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

Exploring the interplay between Eimeria spp. infection and the host: understanding the dynamics of gut barrier function

Coccidiosis is a global disease caused by protozoans, typically including Eimeria spp., which pose a significant threat to the normal growth and development of young animals. Coccidiosis affects mainly the gut, where parasite proliferation occurs. The intestinal barrier, which consists of chemical, mechanical, biological, and immune defences, plays a crucial role in protecting the host against pathogens, xenobiotics, and toxins present in the gastrointestinal tract. When animals ingest sporulated Eimeria spp. oocysts, these parasites primarily reproduce in the intestinal tract, causing damage to the structure and function of the intestine. This disruption of intestinal homeostasis adversely affects animal health. Numerous studies have also revealed that Eimeria-infected animals experience slower bone growth rates, inferior meat quality, reduced egg production and quality, as well as impaired growth and development. Therefore, the purpose of this review is to examine the underlying mechanisms through which Eimeria spp. regulate intestinal damage and disturb the balance of the internal environment. Specifically, this review will focus on their effects on the structural basis of the host intestine's chemical, mechanical, biological and immune barriers. This understanding is crucial for the development of effective drugs to prevent the invasion of Eimeria spp. into the intestine, which is of paramount importance for maintaining host health.

Vaccination with formulations targeting Eimeria maxima and Clostridium perfringens conferred comprehensive protection using a dual-infection challenge model of necrotic enteritis

With increasing regulations restricting antibiotic use in animal feed, the need for alternative strategies to prevent and manage necrotic enteritis (NE) has become imperative. As a result, developing effective vaccines has emerged as a top priority for broiler chicken health management. Coccidial infections are a well-established predisposing factor for NE, underscoring the importance of controlling coccidiosis to help mitigate NE outbreaks. This research aimed to investigate the protective efficacy of vaccine preparations containing Eimeria maxima elongation factor-1α and a multicomponent antigen cocktail of Clostridium perfringens, including a single collagen adhesion protein (CpCna) and two chimeric proteins: CpNA (NetB-Alpha-toxin) and CpFZ (Fructose-1,6-bisphosphate aldolase-Zinc metalloprotease). Two vaccine preparations-recombinant subunit vaccines and DNA vaccines-were developed to assess their immunoprotective effects, determined by relative body weight gain rate, lesion scores, survival rates, and antigen-specific IgY levels using a dual-infection NE challenge model involving E. maxima and C. perfringens. Broilers were administered two subcutaneous immunizations with either adjuvanted proteins or eukaryotic expression plasmids on Days 7 and 17. Chickens vaccinated with the five antigens exhibited significantly higher serum antigen-specific IgY levels, improved weight gains, zero mortality, and reduced lesion scores following the lethal dual-infection challenge. These results indicated that vaccine preparations targeting both C. perfringens and E. maxima represent a promising approach for controlling and preventing coccidiosis-induced NE in chickens.

Protective Efficacy Induced by the Common Eimeria Antigen Elongation Factor 2 against Challenge with Three Eimeria Species in Chickens

Avian coccidiosis arises from co-infection involving multiple Eimeria species, which could give rise to substantial economic losses in the global poultry industry. As a result, multivalent anticoccidial vaccines containing common Eimeria antigens offer considerable promise for controlling co-infection in clinical practice. In our previous study, Elongation factor 2 (EF2) was deemed as an immunogenic common antigen across various Eimeria species. This current investigation aimed to further assess the immunogenicity and protective efficacy of EF2 in recombinant subunit vaccine format against three Eimeria species. The EF2 gene cloned from Eimeria maxima (E. maxima) cDNA was designated as EF2 of E. maxima (EmEF2). The immunogenicity of the recombinant protein EmEF2 (rEmEF2) was assessed through Western blot analysis. The evaluation of the vaccine-induced immune response encompassed the determination of T lymphocyte subset proportions, cytokine mRNA transcription levels, and specific IgY concentrations in rEmEF2-vaccinated chickens using flow cytometry, quantitative real-time PCR (qPCR), and indirect enzyme-linked immunosorbent assay (ELISA). Subsequently, the protective efficacy of rEmEF2 was evaluated through vaccination and challenge experiments. The findings demonstrated that rEmEF2 was effectively recognized by the His-tag monoclonal antibody and E. maxima chicken antiserum. Vaccination with rEmEF2 increased the proportions of CD4+ and CD8+ T lymphocytes, elevated IL-4 and IFN-γ mRNA transcription levels, and enhanced IgY antibody levels compared to the control groups. Moreover, compared to the control groups, vaccination with rEmEF2 led to decreased weight loss, reduced oocyst outputs, and alleviated enteric lesions. Furthermore, in the rEmEF2-immunized groups, challenges with E. maxima and E. acervulina resulted in anticoccidial index (ACI) scores of 166.35 and 185.08, showing moderate-to-excellent protective efficacy. Nevertheless, challenges with E. tenella and mixed Eimeria resulted in ACI scores of 144.01 and 127.94, showing low protective efficacy. In conclusion, EmEF2, a common antigen across Eimeria species, demonstrated the capacity to induce a significant cellular and humoral immune response, as well as partial protection against E. maxima, E. acervulina, and E. tenella. These results highlight EmEF2 as a promising candidate antigen for the development of multivalent vaccines targeting mixed infections by Eimeria species.

