EMBRYO VACCINATION AGAINST EIMERIA TENELLA AND E. ACERVULINA INFECTIONS USING RECOMBINANT PROTEINS AND CYTOKINE ADJUVANTS

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.

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.

Evaluation of immunoprotective effects of recombinant protein and DNA vaccine based on Eimeria tenella surface antigen 16 and 22 in vivo

Coccidiosis triggered by Eimeria tenella is accompanied by haemorrhagic caecum and high morbidity. Vaccines are preferable choices to replace chemical drugs against coccidiosis. Surface antigens of apicomplexan parasites can adhere to host cells during the infection process. Therefore, truncated fragments coding E. tenella surface antigen 16 (EtSAG16) and 22 (EtSAG22) were cloned into pET-28a prokaryotic vector to express recombinant protein 16 (rEtSAG16) and 22 (rEtSAG22), respectively. Likewise, pEGFP-N1-EtSAG16 and pEGFP-N1-EtSAG22 plasmids were constructed using pEGFP-N1 eukaryotic vector. Further, pEGFP-N1-EtSAG4-16-22 multiple gene plasmid carrying EtSAG4, 16 and 22 were designed as cocktail vaccines to study integral immunoprotective effects. Western blot and RT-PCR (reverse transcription) assay were performed to verify expressions of EtSAG16 and 22 genes. Immunoprotective effects of recombinant protein or DNA vaccine were evaluated using different doses (50 or 100 μg) in vivo. All chickens in the vaccination group showed higher cytokine concentration (IFN-γ and IL-17), raised IgY antibody level, increased weight gain, lower caecum lesion score and reduced oocyst shedding compared with infection control groups (p < 0.05). The highest anticoccidial index (ACI) value 173.11 was from the pEGFP-N1-EtSAG4-16-22 plasmid (50 μg) group. In conclusion, EtSAG16 and 22 might be alternative candidate genes for generating vaccines against E. tenella infection.

Specific EtMIC3-binding peptides inhibit Eimeria tenella sporozoites entry into host cells

Avian coccidiosis caused by Eimeria leads to huge economic losses on the global poultry industry. In this study, microneme adhesive repeat regions (MARR) bc1 of E. tenella microneme protein 3 (EtMIC3-bc1) was used as ligand, and peptides binding to EtMIC3 were screened from a phage display peptide library. The positive phage clones were checked by enzyme-linked immunosorbent assay (ELISA). Competitive ELISA was applied to further verify the binding capability between the positive phages and recombinant EtMIC3-bc1 protein or sporozoites protein. The inhibitory effects of target peptides on sporozoites invasion of MDBK cells were measured in vitro. Chickens were orally administrated with target positive phages and the protective effects against homologous challenge were evaluated. The model of three-dimensional (3D) structure for EtMIC3-bc1 was conducted, and molecular docking between target peptides and EtMIC3-bc1 model was analyzed. The results demonstrated that three selected positive phages specifically bind to EtMIC3-bc1 protein. The three peptides A, D and W effectively inhibited invasion of MDBK cells by sporozoites, showing inhibited ratio of 71.8%, 54.6% and 20.8%, respectively. Chickens in the group orally inoculated with phages A displayed more protective efficacies against homologous challenge than other groups. Molecular docking showed that amino acids in three peptides, especially in peptide A, insert into the hydrophobic groove of EtMIC3-bc1 protein, and bind to EtMIC3-bc1 through intermolecular hydrogen bonds. Taken together, the results suggest EtMIC3-binding peptides inhibit sporozoites entry into host cells. This study provides new idea for exploring novel strategies against coccidiosis.

Eimeria tenella: specific EtAMA1-binding peptides inhibit sporozoite entry into host cells

Avian coccidiosis caused by Eimeria inflicts high economic losses to the poultry industry. Application of drugs and live vaccines presents particular challenges in pathogen resistance and cost, hence alternative anti-coccidial strategies are needed. In this study, peptides that specifically bind E. tenella AMA1 (EtAMA1) were screened from a phage display peptide library. The positive clones of target phages were characterized by ELISA after four rounds of biopanning. The binding capabilities with EtAMA1 and sporozoite proteins for the two selected peptides were detected by ELISA. The role of the two target peptides in inhibiting sporozoite invasion of MDBK cells was evaluated in vitro and the anti-coccidial effects of the two phages were assessed by an animal experiment. The three-dimensional (3D) structural model of EtAMA1 extracellular domain (EctoAMA1) protein was constructed based on the crystal template of TgAMA1 (PDB ID: 2 × 2Z), and the molecular docking between target peptides and EctoAMA1 model was analyzed. The results showed that two selected phages strongly interacted with EctoAMA1 and sporozoites protein. Two corresponding specific EtAMA1-binding peptide (named L and C) showed significant effects on inhibiting sporozoite invasion of MDBK cells. Chickens orally fed the two target phages showed partial protection against homologous challenge. Homology modeling analysis showed an apical hydrophobic groove was shaped on the top of the EctoAMA1 model. Molecular docking indicated the interaction between the EctoAMA1 protein and the two peptides, which was mainly reflected by the hydrophobic interaction and formation of intermolecular hydrogen bond. The above results suggest that the peptides L and C, especially L peptide, competed with E. tenella rhotry neck protein 2 (EtRON2) for binding to EtAMA1 located on the surface of sporozoites, and therefore inhibited the parasite invasion into cells.

