Efficacy of a DNA vaccine delivered in attenuated Salmonella typhimurium against Eimeria tenella infection in chickens

Oral immunization with attenuated Salmonella Typhimurium as a carrier of DNA vaccine against infectious hematopoietic necrosis virus (IHNV) in rainbow trout (Oncorhynchus mykiss)

Infectious hematopoietic necrosis virus (IHNV) is a serious pathogen in the salmonid aquaculture industry and leads to economic losses in the world. This study aimed to develop a new oral DNA vaccine designed to protect rainbow trout against infection by IHNV. Fish were administered via the oral route by the attenuated Salmonella enterica serovar Typhimurium as a carrier of pcDNA3.1-IHNG (glycoprotein (G)) plasmid for 7 days and finally, fish were challenged by 105 pfu ml-1 IHNV. The results revealed that the antigen gene was identified in different tissues of rainbow trout at 15-, 30-, and 45 days post-vaccination (dpv). Also, the recombinant vaccine elicited both an innate and specific immune response, resulting in a significant upregulation of the expression levels of ifn-1, mx-1, vig-1, igm, and igt. In addition, serum levels of neutralizing antibodies were observed to be elevated in the vaccinated fish, in contrast to the unvaccinated fish, following 30 dpv. Compared to trout that received empty S. Typhimurium, notable differences in cumulative percentage mortality were evident among the vaccinated fish. The relative percent survival (RPS) was recorded at 58.2 % for the group that received oral vaccine, while the group that received empty S. Typhimurium exhibited an RPS of 18.2 %. Therefore, our results showed that this bacterial vector can be a candidate carrier for pcDNA3.1-IHNG plasmid that may be employed to confer protection to rainbow trout against IHNV.

Effects of natural extract from medicinal herbs on broilers experimentally infected with Eimeria tenella

This study aimed to evaluate the effects of natural extracts from nine medicinal herbs (SMA) on the growth performance, immunity, and intestinal integrity of broilers experimentally infected with Eimeria tenella. A total of 252 one-day-old broiler chicks were divided into 7 groups with 3 replicates per group and 12 broilers per cage. The groups were uninfected-untreated blank control group (BC), infected-untreated negative control group (NC), SMA treatment groups, Chinese medicine positive control group (CM), and chemical drug positive control group (CD). The SMA groups were infected and fed a basal diet supplemented with 0.6 (SMA-L), 0.8 (SMA-M), and 1.0 (SMA-H) g/kg SMA. The CM and CD groups were infected and fed a basal diet supplemented with 15 g/kg Jiqiuchong San and 0.2 g/kg Diclazuril, respectively. Results showed that feeding SMA could significantly reduce the number of oocysts in infected chickens, especially 1.0 g/kg SMA, which exhibited moderate anticoccidial efficacy. When infected with E. tenella, the supplementation of 1.0 g/kg SMA increased the renal index; restored the hepatic, splenic, and bursal indexes to BC levels; increased the levels of immunoglobulin A (IgA), IgM, and IgY; and reduced the contents of tumor necrosis factor (TNF-α), interferon-γ (IFN-γ), interleukin-6 (IL-6), and IL-10 of the infected chickens. Moreover, treatment with 1.0 g/kg SMA alleviated the pathological changes in cecal tissue and increased the contents of zonula occludens-1 (ZO-1), occludin, claudin-1, and mucoprotein 2 (mucin-2) in cecal tissues of E. tenella-infected chickens. We found that 1.0 g/kg SMA reduced the number of oocysts, improved immunity, and alleviated intestinal barrier damage, which could improve the growth performance of infected chickens. Thus, SMA proved to be an effective natural extract against E. tenella and has the potential to be used as an efficient anticoccidial drug or additive.

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.

Poultry Vaccine Technology Platforms

The different technology platforms used to make poultry vaccines are reviewed. Vaccines based on classical technologies are either live attenuated or inactivated vaccines. Genetic engineering is applied to design by deletion, mutation, insertion, or chimerization, genetically modified target microorganisms that are used either as live or inactivated vaccines. Other vaccine platforms are based on one or a few genes of the target pathogen agent coding for proteins that can induce a protective immune response ("protective genes"). These genes can be expressed in vitro to produce subunit vaccines. Alternatively, vectors carrying these genes in their genome or nucleic acid-based vaccines will induce protection by in vivo expression of these genes in the vaccinated host. Properties of these different types of vaccines, including advantages and limitations, are reviewed, focusing mainly on vaccines targeting viral diseases and on technologies that succeeded in market authorization.

Construction of constitutive expression of Eimeria tenella eukaryotic initiation factor U6L5H2 on the surface of Lactobacillus plantarum and evaluation of its immunoprotective efficiency against chicken coccidiosis

Lactobacillus strains exhibit preferable properties that make them attractive candidates for vaccine delivery systems because of their ability to regulate intestinal mucosal immunity in the body. To date, live Lactobacillus delivery vaccines reported for the defense against Eimeria tenella have been inducer-dependent systems whose applications are significantly limited due to their unattainable induction conditions in vivo. Here, a constitutive expression of Lactobacillus plantarum NC8 surface display system was constructed. Then, this system was used to prepare a live oral vaccine to constitutively express the E. tenella U6L5H2 (EtU6) protein on the NC8 surface and to evaluate its protective efficacy against E. tenella challenge in chickens. The results showed that the heterologous protein (EGFP or EtU6) was successfully expressed on the surface of L. plantarum NC8 without any inducer. The immunoprotection of EtU6 with constitutive expression in L. plantarum NC8 system (NC8/Pc-EtU6) was significantly stronger than that of EtU6 with induced expression of L. plantarum NC8 system (NC8/Pi-EtU6) (ACI: 168.28 vs. 152.74) as evidenced by increased body weight, decreased oocyst output and lesion scores. Furthermore, the constitutive system NC8/Pc-EtU6 produced higher levels of specific cecal SIgA, serum IgG, transcription of cytokines IFN-γ and IL-2, and lymphocyte proliferation than the induced system NC8/Pi-EtU6. These results indicate that, compared to the inducible system, the constitutive surface display system of L. plantarum has the advantages of continuously expressing antigens in vivo and stimulating the host immune system. It could be an ideal platform for vaccine expression. The live vector vaccine for coccidiosis constructed by this constitutive system greatly improves the application potential in chicken production and provides a novel platform for the prevention of coccidiosis in chickens.