Protective efficacy of multiepitope vaccines constructed from common antigens of Eimeria species in chickens

Clinical avian coccidiosis is typically caused by coinfection with several Eimeria species. Recombinant protein and DNA vaccines have shown promise in controlling coccidiosis. On this basis, DNA vaccines that encode multiple epitopes from different Eimeria species may provide broad protection against coinfections. In this study, we designed a fusion gene fragment, 14EGT, that contained concentrated T-cell epitopes from four common antigens of Eimeria species (14-3-3, elongation factor 2, glyceraldehyde-3-phosphate dehydrogenase, and transhydrogenase). The multiepitope DNA vaccine pVAX1-14EGT and recombinant protein vaccine pET-32a-14EGT (r14EGT) were then created based on the 14EGT fragment. Subsequently, cellular and humoral immune responses were measured in vaccinated chickens. Vaccination-challenge trials were also conducted, where the birds were vaccinated with the 14EGT preparations and later exposed to single or multiple Eimeria species to evaluate the protective efficacy of the vaccines. According to the results, vaccination with 14EGT preparations effectively increased the proportions of CD4+ and CD8+ T cells and the levels of Th1 and Th2 hallmark cytokines. The levels of serum IgG antibodies were also significantly increased. Animal vaccination trials revealed alleviated enteric lesions, weight loss, and oocyst output compared to those of the control groups. The preparations were found to be moderately effective against single Eimeria species, with the anticoccidial index (ACI) ranging from 160 to 180. However, after challenge with multiple Eimeria species, the protection provided by the 14EGT preparations was not satisfactory, with ACI values of 142.18 and 146.41. Collectively, the results suggest that a multiepitope vaccine that encodes the T-cell epitopes of common antigens derived from Eimeria parasites could be a potential and effective strategy to control avian coccidiosis.

Identification of Eimeria tenella sporozoite immunodominant mimotopes by random phage-display peptide libraries-a proof of concept study

INTRODUCTION

Coccidiosis, caused by parasites of numerous Eimeria species, has long been recognized as an economically significant disease in the chicken industry worldwide. The rise of anti-coccidian resistance has driven a search for other parasite management techniques. Recombinant antigen vaccination presents a highly feasible alternative. Properly identifying antigens that might trigger a potent immune response is one of the major obstacles to creating a viable genetically modified vaccine.

METHODS

This study evaluated a reverse immunology approach for the identification of B-cell epitopes. Antisera from rabbits and hens inoculated with whole-sporozoites of E. tenella were used to identify Western blot antigens. The rabbit IgG fraction from the anti-sporozoite serum exhibited the highest reactogenicity; consequently, it was purified and utilized to screen two random Phage-display peptide libraries (12 mer and c7c mer). After three panning rounds, 20 clones from each library were randomly selected, their nucleotide sequences acquired, and their reactivity to anti-sporozoite E. tenella serum assessed. The selected peptide clones inferred amino acid sequences matched numerous E. tenella proteins.

RESULTS AND CONCLUSIONS

The extracellular domain of the epidermal growth factor-like (EGF-like) repeats, and the thrombospondin type-I (TSP-1) repeats of E. tenella micronemal protein 4 (EtMIC4) matched with the c7c mer selected clones CNTGSPYEC (2/20) and CMSTGLSSC (1/20) respectively. The clone CSISSLTHC that matched with a conserved hypothetical protein of E. tenella was widely selected (3/20). Selected clones from the 12-mer phage display library AGHTTQFNSKTT (7/20), GPNSAFWAGSER (2/20) and HFAYWWNGVRGP (8/20) showed similarities with a cullin homolog, elongation factor-2 and beta-dynein chain a putative E. tenella protein, respectively. Four immunodominant clones were previously selected and used to immunize rabbits. By ELISA and Western blot, all rabbit anti-clone serums detected E. tenella native antigens.

DISCUSSION

Thus, selected phagotopes contained recombinant E. tenella antigen peptides. Using antibodies against E. tenella sporozoites, this study demonstrated the feasibility of screening Phage-display random peptide libraries for true immunotopes. In addition, this study looked at an approach for finding novel candidates that could be used as an E. tenella recombinant epitope-based vaccine.