In ovo delivery of various biological supplements, vaccines and drugs in poultry: current knowledge

The technique of delivering various nutrients, supplements, immunostimulants, vaccines, and drugs via the in ovo route is gaining wide attention among researchers worldwide for boosting production performance, immunity and safeguarding the health of poultry. It involves direct administration of the nutrients and biologics into poultry eggs during the incubation period and before the chicks hatch out. In ovo delivery of nutrients has been found to be more effective than post-hatch administration in poultry production. The supplementation of feed additives, nutrients, hormones, probiotics, prebiotics, or their combination via in ovo techniques has shown diverse advantages for poultry products, such as improved growth performance and feed conversion efficiency, optimum development of the gastrointestinal tract, enhancing carcass yield, decreased embryo mortality, and enhanced immunity of poultry. In ovo delivery of vaccination has yielded a better response against various poultry pathogens than vaccination after hatch. So, this review has aimed to provide an insight on in ovo technology and its potential applications in poultry production to deliver different nutrients, supplements, beneficial microbes, vaccines, and drugs directly into the developing embryo to achieve an improvement in post-hatch growth, immunity, and health of poultry. © 2019 Society of Chemical Industry.

Molecular characterisation and the protective immunity evaluation of Eimeria maxima surface antigen gene

BACKGROUND

Coccidiosis is recognised as a major parasitic disease in chickens. Eimeria maxima is considered as a highly immunoprotective species within the Eimeria spp. family that infects chickens. In the present research, the surface antigen gene of E. maxima (EmSAG) was cloned, and the ability of EmSAG to stimulate protection against E. maxima was evaluated.

METHODS

Prokaryotic and eukaryotic plasmids expressing EmSAG were constructed. The EmSAG transcription and expression in vivo was performed based on the RT-PCR and immunoblot analysis. The expression of EmSAG in sporozoites and merozoites was detected through immunofluorescence analyses. The immune protection was assessed based on challenge experiments. Flow cytometry assays were used to determine the T cell subpopulations. The serum antibody and cytokine levels were evaluated by ELISA.

RESULTS

The open reading frame (ORF) of EmSAG gene contained 645 bp encoding 214 amino acid residues. The immunoblot and RT-PCR analyses indicated that the EmSAG gene were transcribed and expressed in vivo. The EmSAG proteins were expressed in sporozoite and merozoite stages of E. maxima by the immunofluorescence assay. Challenge experiments showed that both pVAX1-SAG and the recombinant EmSAG (rEmSAG) proteins were successful in alleviating jejunal lesions, decreasing loss of body weight and the oocyst ratio. Additionally, these experiments possessed anticoccidial indices (ACI) of more than 170. Higher percentages of CD4⁺ and CD8⁺ T cells were detected in both EmSAG-inoculated birds than those of the negative control groups (P < 0.05). The EmSAG-specific antibody concentrations of both the rEmSAG and pVAX1-EmSAG groups were much higher than those of the negative controls (P < 0.05). Higher concentrations of IL-4, IFN-γ, TGF-β1 and IL-17 were observed more in both the rEmSAG protein and pVAX1-SAG inoculated groups than those of negative controls (P < 0.05).

CONCLUSIONS

Our findings suggest that EmSAG is capable of eliciting a moderate immune protection and could be used as an effective vaccine candidate against E. maxima.

Recombinant lactococcus lactis expressing Eimeria tenella AMA1 protein and its immunological effects against homologous challenge

Avian coccidiosis leads to severe economic losses for the global poultry industry. Apical membrane antigen 1 (AMA1) of E. tenella (EtAMA1) plays a vital role during invasion of parasites into host cells. In the present study, recombinant live Lactococcus lactis expressing cytoplasmic, secreted and cell wall-anchored EtAMA1 protein were respectively constructed. The three live bacteria were respectively administered orally to SPF chickens (100 μl bacteria containing 5 × 10⁹ CFU per chicken) for three times at 10-day intervals. After immunization, the lymphocyte proliferative function, the percentage of CD4⁺ and CD8α⁺ T cells in peripheral blood, and the IgG titers in serum of chickens in each group were respectively measured. The protective effects of live bacteria expressing EtAMA1 protein against E. tenella challenge were evaluated based on body weight gain (BWG), lesion score in cecum, oocyst descrease ratio. The results showed that chickens immunized with three live bacteria, especially the bacteria expressing cell wall-anchored EtAMA1 protein, displayed higher IgG titers and CD4⁺ T cells proportions, thus provided more immune protective effects against homologous challenge compared with the PBS control group and vector control group (lactococci harboring pTX8048). The oocyst decrease ratio of 33.33% from chickens immunized with lactococci expressing cell wall-anchored EctoAMA1 was observed, which was higher than that of 27.67% and 25.37% from the other two bacteria-immunized groups, respectively. The above results suggested that cell wall-anchored EtAMA1 protein delivered by Lactococcus lactis could stimulate an effective immune responses against Eimeria infection.

Chicken immune response following in ovo delivery of bacterial flagellin

In ovo immunization of chicken embryos with live vaccines is an effective strategy to protect chickens against several viral pathogens. We investigated the immune response of chicken embryos to purified recombinant protein. In ovo delivery of Salmonella flagellin to 18-day old embryonated eggs resulted in elevated pro-inflammatory chIL-6 and chIL-8 (CXCL8-CXCLi2) cytokine transcript levels in the intestine but not in the spleen at 24 h post-injection. Analysis of the chicken Toll-like receptor (TLR) repertoire in 19-day old embryos revealed gene transcripts in intestinal and spleen tissue for most chicken TLRs, including TLR5 which recognizes Salmonella flagellin (FliC). The in ovo administration of FliC did not alter TLR transcript levels, except for an increase in intestinal chTLR15 expression. Measurement of the antibody response in sera collected at day 11 and day 21 post-hatch demonstrated high titers of FliC-specific antibodies for the animals immunized at the late-embryonic stage in contrast to the mock-treated controls. The successful in ovo immunization with purified bacterial antigen indicates that the immune system of the chicken embryo is sufficiently mature to yield a strong humoral immune response after single exposure to purified protein. This finding strengthens the basis for the development of in ovo protein-based subunit vaccines.

