Immune response and protective efficacy of Eimeria tenella recombinant refractile body protein, EtSO7, in chickens

Comprehensive analysis of differentially expressed mRNA profiles in chicken jejunum and cecum following Eimeria maxima infection

Coccidiosis, a protozoan disease that substantially impacts poultry production, is characterized by an intracellular parasite. The study utilized 48 one-day-old Horro chickens, randomly divided into the infected (I) and control (C) groups. The challenge group of chickens were administered Eimeria maxima oocysts via oral gavage at 21-days-old, and each chicken received 2 mL containing 7×104 sporulated oocysts. The total RNAs of chicken jejunum and cecum tissues were isolated from three samples, each from I and C groups. Our study aimed to understand the host immune-parasite interactions and compare immune response mRNA profiles in chicken jejunum and cecum tissues at 4 and 7 days postinfection with Eimeria maxima. The results showed that 823 up- and 737 down-regulated differentially expressed mRNAs (DEmRNAs) in jejunum at 4 d infection and control (J4I vs. J4C), and 710 up- and 368 down-regulated DEmRNAs in jejunum at 7 days infection and control (J7I vs. J7C) were identified. In addition, DEmRNAs in cecum tissue, 1424 up- and 1930 down-regulated genes in cecum at 4 days infection and control (C4I vs. C4C), and 77 up- and 191 down-regulated genes in cecum at 7 days infection and control (C7I vs. C7C) were detected. The crucial DEmRNAs, including SLC7A5, IL1R2, GLDC, ITGB6, ADAMTS4, IL1RAP, TNFRSF11B, IMPG2, WNT9A, and FOXF1, played pivotal roles in the immune response during Eimeria maxima infection of chicken jejunum. In addition, the potential detection of FSTL3, RBP7, CCL20, DPP4, PRKG2, TFPI2, and CDKN1A in the cecum during the host immune response against Eimeria maxima infection is particularly noteworthy. Furthermore, our functional enrichment analysis revealed the primary involvement of DEmRNAs in small molecule metabolic process, immune response function, inflammatory response, and toll-like receptor 10 signaling pathway in the jejunum at 4 and 7 days postinfection. Similarly, in the cecum, DEmRNAs at 4 and 7 days postinfection were enriched in processes related to oxidative stress response and immune responses. Our findings provide new insights and contribute significantly to the field of poultry production and parasitology.

Molecular characterization and immune protective efficacy of 3 Eimeria tenella antigens

Avian coccidiosis caused by Eimeria is a serious parasitic disease that poses a threat to the poultry industry. Currently, prevention and treatment mainly rely on the administration of anticoccidials and live oocyst vaccines. However, the prevalence of drug resistance and the inherent limitations of live vaccines have driven the development of novel vaccines. In this study, the surface protein (Et-SAG14), a previously annotated rhoptry protein (Eten5-B), and a gametocyte phosphoglucomutase (Et-PGM1) were characterized and the vaccine potential of the recombinant proteins were evaluated. Et-SAG14 was dispersed in the form of particles in the sporozoite and merozoite stages, whereas Et-PGM1 was distributed in the apical part of the sporozoite and merozoite stages. The previously annotated rhoptry Eten5-B was found not to be located in the rhoptry but distributed in the cytoplasm of sporozoites and merozoites. Immunization with rEten5-B significantly elevated host interferon gamma (IFN-γ) and interleukin 10 (IL-10) transcript levels and exhibited moderate anticoccidial effects with an anticoccidial index (ACI) of 161. Unexpectedly, both recombinant Et-SAG14 and Et-PGM1 immunization significantly reduced host IFN-γ and IL-10 transcription levels, and did not show protection against E. tenella challenge (ACI < 80). These results suggest that the rEten5-B protein can trigger immune protection against E. tenella and may be a potential and effective subunit vaccine for the control of coccidiosis in poultry.

