Assessment of the Immunoprotective Efficacy of Recombinant 14-3-3 Protein and Dense Granule Protein 10 (GRA10) as Candidate Antigens for Rabbit Vaccines against Eimeria intestinalis .

Eimeria intestinalis infects rabbits, causing severe intestinal coccidiosis. Prolonged anticoccidial drug use might lead to coccidia resistance and drug residues in food. Thus, vaccines are required to control rabbit coccidiosis. In this study, recombinant E. intestinalis 14-3-3 and GRA10 proteins (r Ei -14-3-3 and r Ei -GRA10) were obtained via prokaryotic expression and used as recombinant subunit vaccines. Fifty 30-day-old rabbits were randomly grouped as follows: PBS-uninfected group, PBS-infected group, Trx-His-S control group, and r Ei -14-3-3 and r Ei -GRA10 immunized groups. The rabbits were subcutaneously immunized twice at 2-week intervals, challenged with 7 × 104 sporulated oocysts, and sacrificed 14 days later. The protective effects were assessed via clinical signs, relative weight gain, oocyst reduction, mean intestinal lesion score, ACI (anticoccidial index), cytokine, and specific antibody levels in sera. The r Ei -14-3-3 and r Ei -GRA10 groups had higher relative weight gain rates of 81.94% and 73.61% ( p < 0.05), and higher oocyst reduction rates of 86.13% and 84.87% ( p < 0.05), respectively. The two immunized groups had fewer intestinal lesions ( p < 0.05) and higher IgG levels ( p < 0.05). Higher levels of IL-2, IL-4, and IFN-γ cytokines in the r Ei -14-3-3 group ( p < 0.05) and a higher level of IFN-γ in the r Ei -GRA10 group ( p < 0.05) were observed. The ACI values of the r Ei -14-3-3 and r Ei -GRA10 groups were 168.24 and 159.91, with good and moderate protective effects, respectively. Both r Ei -14-3-3 and r Ei -GRA10 induced humoral immunity in the rabbits. In addition, r Ei -14-3-3 induced Th1- and Th2-type immune responses. Both recombinant proteins were protective against E. intestinalis infection in rabbits, with r Ei -14-3-3 showing a better protective effect.