Oral immunization of Escherichia albertii strain DM104 induces protective immunity against Shigella dysenteriae type 4 in mouse model

The recent rise of antibiotic resistance and lack of an effective vaccine make the scenario of shigellosis alarming in developing countries like Bangladesh. In recent years, our group reported the vaccine efficacy of a non-pathogenic Escherichia albertii strain DM104 in different animal models, where an ocularly administered vaccine in the guinea pig eye model against Shigella dysenteriae type 4 challenge showed high protective efficacy and also induced a high titer of serum IgG against S. dysenteriae type 4 whole cell lysate (WCL) and LPS. In this study, we report further evaluation of the non-invasive and non-toxic environmental strain DM104 as a vaccine candidate against S. dysenteriae type 4 in mice model. Oral immunization of live DM104 bacterial strain demonstrated better protective immunity in mice model by showing 90% protection in mice against live S. dysenteriae type 4 lethal dose challenge and by inducing effective humoral and mucosal immune responses.

Spotlight on avian pathology: the importance of recombinant vector platform technologies in poultry vaccination

The use of novel vector vaccines (viral, bacterial and apicomplexan) can have a significant impact on the control of poultry disease. They offer a cost effective, convenient and effective means of mass vaccine delivery combined with the ability to switch on both antibody and cell-mediated immunity. In addition, recent viral vector constructs have enabled farmers to vaccinate against up to three important pathogens with a single in ovo administration. As the technology develops, it is likely that this means of vaccine administration will be utilized further and it will play a key role in the control of both existing and new emerging diseases of poultry in the future.

Recombinant invasive Lactobacillus plantarum expressing the Eimeria tenella fusion gene TA4 and AMA1 induces protection against coccidiosis in chickens

Coccidiosis is an intestinal parasitic disease that is caused by Eimeria tenella and other species, and it seriously restricts the economic development of the broiler breeding industry. In this study, a recombinant Lactobacillus plantarum with an invasive effect was constructed, and it expressed the TA4-AMA1 protein of E. tenella. After oral immunization with recombinant L. plantarum, specific humoral and mucosal immune levels were measured by indirect ELISA, and the differentiation of T cells was analysed by flow cytometry. After challenge with sporulated oocysts, the body weight, oocyst shedding and cecum lesions of the chicken were evaluated. The results indicated that chickens immunized with recombinant invasive L. plantarum produced higher levels of specific antibodies in the serum than did the non-immunized controls, and the secretory IgA (sIgA) levels were increased in the intestinal washes compared to those of the controls (P < 0.05). Flow cytometry showed that recombinant invasive L. plantarum significantly stimulated T cell differentiation compared to the PBS group (P < 0.01, P < 0.001), and a higher proportion of CD4⁺ and CD8⁺ T cells were detected in peripheral blood. Moreover, the lesion scores and histopathological caecum sections showed that immunizing chickens with recombinant invasive L. plantarum can significantly relieve pathological damage in the cecum (P < 0.01), and the relative body weight gain was 89.64 %, which was higher than the 79.83 % gain in the chickens immunized with non-invasive L. plantarum. After the challenge, faeces from ten chickens in each group were collected between 4 and 7 days, and the oocysts per gram (OPG) was determined by the McMaster technique. The data indicated that oocysts in the faeces of chickens immunized with the recombinant invasive L. plantarum were significantly lower than those of the controls (P < 0.01). The results suggest that recombinant invasive L. plantarum effectively activated immune responses against E. tenella infection and can be used as a candidate vaccine against E. tenella infection.

Prolonging and enhancing the protective efficacy of the EtMIC3-C-MAR against eimeria tenella through delivered by attenuated salmonella typhimurium

The microneme adhesive repeats (MAR) of Eimeria tenella microneme protein 3 (EtMIC3) are associated with binding to and invasion of host cells. Adhesion and invasion-related proteins or domains are often strongly immunogenic, immune responses mounted against these factors that play a key role in blocking invasion. In the present study, an oral live vaccine consisting of attenuated Salmonella typhimurium X4550 carrying two MAR domains fragment (St-X4550-MAR) was constructed and its protective efficacies were evaluated. The results showed that St-X4550-MAR was more immunogenic and conferred a higher degree of protection than recombinant MAR polypeptide as reflected by increased body weight, decreased oocyst shedding and lesion scores, increased serum IgG and cecal sIgA antibody production, and increasing levels of interferon-γ and interleukin-10. Thus, MAR domains are highly immunogenic and St-X4550-MAR had moderate activity against E. tenella infection by stimulating humoral, mucosal and cellular immunity. Chickens immunized with our constructed live vaccine provided considerable protections as early as at 10 d post-immunization (ACI: 155.17), and maintained higher protection levels at 20 d post-immunization (ACI: 173.66), and at 30 d post-immunization (ACI: 162.4). While the protective efficacy of chickens immunized with the recombinant MAR peptides showed a decreased trend as the post immunization time prolonging. Thus, using live-attenuated S. typhimurium X4550 as a vaccine expression and delivery system can significantly improve the protective efficacy and duration of protective immunity of MAR of EtMIC3.

Recent advances in delivery of veterinary DNA vaccines against avian pathogens

Veterinary vaccines need to have desired characteristics, such as being effective, inexpensive, easy to administer, suitable for mass vaccination and stable under field conditions. DNA vaccines have been proposed as potential solutions for poultry diseases since they are subunit vaccines with no risk of infection or reversion to virulence. DNA vaccines can be utilized for simultaneous immunizations against multiple pathogens and are relatively easy to design and inexpensive to manufacture and store. Administration of DNA vaccines has been shown to stimulate immune responses and provide protection from challenges in different animal models. Although DNA vaccines offer advantages, setbacks including the inability to induce strong immunity, and the fact that they are not currently applicable for mass vaccination impede the use of DNA vaccines in the poultry industry. The use of either biological or physical carriers has been proposed as a solution to overcome the current delivery limitations of DNA vaccines for veterinary applications. This review presents an overview of the recent development of carriers for delivery of veterinary DNA vaccines against avian pathogens.

Co-immunization with two recombinant Eimeria tenella lines expressing immunoprotective antigens of E. maxima elicits enhanced protection against E. maxima infection

Background

Live anticoccidial vaccines have been a tremendous success for disease prevention. The establishment of the reverse genetic manipulation platform has enabled the development of Eimeria parasites, the live anticoccidial vaccine strains, as vaccine vectors. In our previous study, recombinant E. tenella expressing a single immunodominant antigen of E. maxima (Et-EmIMP1) was able to protect chickens against challenge infection with E. maxima. This promising result encouraged us to further explore strategies to improve the protection efficacy of recombinant Eimeria and develop it as a vaccine vector.