Expression of a SAG protein with a CAP domain from Eimeria necatrix and its role in invasion and immunoprotection

Eimeria necatrix is a high pathogenic pathogen, which seriously endangers the poultry industry. The surface antigens (SAGs) of Apicomplexa are a kind of membrane protein anchored on the surface of the parasites through its carboxyl terminal glycosylphosphatidylinositol (GPI) structure. However, little is known about GPI-linked surface proteins in E. necatrix. In the present work, the E. necatrix sag gene (Ensag-CAP) was amplified and cloned for expression of the recombinant protein (rEnSAG-CAP). The full length Ensag-CAP gene was 813 bp, coding 270 amino acids with a predicated molecular weight of 28.86 kDa and contained a CAP domain with four sequence motifs CAP1, CAP2, CAP3 and CAP4. The rEnSAG-CAP was about 32 kDa and mainly expressed in a soluble form. Western blot analysis indicated that the rEnSAG-CAP could be recognized by anti-rEnSAG-CAP monoclonal antibody (anti-rEnSAG-CAP McAb) and the convalescent serum of chicken infected with E. necatrix. Native protein of EnSAG-CAP was detected in second-generation merozoites (MZ-2) using anti-rEnSAG-CAP polyclonal antibody (anti-rEnSAG-CAP pAb). The findings from the indirect immunofluorescence assay and enzyme digestion utilizing Bacillus cereus phosphoinositide-specific phospholipase C (PI-PLC) revealed that EnSAG-CAP predominantly localized at the surfaces of SZ and MZ-2 via a GPI anchor. It was observed that EnSAG-CAP can be cleaved from MZ-2 by PI-PLC. Real-time quantitative PCR (qPCR) analysis showed that transcript levels of Ensag-CAP in MZ-2 was significantly higher than that in SZ (P < 0.05). The anti-rEnSAG-CAP McAb in vitro could significantly inhibit the sporozoite invasion into MDBK cells (P < 0.01), which suggests that the protein might participate in sporozoite invasion into MDBK cells. rEnSAG-CAP afforded an immune protection against E. necatrix. The ACI value was 164.99 in the chickens immunized with 200 µg rEnSAG-CAP. Chickens immunized with rEnSAG-CAP had a significantly higher antigen-specific serum IgY response (P < 0.0001). The data indicates that EnSAG-CAP could serve as a potential candidate antigen for the development of a recombinant coccidiosis vaccine.

Construction of recombinant SAG22 Bacillus subtilis and its effect on immune protection of coccidia

Avian coccidiosis causes huge economic losses to the global poultry industry. Vaccine is an important means to prevent and control coccidiosis. In this study, Bacillus subtilis was selected as the expression host strain to express anti Eimeria tenella surface protein SAG22. The synthesized surface protein SAG22 gene fragment of E. tenella was ligated with Escherichia coli-bacillus shuttle vector GJ148 to construct the recombinant vector SAG22-GJ148. And then the recombinant Bacillus strain SAG22-DH61 was obtained by electrotransfer. The results of SDS-PAGE and Western Blot showed that the recombinant protein SAG22 was successfully expressed intracellularly. The immunoprotective effect of recombinant Bacillus strain SAG22-DH61 on broiler chickens was evaluated in 3 identically designed animal experiments. The birds were infected with E. tenella on d 14, 21, and 28, respectively. Each batch of experiments was divided into 4 groups: blank control group (NC), blank control group + infected E. tenella (CON), addition of recombinant SAG22-DH61 strain + infected with E. tenella (SAG22-DH61), addition of recombinant empty vector GJ148-DH61 strain + infected with E. tenella (GJ148-DH61). The animal experiments results showed that the average weight gain of the SAG22-DH61 group was higher than that of the infected control group, and the difference was significant in the d 14 and 28 attack tests (P < 0.05); the oocyst reduction rate of the SAG22-DH61 group was much higher than that of the GJ148-DH61 group (P < 0.05); the intestinal lesion count score of the SAG22-DH61 group was much lower than that of the GJ148-DH61 group (P < 0.05). In addition, the SAG22-DH61 group achieved highly effective coccidia resistance in the d 14 attack test and moderately effective coccidia resistance in both the d 21 and 28 attack tests. In summary, recombinant SAG22 B. subtilis has the potential to become one of the technological reserves in the prevention and control of coccidiosis in chickens in production.