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.

Bacillus subtilis Expressing Chicken NK-2 Peptide Enhances the Efficacy of EF-1α Vaccination in Eimeria maxima-Challenged Broiler Chickens

This study was conducted to investigate the synergistic effects of orally delivered B. subtilis-cNK-2 on vaccination with rEF-1α against E. maxima infection in broiler chickens. Chickens were assigned into the following five groups: control (CON, no Eimeria infection), non-immunized control (NC, PBS), component 1 (COM1, rEF-1α only), component 2 (COM2, rEF-1α plus B. subtilis empty vector), and component 3 (COM3, rEF-1α plus B. subtilis-NK-2). The first immunization was administered intramuscularly on day 4, and the second immunization was given one week later with the same concentration of components as the primary immunization. The immunization of B. subtilis spores (COM2 and COM3) was performed by oral administration given for 5 consecutive days a week later than the second immunization. On day 19, all the chickens except the CON group were orally challenged with E. maxima oocysts (1.0 × 10⁴/chicken). The results of the in vivo vaccination showed that all the chickens immunized with rEF-1α (COM1, COM2, and COM3) produced higher (p < 0.05) serum antibodies against EF-1α on 12 days post-E. maxima infection (dpi). The COM3 group showed a significantly (p < 0.05) higher average body weight gain (BWG) on 0-6, 6-9, and 0-12 dpi compared to those of the non-immunized chickens (NC). Immunization with rEF-1α alone (COM1) reduced the gut lesion score on 6 dpi and the fecal oocyst shedding on 9 dpi, whereas co-administration with B. subtilis spores (COM2 or COM3) led to further reduction in the lesion score. E. maxima infection increased the expression levels of IFN-γ and IL-17β in the jejunum, but these expressions were downregulated in the rEF-1α immunized (COM1) group and in the groups immunized with rEF-1α and orally treated with B. subtilis spores (COM2 or COM3) at 4 dpi. A reduced gene expression of occludin in the jejunum of the E. maxima-infected chickens on 4 dpi was upregulated following the immunization with COM2. Collectively, rEF-1α vaccination induced significant protection against E. maxima infection in the broiler chickens, and the efficacy of rEF-1α vaccination was further enhanced by co-administration with orally delivered B. subtilis spores expressing cNK-2.

Oral administration of chicken NK-lysin or recombinant chicken IL-7 improves vaccine efficacy of Eimeria tenella elongation factor-1α (EF-1α) against coccidiosis in commercial broiler chickens

The synergistic effects of orally-delivered chicken NK-lysin peptide 2 (cNK-2) or recombinant chicken IL-7 (rchIL-7) on vaccination with recombinant Eimeria elongation factor-1α (rEF-1α) against Eimeria maxima (E. maxima) infection was investigated in broiler chickens. Chickens were divided into six groups: control (CON, no Eimeria infection), non-immunized control (NC, PBS), Vaccination 1 (VAC 1, rEF-1α plus cNK-2), Vaccination 2 (VAC 2, rchIL-7 plus cNK-2), Vaccination 3 (VAC 3, rEF-1α/rchIL-7 plus cNK-2), and Vaccination 4 (VAC 4, rEF-1α/rchIL-7 plus cNK-2). All groups, except the CON and NC, were orally treated with cNK-2 for 5 days. The first immunization, except for the VAC 4 group, was performed intramuscularly on day 4, and the second immunization was given with the same concentration of components as the primary immunization one week later. The immunization of the VAC 4 group was carried out by an oral inoculation on the same days. On day 19, all chickens except the CON group, were orally challenged with E. maxima (1.0 × 10⁴ oocysts/chicken). The in vivo vaccination results showed that the VAC 1 and VAC 3 groups produced high (p < 0.05) levels of serum antibody titers to rEF-1α, and the VAC 3 showed enhanced (p < 0.05) levels of serum IL-7. Furthermore, the VAC 3 group showed significantly (p < 0.01) greater body weight gains at 6- and 9-days post-E. maxima infection (dpi) with reduced oocyst shedding at 6 dpi. The average jejunal lesion score of the NC group was 2.5 whereas the VAC 1 group showed a significantly (p < 0.05) lower lesion scores at 6 dpi. E. maxima infection significantly (P < 0.05) up-regulated the expression levels of cytokines (IL-6, IL-10 and IFN-γ) in the jejunum at 4 dpi, but those expressions were down-regulated in VAC 1 or VAC 3 groups. Moreover, the gene expression levels of Jam 2 and Occludin, were significantly (P < 0.05) decreased following E. maxima infection in jejunum at 4 dpi (NC), but their expressions were increased in the VAC 3 group. Collectively, these results showed that the efficacy of rEF-1α vaccination was significantly enhanced when rEF-1α vaccine co-immunized with chIL-7 or cNK-2.

