The molecular characterization and immune protection of microneme 2 of Eimeria acervulina

Developing efficient strategies for localizing the enhanced yellow fluorescent protein subcellularly in transgenic Eimeria parasites

Eimeria species serve as promising eukaryotic vaccine vectors. And that the location of heterologous antigens in the subcellular components of genetically modified Eimeria may determine the magnitude and type of immune responses. Therefore, our study aimed to target a heterologous fluorescent protein to the cell surface or microneme, two locations where are more effective in inducing protective immunity, of Eimeria tenella and E. acervulina sporozoites. We used an enhanced yellow fluorescent protein (EYFP) as a tagging biomarker, fusing variously with some localization or whole sequences of compartmental proteins for targeting. After acquiring stable transgenic Eimeria populations, we observed EYFP expressing in expected locations with certain strategies. That is, EYFP successfully localized to the surface when it was fused between signal peptides and mature products of surface antigen 1 (SAG1). Furthermore, EYFP was efficiently targeted to the apical end, an optimal location for secretory organelle known as the microneme, when fused to the C terminus of microneme protein 2. Unexpectedly, EYFP exhibited dominantly in the apical end with only weak expression on the surface of the transgenic sporozoites when the parasites were transfected with plasmid with EYFP fused between signal peptides and mature products of E. tenella SAG 13. These strategies worked in both E. tenella and E. acervulina, laying a solid foundation for studying E. tenella and E. acervulina-based live vaccines that can be further tailored to the inclusion of cargo immunogens from other pathogens.

Microneme-located VP2 in Eimeria acervulina elicits effective protective immunity against infectious bursal disease virus

Using transgenic Eimeria spp. to deliver exogenous antigens is a viable option for developing multivalent live vaccines. Previous research revealed that the location of antigen expression in recombinant Eimeria dictates the magnitude and type of immune responses. In this study, we constructed genetically modified Eimeria acervulina that expressed VP2 protein, a protective antigen from infectious bursal disease virus (IBDV), on the surface or in the microneme of sporozoites. After vaccination, VP2-specific antibody was readily detected in specific pathogen-free chickens receiving transgenic E. acervulina parasites expressing VP2 in microneme, but animals vaccinated with which expressing VP2 on surface failed to produce detectable antibody after two times immunizations. Moreover, the bursal lesion of microneme-located VP2 transgenic E. acervulina immunized chickens was less severe compared with un-immunized animals after IBDV challenge infection. Therefore, genetically modified E. acervulina that express IBDV-derived VP2 in micronemes are effective in inducing specific antibody responses against VP2, while parasites that have VP2 expression on cell surface are not suitable. Thus, the use of Eimeria parasites as vaccine vectors needs to consider the proper targeting of exogenous immunogens. Our results have implications for the design of other vector vaccines.

Vaccination Against Poultry Parasites

The complexity of parasites and their life cycles makes vaccination against parasitic diseases challenging. This review highlights this by discussing vaccination against four relevant parasites of poultry. Coccidia, i.e., Eimeria spp., are the most important parasites in poultry production, causing multiple billions of dollars of damage worldwide. Due to the trend of antibiotic-free broiler production, use of anticoccidia vaccines in broilers is becoming much more important. As of now, only live vaccines are on the market, almost all of which must be produced in birds. In addition, these live vaccines require extra care in the management of flocks to provide adequate protection and prevent the vaccines from causing damage. Considerable efforts to develop recombinant vaccines and related work to understand the immune response against coccidia have not yet resulted in an alternative. Leucozytozoon caulleryi is a blood parasite that is prevalent in East and South Asia. It is the only poultry parasite for which a recombinant vaccine has been developed and brought to market. Histomonas meleagridis causes typhlohepatitis in chickens and turkeys. The systemic immune response after intramuscular vaccination with inactivated parasites is not protective. The parasite can be grown and attenuated in vitro, but only together with bacteria. This and the necessary intracloacal application make the use of live vaccines difficult. So far, there have been no attempts to develop a recombinant vaccine against H. meleagridis. Inactivated vaccines inducing antibodies against the poultry red mite Dermanyssus gallinae have the potential to control infestations with this parasite. Potential antigens for recombinant vaccines have been identified, but the use of whole-mite extracts yields superior results. In conclusion, while every parasite is unique, development of vaccines against them shares common problems, namely the difficulties of propagating them in vitro and the identification of protective antigens that might be used in recombinant vaccines.