Results

We constructed a novel recombinant Eimeria line expressing apical membrane antigen 1 of E. maxima (Et-EmAMA1) and then immunized chickens with Et-EmAMA1 and/or Et-EmIMP1. We found that the E. maxima soluble antigen-specific cell-mediated immunity was much stronger in the birds that were co-immunized with Et-EmAMA1 and Et-EmIMP1 than in those that were immunized with Et-EmAMA1 or Et-EmIMP1 alone. The oocyst production after E. maxima infection was significantly reduced in the recombinant Eimeria-immunized birds compared with the wild-type-immunized and naïve birds. The oocyst production in the birds co-immunized with Et-EmAMA1 and Et-EmIMP1 was consistently the lowest among the treatment groups after E. maxima infection.

Conclusions

These results demonstrated that Eimeria is an effective vaccine vector that can carry and deliver heterologous Eimeria antigens to the host immune system and trigger specific immune responses. Our results also suggested that increasing the number of recombinant Eimeria lines is an effective approach to enhance protective immunity against infections with heterologous pathogens.

An Eimeria acervulina OTU protease exhibits linkage-specific deubiquitinase activity

Ubiquitination is an important post-translational modification process that regulates many cellular processes. Proteins can be modified at single or multiple lysine residues by a single ubiquitin protein or by ubiquitin oligomers. It is important to note that the type of ubiquitin chains determines the functional outcome of the modification. Ubiquitin or ubiquitin chains can be removed by deubiquitinases (DUBs). In our previous study, the Eimeria tenella ovarian tumour (Et-OTU) DUB was shown to regulate the telomerase activity of E. tenella and affect E. tenella proliferation. The amino acid sequences of Et-OTU (GenBank: XP_013229759.1) and Eimeria acervulina (E. acervulina) ovarian tumour (Ea-OTUD3) DUB (XP_013250378.1) are 74% identical. Although Et-OTU may regulate E. tenella telomerase activity, whether Ea-OTUD3 affects E. acervulina growth and reproduction remains unclear. We show here that Ea-OTUD3 belongs to the OTU domain class of cysteine protease deubiquitinating enzymes. Ea-OTUD3 is highly linkage-specific, cleaving K48 (Lys48)-, K63-, and K6-linked diubiquitin but not K29-, K33-, and K11-linked diubiquitin. The precise linkage preference of Ea-OTUD3 among these three nonlinear diubiquitin chains is K6 > K48 > K63. Recombinant Ea-OTUD3, but not its catalytic-site mutant Ea-OTUD3 (C247A), exhibits activity against diubiquitin. Ea-OTUD3 removes ubiquitin from the K48-, but to a lesser extent from the K63-linked ubiquitinated E. acervulina proteins of the modified target protein, thereby exhibiting the characteristics of deubiquitinase. This study reveals that the Ea-OTUD3 is a novel functional deubiquitinating enzyme. Furthermore, the Ea-OTUD3 protein may regulate the stability of some K48-linked ubiquitinated E. acervulina proteins.

Protective immunity against Eimeria maxima induced by vaccines of Em14-3-3 antigen

Eimeria maxima 14-3-3 (Em14-3-3) open reading frame (ORF) which consisted of 861 bp encoding a protein of 286 amino acids was successfully amplified and sequenced. Subsequently, the Em14-3-3 ORF was subcloned into pET-32a (+) and pVAX1, respectively. RT-PCR and immunoblot analyses confirmed that the target gene was successfully transcribed and expressed in vivo. Immunofluorescence analysis showed that Em14-3-3 was expressed in both the sporozoites and merozoites. The animal experiments demonstrated that both rEm14-3-3 and pVAX1-14-3-3 could clearly alleviate jejunum lesions and body weight loss. The Em14-3-3 vaccines could increase oocyst decrease ratio, as well as produce an anticoccidial index of more than 165. The percentages of CD4⁺ in both the Em14-3-3 immunized groups were much higher, when compared with those of PBS, pET32a (+), and pVAX1 controls (P < 0.05). Similarly, the anti-Em14-3-3 antibody titers of both rEm14-3-3 and pVAX1-14-3-3 immunized groups showed higher levels compared with those of PBS, pET32a (+), and pVAX1 controls (P < 0.05). The IFN-γ and tumor growth factor-β (TGF-β) levels showed significant increments in the rEm14-3-3 and pVAX1-14-3-3 immunized groups, when compared with those in the negative controls (P < 0.05). These results demonstrated that Em14-3-3 could be used as a promising antigen candidate for developing vaccines against E. maxima.

An OTU deubiquitinating enzyme in Eimeria tenella interacts with Eimeria tenella virus RDRP

Background

Chicken coccidiosis, a disease caused by seven species of Eimeria (Apicomplexa: Coccidia), inflicts severe economic losses on the poultry industry. Eimeria tenella is the one of the most virulent species pathogenic to chickens. Many parasitic protozoans are parasitised by double-stranded (ds) RNA viruses, and the influence of protozoan viruses on parasitic protozoans has been extensively reported. E. tenella RNA virus 1 (Etv) was identified in E. tenella, and the complete genome sequence of Etv was analysed. Here, we screened Etv-RNA-dependent RNA polymerase (RDRP)-interacting host protein E. tenella ovarian tumour (OTU) protein-like cysteine protease (Et-OTU) using a yeast two-hybrid system with pGBKT7-RDRP plasmid serving as bait. A previous study demonstrated that Et-OTU could regulate the telomerase activity of E. tenella, indicating that Et-OTU affects E. tenella proliferation. However, whether Etv-RDRP affects the molecular biological characteristics of E. tenella by interacting with OTU remains unclear.

Results

We obtained seven positive clones from the initial screen, and six of the seven preys were identified as false-positives. Finally, we identified an RDRP-associated protein predicted to be an E. tenella OTU protein. A α-galactosidase assay showed that the bait vector did not activate the GAL4 reporter gene, indicating no autoactivation activity from the RDRP bait fusion. Pull-down and co-immunoprecipitation assays verified the interaction between Et-OTU and Etv-RDRP both intracellularly and extracellularly. Additionally, Et-OTU was able to deconjugate K48- and K6-linked di-ubiquitin (di-Ub) chains in vitro but not K63-, K11-, K29-, or K33-linked di-Ub chains. The C239A and H351A mutations eliminated the deubiquitinase (DUB) activity of Et-OTU, whereas the D236A mutation did not. Additionally, when combined with RDRP, the DUB activity of Et-OTU towards K48- and K6-linked chains was significantly enhanced.