Protection of hatchlings against coccidiosis by maternal antibodies to four recombinant proteins of Eimeria tenella, Eimeria acervulina and Eimeria maxima

Maternally derived IgG antibodies to protective Eimeria antigens have great potential to control chicken coccidiosis and multivalent vaccines are more practical to resist against co-infection with several species of Eimeria under natural conditions. In this study, five good protective antigens of Eimeria species were combined into two combinations based on previous studies, namely C1(EtROPK-Eten5-A, EtGAM22, Ea3-1E and EmGAM56) and C2(EtM2AP and EtGAM22, Ea3-1E and EmGAM56). Then, five antigens were expressed in the Escherichia coli system and purified to inoculate breeding hens. After three times immunization, the specific antibodies could sustain for 11 and 10 weeks in hens' plasma and egg yolk, respectively. Moreover, maternally derived antibodies against recombinant proteins could retain for 14 days in hatchlings' serum. Then, protective efficacies of specific antibodies on hatchlings against mixed infection of E. tenella, E. acervulina and E. maxima were evaluated. The results showed that the hatchlings of the immunized hens had a higher survival rate on day 7 of hatching. Moreover, body weight gains within the hatchlings of immunized hens were higher than those of unvaccinated hens on 7 days (C1: p = 0.0744; C2: p = 0.4020) and 14 days (p < 0.0001). Moreover, hatchlings from vaccinated hens showed significantly alleviated lesion scores in the small intestine and duodenum at day 7 (p < 0.01) and day 14 (C1: p < 0.05). Particularly, the number of oocyst excretion from hatchlings of immunized hens was significantly reduced at day 7 (p < 0.0001) and day 14 (p < 0.0001). Our findings suggest that the maternal immunization with multivalent recombinant vaccines has the potential to be transmission blocking vaccines against mixed infection of Eimeria.

Vaccines against chicken coccidiosis with particular reference to previous decade: progress, challenges, and opportunities

Chicken coccidiosis is an economically significant disease of commercial chicken industry accounting for losses of more than £10.4 billion (according to 2016 prices). Additionally, the costs incurred in prophylaxis and therapeutics against chicken coccidiosis in developing countries (for instance Pakistan according to 2018 prices) reached US $45,000.00 while production losses for various categories of chicken ranges 104.74 to US $2,750,779.00. The infection has been reported from all types of commercial chickens (broiler, layer, breeder) having a range of reported prevalence of 7-90%. The concern of resistance towards major anticoccidials has provided a way forward to vaccine research and development. For prophylaxis of chicken coccidiosis, live virulent, attenuated, ionophore tolerant strains and recombinant vaccines have been extensively trialed and commercialized. Eimeria antigens and novel vaccine adjuvants have elicited the protective efficacy against coccidial challenge. The cost of production and achieving robust immune responses in birds are major challenges for commercial vaccine production. In the future, research should be focused on the development of multivalent anticoccidial vaccines for commercial poultry. Efforts should also be made on the discovery of novel antigens for incorporation into vaccine designs which might be more effective against multiple Eimeria species. This review presents a recap to the overall progress against chicken Eimeria with particular reference to previous decade. The article presents critical analysis of potential areas for future research in chicken Eimeria vaccine development.

Eimeria falciformis secretes extracellular vesicles to modulate proinflammatory response during interaction with mouse intestinal epithelial cells

BACKGROUND

Protozoan parasite secretions can be triggered by various modified media and diverse physicochemical stressors. Equally, host-parasite interactions are known to co-opt the exchange and secretion of soluble biochemical components. Analysis of Eimeria falciformis sporozoite secretions in response to interaction with mouse intestinal epithelial cells (MIECs) may reveal parasite secretory motifs, protein composition and inflammatory activities of E. falciformis extracellular vesicles (EVs).

METHODS

Eimeria falciformis sporozoites were allowed to interact with inactivated MIECs. Parasite secretions were separated into EV and vesicle-free (VF) fractions by discontinuous centrifugation and ultracentrifugation. Secreted EVs were purified in an iodixanol density gradient medium and the protein composition of both EV and VF fractions were analyzed by liquid chromatoraphy-tandem mass spectroscopy. The inflammatory activities of E. falciformis sporozoite EV on MIECs were then investigated.

