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

Development and Immunogenicity Study of Subunit Vaccines Based on Spike Proteins of Porcine Epidemic Diarrhea Virus and Porcine Transmissible Gastroenteritis Virus

Porcine epidemic diarrhea virus (PEDV) and transmissible gastroenteritis virus (TGEV) are responsible for significant economic losses in the swine industry. The S1 proteins of these viruses serve as key targets for vaccine development. In this study, prokaryotic expression vectors for pCZN1-PEDV S1, pCZN1-TGEV S1, and pCZN1-PEDV S1-TGEV S1 were constructed. The corresponding proteins were expressed, purified, and used to prepare monovalent, bivalent, and mixed (PEDV S1 + TGEV S1) vaccines. Kunming (KM) mice were immunized with subunit vaccines, with PBS as the negative control (NC) and a commercial inactivated vaccine as the positive control (PC). Immune responses, including specific antibody (IgG, IgG1, IgG2a) levels, virus neutralization, and IFN-γ production, were evaluated. All vaccines induced high levels of specific IgG, IgG1, and IgG2a antibodies. At weeks 2 and 8, the PEDV S1 + TGEV S1 vaccine induced significantly higher levels of specific IgG and IgG1 compared to the PC (p < 0.001). The PEDV S1 vaccine also induced significantly higher specific IgG2a levels than the PC at week 4 (p < 0.0001). Virus neutralization assays demonstrated that the subunit vaccines induced neutralizing antibody levels comparable to or exceeding those of the PC. Furthermore, IFN-γ levels were significantly elevated in all vaccinated groups compared to the NC (p < 0.0001), indicating a robust immune response. These results suggest that the subunit vaccines are promising candidates for the safe and effective control of both PEDV and TGEV infections.

Comparative Analysis of Cross-Protective Immunity Among Three Geographically Distinct Isolates of Eimeria kongi

Coccidiosis is one of the most significant diseases affecting the rabbit industry and is caused by Eimeria. In a previous study, we identified a new species of Eimeria kongi (E. kongi-ZJK) from the northern region of China (Zhangjiakou, Hebei Province) and studied its pathogenicity and immunogenicity. The aim of this study was to evaluate the pathogenicity, immunogenicity, and cross-immunogenicity from different geographical isolates of E. kongi for vaccine development. Two geographical isolates of E. kongi-QD from Qingdao, Shandong Province (eastern China), and E. kongi-CD from Chengdu, Sichuan Province (southwestern China), were isolated and identified. The pathogenicity, immunogenicity, and cross-immunogenicity among the three geographical isolates were evaluated. The pathogenicity results showed that after infecting rabbits with doses of 1 × 103 or fewer sporulated oocysts of E. kongi-QD and E. kongi-CD, the rabbits exhibited clinical symptoms but recovered quickly, indicating lower pathogenicity. Immunogenicity studies revealed that after immunizing rabbits with 1 × 103 sporulated oocysts of E. kongi-QD and E. kongi-CD for 14 days, followed by challenge with 1 × 104 homologous sporulated oocysts, the oocyst reduction rates in the immunized groups were 99.39% and 99.12%, respectively, compared with the non-immunized groups, demonstrating good immunogenicity. In cross-immunogenicity studies, rabbits were immunized with 1 × 103 sporulated oocysts of E. kongi-ZJK, E. kongi-QD, or E. kongi-CD and then challenged with 1 × 104 sporulated oocysts of heterologous isolate. The immunized groups showed no significant clinical symptoms, and the oocyst reduction rates ranged from 55.9% to 98.4%. E. kongi-CD exhibited cross-protection against E. kongi-ZJK and E. kongi-QD, making it an ideal candidate formulation for vaccine development.

Preliminary evaluation of the protective effect of rEi-SAG19 on Eimeria intestinalis infection in rabbits