Conclusion

Etv-RDRP interacts with Et-OTU both intracellularly and extracellularly. Etv-RDRP enhances the hydrolysis of Et-OTU to K6- or K48-linked ubiquitin chains. This study lays the foundation for further research on the relationship between E. tenella and Etv.

Immuno-Efficacy of a T. gondii Secreted Protein with an Altered Thrombospondin Repeat (TgSPATR) As a Novel DNA Vaccine Candidate against Acute Toxoplasmosis in BALB/c Mice

Toxoplasma gondii (T.gondii) is distributed worldwide and infects most species of warm-blooded animals, including humans. Toxoplasmosis has serious consequences, especially in people with an impaired or immature immune system. Thus, an effective vaccine is urgently required. Secretory microneme proteins are essential for the adhesion and invasion of T. gondii. The gene encoding the microneme protein, T. gondii secreted protein with an altered thrombospondin repeat (TgSPATR), we constructed a recombinant eukaryotic plasmid, pVAX1-TgSPATR, as a DNA vaccine, injected it intramuscularly into BALB/c mice and evaluated the induced immune response. Lymphocyte proliferation assays, cytokine (IFN-γ, IL-2, IL-4, IL-10), and antibody determinations showed that mice immunized with pVAX1-TgSPATR produced humoral and mixed Th1/Th2 type cellular immune responses. The survival times of mice immunized with pVAX1-TgSPATR were also significantly prolonged (15.7 ± 1.42 days) compared with control groups, which died within 7 days of challenge (p < 0.05). The current study indicated that pVAX1-TgSPATR induce a T. gondii specific immune response and might be a promising vaccine candidate against toxoplasmosis. To the best of our knowledge, this is the first report to evaluate the immunoprotective value of TgSPATR against T. gondii.

Identification of immune protective genes of Eimeria maxima through cDNA expression library screening

Background

Eimeria maxima is one of the most prevalent Eimeria species causing avian coccidiosis, and results in huge economic loss to the global poultry industry. Current control strategies, such as anti-coccidial medication and live vaccines have been limited because of their drawbacks. The third generation anticoccidial vaccines including the recombinant vaccines as well as DNA vaccines have been suggested as a promising alternative strategy. To date, only a few protective antigens of E. maxima have been reported. Hence, there is an urgent need to identify novel protective antigens of E. maxima for the development of neotype anticoccidial vaccines.

Methods

With the aim of identifying novel protective genes of E. maxima, a cDNA expression library of E. maxima sporozoites was constructed using Gateway technology. Subsequently, the cDNA expression library was divided into 15 sub-libraries for cDNA expression library immunization (cDELI) using parasite challenged model in chickens. Protective sub-libraries were selected for the next round of screening until individual protective clones were obtained, which were further sequenced and analyzed.

Results

Adopting the Gateway technology, a high-quality entry library was constructed, containing 9.2 × 10⁶ clones with an average inserted fragments length of 1.63 kb. The expression library capacity was 2.32 × 10⁷ colony-forming units (cfu) with an average inserted fragments length of 1.64 Kb. The expression library was screened using parasite challenged model in chickens. The screening yielded 6 immune protective genes including four novel protective genes of EmJS-1, EmRP, EmHP-1 and EmHP-2, and two known protective genes of EmSAG and EmCKRS. EmJS-1 is the selR domain-containing protein of E. maxima whose function is unknown. EmHP-1 and EmHP-2 are the hypothetical proteins of E. maxima. EmRP and EmSAG are rhomboid-like protein and surface antigen glycoproteins of E. maxima respectively, and involved in invasion of the parasite.

Conclusions

Our results provide a cDNA expression library for further screening of T cell stimulating or inhibiting antigens of E. maxima. Moreover, our results provide six candidate protective antigens for developing new vaccines against E. maxima.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2029-4) contains supplementary material, which is available to authorized users.

DNA Vaccination in Chickens

Robust and sustainable development of poultry industry requires prevention of deadly infectious diseases. Vigorous vaccination of the birds is a routine practice; however, the live and inactivated vaccines that are used have inherent disadvantages. New-generation vaccines such as DNA vaccines offer several advantages over conventional vaccines. DNA vaccines, which encode an antigen of interest or multiple antigens in the target host, are stable, easy to produce and administer, do not require cold chain maintenance, and are not affected by the maternal antibodies. In addition, DNA vaccines can also be administered in ovo, and thus, mass vaccination and early induction of immune response can effectively be achieved. In this chapter, we focus on the development of DNA vaccines against important infectious viral as well as parasitic diseases of poultry.

DNA vaccination of poultry: The current status in 2015

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Poultry DNA vaccination studies are regularly being published since 1993.

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These studies are mainly, but not only, concerned with vaccination against viruses.

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The different strategies of improving DNA vaccine efficacies are presented.

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The fate of the vaccine plasmid, immune properties and other applications are described.

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Despite the compiling preclinical reports, a poultry DNA vaccine is yet unavailable in the market.

DNA vaccination is a promising alternative strategy for developing new human and animal vaccines. The massive efforts made these past 25 years to increase the immunizing potential of this kind of vaccine are still ongoing. A relatively small number of studies concerning poultry have been published. Even though there is a need for new poultry vaccines, five parameters must nevertheless be taken into account for their development: the vaccine has to be very effective, safe, inexpensive, suitable for mass vaccination and able to induce immune responses in the presence of maternal antibodies (when appropriate). DNA vaccination should meet these requirements. This review describes studies in this field performed exclusively on birds (chickens, ducks and turkeys). No evaluations of avian DNA vaccine efficacy performed on mice as preliminary tests have been taken into consideration. The review first describes the state of the art for DNA vaccination in poultry: pathogens targeted, plasmids used and different routes of vaccine administration. Second, it presents strategies designed to improve DNA vaccine efficacy: influence of the route of administration, plasmid dose and age of birds on their first inoculation; increasing plasmid uptake by host cells; addition of immunomodulators; optimization of plasmid backbones and codon usage; association of vaccine antigens and finally, heterologous prime-boost regimens. The final part will indicate additional properties of DNA vaccines in poultry: fate of the plasmids upon inoculation, immunological considerations and the use of DNA vaccines for purposes other than preventing infectious diseases.