RESULTS

During the interaction of E. falciformis sporozoites with inactivated MIECs, the parasite secreted VF and vesicle-bound molecules. Eimeria falciformis vesicles are typical pathogenic protozoan EVs with a mean diameter of 264 ± 2 nm, and enclosed heat shock protein (Hsp) 70 as classical EV marker. Refractile body-associated aspartyl proteinase (or eimepsin), GAP45 and aminopeptidase were the main components of E. falciformis sporozoite EVs, while VF proteins include Hsp90, actin, Vps54 and kinases, among others. Proteomic data revealed that E. falciformis EV and VF proteins are aggregates of bioactive, antigenic and immunogenic molecules which act in concert for E. falciformis sporozoite motility, pathogenesis and survival. Moreover, in MIECs, E. falciformis EVs induced upregulation of gene expression and secretion of IL-1β, IL-6, IL-17, IL-18, MCP1 as well as pyroptosis-dependent caspase 11 and NLRP6 inflammasomes with the concomitant secretion of lactate dehydrogenase.

CONCLUSIONS

Eimeria falciformis sporozoite interaction with MIECs triggered the secretion of immunogenic and antigenic proteins. In addition, E. falciformis sporozoite EVs constitute parasite-associated molecular pattern that induced inflammatory response and cell death. This study offers additional insight in the secretion and protein composition of E. falciformis secretomes as well as the proinflammatory functions of E. falciformis sporozoite EVs.

Co-administration of chicken IL-7 or NK-lysin peptide 2 enhances the efficacy of Eimeria elongation factor-1α vaccination against Eimeria maxima infection in broiler chickens

This study was conducted to develop a recombinant Eimeria elongation factor-1α (EF-1α)-vaccination strategy against Eimeria maxima (E. maxima) infection by co-administering with chicken IL-7 (chIL-7) or chicken NK-lysin peptide 2 (cNK-2) in commercial broiler chickens. Chickens were divided into the following 5 groups: control (CON, no Eimeria infection), nonimmunized control (NC, PBS plus Montanide ISA 78 VG), Vaccination 1 (VAC1, 100 µg of recombinant EF-1α plus Montanide ISA 78 VG), Vaccination 2 (VAC2, VAC1 plus 1 µg of chIL-7), and Vaccination 3 (VAC3, VAC2 plus 5 µg of cNK-2 peptide). The first immunization except the cNK-2 injection was performed intramuscularly on day 4, and the secondary immunization was given with the same concentration of components as the primary immunization 1 wk later. All chickens except the CON group were orally inoculated with freshly prepared E. maxima (1.0 × 10⁴ oocysts per chicken) oocysts on Day 19. The results of the in vivo vaccination trial showed that chickens of all groups immunized with recombinant EF-1α antigen (VAC1, VAC2, and VAC3) showed higher serum antibody levels to EF-1α, and co-injection with chIL-7 further increased the serum IL-7 level in the VAC2 and VAC3 groups. Chickens in the VAC2 group showed significantly (P < 0.01) higher body weight gains at 6 and 9 d post-E. maxima challenge infection (dpi) with reduced gut lesions in the jejunum at 6 dpi. The VAC3 group showed reduced fecal oocyst shedding compared to the nonimmunized and infected chickens (NC). At 4 dpi, E. maxima infection significantly (P < 0.05) up-regulated the expression levels of proinflammatory cytokines (IL-β and IL-17F) and type Ι cytokines (IFN-γ and IL-10) in the jejunum (NC), but the expression of these cytokines was significantly (P < 0.05) down-regulated in the VAC1, VAC2, and VAC3 groups. Furthermore, E. maxima challenge infection significantly (P < 0.05) down-regulated the expressions of jejunal tight junction (TJ) proteins (Jam2 and Occludin) at 4 dpi, but their expression was up-regulated in the VAC2 and VAC3 groups. Collectively, these results show the protective effects of the EF-1α recombinant vaccine, which can be further enhanced by co-injection with chIL-7 or cNK-2 peptide against E. maxima infection.