The microneme adhesive repeat domain of MIC3 protein determined the site specificity of Eimeria acervulina, Eimeria maxima, and Eimeria mitis

Understanding the determinants of host and tissue tropisms among parasites of veterinary and medical importance has long posed a substantial challenge. Among the seven species of Eimeria known to parasitize the chicken intestine, a wide variation in tissue tropisms has been observed. Prior research suggested that microneme protein (MIC) composed of microneme adhesive repeat (MAR) domain responsible for initial host cell recognition and attachment likely dictated the tissue tropism of Eimeria parasites. This study aimed to explore the roles of MICs and their associated MARs in conferring site-specific development of E. acervuline, E. maxima, and E. mitis within the host. Immunofluorescence assays revealed that MIC3 of E. acervuline (EaMIC3), MIC3 of E. maxima (EmMIC3), MIC3 of E. mitis (EmiMIC3), MAR3 of EaMIC3 (EaMIC3-MAR3), MAR2 of EmMIC3 (EmMIC3-MAR2), and MAR4 of EmiMIC3 (EmiMIC3-MAR4), exhibited binding capabilities to the specific intestinal tract where these parasites infect. In contrast, the invasion of sporozoites into host intestinal cells could be significantly inhibited by antibodies targeting EaMIC3, EmMIC3, EmiMIC3, EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4. Substitution experiments involving MAR domains highlighted the crucial roles of EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4 in governing interactions with host ligands. Furthermore, animal experiments substantiated the significant contribution of EmiMIC3, EmiMIC3-MAR4, and their polyclonal antibodies in conferring protective immunity to Eimeria-affiliated birds. In summary, EaMIC3, EmMIC3, and EmiMIC3 are the underlying factors behind the diverse tissue tropisms exhibited by E. acervuline, E. maxima, and E. mitis, and EaMIC3-MAR3, EmMIC3-MAR2, and EmiMIC3-MAR4 are the major determinants of MIC-mediated tissue tropism of each parasite. The results illuminated the molecular basis of the modes of action of Eimeria MICs, thereby facilitating an understanding and rationalization of the marked differences in tissue tropisms among E. acervuline, E. maxima, and E. mitis.

What Do We Know about Surface Proteins of Chicken Parasites Eimeria?

Poultry is the first source of animal protein for human consumption. In a changing world, this sector is facing new challenges, such as a projected increase in demand, higher standards of food quality and safety, and reduction of environmental impact. Chicken coccidiosis is a highly widespread enteric disease caused by Eimeria spp. which causes significant economic losses to the poultry industry worldwide; however, the impact on family poultry holders or backyard production-which plays a key role in food security in small communities and involves mainly rural women-has been little explored. Coccidiosis disease is controlled by good husbandry measures, chemoprophylaxis, and/or live vaccination. The first live vaccines against chicken coccidiosis were developed in the 1950s; however, after more than seven decades, none has reached the market. Current limitations on their use have led to research in next-generation vaccines based on recombinant or live-vectored vaccines. Next-generation vaccines are required to control this complex parasitic disease, and for this purpose, protective antigens need to be identified. In this review, we have scrutinised surface proteins identified so far in Eimeria spp. affecting chickens. Most of these surface proteins are anchored to the parasite membrane by a glycosylphosphatidylinositol (GPI) molecule. The biosynthesis of GPIs, as well as the role of currently identified surface proteins and interest as vaccine candidates has been summarised. The potential role of surface proteins in drug resistance and immune escape and how these could limit the efficacy of control strategies was also discussed.