Chimeric DNA vaccines encoding Eimeria acervulina macrophage migration inhibitory factor (E.MIF) induce partial protection against experimental Eimeria infection

Chimeric DNA vaccines co-expressing Eimeria acervulina macrophage migration inhibitory factor (E.MIF) and chicken IL-2 (IL-2) or interferon-γ (IFN-γ) were constructed and their efficacies against E. acervulina were evaluated. The open reading frame (ORF) of E.MIF was cloned from E. acervulina merozoites and subcloned into the eukaryotic expression vector pVAX1 with chicken cytokine gene IFN-γ or IL-2 to construct the DNA vaccines pVAX-E.MIF-IFN-γ, pVAX-E.MIF-IL-2 and pVAX-E.MIF. The in vivo transfection of the target genes was detected by use of reverse transcription polymerase chain reaction (RT-PCR) and Western blot. Immunizations were carried out by vaccinating chickens twice with a dose rate of 100 μg intramuscularly. Seven days post second immunization, all chickens except the unchallenged control group were challenged orally with 1 × 105 sporulated oocysts of E. acervulina. Seven days later, the duodenum was collected. The results showed that the target genes were expressed effectively in vivo. DNA vaccines and the recombinant E.MIF protein could alleviate body weight loss and duodenal lesions significantly compared to the control groups. Furthermore, pVAX-E.MIF-IL-2 and pVAX-E.MIF-IFN-γ induced anticoccidial indexs (ACIs) of 179.12 and 170, respectively, which were significantly higher than that of pVAX-E.MIF (ACI = 162.31). Our results demonstrated that E.MIF is a potential vaccine candidate against E. acervulina and chicken IFN-γ or IL- 2 may be used as genetic adjuvants to improve the efficacies of DNA vaccines against avian coccidiosis.

Antiparasitic DNA vaccines in 21st century

Demands for effective vaccines to control parasitic diseases of humans and livestock have been recently exacerbated by the development of resistance of most pathogenic parasites to anti-parasitic drugs. Novel genomic and proteomic technologies have provided opportunities for the discovery and improvement of DNA vaccines which are relatively easy as well as cheap to fabricate and stable at room temperatures. However, their main limitation is rather poor immunogenicity, which makes it necessary to couple the antigens with adjuvant molecules. This paper review recent advances in the development of DNA vaccines to some pathogenic protozoa and helminths. Numerous studies were conducted over the past 14 years of 21st century, employing various administration techniques, adjuvants and new immunogenic antigens to increase efficacy of DNA vaccines. Unfortunately, the results have not been rewarding. Further research is necessary using more extensive combinations of antigens; alternate delivery systems and more efficient adjuvants based on knowledge of the immunomodulatory capacities of parasitic protozoa and helminths.

Efficacy of chimeric DNA vaccines encoding Eimeria tenella 5401 and chicken IFN-γ or IL-2 against coccidiosis in chickens

Chimeric DNA vaccines encoding Eimeria tenella (E. tenella) surface antigen 5401 were constructed and their efficacies against E. tenella challenge were studied. The open reading frame (ORF) of 5401 was cloned into the prokaryotic expression vector pGEX-4T2 to express the recombinant protein and the expressed recombinant protein was identified by Western blot. The ORF of 5401 and chicken cytokine gene IFN-γ or IL-2 were cloned into the eukaryotic expression vector pVAX1 consecutively to construct DNA vaccines pVAX-5401-IFN-γ, pVAX-5401-IL-2 and pVAX-5401. The expression of aim genes in vivo was detected by reverse transcription-polymerase chain reaction and Western blot. Fourteen-day-old chickens were inoculated twice at an interval of 7 days with 100 µg of plasmids pVAX-5401, pVAX-5401-IFN-γ and pVAX-5401-IL-2 or 200 µg of recombinant 5401 protein by leg intramuscular injection, respectively. Seven days after the second inoculation, all chickens except the unchallenged control group were challenged orally with 5 × 10(4) sporulated oocysts of E. tenella. Seven days after challenge, all chickens were weighted and slaughtered to determine the effects of immunization. The results showed the recombinant protein was about 90 kDa and reacted with antiserum against soluble sporozoites. The animal experiment showed that all the DNA vaccines pVAX-5401, pVAX-5401-IFN-γ or pVAX-5401-IL-2 and the recombinant 5401 protein could obviously alleviate body weight loss and cecal lesions as compared with non-vaccinated challenged control and empty vector pVAX1control. Furthermore, pVAX-5401-IFN-γ or pVAX-5401-IL-2 induced anti-coccidial index (ACI) of 180.01 or 177.24 which were significantly higher than that of pVAX-5401. The results suggested that 5401 was an effective candidate antigen for vaccine. This finding also suggested that chicken IFN-γ or IL-2 could effectively improve the efficacies of DNA vaccines against avian coccidiosis.

Induction of protective immunity against Eimeria tenella, Eimeria necatrix, Eimeria maxima and Eimeria acervulina infections using multivalent epitope DNA vaccines

Avian coccidiosis is mostly caused by mixed infection of several Eimeria species under natural conditions and immunity to avian coccidiosis is largely dependent on T-cell immune response. In this study, 14 T-cell epitope fragments from eight antigens of Eimeria tenella (E. tenella), Eimeria necatrix (E. necatrix), Eimeria maxima (E. maxima) and Eimeria acervulina (E. acervulina) were ligated with pVAX1 producing 14 monovalent DNA vaccines, respectively. Protective immunity of the monovalent DNA vaccines was assessed by in vivo challenge experiments and then four most protective fragments of each species were chosen to construct multivalent epitope DNA vaccines with or without chicken IL-2 as genetic adjuvant. Protective efficacies of the epitope DNA vaccines on chickens against E. tenella, E. necatrix, E. maxima and E. acervulina were evaluated. The results showed that the constructed multivalent epitope DNA vaccines significantly increased body weight gain, alleviated enteric lesions and reduced oocyst output of the infected birds. Especially, the multivalent epitope DNA vaccines of pVAX1-NA4-1-TA4-1-LDH-2-EMCDPK-1 and pVAX1-NA4-1-TA4-1-LDH-2-EMCDPK-1-IL-2 not only significantly increased body weight gain, alleviated enteric lesions and reduced oocyst output of the infected birds, but also resulted in anti-coccidial index (ACI) more than 170 against E. tenella, E. necatrix, E. maxima and E. acervulina, which indicated they could induce protective immunity against E. tenella, E. necatrix, E. maxima and E. acervulina. Our findings suggest the constructed multivalent epitope DNA vaccines are the potential candidate multivalent vaccines against mixed infection of Eimeria.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Eimeria tenella: 14-3-3 protein interacts with telomerase

Telomerase, consisting of telomerase RNA and telomerase reverse transcriptase (TERT), is responsible for the maintenance of the end of linear chromosomes. TERT, as the catalytic subunit of telomerase, plays a critical role in telomerase activity. Researches indicate TERT-associated proteins participate in the regulation of telomerase assembly, posttranslational modification, localization, and enzymatic function. Here, the telomerase RNA-binding domain of Eimeria tenella TERT (EtTRBD) was cloned into pGBKT7 and performed as the bait. α-Galactosidase assay showed that the bait plasmid did not activate Gal4 reporter gene. Further, we isolated an EtTRBD-associated protein, 14-3-3, by yeast two-hybrid screening using the constructed bait plasmid. To confirm the interaction, EtTRBD and 14-3-3 were expressed by prokaryotic and eukaryotic expression systems. Pull-down assays by purified proteins demonstrated a direct bind between EtTRBD and 14-3-3. Co-immunoprecipitation techniques successfully validated that 14-3-3 interacted with EtTRBD in 293T cells. The protein-protein interaction provides a starting point for more in-depth studies on telomerase and telomere regulation in E. tenella.