PLGA Nanospheres as Delivery Platforms for Eimeria mitis 1a Protein: A Novel Strategy to Improve Specific Immunity

The infections of chicken coccidiosis impact the welfare of chickens and the economical production of poultry. Eimeria mitis is ubiquitous in chicken coccidiosis, and E. mitis infection can significantly affect the productivity of birds. Up to now, few efficient vaccines against E. mitis have been reported, whereas the recombinant subunit vaccines delivered by nanomaterials may elicit an encouraging outcome. Thus, in this study, we chose E. mitis 1a (Em1a) protein as the candidate antigen to generate Em1a preparations. The recombinant Em1a (rEm1a) protein was encapsulated with poly lactic-co-glycolic acid (PLGA) and chitosan (CS) nanospheres. The physical characterization of the rEm1a-PLGA and rEm1a-CS nanospheres was investigated, and the resulting nanospheres were proven to be nontoxic. The protective efficacy of rEm1a-PLGA and rEm1a-CS preparations was evaluated in E. mitis-challenged birds in comparison with two preparations containing rEm1a antigen emulsified in commercially available adjuvants. ELISA assay, flow cytometry analysis, and quantitative real-time PCR (qPCR) analysis indicated that vaccination with rEm1a-loaded nanospheres significantly upregulated the secretions of antibodies and cytokines and proportions of CD4⁺ and CD8⁺ T lymphocytes. Compared with the other three preparations, rEm1a-PLGA nanosphere was more effective in improving growth performance and inhibiting oocyst output in feces, indicating that the PLGA nanosphere was associated with optimal protection against E. mitis. Collectively, our results highlighted the advantages of nanovaccine in eliciting protective immunity and may provide a new perspective for developing effective vaccines against chicken coccidiosis.

Characterization of the Eimeria tenella rhoptry protein with a nuclear localization sequence (EtROP30)

Rhoptry proteins (ROPs), secreted by specific rhoptry organelles of apicomplexan parasites, are determinants of parasite pathogenesis and sources of vaccine candidates. Twenty-eight ROPs of Eimeria tenella have been predicted by genomic approaches, and in the present study, E. tenella rhoptry protein 30 (EtROP30) was characterized. Subcellular localizations of EtROP30 in sporozoites and merozoites were in the apical complex and rhoptry-like bulb, suggesting that EtROP30 is a member of ROPs in E. tenella. Sequence analysis showed that EtROP30 contained an N-terminal secretory signal, a protein kinase domain with eight E. tenella-specific rhoptry kinase 1 subfamily (ROPK-Eten1) motifs, and a C-terminal nuclear localization sequence (NLS), making EtROP30 the only ROP that contains both a secretory signal and an NLS in E. tenella. Subsequent experiments showed that EtROP30 was a secreted protein in the sporozoite stage, relying on NLS for migration to the host nucleus. In addition, EtROP30 showed significantly higher expression levels in the parasite merozoite stage, indicating that EtROP30 plays a critical role during parasite reinvasion and development and may be a viable option as a vaccine candidate for anti-parasitic infection. The immunization protection efficacies of EtROP30 were evaluated. Significant improvements in mean body weight gain, reduction of cecum lesion score, and number of oocysts excreted were observed, indicating that EtROP30 has good immunogenicity against E. tenella. In the present study, a ROP of E. tenella with secretory and nuclear localization characteristics has been identified, and proved to be an effective vaccine candidate against this parasite.

Coccidiosis: Recent Progress in Host Immunity and Alternatives to Antibiotic Strategies

Coccidiosis is an avian intestinal disease caused by several distinct species of Eimeria parasites that damage the host’s intestinal system, resulting in poor nutrition absorption, reduced growth, and often death. Increasing evidence from recent studies indicates that immune-based strategies such as the use of recombinant vaccines and various dietary immunomodulating feed additives can improve host defense against intracellular parasitism and reduce intestinal damage due to inflammatory responses induced by parasites. Therefore, a comprehensive understanding of the complex interactions between the host immune system, gut microbiota, enteroendocrine system, and parasites that contribute to the outcome of coccidiosis is necessary to develop logical strategies to control coccidiosis in the post-antibiotic era. Most important for vaccine development is the need to understand the protective role of the local intestinal immune response and the identification of various effector molecules which mediate anti-coccidial activity against intracellular parasites. This review summarizes the current understanding of the host immune response to coccidiosis in poultry and discusses various non-antibiotic strategies which are being developed for coccidiosis control. A better understanding of the basic immunobiology of pertinent host–parasite interactions in avian coccidiosis will facilitate the development of effective anti-Eimeria strategies to mitigate the negative effects of coccidiosis.