Identification and immunogenicity of microneme protein 2 (EbMIC2) of Eimeria brunetti

There have been only a few antigen genes of Eimeria brunetti reported up to now. In this study, the gene encoding the microneme protein 2 (EbMIC2) was isolated from oocysts of E. brunetti by RT-PCR and the immunogenicity of recombinant EbMIC2 was observed. The EbMIC2 was cloned into vector pMD19-T for sequencing. The sequence was compared with the published EbMIC2 gene from GenBank revealed homology of the nucleotide sequence and amino acids sequence were 99.43 and 98.63%, respectively. The correct recombinant pMD-EbMIC2 plasmid was inserted into the pET-28a (+) expressing vector and transformed into competent Escherichia coli BL21 cells for expression. The expressed product was analyzed using SDS-PAGE and Western-blot. The results indicated that the recombinant EbMIC2 protein was recognized strongly by serum from naturally infected chicken with E. brunetti. Rat rcEbMIC2 antisera bound to bands of about 36 kDa in the somatic extract of E. brunetti sporozoites. The recombinant plasmid pVAX1-EbMIC2 was constructed and then the efficacies of recombinant plasmid and recombinant protein were evaluated. The results of IgG antibody level and cytokines concentration suggested that recombinant EbMIC2 could increase the IgG antibody level and induce the expressions of cytokines. Animal challenge experiments demonstrated that the recombinant EbMIC2 protein and recombinant plasmid pVAX1-EbMIC2 could significantly increase the average body weight gains, decrease the mean lesion scores and the oocyst outputs of the immunized chickens and presented high anti-coccidial index. All results suggested that EbMIC2 could become an effective candidate for the development of new vaccine against E. brunetti infection.

Protective immunity against Eimeria tenella infection in chickens induced by immunization with a recombinant C-terminal derivative of EtIMP1

Immune mapped protein-1 (IMP1) is a new protective protein in apicomplexan parasites, and exits in Eimeria tenella. Cloning and sequence analysis has predicted the antigen to be a novel membrane protein of apicomplexan parasites. In order to assess the immunogenicity of EtIMP1, a C-terminal derivative of EtIMP1 was expressed in a bacterial host system and was used to immunize chickens. The protective efficacy against a homologous challenge was evaluated by body weight gains, lesion scores and fecal oocyst shedding. The results showed that the subunit vaccine can improve weight gains, reduced cecal pathology and lower oocyst fecal shedding compared with non immunized controls. The results suggested that the C-terminal derivative of EtIMP1 might be considered as a candidate in the development of subunit vaccines against Eimeria infection.

Effects of salinomycin and Bacillus subtilis on growth performance and immune responses in broiler chickens

The present study was undertaken to compare the effect of salinomycin and Bacillus subtilis on growth performance, serum antibody levels against Clostridium spp. and Eimeria spp., and cytokine mRNA expression levels in broiler chickens raised in the used litter. Broiler chickens fed a diet containing salinomycin showed lower (P < 0.05) body weights compared with the control diet-fed counterparts. Serum nitric oxide levels were significantly (P < 0.05) elevated in chickens fed the B. subtilis-enriched diet compared with those on either the salinomycin-fed or control diet-fed chickens. None of the dietary treatments affected (P > 0.05) serum antibody levels against Clostridium perfringens toxins. Both salinomycin and B.subtilis significantly lowered (P < 0.05) the serum levels of Eimeria-specific antibodies compared with the control group. Salinomycin, but not B. subtilis, significantly modulated (P < 0.05) the expression of cytokines encoding interferon-γ (IFN-γ), interleukin10 (IL-10) and tumor necrosis factor superfamily 15 (TNFSF15) compared with the control group. In conclusion, dietary salinomycin and B. subtilis affected serum anticoccidial antibody and intestinal cytokine expression, but failed to improve growth performance in broiler chickens. Further study is warranted to investigate the mode of action of salinomycin on host immune response and growth performance in broiler chickens.

Effect of Bacillus Subtilis-based Direct-fed Microbials on Immune Status in Broiler Chickens Raised on Fresh or Used Litter

Type of dietary direct-fed microbials (DFMs) or poultry litter could directly influence the composition of gut microbiota. Gut microbiota plays an important role in shaping the developing immune system and maintaining the homeostasis of the mature immune system in mammal and chickens. The present study was carried out to investigate the interaction among litter, DFMs and immunity in broiler chickens exposed to a field-simulated environment. Immune status of broiler chickens was assessed by serum antibodies against Eimeria spp. and Clostridium spp. and intestinal cytokine mRNA expression. The current experimental design had a 3 ×2 factorial arrangement of treatments with three types of litter, i.e., fresh litter or used litter that was obtained from a farm with no disease outbreak (used litter) or a farm with history of a gangrenous dermatitis outbreak (GD litter), and two dietary treatments with or without DFMs. It was found that either DFM addition or type of litter significantly affected anticoccidial antibody levels of broiler chickens at d 42. In general, dietary DFMs increased the anticoccidial antibodies in the fresh-litter raised chickens, but lowered the levels in the GD-litter raised chickens. Serum antibodies against Clostridium perfringens α-toxin were significantly (p<0.05) higher in chickens raised on GD litter compared with those raised on fresh litter. Cytokine mRNA expression was significantly (p<0.05) altered by either the type of litter or DFMs. Of interest, dietary DFMs lowered interferon-γ, interleukin 1beta, and CXCLi2 cytokine mRNA expression in chickens raised on fresh litter but increased them in GD-litter raised chickens. In conclusion, dietary DFMs modulate various immune parameters of broiler chickens, but the DFM-mediated effects were dependent upon the type of litter on which chickens were raised.