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.

Safety and immunogenicity of an oral DNA vaccine encoding Sip of Streptococcus agalactiae from Nile tilapia Oreochromis niloticus delivered by live attenuated Salmonella typhimurium

Attenuated Salmonella typhimurium SL7207 was used as a carrier for a reconstructed DNA vaccine against Streptococcus agalactiae. A 1.02 kb DNA fragment, encoding for a portion of the surface immunogenic protein (Sip) of S. agalactiae was inserted into pVAX1. The recombinant plasmid pVAX1-sip was transfected in EPC cells to detect the transient expression by an indirect immunofluorescence assay, together with Western blot analysis. The pVAX1-sip was transformed by electroporation into SL7207. The stability of pVAX1-sip into Salmonella was over 90% after 50 generations with antibiotic selection in vitro while remained stable over 80% during 35 generations under antibiotic-free conditions. The LD50 of SL/pVAX1-sip was 1.7 × 10(11) CFU/fish by intragastric administration which indicated a quite low virulence. Tilapias were inoculated orally at 10(8) CFU/fish, the recombinant bacteria were found present in intestinal tract, spleens and livers and eventually eliminated from the tissues 4 weeks after immunization. Fish immunized at 10(7), 10(8) and 10(9) CFU/fish with different immunization times caused various levels of serum antibody and an effective protection against lethal challenge with the wild-type strain S. agalactiae. Integration studies showed that the pVAX1-sip did not integrate with tilapia chromosomes. The DNA vaccine SL/pVAX1-sip was proved to be safe and effective in protecting tilapias against S. agalactiae 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.

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.

Evaluation of novel adjuvant Eimeria profilin complex on intestinal host immune responses against live E. acervulina challenge infection

The effects against avian coccidiosis of two novel adjuvants, Quil A/cholesterol/dimethyl dioctadecyl ammonium bromide/Carbopol (QCDC) and QCDC/Bay R1005 (R)/cytosine-phosphate-guanosine (CpG) oligodeoxynucleotides (CpG ODN [T]) (QCDCRT) emulsified with profilin, a conserved Eimeria recombinant protein, were determined in broiler chickens. Chickens were subcutaneously immunized with isotonic saline (control group), profilin (P), profilin emulsified with QCDC (P-Q), or profilin with QCDCRT (P-QR) at 2 and 9 days post-hatch and orally challenged with 1.0 x 10(4) sporulated oocysts of Eimeria acervulina (EA) at 7 days postimmunization. All profilin-immunized groups showed increased body weight gain when compared to the control group, and the P-QR group had significantly higher body weight gain than did those of the P and P-Q groups following EA challenge infection. All groups immunized with profilin showed significantly decreased intestinal lesions compared with the control group, with the P-QR group showing the lowest intestinal lesions among the profilin-treated groups. Finally, the P-QR group showed greater CD4+/CD8+ and TCR1+/TCR2+ splenocytes and higher antiprofilin serum antibody titers compared with the P and P-Q (or both) groups following EA challenge infection. These results further suggest that vaccination of chickens with profilin, in combination with the QCDCRT adjuvant, may provide a novel control strategy against EA infection in commercial flocks.

Attenuated Salmonella typhimurium SV4089 as a potential carrier of oral DNA vaccine in chickens

Attenuated Salmonella has been used as a carrier for DNA vaccine. However, in vitro and in vivo studies on the bacteria following transfection of plasmid DNA were poorly studied. In this paper, eukaryotic expression plasmids encoding avian influenza virus (AIV) subtype H5N1 genes, pcDNA3.1/HA, NA, and NP, were transfected into an attenuated Salmonella enteric typhimurium SV4089. In vitro stability of the transfected plasmids into Salmonella were over 90% after 100 generations. The attenuated Salmonella were able to invade MCF-7 (1.2%) and MCF-10A (0.5%) human breast cancer cells. Newly hatched specific-pathogen-free (SPF) chicks were inoculated once by oral gavage with 10(9) colony-forming unit (CFU) of the attenuated Salmonella. No abnormal clinical signs or deaths were recorded after inoculation. Viable bacteria were detected 3 days after inoculation by plating from spleen, liver, and cecum. Fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR) were carried out for confirmation. Salmonella was not detected in blood cultures although serum antibody immune responses to Salmonella O antiserum group D1 factor 1, 9, and 12 antigens were observed in all the inoculated chickens after 7 days up to 35 days. Our results showed that live attenuated S. typhimurium SV4089 harboring pcDNA3.1/HA, NA, and NP may provide a unique alternative as a carrier for DNA oral vaccine in chickens.

Effects of novel vaccine/adjuvant complexes on the protective immunity against Eimeria acervulina and transcriptome profiles

SUMMARY. This study investigated the ability of two novel adjuvant formulations, QCDC (Quil A/cholesterol/DDA/ Carbopol) and QCDCR (QCDC/Bay R1005), in combination with a recombinant profilin vaccine, to modulate host protective immunity and to alter gene expression during experimental avian coccidiosis. Vaccination with profilin plus QCDCR significantly reduced the severity of intestinal lesions and increased mitogen-induced lymphocyte proliferation in infected chickens compared with immunization with profilin alone or profilin plus QCDC. Immunization with profilin plus QCDC or profilin plus QCDCR increased body weight gain but had no effect on fecal oocyst shedding of chickens infected with Eimeria acervulina compared with birds vaccinated with profilin alone. The results of global gene expression analysis revealed that, compared with PBS controls, (a) chickens vaccinated with profilin alone had 71 up-regulated and 56 down-regulated mRNA transcripts, (b) chickens immunized with profilin plus QCDC had 198 up-regulated and 247 down-regulated mRNAs, and (c) birds immunized with profilin plus QCDCR had 210 up-regulated and 267 down-regulated mRNAs. Compared with birds vaccinated with profilin alone, (a) chickens given profilin plus QCDC had 60 up-regulated and 104 down-regulated transcripts and (b) chickens immunized with profilin plus QCDCR had 103 up-regulated and 130 down-regulated mRNAs. Finally, chickens vaccinated with profilin plus QCDCR had 193 up-regulated and 204 down-regulated transcripts compared with birds given profilin plus QCDC. Biological function and network analysis revealed that the majority of altered transcripts were encoded by immune-related genes.