Eimeria proteins: order amidst disorder

Apicomplexans are important pathogens that cause severe infections in humans and animals. The biology and pathogeneses of these parasites have shown that proteins are intrinsically modulated during developmental transitions, physiological processes and disease progression. Also, proteins are integral components of parasite structural elements and organelles. Among apicomplexan parasites, Eimeria species are an important disease aetiology for economically important animals wherein identification and characterisation of proteins have been long-winded. Nonetheless, this review seeks to give a comprehensive overview of constitutively expressed Eimeria proteins. These molecules are discussed across developmental stages, organelles and sub-cellular components vis-à-vis their biological functions. In addition, hindsight and suggestions are offered with intention to summarise the existing trend of eimerian protein characterisation and to provide a baseline for future studies.

Roles of TNF receptor-associated and Fas-associated death domain proteins in the apoptosis of Eimeria tenella host cells

The present study aimed to investigate the effects of death receptor adapter proteins, namely, TNF receptor-associated death domain (TRADD) and Fas-associated death domain (FADD) proteins, on Eimeria tenella-induced host cell apoptosis. Gene silencing, culture technique for primary chick embryo cecal epithelial cells, enzyme-linked immunosorbent assay, Hoechst-Annexin V/PI apoptosis staining, fluorescence quantitative PCR, and flow cytometry were used to detect the E. tenella host cell apoptotic rate, RIP1 and FADD protein expression levels, and caspase-8 activity of the TRADD siRNA-treated and FADD siRNA-treated groups. Results showed that the apoptotic rate in the TRADD siRNA group was significantly higher than that in the NC siRNA group at 4 h post-infection with E. tenella (P < 0.05). The RIP1 protein expression level in the TRADD siRNA group was significantly lower than that in the NC siRNA group at 4-24 h (P < 0.05). The FADD expression and apoptotic rates in the TRADD siRNA group were significantly lower than those in the NC siRNA group at 24-120 h (P < 0.05). The caspase-8 activity and apoptotic rates in the FADD siRNA group were significantly lower than those in the NC siRNA group (P < 0.05) at 24-120 h. These findings indicated that E. tenella inhibited the host cell apoptosis through the TRADD-RIP1 pathway at the early developmental stage and promoted host cell apoptosis via the TRADD-FADD-caspase-8 apoptotic pathway at the middle and late developmental stages.

Evaluation of 4 merozoite antigens as candidate vaccines against Eimeria tenella infection

Coccidiosis, caused by parasites of the genus Eimeria, is one of the most widespread and economically detrimental diseases in the global poultry industry. Because the merozoite stage of Eimeria tenella is immunologically vulnerable, motile, and functionally important for the parasites, the proteins expressed in these stages are considered to be potentially immunoprotective antigens, especially the secreted antigens and surface antigens. Here, we detected a previously unidentified MIC2-associated protein (Et-M2AP) from E. tenella and determined its localization. An immunofluorescence assay revealed that Et-M2AP was distributed in the apical part of second generation merozoites and sporozoites. In addition, an expression profile analysis revealed that the transcriptional level of Et-M2AP is significantly higher in the merozoite stage. To assess the potential of Et-M2AP protein as a coccidiosis vaccine, we expressed recombinant Et-M2AP (rEt-M2AP) and compared the immune protective efficacy of rEt-M2AP with 3 surface antigens that are highly expressed by merozoites (rEt-SAG23, rEt-SAG16, and rEt-SAG2 proteins). The immune protective efficacy of these vaccine candidates was assessed based on survival rate, lesion score, BW gain, relative BW gain, and oocyst output. The results show that the survival rate was 90%, which are significantly higher than those in the challenge control group. The BW gain rate was 42% (P < 0.001) in rEt-M2AP-immunized chickens, which are significantly higher than those in the challenge control group and rEt-SAG23, rEt-SAG16, and rEt-SAG2 proteins-immunized chickens. In addition, chickens immunized with rEt-M2AP (88% oocyst output decrease rate, P < 0.001) had the least oocyst output, compared with those immunized with rEt-SAG16 (59.2% oocyst output decrease rate, P < 0.001), rEt-SAG23 (22% oocyst output decrease rate), and rEt-SAG2 (1.36% oocyst output decrease rate). These results demonstrate that rEt-M2AP provided effective protection against challenge with E. tenella, suggesting that rEt-M2AP is a promising candidate antigen gene for development as a coccidiosis vaccine.