Co-expression of EtMic2 protein and chicken interleukin-18 for DNA vaccine against chicken coccidiosis

In the present study, a naked EtMIC2 DNA vaccine, a ChIL-18 expression vector and a EtMIC2 and ChIL-18 co-expression DNA vaccine were constructed and their protective efficacies against homologous challenge were compared and evaluated by examining the body weight gain, oocyst shedding, cecal lesion, ACI as well as specific anti-EtMic2 antibody level, the proliferation ability and percentages of CD4+ and CD8+ of splenocytes. The results showed the naked EtMIC2 DNA vaccine could increase the weight gain and decrease the oocyst shedding, but could not alleviate the cecal lesion of immunized chickens compared to unimmunized chickens. Chickens immunized with the co-expression vector pVAX1-MIC2-IL-18 exhibited much improved immune protection against challenge compared to chickens immunized with naked EtMIC2 DNA vaccine, or with naked EtMIC2 DNA vaccine and ChIL-18 expression vector applied separately. These results suggest that the co-expression of ChIL-18 with EtMic2 together could significantly improve the immune protection of the EtMic2 protein.

Analysis of humoral immune response and cytokines in chickens vaccinated with Eimeria brunetti apical membrane antigen-1 (EbAMA1) DNA vaccine

This study aimed to determine the changes of cytokines, specific serum IgG and several parameters in chickens vaccinated with DNA vaccine encoding Eimeria brunetti apical membrane antigen-1 (EbAMA1) antigen. Two-week-old chickens were divided into five groups (four groups for experiment) randomly. Experimental groups of chickens were immunized with DNA vaccine while control group of chickens were injected with pVAX1 plasmid alone or TE buffer solution. All immunizations were boosted 2 weeks later. The EbAMA1 specific IgG antibody responses were measured at weeks 1-6 post-second immunizations and several parameters were also identified. The result showed that the antibody titers in chickens vaccinated with DNA vaccines were significantly different from those of the control groups 1 week after the second immunization and reached the maximum values 3 weeks post-second immunization. IFN-γ concentration was increased the highest level against EbAMA1 of all chickens vaccinated with vaccines up to 56-fold, follow by the specific IgG antibody levels were increased 10-17-fold compared with those of TE solution and plasmid (pVAX1) control chickens 1-6 weeks post-second immunization. In case of the levels of IL-10 and IL-17 was increased in experimental chickens with 4-5-fold. Even though it was statistically significant, TGF-β and IL-4 levels were higher in vaccinated than unvaccinated chickens. The results suggested that DNA vaccines encoding E. brunetti apical membrane antigen-1 (EbAMA1) could increase serum specific IgG antibody and cytokines concentration and could give protection against E. brunetti infection.

Display of Eimeria tenella EtMic2 protein on the surface of Saccharomyces cerevisiae as a potential oral vaccine against chicken coccidiosis

S. cerevisiae is generally regarded as safe and benign organism and its surface display system may be used as a unique eukaryotic expression system that is suitable for expressing eukaryotic antigen. In addition to the convenience of vaccine delivery, the yeast cell wall has been shown to enhance the innate immunity when immunized with the yeast live oral vaccine. In the present study, we expressed the chicken coccidian E. tenella EtMic2, a microneme protein, on the surface of the S. cerevisiae and evaluated it as a potential oral vaccine for chicken against E. tenella challenge. The protective efficacy against a homologous challenge was evaluated by body weight gains, lesion scores and fecal oocyst shedding. The results showed that the live oral vaccine can improve weight gains, reduced cecal pathology and lower oocyst fecal shedding compared with non immunized controls. In addition, the yeast oral vaccine could stimulate humoral as well as cell mediate immune responses. These results suggested that EtMic2 displayed on the cell surface of S. cerevisiae could be used as potential live vaccine against chicken coccidiosis.

Poultry coccidiosis: recent advancements in control measures and vaccine development

Coccidiosis is recognized as the major parasitic disease of poultry and is caused by the apicomplexan protozoan Eimeria. Coccidiosis seriously impairs the growth and feed utilization of infected animals resulting in loss of productivity. Conventional disease control strategies rely heavily on chemoprophylaxis and, to a certain extent, live vaccines. Combined, these factors inflict tremendous economic losses to the world poultry industry in excess of USD 3 billion annually. Increasing regulations and bans on the use of anticoccidial drugs coupled with the associated costs in developing new drugs and live vaccines increases the need for the development of novel approaches and alternative control strategies for coccidiosis. This paper aims to review the current progress in understanding the host immune response to Eimeria and discuss current and potential strategies being developed for coccidiosis control in poultry.

Properties and prospects of adjuvants in influenza vaccination - messy precipitates or blessed opportunities?

Influenza is a major challenge to healthcare systems world-wide. While prophylactic vaccination is largely efficient, long-lasting immunity has not been achieved in immunized populations, at least in part due to the challenges arising from the antigen variation between strains of influenza A virus as a consequence of genetic drift and shift. From progress in our understanding of the immune system, the mode-of-action of vaccines can be divided into the stimulation of the adaptive system through inclusion of appropriate vaccine antigens and of the innate immune system by the addition of adjuvant to the vaccine formulation. A shared property of many vaccine adjuvants is found in their nature of water-insoluble precipitates, for instance the particulate material made from aluminum salts. Previously, it was thought that embedding of vaccine antigens in these materials provided a "depot" of antigens enabling a long exposure of the immune system to the antigen. However, more recent work points to a role of particulate adjuvants in stimulating cellular parts of the innate immune system. Here, we briefly outline the infectious medicine and immune biology of influenza virus infection and procedures to provide sufficient and stably available amounts of vaccine antigen. This is followed by presentation of the many roles of adjuvants, which involve humoral factors of innate immunity, notably complement. In a perspective of the ultrastructural properties of these humoral factors, it becomes possible to rationalize why these insoluble precipitates or emulsions are such a provocation of the immune system. We propose that the biophysics of particulate material may hold opportunities that could aid the development of more efficient influenza vaccines.