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.

Multilocus Sequence Typing of Eimeria maxima in Commercial Broiler Flocks

About 35% of all broiler flocks in the United States receive an anticoccidial vaccine, but it is not possible to easily differentiate Eimeria vaccine strains from Eimeria field isolates. Being able to do that would allow using vaccines in a more targeted way. The objective of this study was to collect Eimeria maxima isolates from broiler flocks that received anticoccidial feed additives and flocks that had been vaccinated against coccidia and then test them with a multilocus sequencing typing (MLST) scheme developed for this study. Fecal samples were obtained from commercial broiler flocks in Alabama and Tennessee. Oocyst counts in samples tended to be lower in flocks receiving anticoccidial feed additives and higher in vaccinated flocks. Selected samples were screened for presence of E. maxima by quantitative PCR, and Eimeria spp. composition was investigated by next-generation amplicon sequencing (NGAS) in 37 E. maxima positive samples. Other detected Eimeria spp. besides E. maxima were Eimeria acervulina in 35 samples, Eimeria praecox in 23 samples, Eimeria mitis or Eimeria mivati in 17 samples, and Eimeria necatrix or Eimeria tenella in 10 samples. Six partial E. maxima genes (dnaJ domain containing protein, 70-kDa heat shock protein, prolyl endopeptidase, regulator of chromosome condensation domain containing protein, serine carboxypeptidase, and vacuolar proton-translocating ATPase subunit) of 46 samples were sequenced. The MLST scheme was able to differentiate two vaccines from each other. Three of 17 samples from vaccinated flocks differed from the vaccine used in the flock, while 16 of 29 samples from unvaccinated flocks differed from the vaccine. However, there was also a large number of low-quality, ambiguous chromatograms and negative PCRs for the selected genes. If and when more advanced, possibly next-generation sequencing-based methods will be developed, the genes should be considered as targets.

Comparison of endogenous development, invasion ability and apoptotic features between diclazuril resistant and sensitive strains of Eimeria tenella

Diclazuril (DIC) is widely used in the poultry industry to control coccidiosis. However, drug resistance makes it less effective, and the underlying mechanism remains unclear. One DIC-resistant E. tenella (RE) isolate and one sensitive E. tenella (SE) isolate were used to compare the differences in their endogenous development, pathogenicity, invasion-related gene expression and apoptotic characteristics. Chickens were allocated into four groups to receive RE or SE strain and their corresponding DIC treatment or not. Caeca tissues were sampled at 96 h, 120 h and 144 h post-infection (PI) for pathological analysis. Meanwhile, second-generation merozoites (Mz2) were separated at 120 h PI to detect alterations in mitochondrial membrane potential (MMP), apoptotic rate and caspase-3 activity and mRNA expression of protein phosphatase 5 (PP5), glyceraldehyde 3-phosphate dehydrogenase (GAPDH), actin depolymerizing factor (ADF) and microneme proteins (MICs). Haematoxylin and eosin staining revealed that DIC treatment strictly blocked the development of the SE strain but slightly affected the RE strain. Meanwhile, the number of SE Mz2 and their MMP decreased at the same time the apoptotic rate increased after DIC treatment. Real-time quantitative PCR and caspase-3 activity studies demonstrated that Mz2 from the RE strain had higher mRNA expression of ADF and MICs along with no significant changes in GAPDH and caspase-3 activity under DIC pressure compared to its control; in contrast, the mRNA expression of ADF, MICs and PP5 was markedly suppressed in Mz2 from SE with upregulated caspase-3 activity and GAPDH transcription. In addition, the mRNA expression of GAPDH and PP5 in Mz2 from RE was remarkably higher than that of SE. Taken together, the higher mRNA expression of invasion-related genes and almost unaffected endogenous development provide a better understanding of coccidian resistance to DIC.

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.

Immunoproteomic analysis of the sporozoite antigens of Eimeria necatrix

Eimeria necatrix, an apicomplexan protozoa of the genus Eimeria, causes intestinal coccidiosis that can reduce growth performance of poultry and result in high mortality in older chickens. In this report, the whole sporozoite proteins of E.necatrix were studied by two-dimensional electrophoresis (2-DE) and Western blotting using hyper-immune chicken serum containing E.necatrix-specific antibodies. Approximately 680 protein spots for E.necatrix sporozoite were detected by 2-DE with silver staining, where 98 spots were cross-reacted with the E. necatrix-specific immune sera. Out of the 56 spots that were selected for MALDI-TOF-MS/MS analysis, 50 unique proteins were identified using the MASCOT software, 8 proteins were identified as known E.necatrix proteins and the rest were all putative proteins. These proteins have a wide range of known or predicted structures, cellular locations and functions, including proteins in category nuclear location & function, multifunctional- or multifunctional motifs-containing proteins, cellular transport and structure-related proteins, proteins of enzymatic activities, motor proteins-related, cell surface and organelle-related proteins. These new findings will enhance our understandings of parasite immunogenicity and immune evasion mechanisms of E. necatrix and facilitate the discovery phase of highly effective vaccine candidates.

