior works, we obtained a ROM2 sequence of Eimeria maxima (EmROM2) which is the homologous gene with ROM2 of Toxoplasma gondii. This study was conducted to evaluate the immunogenicity and protective efficacy of EmROM2 recombinant protein (rEmROM2) and EmROM2 DNA (pVAX1-EmROM2) against infection by Eimeria maxima (E. maxima).Methods: Western blot assay was conducted to analyze the immunogenicity of rEmROM2. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assay were performed to determine the transcription and expression of pVAX1-EmROM2 recombinant plasmid. EmROM2-induced changes in transcriptional level of cytokines, T lymphocytes subsets and specific serum IgG antibody were detected through qPCR (quantitative real-time PCR), flow cytometry and indirect ELISA, respectively. Ultimately, a vaccination-challenge trial was performed to evaluate the protective efficacy of rEmROM2 and pVAX1-EmROM2 against infection with E. maxima. Results: The purified rEmROM2 was recognized with chicken anti-E. maxima serum. After vaccination with pVAX1-EmROM2, apparent transcription and translation of EmROM2 were observed in the vaccinated chickens. Vaccination with rEmROM2 and EmROM2 DNA significantly upregulated the proportion of CD8+ and CD4+ T lymphocytes, the transcription level of cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-17, TGF-β and TNF SF15) and serum IgG antibody response. Meanwhile, the vaccination significantly alleviated enteric lesions, weight loss, and reduced oocyst output caused by challenge infection of E. maxima, and provided anticoccidial index (ACI) of more than 160, indicating partial protection against E. maxima.Conclusions: Vaccination with rEmROM2 and pVAX1-EmROM2 activated notable humoral and cell-mediated immunity and provided partial protection against infection by E. maxima. These results demonstrated that EmROM2 protein and DNA are promising vaccine candidates against E. maxima infection.