Prokaryotic Expression of Eimeria magna SAG10 and SAG11 Genes and the Preliminary Evaluation of the Effect of the Recombinant Protein on Immune Protection in Rabbits

Eimeria magna is a common coccidia in the intestines of rabbits, causing anorexia, weight loss, diarrhea, and bloody stools. This study cloned and determined the expression levels of four Eimeria surface antigens (EmSAGs) at different developmental stages and showed that EmSAG10 and EmSAG11 are highly expressed at the merozoite stage. Rabbits were immunized with rEmSAG10 and rEmSAG11, and then challenged with E. magna after 2 weeks. Serum-specific antibodies and cytokine levels were detected using ELISA. Immune protection was evaluated based on the rate of the oocysts decrease, the output of oocysts (p < 0.05), the average weight gain, and the feed: meat ratio. Our results showed that rabbits immunized with rEmSAG10 and rEmSAG11 had a higher average weight gain (62.7%, 61.1%), feed; meat ratio (3.8:1, 4.5:1), and the oocysts decrease rate (70.8%, 81.2%) than those in the control group, and also significantly reduced intestinal lesions. The specific IgG level increased one week after the first rEmSAG10 and rEmSAG11 immunization and was maintained until two weeks after the challenge (p < 0.05). The TGF-β, IL-4, and IL-10 levels in the serum increased significantly after the secondary immunization with rEmSAG10 and rEmSAG11, while the IL-2 levels increased significantly after the secondary immunization with rEmSAG11 (both p < 0.05), suggesting that rEmSAG10 can induce a humoral and cellular immunity, while rEmSAG11 can only induce a humoral immunity. Therefore, rEmSAG10 is a candidate antigen for E. magna recombinant subunit vaccines.

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.

Eimeria maxima Rhomboid-like Protein 5 Provided Partial Protection against Homologous Challenge in Forms of Recombinant Protein and DNA Plasmid in Chickens

Eimeria maxima (E. maxima) is one of the most prevalent species that causes chicken coccidiosis on chicken farms. During apicomplexan protozoa invasion, rhomboid-like proteins (ROMs) cleave microneme proteins (MICs), allowing the parasites to fully enter the host cells, which suggests that ROMs have the potential to be candidate antigens for the development of subunit or DNA vaccines against coccidiosis. In this study, a recombinant protein of E. maxima ROM5 (rEmROM5) was expressed and purified and was used as a subunit vaccine. The eukaryotic expression plasmid of pVAX-EmROM5 was constructed and was used as a DNA vaccine. Chickens who were two weeks old were vaccinated with the rEmROM5 and pVAX-EmROM5 vaccines twice, with a one-week interval separating the vaccination periods. The transcription and expression of pVAX-EmROM5 in the injected sites were detected through reverse transcription PCR (RT-PCR) and Western blot (WB) assays. The cellular and humoral immune responses that were induced by EmROM5 were determined by detecting the proportion of CD4⁺ and CD8⁺ T lymphocytes, the cytokine levels, and the serum antibody levels. Finally, vaccination-challenge trials were conducted to evaluate the protective efficacy of EmROM5 in forms of the recombinant protein (rEmROM5) and in the DNA plasmid (pVAX-EmROM5) separately. The results showed that rEmROM5 was about 53.64 kDa, which was well purified and recognized by the His-Tag Mouse Monoclonal antibody and the chicken serum against E. maxima separately. After vaccination, pVAX-EmROM5 was successfully transcribed and expressed in the injected sites of the chickens. Vaccination with rEmROM5 or pVAX-EmROM5 significantly promoted the proportion of CD4⁺/CD3⁺ and CD8⁺/CD3⁺ T lymphocytes, the mRNA levels of the cytokines IFN-γ, IL-2, IL-4, IL-17, TNF SF15, and IL-10, and specific IgG antibody levels compared to the control groups. The immunization also significantly reduced the weight loss, oocyst production, and intestinal lesions that are caused by E. maxima infection. The anticoccidial index (ACI)s of the vaccinated groups were beyond 160, showing moderate protection against E. maxima infection. In summary, EmROM5 was able to induce a robust immune response and effective protection against E. maxima in chickens in the form of both a recombinant protein and DNA plasmid. Hence, EmROM5 could be used as a candidate antigen for DNA vaccines and subunit vaccines against avian coccidiosis.