Protective Immunity Induced by an Eimeria tenella Whole Sporozoite Vaccine Elicits Specific B-Cell Antigens

Simple Summary

Coccidiosis caused by Eimeria tenella is a dreadful disease with a significant economic impact to the poultry industry. The disease has been controlled by routine medication of feed with synthetic chemicals or ionophore drugs. However, the rising appearance of drug resistance and public demands for reduced drug use in poultry production have driven a dramatic change, replacing anticoccidial drugs with alternative methods, such as vaccination with either virulent or attenuated Eimeria oocysts. Based on preliminary studies, the immune protection evaluating whole-sporozoites of E. tenella vaccine was verified. After this vaccine provided successful protection, the humoral response of a heterologous species like the rabbit was compared with the natural host immune response. Several B-cells antigens from the E. tenella sporozoite suitable for a genetically engineered vaccine were identified. Vaccination with newly identified recombinant antigens offers a feasible alternative for the control of avian coccidiosis into the broiler barns favoring the gradual withdrawal of the anticoccidial drugs.

Abstract

This study investigated protection against Eimeria tenella following the vaccination of chicks with 5.3 × 10⁶E. tenella whole-sporozoites emulsified in the nanoparticle adjuvant IMS 1313 N VG Montanide™ (EtSz-IMS1313). One-day-old specific pathogen-free (SPF) chicks were subcutaneously injected in the neck with EtSz-IMS1313 on the 1st and 10th days of age. Acquired immunity was assayed through a challenge with 3 × 10⁴ homologous sporulated oocysts at 21 days of age. The anticoccidial index (ACI) calculated for every group showed the effectiveness of EtSz-IMS1313 as a vaccine with an ACI of 186; the mock-injected control showed an ACI of 18 and the unimmunized, challenged control showed an ACI of −28. In a comparison assay, antibodies from rabbits and SPF birds immunized with EtSz-IMS1313 recognized almost the same polypeptides in the blotting of E. tenella sporozoites and merozoites. However, rabbit antisera showed the clearest recognition pattern. Polypeptides of 120, 105, 94, 70, 38, and 19 kDa from both E. tenella life cycle stages were the most strongly recognized by both animal species. The E. tenella zoite-specific IgG antibodies from the rabbits demonstrated the feasibility for successful B cell antigen identification.

Actin-depolymerizing factor from Eimeria tenella promotes immunogenic function of chicken dendritic cells

Dendritic cells play a crucial role in inducing antigen-specific immunity to pathogens. During host-parasite interaction, host immune response to the parasite molecules is considered essential for recognizing novel antigens for control strategies. Therefore, in the present study, chicken dendritic cells (DCs) (ChDCs), derived from spleens were used to evaluate their capacity to proliferate and differentiate autologous T lymphocytes in response to actin-depolymerizing factor from Eimeria tenella (EtADF). Immunoblot analysis showed that recombinant EtADF protein (rEtADF) was able to interact with rat anti-rEtADF antibodies. The immunofluorescence test confirmed rEtADF binding on ChDCs surface. Flow cytometric analysis revealed that phenotypes for MHCII, CD1.1, CD11c, CD80, and CD86 were increased in ChDCs after rEtADF treatment. qRT-PCR results indicated that ChDCs triggered TLR signaling in response to rEtADF, and suppressed Wnt signaling. Transcript levels of CD83, CCL5, and CCR7 in ChDCs were improved following rEtADF treatment. In addition, rEtADF promoted DC-directed T cell proliferation and differentiation of naïve T cells into CD3⁺/CD4⁺ T cells in DC/T cell co-incubation system. Cytokine analysis of rEtADF-pulsed ChDCs showed increased levels of IL-12 and IFN-γ, while IL-10 and TGF-β remained unchanged. Moreover, rEtADF-treated ChDCs enhanced production of IFN-γ when incubated with T cells, and IL-4 secretion remained unchanged. Our findings indicted that rEtADF could facilitate the polarization of Th1 immune cells by triggering both host DCs and T cells. Our findings provide useful insights into future work aimed at anticoccidial vaccine strategies.

