Efficacy of Eimeria tenella rhomboid-like protein as a subunit vaccine in protective immunity against homologous challenge

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.

Degrade to survive: the intricate world of piroplasmid proteases

Piroplasmids of the genera Babesia, Theileria, and Cytauxzoon are tick-transmitted parasites with a high impact on animals and humans. They have complex life cycles in their definitive arthropod and intermediate vertebrate hosts involving numerous processes, including invasion of, and egress from, host cells, parasite growth, transformation, and migration. Like other parasitic protozoa, piroplasmids are equipped with different types of protease to fulfill many of such essential processes. Blockade of some key proteases, using inhibitors or antibodies, hinders piroplasmid growth, highlighting their potential usefulness in drug therapies and vaccine development. A better understanding of the functional significance of these enzymes will contribute to the development of improved control measures for the devastating animal and human diseases caused by these pathogens.

Comparative Degradome Analysis of the Bovine Piroplasmid Pathogens Babesia bovis and Theileria annulata

Babesia bovis and Theileria annulata are tick-borne hemoprotozoans that impact bovine health and are responsible for considerable fatalities in tropical and subtropical regions around the world. Both pathogens infect the same vertebrate host, are closely related, and contain similar-sized genomes; however, they differ in invertebrate host specificity, absence vs. presence of a schizont stage, erythrocyte invasion mechanism, and transovarial vs. transstadial transmission. Phylogenetic analysis and bidirectional best hit (BBH) identified a similar number of aspartic, metallo, and threonine proteinases and nonproteinase homologs. In contrast, a considerably increased number of S54 serine rhomboid proteinases and S9 nonproteinase homologs were identified in B. bovis, whereas C1A cysteine proteinases and A1 aspartic nonproteinase homologs were found to be expanded in T. annulata. Furthermore, a single proteinase of families S8 (subtilisin-like protein) and C12 (ubiquitin carboxyl-terminal hydrolase), as well as four nonproteinase homologs, one with dual domains M23-M23 and three with S9-S9, were exclusively present in B. bovis. Finally, a pronounced difference in species-specific ancillary domains was observed between both species. We hypothesize that the observed degradome differences represent functional correlates of the dissimilar life history features of B. bovis and T. annulata. The presented improved classification of piroplasmid proteinases will facilitate an informed choice for future in-depth functional studies.

Protective efficacy induced by Eimeria maxima rhomboid-like protein 1 against homologous infection

Introduction

Avian coccidiosis, caused by apicomplexan protozoa belonging to the Eimeria genus, is considered one of the most important diseases in the intensive poultry industry worldwide. Due to the shortcomings of live anticoccidial vaccines and drugs, the development of novel anticoccidial vaccines is increasingly urgent.

Methods

Eimeria maxima rhomboid-like protein 1 (EmROM1), an invasion-related molecule, was selected as a candidate antigen to evaluate its protective efficacy against E. maxima in chickens. Firstly, the prokaryotic recombinant plasmid pET-32a-EmROM1 was constructed to prepare EmROM1 recombinant protein (rEmROM1), which was used as a subunit vaccine. The eukaryotic recombinant plasmid pVAX1.0-EmROM1 (pEmROM1) was constructed as a DNA vaccine. Subsequently, 2-week-old chicks were separately vaccinated with the rEmROM1 and pEmROM1 twice every 7 days. One week post the booster vaccination, induced cellular immune responses were determined by evaluating the mRNA level of cytokines including IL-2, IFN-γ, IL-4, IL-10, TGF-β, IL-17, and TNFSF15, as well as the percentages of CD4⁺ and CD8⁺ T cells from spleens of vaccinated chickens. Specific serum antibody level in the vaccinated chickens was determined to assess induced humoral immune responses. Finally, the protective efficacy of EmROM1 was evaluated by a vaccination-challenge trial.

Results

EmROM1 vaccination significantly upregulated the cytokine transcription levels and CD4⁺/CD8⁺ T cell percentages in vaccinated chickens compared with control groups, and also significantly increased the levels of serum-specific antibodies in vaccinated chickens. The animal trial showed that EmROM1 vaccination significantly reduced oocyst shedding, enteric lesions, and weight loss of infected birds compared with the controls. The anticoccidial index (ACI) from the rEmROM-vaccination group and pEmROM1-vaccination group were 174.11 and 163.37, respectively, showing moderate protection against E. maxima infection.