Molecular characterization and immune protection by cystathionine β-synthase from Eimeria tenella

Eimeria tenella is an obligate intracellular apicomplexan parasite that causes avian coccidiosis and leads to severe economic losses in the global poultry industry. Cystathionine β-synthase (CBS) and cystathionine γ-lyase (CGL) act together to generate H2S in the reverse transsulfuration pathway. In this study, E. tenella Cystathionine β-synthase (EtCBS) was cloned using rapid amplification of cDNA 5'-ends (5'RACE) and characterized, and its immunoprotective effects were evaluated. The recombinant EtCBS protein (rEtCBS) was expressed and successfully recognized by anti-sporozoites (Spz) protein rabbit serum. EtCBS mRNA levels were highest in Spz by qPCR, and the protein expression levels were higher in unsporulated oocysts (UO) than in other stages by Western blot. Indirect immunofluorescence showed that EtCBS protein was found on the surface of Spz and second-generation merozoites (Mrz). The invasion inhibition assays showed that rabbit anti-rEtCBS polyclonal antibodies effectively inhibited parasite invasion host cells. Chickens immunized with rEtCBS protein showed prominently increased weight gains and decreased oocyst output compared to nonimmunized and infected control group. The results suggest that EtCBS could be a potential vaccine candidate against E. tenella.

Evaluation of immunoprotective effects of recombinant proteins and DNA vaccines derived from Eimeria tenella surface antigen 6 and 15 in vivo

Coccidiosis is an intestinal parasitic disease that causes huge economic losses to the poultry industry globally. Eimeria tenella belonging to protozoon is the causative agent of cecal coccidiosis in chicken, and it causes enormous damage to poultry industry. The surface antigens (SAGs) of apicomplexan parasites have functions of attachment and invasion in host-parasite interaction. As a result of parasitic invasion, host immune response is triggered. However, the immunogenicity and potency of E. tenella surface antigen 6 and 15 (EtSAG 6 and 15), as vaccinal candidate antigen, remain largely unknown. Therefore, gene fragments of E. tenella EtSAG 6 and 15 were amplified and transformed to pET28a prokaryotic vector for recombinant protein expression. The pEGFP-N1 eukaryotic vectors with EtSAG 6 and 15 amplification fragments (pEGFP-N1-EtSAG 5 and 16) were transformed into 293 T cell line. The results of reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis revealed successful expressions of EtSAG 6 and 15 in Escherichia coli and 293 T cells. Subsequently, animal experiments of 49 cobb broilers were performed to evaluate immunoprotection of recombinant proteins and DNA vaccines derived from E. tenella EtSAG 5 and 16 with an immunizing dose of 100 μg, respectively. Chickens vaccinated with rEtSAG 6 protein, rEtSAG 15 protein, pEGFP-N1-EtSAG 6 plasmid, or pEGFP-N1-EtSAG 15 plasmid showed no significant increase in IFN-γor interleukin-4 (IL-4) level compared with control groups. Chickens vaccinated with protein rEtSAG 6, protein rEtSAG 15, pEGFP-N1-EtSAG 6 plasmid, or pEGFP-N1-EtSAG 15 exhibited higher weight gains, lower oocyst output, and lower mean lesion scores, compared with infection control group. Among the four immunized groups, plasmid EGFP-N1-EtSAG 6 (100 μg) group exhibited the highest anticoccidial index (ACI) value (150.20). Overall, plasmids EGFP-N1-EtSAG 6 and 15, as DNA vaccines, provided a more effective immunoprotection for chickens against E. tenella than protein rEtSAG 6 and protein rEtSAG 15 as subunit vaccines. EtSAG 6 and 15 are promising candidate antigen genes for developing coccidiosis vaccine.