Glyceraldehyde-3-phosphate dehydrogenase from Eimeria acervulina modulates the functions of chicken dendritic cells to boost Th1 type immune response and stimulates autologous CD4+ T cells differentiation in-vitro

Dendritic cells (DCs) play a pivotal role to amplify antigen-specific immune responses. Antigens that sensitize T cells via antigen-presentation by DCs could enhance the capacity of host immunity to fight infections. In this study, we tested the immunogenic profiles of chicken DCs towards Glyceraldehyde-3-phosphate dehydrogenase from Eimeria acervulina (EaGAPDH). Immunoblot analysis showed that recombinant EaGAPDH (rEaGAPDH) protein was successfully recognized by rat sera generated against rEaGAPDH. Interaction and internalisation of rEaGAPDH by chicken splenic-derived DCs (chSPDCs) was confirmed by immunofluorescence analysis. Flow cytometry revealed that chSPDCs upregulated MHCII, CD1.1, CD11c, CD80, and CD86 cell-surface markers. Moreover, mRNA expressions of DC maturation biomarkers (CCL5, CCR7, and CD83) and TLR signalling genes (TLR15 and MyD88) were also upregulated whereas those of Wnt signalling were non-significant compared to negative controls. rEaGAPDH treatment induced IL-12 and IFN-γ secretion in chSPDCs but had no effect on IL-10 and TGF-β. Likewise, DC-T cell co-culture promoted IFN-γ secretion and the level of IL-4 was unaffected. Proliferation of T cells and their differentiation into CD3⁺/CD4⁺ T cells were triggered in chSPDCs-T cells co-culture system. Taken together, rEaGAPDH could promote Th1 polarization by activating both host DCs and T cells and sheds new light on the role of this important molecule which might contribute to the development of new DCs-based immunotherapeutic strategies against coccidiosis.

Heat stress reduces sexual development and affects pathogenesis of Eimeria maxima in meat-type chickens

Coccidiosis, caused by Eimeria spp. presents a self-limiting intestinal infection of poultry. Intestinal replication of the parasite causes severe morphological alterations to the host gastrointestinal tract, marked, among others, by the disruption of the intestinal barrier. We have previously reported a significant reduction in merozoite replication and oocyst shedding in E. tenella in vitro and in vivo. The objective of this study was to investigate the pathogenesis of E. maxima infection in broiler chickens under heat stress (HS) and mRNA expression of host cytokines that might affect the curtailed development of the parasite. We herein demonstrate that there is a significant detrimental effect of HS on the pathogenesis of E. maxima infection in broilers. There was a restricted replication of the parasite in HS chickens evidenced by significantly reduced oocyst shedding and disruption of the intestinal blood barrier. Gene expression of parasite genes demonstrated curtailed sexual reproduction of E. maxima in HS chickens. There was downregulation of Eimeria spp. genes related to gamete fusion, oocyst shedding, mitosis and spermiogenesis. Host gene expression indicates alterations in the cytokine expression that could be related to reduced parasite development in vivo.

Genome-wide analysis of differentially expressed profiles of mRNAs, lncRNAs and circRNAs in chickens during Eimeria necatrix infection

BACKGROUND

Eimeria necatrix, the most highly pathogenic coccidian in chicken small intestines, can cause high morbidity and mortality in susceptible birds and devastating economic losses in poultry production, but the underlying molecular mechanisms in interaction between chicken and E. necatrix are not entirely revealed. Accumulating evidence shows that the long-non-coding RNAs (lncRNAs) and circular RNAs (circRNAs) are key regulators in various infectious diseases. However, the expression profiles and roles of these two non-coding RNAs (ncRNAs) during E. necatrix infection are still unclear.

METHODS

The expression profiles of mRNAs, lncRNAs and circRNAs in mid-segments of chicken small intestines at 108 h post-infection (pi) with E. necatrix were analyzed by using the RNA-seq technique.

RESULTS

After strict filtering of raw data, we putatively identified 49,183 mRNAs, 818 lncRNAs and 4153 circRNAs. The obtained lncRNAs were classified into four types, including 228 (27.87%) intergenic, 67 (8.19%) intronic, 166 (20.29%) anti-sense and 357 (43.64%) sense-overlapping lncRNAs; of these, 571 were found to be novel. Five types were also predicted for putative circRNAs, including 180 exonic, 54 intronic, 113 antisense, 109 intergenic and 3697 sense-overlapping circRNAs. Eimeria necatrix infection significantly altered the expression of 1543 mRNAs (707 upregulated and 836 downregulated), 95 lncRNAs (49 upregulated and 46 downregulated) and 13 circRNAs (9 upregulated and 4 downregulated). Target predictions revealed that 38 aberrantly expressed lncRNAs would cis-regulate 73 mRNAs, and 1453 mRNAs could be trans-regulated by 87 differentially regulated lncRNAs. Additionally, 109 potential sponging miRNAs were also identified for 9 circRNAs. GO and KEGG enrichment analysis of target mRNAs for lncRNAs, and sponging miRNA targets and source genes for circRNAs identified associations of both lncRNAs and circRNAs with host immune defense and pathogenesis during E. necatrix infection.