Eimeria intestinalis is one of the most pathogenic coccidia species in rabbits. Anticoccidial treaments are the main measures to control rabbit coccidiosis now, but there are drug resistance and residues concerns. Therefore, vaccine has been used as an alternative strategy. The surface antigens (SAGs) of apicomplexan protozoa play a role in adhesion and invasion of host intestinal cells, and are considered to be potential candidate antigens for vaccines. In this study, transcriptional analysis of 5 Ei-SAGs genes at four developmental stages was conducted, then the Ei-SAG19 gene were screened out for prokaryotic expression and the reactogenicity of recombinant SAG19 (rEi-SAG19) was investigated by immunoblotting. To assessment the protective effects of rEi-SAG19, rabbits (n = 40) were randomly divided into four groups (Blank control, PBS-infected, Trx-His-S-Quil-A-infected and rEi-SAG19 immunized groups), the rEi-SAG19 immunized group was subcutaneously immunized with 100 μg rEi-SAG19 in the neck with an interval of two weeks, and challenged with 5 × 104 homologous oocysts two weeks after the second immunization. Two weeks after the challenge, all rabbits were sacrificed. After that, the level of serum specific IgG antibody was detected weekly and the level of cytokines in serum before the challenge were determined. At the end of the experiment, the weight gain, oocyst reduction rate, lesion score and anticoccidial index (ACI) were calculated. The results showed that rEi-SAG19 has a good reactogenicity. The relative weight gain rate, oocyst reduction rate and ACI of the rabbits in rEi-SAG19 immunized group were 80.51%, 72.6%, and 165.1, respectively, which has a moderate protective effect. The level of serum specific IgG antibody and IL-4 rised significantly (P < 0.05), but the levels of IL-2, IFN-γ and IL-10 had no significant difference (P > 0.05). Our results indicated that rEi-SAG19 could provides moderate protective effect against E. intestinalis infection in rabbits (ACI = 165.1). Therefore, rEi-SAG19 could be used as a vaccine candidate antigen for E. intestinalis.

Evaluation of the immunoprotective effect of the recombinant Eimeria intestinalis rhoptry protein 25 and rhoptry protein 30 on New Zealand rabbits

BACKGROUND

Rabbit coccidiosis is a parasitism caused by either one or multiple co-infections of Eimeria species. Among them, Eimeria intestinalis is the primary pathogen responsible for diarrhea, growth retardation, and potential mortality in rabbits. Concerns regarding drug resistance and drug residues have led to the development of recombinant subunit vaccines targeting Eimeria species as a promising preventive measure. The aim of this study was to assess the immunoprotective efficacy of recombinant subunit vaccines comprising EiROP25 and EiROP30 (rhoptry proteins (ROPs)) against E. intestinalis infection in rabbits.

METHODS

Cloning, prokaryotic expression, and protein purification were performed to obtain EiROP25 and EiROP30. Five groups of fifty 35-day-old Eimeria-free rabbits were created (unchallenged control group, challenged control group, vector protein control group, rEiROP25 group, and rEiROP30 group), with 10 rabbits in each group. Rabbits in the rEiROP25 and rEiROP30 groups were immunized with the recombinant proteins (100 μg per rabbit) for primary and booster immunization (100 μg per rabbit) at a two-week intervals, and challenged with 7 × 104 oocysts per rabbit after an additional two-week interval. Two weeks after the challenge, the rabbits were euthanized for analysis. Weekly collections of rabbit sera were made to measure changes in specific IgG and cytokine level. Clinical symptoms and pathological changes after challenge were observed and recorded. At the conclusion of the animal experiment, lesion scores, the relative weight increase ratio, the oocyst reduction rate, and the anticoccidial index were computed.

RESULTS

Rabbits immunized with rEiROP25 and rEiROP30 exhibited relative weight gain ratios of 56.57% and 72.36%, respectively. Oocysts decreased by 78.14% and 84.06% for the rEiROP25 and rEiROP30 groups, respectively. The anticoccidial indexes were 140 and 155. Furthermore, there was a noticeable drop in intestinal lesions. After the primary immunization with rEiROP25 and rEiROP30, a week later, there was a notable rise in specific IgG levels, which remained elevated for two weeks following challenge (P < 0.05). Interleukin (IL)-2 levels increased markedly in the rEiROP25 group, whereas IL-2, interferon gamma (IFN-γ), and IL-4 levels increased substantially in the rEiROP30 group (P < 0.05).

CONCLUSION

Immunization of rabbits indicated that both rEiROP25 and rEiROP30 are capable of inducing an increase in specific antibody levels. rEiROP25 triggered a Th1-type immune protection response, while rEiROP30 elicited a Th1/Th2 mixed response. EiROP25 and EiROP30 can generate a moderate level of immune protection, with better efficacy observed for EiROP30. This study provides valuable insights for the promotion of recombinant subunit vaccines targeting rabbit E. intestinalis infection.