The excretory-secretory antigen HcADRM1 to generate protective immunity against Haemonchus contortus

The prevention, treatment and control of Haemonchus contortus have been increasingly problematic due to its widespread occurrence and anthelmintic resistance. There are very few descriptions of recombinant antigens being protective for H. contortus, despite the success of various native antigen preparations, including Barbervax. We recently identified an H. contortus excretory–secretory antigen, H. contortus adhesion-regulating molecule 1 (HcADRM1), that served as an immunomodulator to impair host T-cell functions. Given the prophylactic potential of HcADRM1 protein as a vaccine candidate, we hereby assessed the efficacies of HcADRM1 preparations against H. contortus infection. Parasitological and immunological parameters were evaluated throughout all time points of the trials, including fecal egg counts (FEC), abomasal worm burdens, complete blood counts, cytokine production profiles and antibody responses. Active vaccination with recombinant HcADRM1 (rHcADRM1) protein induced protective immunity in inoculated goats, resulting in reductions of 48.9 and 58.6% in cumulative FEC and worm burdens. Simultaneously, passive administration of anti-HcADRM1 antibodies generated encouraging levels of protection with 46.7 and 56.2% reductions in cumulative FEC and worm burdens in challenged goats. In addition, HcADRM1 preparations-immunized goats showed significant differences in mucosal and serum antigen-specific immunoglobulin G (IgG) levels, total mucosal IgA levels, haemoglobin values and circulating interferon-γ, interleukin (IL)-4 and IL-17A production compared to control goats in both trials. The preliminary data of these laboratory trials validated the immunoprophylactic effects of rHcADRM1 protein. It can be pursued as a potential vaccine antigen to develop an effective recombinant subunit vaccine against H. contortus under field conditions.

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.

Molecular characterization of a potential receptor of Eimeria acervulina microneme protein 3 from chicken duodenal epithelial cells

Eimeria acervulina is one of seven Eimeria spp. that can infect chicken duodenal epithelial cells. Eimeria microneme protein 3 (MIC3) plays a vital role in the invasion of host epithelial tissue by the parasite. In this study, we found that chicken (Gallus gallus) ubiquitin conjugating enzyme E2F (UBE2F) could bind to the MIC3 protein of E. acervulina (EaMIC3), as screened using the yeast two-hybrid system, and that it might be the putative receptor protein of EaMIC3. The UBE2F gene was cloned from chicken duodenal epithelial cells. The recombinant protein of UBE2F (rUBE2F) was expressed in E. coli and the reactogenicity of rUBE2F was analyzed by Western blot. Gene sequencing revealed that the opening reading frame (ORF) of UBE2F was 558 base pairs and encoded a protein of 186 amino acids with a molecular weight of 20.46 kDa. The predicted UBE2F protein did not contain signal peptides or a transmembrane region, but had multiple O-glycosylation and phosphorylation sites. A phylogenetic analysis showed that the chicken UBE2F protein is closely related to those of quail and pigeon (Coturnix japonica and Columba livia). A sporozoite invasion-blocking assay showed that antisera against rUBE2F significantly inhibited the invasion of E. acervulina sporozoites in vitro. Animal experiments indicated that the antisera could significantly enhance average body weight gains and reduce mean lesion scores following a challenge with E. acervulina. These results therefore imply that the chicken UBE2F protein might be the target receptor molecule of EaMIC3 that is involved in E. acervulina invasion.

In vivo immunoprotective comparison between recombinant protein and DNA vaccine of Eimeria tenella surface antigen 4