CONCLUSIONS

To the best of our knowledge, the present study provides the first genome-wide analysis of mRNAs, lncRNAs and circRNAs in chicken small intestines infected with E. necatrix. The obtained data will offer novel clues for exploring the interaction mechanisms between chickens and Eimeria spp.

Recombinant ubiquitin-conjugating enzyme of Eimeria maxima induces immunogenic maturation in chicken splenic-derived dendritic cells and drives Th1 polarization in-vitro

Dendritic cells (DCs) are key linkages between innate immunity and acquired immunity. The antigens that promote the functions of DCs might be the effective candidates of novel vaccine. In this research, the ability of ubiquitin-conjugating enzyme (UCE), a recognized common antigens among chicken Eimeria species, to stimulate DCs of chickens were evaluated. We cloned UCE gene from Eimeria maxima (EmUCE), and its protein expression was confirmed by SDS-PAGE and western-blot. Immunofluorescence assay confirmed the binding of rEmUCE on the surface of chicken splenic-derived DCs (ChSP-DCs). Flow cytometric analysis showed that rEmUCE-treated ChSP-DCs increased MHCII, CD1.1, CD11c, CD80, and CD86 phenotypes. qRT-PCR indicated that transcript levels of maturation markers CCL5, CCR7, and CD83 in ChSP-DCs were upregulated in response to rEmUCE. Following rEmUCE treatment, chSP-DCs activated TLR signaling and inhibited Wnt signaling. Moreover, rEmUCE promoted DC-mediated T-cell proliferation in DC/T-cell co-incubation. Interestingly, CD3⁺/CD4⁺ T-cells were significantly enhanced when rEmUCE-treated chSP-DCs were co-incubated with T-cells. Cytokine secretion pattern of rEmUCE-stimulated ChSP-DCs revealed that the production of IL-12 and IFN-γ was increased whereas IL-10 and TGF-β were unchanged. Likewise, the co-incubation of ChSP-DCs with T-cells indicated increased production of IFN-γ but not IL-4. Collectively, rEmUCE could polarize DCs to immunogenic phenotype and shift the immune cells towards Th1 response. Our observations provide valuable insight for future research aimed at vaccine development against avian coccidiosis.

Immunoproteomic and mass spectrometric analysis of Eimeria acervulina antigens recognized by antisera from chickens infected with E. acervulina, E. tenella or E. necatrix

Background

Coccidiosis is caused by Eimeria spp. and can result in severe economic losses to the global poultry industry. Due to anticoccidial drug resistance rapidly developing in the parasites and drug residues in poultry products, efficacious and safe alternative coccidia control measures are needed. The objective of the present study was to identify common protective antigens which may be used as vaccine candidates in the development of subunit, multivalent, cross-protective vaccines against most of the economically important Eimeria species.

Methods

Whole sporozoite proteins of Eimeria acervulina were prepared and analyzed by 2-dimensional gel electrophoresis (2-DE) followed by western blotting using immune sera specific to E. tenella, E. acervulina, or E. necatrix. The protein spots detected by all three immune sera were then excised from the preparative gel and protein ID was performed by MALDI-TOF-MS/MS.

Results

Approximately 620 E. acervulina sporozoite protein spots were demonstrated by 2-DE with silver staining, among which 23 protein spots were recognized by immune sera specific to all three Eimeria species. The results showed that 21 putative E. acervulina proteins were identified, which include proteins with known enzymatic properties, and those which are involved in protein translation, transport and trafficking, and ribosomal biogenesis and functions. There is one protein which may be involved in transcription and one heat-shock protein. Two proteins contain predicted domains, but with no apparent functions known. There were 2 protein spots which had no detectable proteins. None of the proteins has a predicted signal peptide or a transmembrane domain; however, 6 of the 21 putative proteins were predicted to be potentially secretory through the non-classical pathway.

Conclusions

Our study identified a diverse group of antigens immunologically common to all three Eimeria species, none of which was previously characterized and tested as a vaccine candidate. Further research on immunogenicity and cross-protective potential of these individual proteins as vaccine candidates will aid the development of vaccines against the most common and pathogenic Eimeria spp.