Recent progress in host immunity to avian coccidiosis: IL-17 family cytokines as sentinels of the intestinal mucosa

The molecular and cellular mechanisms leading to immune protection against coccidiosis are complex and include multiple aspects of innate and adaptive immunities. Innate immunity is mediated by various subpopulations of immune cells that recognize pathogen associated molecular patterns (PAMPs) through their pattern recognition receptors (PRRs) leading to the secretion of soluble factors with diverse functions. Adaptive immunity, which is important in conferring protection against subsequent reinfections, involves subtypes of T and B lymphocytes that mediate antigen-specific immune responses. Recently, global gene expression microarray analysis has been used in an attempt to dissect this complex network of immune cells and molecules during avian coccidiosis. These new studies emphasized the uniqueness of the innate immune response to Eimeria infection, and directly led to the discovery of previously uncharacterized host genes and proteins whose expression levels were modulated following parasite infection. Among these is the IL-17 family of cytokines. This review highlights recent progress in IL-17 research in the context of host immunity to avian coccidiosis.

An Eimeria vaccine candidate based on Eimeria tenella immune mapped protein 1 and the TLR-5 agonist Salmonella typhimurium FliC flagellin

Immune mapped protein-1 (IMP1) is a new protective protein in apicomplexan parasites, and exits in Eimeria tenella. But its structure and immunogenicity in E. tenella are still unknown. In this study, IMPI in E. tenella was predicted to be a membrane protein. To evaluate immunogenicity of IMPI in E. tenella, a chimeric subunit vaccine consisting of E. tenella IMP1 (EtIMP1) and a molecular adjuvant (a truncated flagellin, FliC) was constructed and over-expressed in Escherichia coli and its efficacy against E. tenella infection was evaluated. Three-week-old AA broiler chickens were vaccinated with the recombinant EtIMP1-truncated FliC without adjuvant or EtIMP1 with Freund's Complete Adjuvant. Immunization of chickens with the recombinant EtIMP1-truncated FliC fusion protein resulted in stronger cellular immune responses than immunization with only recombinant EtIMP1 with adjuvant. The clinical effect of the EtIMP1-truncated FliC without adjuvant was also greater than that of the EtIMP1 with adjuvant, which was evidenced by the differences between the two groups in body weight gain, oocyst output and caecal lesions of E. tenella-challenged chickens. The results suggested that the EtIMP1-flagellin fusion protein can be used as an effective immunogen in the development of subunit vaccines against Eimeria infection. This is the first demonstration of antigen-specific protective immunity against avian coccidiosis using a recombinant flagellin as an apicomplexan parasite vaccine adjuvant in chickens.

Construction of novel cytokine by fusion of chicken IL-2 signal peptide to mature chicken IL-15 and comparison of the adjuvant effects by DNA immunization against Eimeria challenge

A novel fusion cytokine was constructed by replacing signal peptide (SP) of chicken IL-15 (ChIL-15) with SP of chicken IL-2 (ChIL-2). The fusion cytokine (NChIL-15) was cloned into the expression vector pcDNA3.1(+) to generate pcDNA-NChIL-15. An animal experiment was carried out to evaluate the adjuvant effects of NChIL-15 on DNA vaccine pcDNA-3-1E against Eimeria acervulina challenge. The mRNA profiles of ChIL-2 and ChIFN-γ in spleen were characterized by means of real-time PCR. The recombinant positive eukaryotic expression plasmid pcDNA-NChIL-15 were constructed successfully. The protective effects provided by co-immunization with 100 μg pcDNA-3-1E and 50 μg pcDNA-NChIL-15, measured by relative body weight gain (BWG), average lesion score in duodenum and oocyst decrease ratio, showed no significant difference with 50 μg pcDNA-ChIL-15 as an adjuvant on day 6 post infection (PI). However, chickens co-immunized with pcDNA-3-1E and pcDNA-NChIL-15 exhibited significant upregulated level of ChIL-2 and ChIFN-γ transcripts in spleen. Our original data suggests the constructed novel cytokine NChIL-15 could be a potential adjuvant used to enhance the immune protective effects, although the optimized dosage need to be explored further.

Protective effects of oral immunization with live Lactococcus lactis expressing Eimeria tenella 3-1E protein

The codon-optimized Eimeria tenella 3-1E gene was introduced into the lactic acid bacterial vector pTX8048 to construct plasmid pTX8048-3-1E. The plasmid pTX8048-3-1E was transformed into Lactococcus lactis NZ9000 by electroporation to create the strain of L. lactis pTX8048-3-1E. The expression of objective protein was verified by Western blot. The live bacteria L. lactis pTX8048-3-1E were administered orally, and an animal challenge experiment was carried out to evaluate the protective efficacy. The results indicated the strain of L. lactis pTX8048-3-1E was constructed successfully. Oral immunization to specific pathogen-free (SPF) chickens with L. lactis pTX8048-3-1E provided partial protection against homologous challenge including significant increased oocyst decrease ratio, reduced average lesion score in cecum, and improved body weight gain compared to control bacteria L. lactis pTX8048. These results demonstrate the use of Lactococcus as live vector for delivery of Eimeria antigen is feasible and promising method to control coccidiosis in poultry.