Eimeria tenella, belonging to protozoon, is the causative agent of cecal coccidiosis in chicken and causes enormous impacts for poultry industry. The surface antigens of apicomplexan parasites function as attachment and invasion in host-parasite interaction. Meanwhile, host immune response is triggered as a result of parasitic invasion. Immunogenicity and potency as a vaccinal candidate antigen of E. tenella surface antigen 4 (EtSAG4) have been unknown. Therefore, a gene segment of E. tenella EtSAG4 was amplified and transplanted to pET28a prokaryotic vector for recombinant protein expression. Similarly, pEGFP-N1 eukaryotic vectors with EtSAG4 gene segment (pEGFP-N1-EtSAG4) amplified in 293 T cells as DNA vaccines. Reverse transcription-polymerase chain reaction (RT-PCR) assay and western blot analysis were used to demonstrate successful expressions of EtSAG4 in Escherichia coli or 293 T cells. Subsequently, animal experiments (72 cobb broilers) were performed to evaluate immunoprotective between recombinant protein and DNA vaccine of E. tenella EtSAG4 using different immunizing doses (50 or 100 μg), respectively. Serum from chickens infected with E. tenella identified recombinant EtSAG4 (rEtSAG4) protein. Chickens vaccinated with either rEtSAG4 protein or pEGFP-N1-EtSAG4 plasmids both shown a significant increase in concentration of IFN-γ (p < 0.05) compared with control groups indicating production of cell-mediated immunity. Besides, pEGFP-N1-EtSAG4 plasmids motivated more intense immune responses for immunoglobulin Y (IgY) and interleukin 17 (IL-17) (p < 0.05) contrast to control groups. However, there was no increase in concentration of interleukin 10 (IL-10) and interleukin 4 (IL-4) for both rEtSAG4 protein and pEGFP-N1-EtSAG4 plasmids. Chickens vaccinated with rEtSAG4 protein or pEGFP-N1-EtSAG4 plasmids both show higher weight, lower oocyst output and mean lesion scores compared with infection control groups. The highest anticoccidial index (ACI) value of immunized groups was 168.24 from EGFP-N1-EtSAG4 plasmids (100 μg) group. Generally, EGFP-N1-EtSAG4 plasmids as DNA vaccines provided a more effective immunoprotective for chickens against E. tenalla than that of rEtSAG4 protein as subunit vaccines. EtSAG4 is a promising candidate antigen gene for development of coccidiosis vaccine.

Molecular characterization and protective efficacy of the microneme 2 protein from Eimeria tenella

Microneme proteins play an important role in the adherence of apicomplexan parasites to host cells during the invasion process. In this study, the microneme 2 protein from the protozoan parasite Eimeria tenella (EtMIC2) was cloned, characterized, and its protective efficacy as a DNA vaccine investigated. The EtMIC2 gene, which codes for a 35.07 kDa protein in E. tenella sporulated oocysts, was cloned and recombinant EtMIC2 protein (rEtMIC2) was produced in an Escherichia coli expression system. Immunostaining with an anti-rEtMIC2 antibody showed that the EtMIC2 protein mainly localized in the anterior region and membrane of sporozoites, in the cytoplasm of first- and second-generation merozoites, and was strongly expressed during first-stage schizogony. In addition, incubation with specific antibodies against EtMIC2 was found to efficiently reduce the ability of E. tenella sporozoites to invade host cells. Furthermore, animal-challenge experiments demonstrated that immunization with pcDNA3.1(+)-EtMIC2 significantly increased average body weight gain, while decreasing the mean lesion score and oocyst output in chickens. Taken together, these results suggest that EtMIC2 plays an important role in parasite cell invasion and may be a viable candidate for the development of new vaccines against E. tenella infection in chickens.

The molecular characterization and protective efficacy of microneme 3 of Eimeria mitis in chickens

E. mitis is ubiquitous in clinical coccidiosis caused by mixed infection of Eimeria species and the infection by E. mitis usually significantly impairs productivity of the infected chickens. To date, however, few protective antigens from E. mitis have been reported. In this study, the molecular characterization and protective efficacy of microneme 3 of Eimeria mitis (EmiMIC3) were analyzed. EmiMIC3 gene was cloned from sporozoites of E. mitis and its MARs (microneme adhesive repeats domain) were predicted. Recombinant EmiMIC3 (rEmiMIC3) was expressed in E. coli and purified and then was analyzed by western blot with anti-E. mitis chicken serum. Meanwhile, native EmiMIC3 from sporozoites was analyzed by anti-rEmiMIC3 rat serum. The expressions of EmiMIC3 in E. mitis sporozoites and merozoites were analyzed by immunofluorescence assay. The rEmiMIC3-induced changes of T lymphocytes subpopulation, serum cytokines and IgY levels and the protective efficacy of rEmiMIC3 were determined in animal experiments. The results showed that the deduced open reading frame (ORF) of EmiMIC3 was composed of 1145 amino acids, possessing 9 MARs. EmiMIC3 gene was submitted to GenBank (accession number: MG888670). EmiMIC3 could express in sporozoites and merozoites respectively and located at the apex of E. mitis sporozoite. Western blot assay revealed that the rEmiMIC3 could be recognized by serum of chicken infected by E. mitis and the native EmiMIC3 from sporozoites could also be recognized by rat serum against rEmiMIC3. Following vaccination with rEmiMIC3, higher levels of IL-10, IFN-γ, TGF-βand IL-17, higher proportions of CD4+/CD3+ and CD8+/CD3 + T lymphocytes and higher level of IgY antibody were induced compared to the controls. Vaccination with rEmiMIC3 prominently increased the weight gains and decreased oocyst output of the vaccinated chickens after challenge infection. Our result not only enriches protective candidate antigen of E. mitis, but also provides available protective antigen of E. mitis for the development of multivalent vaccines against infection caused by mixture of Eimeria species in clinical coccidiosis.