Mucosal Delivery of a Self-destructing Salmonella-Based Vaccine Inducing Immunity Against Eimeria

A programmed self-destructive Salmonella vaccine delivery system was developed to facilitate efficient colonization in host tissues that allows release of the bacterial cell contents after lysis to stimulate mucosal, systemic, and cellular immunities against a diversity of pathogens. Adoption and modification of these technological improvements could form part of an integrated strategy for cost-effective control and prevention of infectious diseases, including those caused by parasitic pathogens. Avian coccidiosis is a common poultry disease caused by Eimeria. Coccidiosis has been controlled by medicating feed with anticoccidial drugs or administering vaccines containing low doses of virulent or attenuated Eimeria oocysts. Problems of drug resistance and nonuniform administration of these Eimeria resulting in variable immunity are prompting efforts to develop recombinant Eimeria vaccines. In this study, we designed, constructed, and evaluated a self-destructing recombinant attenuated Salmonella vaccine (RASV) lysis strain synthesizing the Eimeria tenella SO7 antigen. We showed that the RASV lysis strain χ11791(pYA5293) with a ΔsifA mutation enabling escape from the Salmonella-containing vesicle (or endosome) successfully colonized chicken lymphoid tissues and induced strong mucosal and cell-mediated immunities, which are critically important for protection against Eimeria challenge. The results from animal clinical trials show that this vaccine strain significantly increased food conversion efficiency and protection against weight gain depression after challenge with 105E. tenella oocysts with concomitant decreased oocyst output. More importantly, the programmed regulated lysis feature designed into this RASV strain promotes bacterial self-clearance from the host, lessening persistence of vaccine strains in vivo and survival if excreted, which is a critically important advantage in a vaccine for livestock animals. Our approach should provide a safe, cost-effective, and efficacious vaccine to control coccidiosis upon addition of additional protective Eimeria antigens. These improved RASVs can also be modified for use to control other parasitic diseases infecting other animal species.

A Novel Rhoptry Protein as Candidate Vaccine against Eimeria tenella Infection

Eimeria tenella (E. tenella) is a highly pathogenic and prevalent species of Eimeria that infects chickens, and it causes a considerable disease burden worldwide. The secreted proteins and surface antigens of E. tenella at the sporozoite stage play an essential role in the host–parasite interaction, which involves attachment and invasion, and these interactions are considered vaccine candidates based on the strategy of cutting off the invasion pathway to interrupt infection. We selected two highly expressed surface antigens (SAGs; Et-SAG13 and Et-SAG) and two highly expressed secreted antigens (rhoptry kinases Eten5-A, Et-ROPK-Eten5-A and dense granule 12, Et-GRA12) at the sporozoite stage. Et-ROPK-Eten5-A and Et-GRA12 were two unexplored proteins. Et-ROPK-Eten5-A was an E. tenella-specific rhoptry (ROP) protein and distributed in the apical pole of sporozoites and merozoites. Et-GRA12 was scattered in granular form at the sporozoite stage. To evaluate the potential of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG proteins as a coccidiosis vaccine, the protective efficacy was examined based on survival rate, lesion score, body weight gain, relative body weight gain and oocyst output. The survival rate was significantly improved in rEt-ROPK-Eten5-A (100%) and rEt-GRA12 (100%) immune chickens compared to the challenged control group (40%). The average body weight gains of rEt-ROPK-Eten5-A, rEt-GRA12, rEt-SAG13 and rEt-SAG immunized chickens were significantly higher than those of unimmunized chickens. The mean lesion score and oocyst output of the rEt-ROPK-Eten5-A immunized chickens were significantly reduced compared to unimmunized challenged chickens. These results suggest that the rEt-ROPK-Eten5-A protein effectively triggered protection against E. tenella in chickens and provides a useful foundation for future work developing anticoccidial vaccines.