Salmonella vaccines in poultry: past, present and future

Salmonella species are important zoonotic pathogens that cause gastrointestinal disease in humans and animals. Poultry products contaminated with these pathogens are one of the major sources of human Salmonella infections. Vaccination of chickens, along with other intervention measures, is an important strategy that is currently being used to reduce the levels of Salmonella in poultry flocks, which will ultimately lead to lower rates of human Salmonella infections. However, despite numerous studies that have been performed, there is still a need for safer, well-defined Salmonella vaccines. This review examines the different classes of Salmonella vaccines that have been tested, highlighting the merits and problems of each, and provides an insight into the future of Salmonella vaccines and the platforms that can be used for delivery.

Efficacy of a DNA vaccine carrying Eimeria maxima Gam56 antigen gene against coccidiosis in chickens

To control coccidiosis without using prophylactic medications, a DNA vaccine targeting the gametophyte antigen Gam56 from Eimeria maxima in chickens was constructed, and the immunogenicity and protective effects were evaluated. The ORF of Gam56 gene was cloned into an eukaryotic expression vector pcDNA3.1(zeo)+. Expression of Gam56 protein in COS-7 cells transfected with recombinant plasmid pcDNA-Gam56 was confirmed by indirect immunofluorescence assay. The DNA vaccine was injected intramuscularly to yellow feathered broilers of 1-week old at 3 dosages (25, 50, and 100 µg/chick). Injection was repeated once 1 week later. One week after the second injection, birds were challenged orally with 5×10(4) sporulated oocysts of E. maxima, then weighed and killed at day 8 post challenge. Blood samples were collected and examined for specific peripheral blood lymphocyte proliferation activity and serum antibody levels. Compared with control groups, the administration of pcDNA-Gam56 vaccine markedly increased the lymphocyte proliferation activity (P<0.05) at day 7 and 14 after the first immunization. The level of lymphocyte proliferation started to decrease on day 21 after the first immunization. A similar trend was seen in specific antibody levels. Among the 3 pcDNA-Gam56 immunized groups, the median dosage group displayed the highest lymphocyte proliferation and antibody levels (P<0.05). The median dosage group had the greatest relative body weight gain (89.7%), and the greatest oocyst shedding reduction (53.7%). These results indicate that median dosage of DNA vaccine had good immunogenicity and immune protection effects, and may be used in field applications for coccidiosis control.

Comparison of live Eimeria vaccination with in-feed salinomycin on growth and immune status in broiler chickens

Coccidiosis vaccines and anticoccidial drugs are commonly used to control Eimeria infection during commercial poultry production. The present study was conducted to compare the relative effectiveness of these two disease control strategies in broiler chickens in an experimental research facility. Birds were orally vaccinated with a live, attenuated vaccine (Inovocox), or were provided with in-feed salinomycin (Bio-Cox), and body weights, serum levels of nitric oxide (NO) and antibodies against Eimeria profilin and Clostridium perfringens PFO proteins, and intestinal levels of cytokine gene transcripts were measured. Vaccinated chickens had increased body weights, greater NO levels, and higher profilin and PFO antibody levels compared with salinomycin-fed birds. Transcripts for interleukin-6 (IL-6), tumor necrosis factor superfamily 15, and interferon-γ were increased, while mRNAs for IL-4 and IL-10 were decreased, in immunized chickens compared with salinomycin-treated chickens. In conclusion, vaccination against avian coccidiosis may be more effective compared with dietary salinomycin for increasing body weight and augmenting pro-inflammatory immune status during commercial poultry production.

Effects of in ovo vaccination and anticoccidials on the distribution of Eimeria spp. in poultry litter and serum antibody titers against coccidia in broiler chickens raised on the used litters

The present study reports the effects of various field anticoccidial programs on the distribution of Eimeria spp. in poultry litter and serum antibody titers against coccidia in broiler chickens raised on the used litters. The programs included in ovo vaccination and various medications with either chemicals, ionophores, or both. In general, serum samples from these chickens showed anticoccidial antibody titers when tested at days 7 and 14 post hatch with the peak response at day 43. Serum anticoccidial titers were highest in birds fed a non-medicated diet compared with those vaccinated or fed medicated diets. Total number of Eimeria oocysts and the composition of Eimeria spp. present in the litter samples from different treatment groups varied depending on the type of anticoccidial program. Oocyst counts in general ranged from 3.7×10(3) to 7.0×10(4) per g of litter. Importantly, both morphological and molecular typing studies revealed four major predominant Eimeria spp., E. acervulina, E. maxima, E. praecox, and E. tenella in the litter samples. Collectively, these results indicate that the field anticoccidial programs influenced the type and abundance of Eimeria spp. present in the litter samples and also modulated host immune response to Eimeria.

Induction of Cellular Immune Response by DNA Vaccine Coexpressing E. acervulina 3-1E Gene and Mature CHIl-15 Gene

We previously reported that the chimeric DNA vaccine pcDNA-3-1E-linker-mChIL-15, fused through linking Eimeria acervulina 3-1E encoding gene and mature chicken IL-15 (mChIL-15) gene with four flexible amino acid SPGS, could significantly offer protection against homologous challenge. In the present study, the induction of cellular immune response induced by the chimeric DNA vaccine pcDNA-3-1E-linker-mChIL-15 was investigated. Spleen lymphocyte subpopulations were characterized by flow cytometric analysis. The spleen lymphocyte proliferation assays were measured by 3-[4,5-dimethylthiazol-2-y1]-2,5-diphenyltetrazolium bromide (MTT) method. The mRNA profiles of ChIL-2 and ChIFN-γ in spleen were characterized by means of real-time PCR. Chickens immunized with pcDNA-3-1E-linker-mChIL-15 exhibited significant upregulated level of ChIL-2 and ChIFN-γ transcripts in spleen following two immunizations compared with chickens in other groups (P < 0.01). In comparison with pcDNA3.1-immunized and control groups, lymphocyte proliferation, percentage of CD8α(+) cell, and levels of ChIL-2 and ChIFN-γ transcripts in the group immunized with pcDNA-3-1E-linker-mChIL-15 were significantly increased on day 6 following challenge (P < 0.05, P < 0.01, and P < 0.01, resp.). Our data suggested that the fusion antigen 3-1E-linker-mChIL-15 could be a potential candidate for E. acervulina vaccine development.