Improved immune responses against avian influenza virus following oral vaccination of chickens with HA DNA vaccine using attenuated Salmonella typhimurium as carrier

This study evaluates the immune responses of single avian influenza virus (AIV) HA DNA vaccine immunization using attenuated Salmonella enterica sv. Typhimurium as an oral vaccine carrier and intramuscular (IM) DNA injection. One-day-old specific-pathogen-free (SPF) chicks immunized once by oral gavage with 10(9) Salmonella colony-forming units containing plasmid expression vector encoding the HA gene of A/Ck/Malaysia/5858/04 (H5N1) (pcDNA3.1.H5) did not show any clinical manifestations. Serum hemagglutination inhibition (HI) titer samples collected from the IM immunized chickens were low compared to those immunized with S. typhimurium.pcDNA3.1.H5. The highest average antibody titers were detected on day 35 post immunization for both IM and S. typhimurium.pcDNA3.1.H5 immunized groups, at 4.0±2.8 and 51.2±7.5, respectively. S. typhimurium.pcDNA3.1.H5 also elicited both CD4(+) and CD8(+) T cells from peripheral blood mononuclear cells (PBMCs) of immunized chickens as early as day 14 after immunization, at 20.5±2.0 and 22.9±1.9%, respectively. Meanwhile, the CD4(+) and CD8(+) T cells in chickens vaccinated intramuscularly were low at 5.9±0.9 and 8.5±1.3%, respectively. Immunization of chickens with S. typhimurium.pcDNA3.1.H5 enhanced IL-1β, IL-12β, IL-15 and IL-18 expressions in spleen although no significant differences were recorded in chickens vaccinated via IM and orally with S. typhimurium and S. typhimurium.pcDNA3.1. Hence, single oral administrations of the attenuated S. typhimurium containing pcDNA3.1.H5 showed antibody, T cell and Th1-like cytokine responses against AIV in chickens. Whether the T cell response induced by vaccination is virus-specific and whether vaccination protects against AIV infection requires further study.

Eimeria tenella heat shock protein 70 enhances protection of recombinant microneme protein MIC2 subunit antigen vaccination against E. tenella challenge

Heat shock proteins have been reported to stimulate the immune system via innate receptors. Our study found that the novel immunopotentiator, Eimeria tenella (E. tenella) heat shock protein 70 (HSP70), enhanced protective immunity elicited by E. tenella antigen microneme protein 2 (EtMIC2) against avian coccidiosis. It demonstrated that the expression of TLR2 and TLR4 were strongly upregulated in EtHSP70 and EtMIC2 plus EtHSP70 stimulated chicken embryo fibroblasts (CEF) compared with untreated controls and EtMIC2 alone. In addition, the same treatment induced high levels of interleukin (IL)-12 and interferon (IFN)-γ that are critical cytokines of innate immunity. In vivo experiments involved using broiler chickens subcutaneously immunized with EtMIC2 alone or EtMIC2 plus EtHSP70 at 7 and 14 days post-hatch, which were then orally challenged with live E. tenella at 7 days following secondary immunization. Body weight gains, cecal lesion scores, fecal oocyst shedding, serum antibody responses against MIC2, and intestinal cytokine transcript levels were assessed as measures of protective immunity. Chickens immunized with EtMIC2 plus EtHSP70 showed increased body weight gains, decreased oocyst shedding, increased serum antibody responses, and high levels of IL-12, IFN-γ, and IL-17 compared with the EtMIC2 only or control groups. Moreover, chickens immunized with EtHSP70 alone showed significantly protective effect against E. tenella infection. In summary, this study provides the first evidence of the immunoenhancing activities of EtHSP70 in poultry.

Anticoccidial effect of halofuginone hydrobromide against Eimeria tenella with associated histology

Halofuginone (stenorol) has been used as an effective anticoccidial reagent for decades but very little is known about its mode of action. In this study, chickens were inoculated with Eimeria tenella oocysts on 14-day-old and medicated with halofuginone at days 0, 1, 2, 3, 4, 5 and 6 post inoculations (groups 0, 1, 2, 3, 4, 5 and 6, respectively). Chickens in group 7 were taken as challenge-unmedicated control and in group 8 unchallenged-unmedicated control. The survival rate, body weight gains (BWG), oocysts production, cecal scores, bloody diarrhea and histological examinations were analyzed to evaluate the anticoccidial efficacy of halofuginone and to initially elucidate its mechanisms. Results showed that halofuginone which acted as a coccidiostatic can significantly enhance the BWG, and decrease both the oocyst shedding and cecal destruction caused by E. tenella infection. The histological slide examination noted that halofuginone was effective when provided 0-2 days post inoculation but only partially effective when applied 3-7 days post infection. The second-generation schizonts treated with halofuginone appeared vacuolated and degenerated. It is concluded that halofuginone can inhibit the parasite's invasion of host cecal hypothetical cell at the early stages of life cycle and later disturb the parasite's development by vacuolation of the schizonts. The resulting abnormal schizonts could not divide into schizoites and were eventually eliminated by the host's immune response.

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.

The effects of a novel adjuvant complex/Eimeria profilin vaccine on the intestinal host immune response against live E. acervulina challenge infection

The effects of a novel adjuvant composed of Quil A, cholesterol, dimethyl dioctadecyl ammonium bromide, and Carbopol (QCDC) on protective immunity against avian coccidiosis following immunization with an Eimeria recombinant protein were determined. Broiler chickens were subcutaneously immunized with isotonic saline (control), Eimeria recombinant profilin alone, or profilin emulsified with QCDC at 1 and 7 days post-hatch, and orally challenged with live Eimeria acervulina at 7 days following the last immunization. Body weight gains, gut lesion scores, fecal oocyst outputs, profilin serum antibody titers, lymphocyte proliferation, and intestinal cytokine transcript levels were assessed as measures of protective immunity. Chickens immunized with profilin plus QCDC showed increased body weight gains and decreased intestinal lesion scores compared with the profilin only or control groups. However, no differences were found in fecal oocyst shedding among the three groups. Profilin serum antibody titers and antigen-induced peripheral blood lymphocyte proliferation in the profilin/QCDC group were higher compared with the profilin only and control groups. Finally, while immunization with profilin alone or profilin plus QCDC uniformly increased the levels of intestinal transcripts encoding all cytokines examined (IL-1β, IL-10, IL-12, IL-15, IL-17F, and IFN-γ) compared with the control group, transcripts for IL-10 and IL-17F were further increased in the profilin/QCDC group compared with the profilin only group. In summary, this study provides the first evidence of the immunoenhancing activities of QCDC adjuvant in poultry.