Molecular characterization and immune protection of an AN1-like zinc finger protein of Eimeria tenella

Coccidiosis is caused by multiple species of the apicomplexan protozoa Eimeria. Among them, Eimeria tenella is frequently considered to be the most pathogenic. Zinc finger proteins (ZnFPs) are a type of protein containing zinc finger domains. In the present study, a putative Eimeria tenella AN1-like ZnFP (E. tenella AN1-like zinc finger domain-containing protein, putative partial mRNA, EtAN1-ZnFP) was cloned and characterized, and its immune protective effects were evaluated. The 798-bp ORF sequence of EtAN1-ZnFP that encoded a protein of approximately 27.0 kDa was obtained. The recombinant EtAN1-ZnFP protein (rEtAN1-ZnFP) was expressed in Escherichia coli. Western blot analysis showed that the recombinant protein was recognized by the anti-GST monoclonal antibody and anti-sporozoite protein rabbit serum. qPCR analysis revealed that EtAN1-ZnFP was highly expressed in unsporulated oocysts and sporozoites. Immunostaining with an anti-rEtAN1-ZnFP antibody indicated that EtAN1-ZnFP was uniformly distributed in the cytoplasm of sporozoites, except for the refractive body; furthermore, this protein was evenly distributed in the cytoplasm of immature schizonts but seldom distributed in mature schizonts. The results of the in vitro invasion inhibition assay indicated that the antibodies against rEtAN1-ZnFP efficiently reduced the ability of E. tenella sporozoites to invade host cells. Animal challenge experiments demonstrated that the chickens immunized with rEtAN1-ZnFP protein significantly decreased mean lesion scores and fecal oocyst output compared with challenged control group. The results suggest that EtAN1-ZnFP can induce partial immune protection against infection with E. tenella and could be an effective candidate for the development of new vaccines.

A review of Eimeria antigen identification for the development of novel anticoccidial vaccines

Coccidiosis is a major poultry disease which compromises animal welfare and costs the global chicken industry a huge economic loss. As a result, research entailing coccidial control measures is crucial. Coccidiosis is caused by Eimeria parasites that are highly immunogenic. Consequently, a low dosage of the Eimeria parasite supplied by a vaccine will enable the host organism to develop an innate immune response towards the pathogen. The production of traditional live anticoccidial vaccines is limited by their low reproductive index and high production costs, among other factors. Recombinant vaccines overcome these limitations by eliciting undesired contaminants and prevent the reversal of toxoids back to their original toxigenic form. Recombinant vaccines are produced using defined Eimeria antigens and harmless adjuvants. Thus, studies regarding the identification of potent novel Eimeria antigens which stimulate both cell-mediated and humoral immune responses in chickens are essential. Although the prevalence and risk posed by Eimeria have been well established, there is a dearth of information on genetic and antigenic diversity within the field. Therefore, this paper discusses the potential and efficiency of recombinant vaccines as an anticoccidial control measure. Novel protective Eimeria antigens and their antigenic diversity for the production of cheap, easily accessible recombinant vaccines are also reviewed.

Immunoprophylactic evaluation of recombinant gametocyte 22 antigen of Eimeria tenella in broiler chickens

Gametocyte proteins are being explored as potential vaccine candidates against Eimeria sp. in chicken since they are the components of the resilient oocyst wall. The aim of this study was to investigate the immunoprophylactic efficacy of recombinant Eimeria tenella gametocyte antigen 22 (EtGam22) in chickens against homologous oocyst challenge. Broiler chicks were subcutaneously immunized individually with 100 μg of recombinant EtGam22 adjuvanted with Montanide ISA 71 VG at 7 days of age and boosted 2 weeks later. The immunized chickens were challenged individually with 1 × 10⁴ sporulated oocysts of E. tenella 1 week post-booster immunization. The anti-EtGam22 IgY and serum cytokine response was measured post-immunization. The results showed that the anti-EtGam22 IgY antibody, serum IFN-γ, IL-2, TGF-β, and IL-4 levels in chickens vaccinated with recombinant protein were significantly increased post-immunization as compared to unimmunized challenged controls (P < 0.05). The peripheral blood lymphocyte proliferation activity was also found significantly higher in EtGam22-immunized group on day 28, i.e., pre-challenge (P < 0.05). Upon homologous oocyst challenge, chickens immunized with rEtGam22 exhibited a significant drop in the total oocyst output per bird (246.78 ± 36.9 × 10⁶, 45.23% reduction) and a significantly higher weight gain (497.7 ± 19.2 g) as compared to unimmunized challenged controls. Taken together, these data indicate that EtGam22 is a potent immunogen for use as a subunit vaccine against cecal coccidiosis in chickens as it induces a diverse and robust immune response involving multiple cytokines and strong antibody titers.