Plant expressed coccidial antigens as potential vaccine candidates in protecting chicken against coccidiosis

Coccidiosis is a disease caused by intracellular parasites belonging to the genus Eimeria. In the present study, we transiently expressed two coccidial antigens EtMIC1 and EtMIC2 as poly histidine-tagged fusion proteins in tobacco. We have evaluated the protective efficacy of plant expressed EtMIC1 as monovalent and as well as bi-valent formulation where EtMIC1 and EtMIC2 were used in combination. The protective efficacy of these formulations was evaluated using homologous challenge in chickens. We observed better serum antibody response, weight gain and reduced oocyst shedding in birds immunized with EtMIC1 and EtMIC2 as bivalent formulation compared to monovalent formulation. However, IFN-γ response was not significant in birds immunized with EtMIC1 compared to the birds immunized with EtMIC2. Our results indicate the potential use of these antigens as vaccine candidates.

Plant expressed EtMIC2 is an effective immunogen in conferring protection against chicken coccidiosis

Coccidiosis is an economically important disease affecting poultry industry and remains one of the major problems globally. Developing a cost effective sub-unit vaccine may help mitigate loss in the industry. Here, we report expressing one of the microneme proteins, EtMIC2 from Eimeria tenella in tobacco using Agrobacterium-mediated transient expression. The ability of plant expressed recombinant EtMIC2 in eliciting both humoral and cell-mediated immune responses were measured in the immunized birds. The protective efficacy in the vaccinated birds against a homologous challenge was also evaluated. Birds immunized with plant expressed EtMIC2 showed good sero-conversion, reduced oocyst output and increased weight gain when compared to control birds. Our data indicate that use of plant expressed recombinant EtMIC2 in birds was safe and had the potential in imparting partial protection in chickens against homologous challenge.

Control of poultry coccidiosis: changing trends

Coccidiosis is the most important protozoan disease affecting the poultry industry worldwide. Control of poultry coccidiosis is presently based on managerial skills and the use of prophylactic coccidiostatic drugs. With the emergence of drug resistant Eimeria strains, emphasis has been laid on development and use of safer vaccines; some of them have been commercialized successfully. The present review deals with the various factors responsible for the development of clinical coccidiosis in poultry as well as an overview of the currently available inducers and boosters of immunity against coccidiosis. There are three groups of vaccines currently available against coccidiosis which can be distinguished on the basis of characteristics of the Eimeria species included in the respective products, viz. vaccines based on live virulent strains, vaccines based on live attenuated strains, and vaccines based on live strains that are relatively tolerant to the ionophore compounds. The latter vaccine combines the early chemotherapeutic effect of ionophores with the late prophylactic effect of vaccination. Although in the near future more varieties of oocyst based live vaccines are expected, identification of selective coccidian-specific immunoprotective molecules is likely to get more attention to facilitate the sustainable control of poultry coccidiosis.

Embryo vaccination of chickens using a novel adjuvant formulation stimulates protective immunity against Eimeria maxima infection

Our previous study demonstrated that chickens immunized subcutaneously with an Eimeria recombinant profilin protein vaccine emulsified in a Quil A/cholesterol/DDA/Carbopol (QCDC) adjuvant developed partial protection against experimental avian coccidiosis compared with animals immunized with profilin alone. Because in ovo vaccination is presently used in commercial applications worldwide throughout the poultry industry, the current study was undertaken to investigate chicken embryo vaccination with profilin plus QCDC adjuvant. Eighteen day-old embryos were immunized with isotonic saline (control), profilin alone, QCDC alone, or profilin plus QCDC, and orally challenged with live Eimeria maxima at 7 days post-hatch. Body weight gain, fecal oocyst output, and intestinal cytokine transcript levels were assessed as measures of protective immunity. While immunization with profilin alone or QCDC alone did not alter body weight gain of infected chickens compared with the saline control group, vaccination with profilin plus QCDC increased body weight gain such that it was equal to the uninfected controls. Immunization with profilin plus QCDC also reduced fecal oocyst shedding compared with unimmunized controls, although in this case QCDC failed to provide an adjuvant effect since no difference was observed between the profilin-only and profilin/QCDC groups. Finally, increased levels of transcripts encoding IL-1β, IL-15, and IFN-γ were seen in the intestinal tissues of animals given profilin plus QCDC compared with the profilin-only or QCDC-only groups. In summary, this study demonstrates an adjuvant effect of QCDC on body weight gain and intestinal cytokine responses following in ovo vaccination of chickens with an Eimeria profilin vaccine.

Eimeria maxima recombinant Gam82 gametocyte antigen vaccine protects against coccidiosis and augments humoral and cell-mediated immunity

Intestinal infection with Eimeria, the etiologic agent of avian coccidiosis, stimulates protective immunity to subsequent colonization by the homologous parasite, while cross-protection against heterologous species is poor. As a first step toward the development of a broad specificity Eimeria vaccine, this study was designed to assess a purified recombinant protein from Eimeria maxima gametocytes (Gam82) in stimulating immunity against experimental infection with live parasites. Following Gam82 intramuscular immunization and oral parasite challenge, body weight gain, fecal oocyst output, lesion scores, serum antibody response, and cytokine production were assessed to evaluate vaccination efficacy. Animals vaccinated with Gam82 and challenged with E. maxima showed lower oocyst shedding and reduced intestinal pathology compared with non-vaccinated and parasite-challenged animals. Gam82 vaccination also stimulated the production of antigen-specific serum antibodies and induced greater levels of IL-2 and IL-15 mRNAs compared with non-vaccinated controls. These results demonstrate that the Gam82 recombinant protein protects against E. maxima and augments humoral and cell-mediated immunity.