Identification of common immunodominant antigens of Eimeria tenella, Eimeria acervulina and Eimeria maxima by immunoproteomic analysis

Clinical chicken coccidiosis is mostly caused by simultaneous infection of several Eimeria species, and host immunity against Eimeria is species-specific. It is urgent to identify common immunodominant antigen of Eimeria for developing multivalent anticoccidial vaccines. In this study, sporozoite proteins of Eimeria tenella, Eimeria acervulina and Eimeria maxima were analyzed by two-dimensional electrophoresis (2DE). Western bot analysis was performed on the yielded 2DE gel using antisera of E. tenella E. acervulina and E. maxima respectively. Next, the detected immunodominant spots were identified by comparing the data from MALDI-TOF-MS/MS with available databases. Finally, Eimeria common antigens were identified by comparing amino acid sequence between the three Eimeria species. The results showed that analysis by 2DE of sporozoite proteins detected 629, 626 and 632 protein spots from E. tenella, E. acervulina and E. maxima respectively. Western bot analysis revealed 50 (E. tenella), 64 (E. acervulina) and 57 (E. maxima) immunodominant spots from the sporozoite 2DE gels of the three Eimeria species. The immunodominant spots were identified as 33, 27 and 25 immunodominant antigens of E. tenella, E. acervulina and E. maxima respectively. Fifty-four immunodominant proteins were identified as 18 ortholog proteins among the three Eimeria species. Finally, 5 of the 18 ortholog proteins were identified as common immunodominant antigens including elongation factor 2 (EF-2), 14-3-3 protein, ubiquitin-conjugating enzyme domain-containing protein (UCE) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In conclusion, our results not only provide Eimeria sporozoite immunodominant antigen map and additional immunodominant antigens, but also common immunodominant antigens for developing multivalent anticoccidial vaccines.

The Molecular Characterization and Immunity Identification of Microneme 3 of Eimeria acervulina

The gene of Eimeria acervulina microneme protein 3 (EaMIC3) was cloned and characterized. According to the conserved sequence, the 3'- and 5'-ends of EaMIC3 were amplified by the rapid amplification of cDNA ends (RACE). The full length cDNA of this gene was obtained by overlapping the sequences of 3'- and 5'-extremities and amplification by reverse transcription PCR. The sequence analysis revealed that the opening reading frame (ORF) of EaMIC3 was 2,607 bp and encoded a protein of 868 amino acids with 93.04 kDa. Western blotting assay showed that the recombinant protein was successfully recognized by the sera of chickens experimentally infected with E. acervulina, whereas the native protein in the somatic extract of sporozoites was as well detected by sera from rats immunized with the recombinant protein of EaMIC3. Immunofluorescence analysis indicated that EaMIC3 was expressed in the sporozoites and merozoites stages of E. acervulina. Animal challenge experiments demonstrated that the recombinant protein of EaMIC3 could significantly increase the average body weight gains, decrease the mean lesion scores and the oocyst outputs of the immunized chickens and presented anticoccidial index (ACI) more than 165. Moreover, EaMIC3 protein produced significantly high level of IgG antibody, IFN-γ, IL-10, IL-17 TGF-β, CD4⁺ , and CD8⁺ .