Involvement of T Cell Immunity in Avian Coccidiosis

Avian coccidiosis is caused by Eimeria, which is an intracellular apicomplexan parasite that invades through the intestinal tract to cause devastating disease. Upon invasion through the intestinal epithelial cells, a strong inflammatory response is induced that results in complete villous destruction, diarrhea, hemorrhage, and in severe cases, death. Since the life cycle of Eimeria parasites is complex and comprises several intra- and extracellular developmental stages, the host immune responses are diverse and complex. Interferon-γ-mediated T helper (Th)1 response was originally considered to be the predominant immune response in avian coccidiosis. However, recent studies on other avian T cell lineages such as Th17 and T regulatory cells have implicated their significant involvement in maintaining gut homeostasis in normal and disease states including coccidiosis. Therefore, there is a need to understand better their role in coccidiosis. This review focuses on research findings concerning the host immune response induced by avian coccidiosis in the context of T cell immunity, including expression of T-cell-related cytokines and surface molecules that determine the phenotype of T lymphocytes.

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.

Protective immunity induced by Eimeria common antigen 14-3-3 against Eimeria tenella, Eimeria acervulina and Eimeria maxima

Background

Avian coccidiosis is often caused by co-infection with several species of Eimeria worldwide. Developing a multivalent vaccine with an antigen common to multiple Eimeria species is a promising strategy for controlling clinical common co-infection of Eimeria. In the previous study, 14–3-3 was identified as one of the immunogenic common antigen in E. tenella, E. acervulina and E. maxima. The aim of the present study was to evaluate the immunogenicity and protective efficacy of Ea14–3-3 in the form of DNA vaccine against infection with three species of Eimeria both individually and simultaneously.

Results

After vaccination with pVAX-Ea14–3-3, the Ea14–3-3 gene was transcribed and expressed in the injected muscles. Vaccination with pVAX-Ea14–3-3 significantly increased the proportion of CD4⁺ and CD8⁺ T lymphocytes and produced a strong IgY response in immunized chickens. Similarly, pVAX-Ea14–3-3 stimulated the chicken’s splenocytes to produce high levels of Th1-type (IFN-γ, IL-2) and Th2-type (IL-4) cytokines. The vaccine-induced immune response was responsible to increase weight gain, decreased the oocyst output, and alleviated enteric lesions significantly in immunized chickens as compared to control group, in addition to induce moderate anti-coccidial index (ACI).

Conclusion

These results indicate that Ea14–3-3 is highly immunogenic and capable to induce significant immune responses. Furthermore, Ea14–3-3 antigen can provide effective protection against infection with Eimeria tenella, Eimeria acervulina, Eimeria maxima both individually and in combination with three Eimeria species. Significant outcomes of our study provide an effective candidate antigen for developing a multivalent Eimeria vaccine against mixed infection with various Eimeria species under natural conditions.

Electronic supplementary material

The online version of this article (10.1186/s12917-018-1665-z) contains supplementary material, which is available to authorized users.

Protective Efficacy of Coccidial Common Antigen Glyceraldehyde 3-Phosphate Dehydrogenase (GAPDH) against Challenge with Three Eimeria Species

Coccidiosis is an intestinal disorder of poultry and often caused by simultaneous infections of several Eimeria species. GAPDH is one of the immunogenic common antigens among Eimeria tenella, E. acervulina, and E. maxima identified in our previous study. The present study was performed to further evaluate its immunogenicity and protective efficacy. The genes of GAPDH cloned from E. acervulina and E. maxima were named as EaGAPDH and EmGAPDH, respectively. The immunogenicity of recombinant proteins of EaGAPDH and EmGAPDH were analyzed by Western blot. The transcription and expression of pVAX-EaGAPDH and pVAX-EmGAPDH in the injected muscles were detected by reverse transcription PCR (RT-PCR) and Western blot, respectively. GAPDH-induced changes of T lymphocytes subpopulation, cytokines production, and antibody were determined using flow cytometry, quantitative real-time PCR (qPCR), and ELISA, respectively. Finally, the protective efficacies of pVAX-EaGAPDH and pVAX-EmGAPDH were evaluated by vaccination and challenge experiments. The results revealed that the recombinant GAPDH proteins reacted with the corresponding chicken antisera. The EaGAPDH genes were successfully transcribed and expressed in the injected muscles. Vaccination with pVAX-EaGAPDH and pVAX-EmGAPDH significantly increased the proportion of CD4⁺ and CD8⁺ T lymphocytes, the cytokines productions of IFN-γ, IL-2, IL-4 et al., and IgG antibody levels compared to controls. The vaccination increased the weight gains, decreased the oocyst outputs, alleviate the enteric lesions compared to controls, and induced moderate anti-coccidial index (ACI). In conclusion, the coccidial common antigen of GAPDH induced significant humoral and cellular immune response and effective protection against E. tenella, E. acervulina, E. maxima, and mixed infection of the three Eimeria species.