Changes of cytokines and IgG antibody in chickens vaccinated with DNA vaccines encoding Eimeria acervulina lactate dehydrogenase

The aim of this study was to investigate the changes of cytokines and specific serum IgG in chickens following vaccination with DNA vaccines encoding either Eimeria acervulina (E. acervulina) lactate dehydrogenase (LDH) antigen or LDH and chicken IL-2 or IFN-γ. Two-week-old chickens were randomly divided into five groups. Experimental group of chickens were immunized with DNA vaccines while control group of chickens were injected with pVAX1 plasmid alone or sterile water. All immunizations were boosted 2 weeks later. The LDH-specific IgG antibody response was measured at weeks 1-6 post-second immunization. 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 (P<0.05) and reached the maximum values 3 weeks post-second immunization. The systemic and local cytokine mRNA expression was determined by quantitative RT-PCR 7 days post-second immunization. The specific IgG antibody levels against LDH of all chickens vaccinated with vaccines were increased compared to those of sterile water (H(2)O) and plasmid (pVAX1) control chickens 1-6 weeks post-second immunization (P<0.05). The mRNA levels of IFN-γ, IL-2, TNFSF15, IL-17D as well as TGF-β4 in both spleen and cecal tonsil were also increased in experimental chickens. In contrast, the only significant change of IL-4 mRNA level was observed in spleen of chickens immunized with pVAX-LDH-IL-2 compared with pVAX-LDH and control groups (P<0.05). These results suggested that DNA vaccines could increase the IgG antibody level and induce the expressions of cytokines.

Efficacy of DNA vaccines carrying Eimeria acervulina lactate dehydrogenase antigen gene against coccidiosis

The efficacies of DNA vaccines encoding either Eimeria acervulina lactate dehydrogenase (LDH) antigen or a combination of LDH antigen and chicken IL-2 or IFN-gamma were evaluated against chicken coccidiosis. Three vaccine plasmids pVAX-LDH, pVAX-LDH-IFN-gamma and pVAX-LDH-IL-2 were constructed using the eukaryotic expression vector pVAX1. Expressions of proteins encoded by plasmids DNA in vivo were detected by reverse transcription-polymerase chain reaction (RT-PCR) and western blot assay. Average body weight gain, oocyst output, survival rate and lesion scores were measured to evaluate the protective effects of vaccination on challenge infection. The results showed that DNA vaccines could obviously alleviate body weight loss, duodenal lesions, oocyst output and enhance oocyst decrease ratio. Anti-coccidial indexes (ACIs) of pVAX-LDH-IFN-gamma and pVAX-LDH-IL-2 groups were higher than that of other groups. Flow cytometric analysis of T lymphocytes in spleen and cecal tonsil demonstrated that DNA vaccines had significantly increased percentages of CD3(+) T cells compared with pVAX1 alone or TE buffer. The results provided the first proof that DNA vaccine carrying E. acervulina LDH antigen gene induced protective immunity against homologous infection and its effect could be enhanced by co-expression of chicken IL-2 or IFN-gamma.

Mucosal vaccination with a codon-optimized hemagglutinin gene expressed by attenuated Salmonella elicits a protective immune response in chickens against highly pathogenic avian influenza

The purpose of this study was to evaluate clinical protection from challenge conferred by two attenuated Salmonella enteria serovar typhimurium vaccine strains expressing the hemagglutinin (HA1) gene from a highly pathogenic avian influenza (HPAI) H5N1 (A/whooper swan/Mongolia/3/2005), under control of the anaerobically inducible nir15 promoter. Two-week-old White Leghorn chickens were immunized by oral gavage with one milliliter doses of >109 Salmonella colony-forming units once weekly for 4 weeks prior to challenge. Expression of recombinant protein was confirmed via Western blot. Serum and mucosal gavage samples were collected prior to, and following immunization and antibodies against avian influenza HA were confirmed by Western blot and hemagglutination-inhibition (HI) assay. Chickens were challenged with homologous (A/whooper swan/Mongolia/3/2005), or heterologous (A/Chicken/Queretaro/14588-19/95) HPAI virus strains. Chickens immunized with attenuated Salmonella strains containing plasmid expression vector (pTETnir15HA) demonstrated a statistically significant increase in survival compared to control groups. Results provide evidence of effectiveness of attenuated Salmonella strains for delivery of recombinant avian influenza HA antigens and induction of mucosal and systemic immune responses protective against lethal challenge with HPAI.

Vaccination of mice with salmonella expressing VapA: mucosal and systemic Th1 responses provide protection against Rhodococcus equi infection

Conventional vaccines to prevent the pneumonia caused by Rhodococcus equi have not been successful. We have recently demonstrated that immunization with Salmonella enterica Typhimurium expressing the VapA antigen protects mice against R. equi infection. We now report that oral vaccination of mice with this recombinant strain results in high and persistent fecal levels of antigen-specific IgA, and specific proliferation of the spleen cells of immunized mice in response to the in vitro stimulation with R. equi antigen. After in vitro stimulation, spleen cells of immunized mice produce high levels of Th1 cytokines and show a prominent mRNA expression of the Th1 transcription factor T-bet, in detriment of the Th2 transcription factor GATA-3. Following R. equi challenge, a high H₂O₂, NO, IL-12, and IFN-γ content is detected in the organs of immunized mice. On the other hand, TNF-α and IL-4 levels are markedly lower in the organs of vaccinated mice, compared with the non-vaccinated ones. The IL-10 content and the mRNA transcription level of TGF-β are also higher in the organs of immunized mice. A greater incidence of CD4⁺ and CD8⁺ T cells and B lymphocytes is verified in vaccinated mice. However, there is no difference between vaccinated and non-vaccinated mice in terms of the frequency of CD4⁺CD25⁺Foxp3⁺ T cells. Finally, we show that the vaccination confers a long-term protection against R. equi infection. Altogether, these data indicate that the oral vaccination of mice with S. enterica Typhimurium expressing VapA induces specific and long-lasting humoral and cellular responses against the pathogen, which are appropriately regulated and allow tissue integrity after challenge.