Characterization of monoclonal antibodies that recognize the Eimeria tenella microneme protein MIC2

The apicomplexan pathogens of Eimeria cause coccidiosis, an intestinal disease of chickens, which has a major economic impact on the poultry industry. Members of the Apicomplexa share an assortment of unique secretory organelles (rhoptries, micronemes and dense granules) that mediate invasion of host cells and formation and modification of the parasitophorous vacuole. Among these, microneme protein 2 from Eimeria tenella(EtMIC2) has a putative function in parasite adhesion to the host cell to initiate the invasion process. To investigate the role of EtMIC2 in host parasite interactions, the production and characterization of 12 monoclonal antibodies (mabs) produced against recombinant EtMIC2 proteins is described. All mabs reacted with molecules belonging to the apical complex of sporozoites and merozoites of E. tenella, E. acervulina and E. maxima in an immunofluorescence assay. By Western blot analysis, the mabs identified a developmentally regulated protein of 42 kDa corresponding to EtMIC 2 and cross-reacted with proteins in developmental stages of E. acervulina. Collectively, these mabs are useful tools for the detailed investigation of the characterization of EtMIC2 related proteins in Eimeria species.

Characterization of the antigen SO7 during development of Eimeria tenella

The developmental expression of the antigen SO7, which has been previously shown to protect chickens against infection by several Eimeria species, was investigated. Using RT-PCR, mRNA for SO7 was found to be restricted primarily to unsporulated oocysts (0 hr). Western blot (WB) analysis with an antibody to recombinant SO7 (rbSO7) revealed expression of the protein from 6 to 72 hr (fully sporulated) of sporulation and in sporozoites (SZ). SO7 was absent in host-derived second-stage merozoites (MZ) and was present in culture-derived first-stage MZ but at a level of only 25% of that exhibited by SZ. During invasion of Madin-Darby bovine kidney (MDBK) cells by SZ in vitro, the level of SO7 within cells, as determined by WB analysis, remained relatively constant until 48 hr of development and then decreased by about 40% at the next time point (72 hr). The SO7 secreted into the culture media during in vitro development increased to a relative maximum at 48 hr and then decreased to about 20% of maximum at 72 hr. Immunostaining with anti-rbSO7 indicates that SO7 is highly concentrated in both refractile bodies (RB) of SZ, with some limited distribution in the apical complex. Anti-rbSO7 intensively stained the intracellular parasites and the first-stage schizonts during in vitro development of E. tenella in MDBK cells. Upon release from the schizonts, the first-stage merozoites stained with 1 or 2 bright spots typically at each end. The results suggest that SO7 is closely associated with the SZ RB and is developmentally regulated but may not play a direct role in cellular invasion.

Serine protease activity in developmental stages of Eimeria tenella

A number of complex processes are involved in Eimeria spp. survival, including control of sporulation, intracellular invasion, evasion of host immune responses, successful reproduction, and nutrition. Proteases have been implicated in many of these processes, but the occurrence and functions of serine proteases have not been characterized. Bioinformatic analysis suggests that the Eimeria tenella genome contains several serine proteases that lack homology to trypsin. Using RT-PCR, a gene encoding a subtilisin-like and a rhomboid protease-like serine protease was shown to be developmentally regulated, both being poorly expressed in sporozoites (SZ) and merozoites (MZ). Casein substrate gel electrophoresis of oocyst extracts during sporulation demonstrated bands of proteolytic activity with relative molecular weights (Mr) of 18, 25, and 45 kDa that were eliminated by coincubation with serine protease inhibitors. A protease with Mr of 25 kDa was purified from extracts of unsporulated oocysts by a combination of affinity and anion exchange chromatography. Extracts of SZ contained only a single band of inhibitor-sensitive proteolytic activity at 25 kDa, while the pattern of proteases from extracts of MZ was similar to that of oocysts except for the occurrence of a 90 kDa protease, resistant to protease inhibitors. Excretory-secretory products (ESP) from MZ contained AEBSF (4-[2-Aminoethyl] benzenesulphonyl fluoride)-sensitive protease activity with a specific activity about 10 times greater than that observed in MZ extracts. No protease activity was observed in the ESP from SZ. Pretreatment of SZ with AEBSF significantly reduced SZ invasion and the release of the microneme protein, MIC2. The current results suggest that serine proteases are present in all the developmental stages examined.

In ovo administration of CpG oligodeoxynucleotides and the recombinant microneme protein MIC2 protects against Eimeria infections

We have previously demonstrated that short oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODNs) exert a positive effect on weight loss and oocyst shedding associated with Eimeria infection when injected in vivo. The present work investigated the effects of in ovo vaccination with CpG ODNs and an Eimeria recombinant microneme protein (MIC2), alone or in combination, on susceptibility to coccidiosis. In ovo injection of CpG ODNs alone enhanced resistance to experimental Eimeria acervulina infection as best exemplified by reduced oocyst shedding. Two CpG ODNs reduced the oocyst load, but did not affect weight gain. When co-administered with the recombinant microneme protein, both ODNs reduced oocyst shedding; however, only ODN D19 plus MIC2 consistently improved weight gain. Vaccinating with ODN 2006 or MIC2 protein curtailed oocyst shedding but did not enhance weight gain in Eimeria tenella-infected birds. Co-administration of CpG ODN and MIC2 did not have an additive effect in reducing the oocyst output; however, it resulted in the highest and lowest Ab response before and after Eimeria tenella infection, respectively. Collectively, CpG ODNs administered in ovo demonstrated immunoenhancing and adjuvant effects following Eimeria infections.