Discussion

EmROM1 is an effective candidate antigen for developing DNA or subunit vaccines against avian coccidiosis.

Unraveling the Complexity of the Rhomboid Serine Protease 4 Family of Babesia bovis Using Bioinformatics and Experimental Studies

Babesia bovis, a tick-transmitted apicomplexan protozoon, infects cattle in tropical and subtropical regions around the world. In the apicomplexans Toxoplasma gondii and Plasmodium falciparum, rhomboid serine protease 4 (ROM4) fulfills an essential role in host cell invasion. We thus investigated B. bovis ROM4 coding genes; their genomic organization; their expression in in vitro cultured asexual (AS) and sexual stages (SS); and strain polymorphisms. B. bovis contains five rom4 paralogous genes in chromosome 2, which we have named rom4.1, 4.2, 4.3, 4.4 and 4.5. There are moderate degrees of sequence identity between them, except for rom4.3 and 4.4, which are almost identical. RT-qPCR analysis showed that rom4.1 and rom4.3/4.4, respectively, display 18-fold and 218-fold significantly higher (p < 0.01) levels of transcription in SS than in AS, suggesting a role in gametogenesis-related processes. In contrast, transcription of rom4.4 and 4.5 differed non-significantly between the stages. ROM4 polymorphisms among geographic isolates were essentially restricted to the number of tandem repeats of a 29-amino acid sequence in ROM4.5. This sequence repeat is highly conserved and predicted as antigenic. B. bovis ROMs likely participate in relevant host−pathogen interactions and are possibly useful targets for the development of new control strategies against this pathogen.

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

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

The repertoire of serine rhomboid proteases of piroplasmids of importance to animal and human health

Babesia, Theileria and Cytauxzoon are tick-borne apicomplexan protozoans of the order Piroplasmida, notorious for the diseases they cause in livestock, pets and humans. Host cell invasion is their Achilles heel, allowing for the development of drug or vaccine-based therapies. In other apicomplexans, cleavage of the transmembrane domain of adhesins by the serine rhomboid proteinase ROM4 is required for successful completion of invasion. In this study, we record and classify the rhomboid repertoire encoded in the genomes of 10 piroplasmid species pertaining to the lineages Babesia sensu stricto (s.s., Clade VI), Theileria sensu stricto (Clade IV), Theileria equi (Clade IV), Cytauxzoon felis (Clade IIIb) and Babesia microti (Clade I), as defined by Schnittger et al. (2012). Fifty-six piroplasmid rhomboid-like proteins were assigned by phylogenetic analysis and bidirectional best hit to the ROM4, ROM6, ROM7 or ROM8 groups, and their crucial motifs for conformation and function were identified. Forty-four of these rhomboids had either been incorrectly classified or misannotated. Babesia s.s. encode five or three ROM4 proteinase paralogs, whereas the remaining piroplasmids encode two ROM4 paralogs. All piroplasmids encode a single ROM6, ROM7 and ROM8. Thus, an increased paralog number of ROM4 is the only feature distinguishing Babesia s.s. from other piroplasmid lineages. Piroplasmid ROM6 is related to the mammalian mitochondrial rhomboid and, accordingly, N-terminal mitochondrial targeting signal sequences was found in some cases. ROM6 is the only rhomboid encoded by piroplasmids that is ubiquitous in other organisms. ROM8 represents a pseudoproteinase that is highly conserved between studied piroplasmids, suggesting that it is important in regulatory functions. ROM4, ROM6, ROM7 and ROM8 are exclusively present in Aconoidasida, which comprises piroplasmids and Plasmodium, suggesting a relevant functional role in erythrocyte invasion. The correct classification and designation of piroplasmid rhomboids presented in this study facilitates an informed choice for future in-depth study of their functions.

Rhomboid protein 2 of Eimeria maxima provided partial protection against infection by homologous species

Rhomboid-like proteases (ROMs) are considered as new candidate antigens for developing new-generation vaccines due to their important role involved in the invasion of apicomplexan protozoa. In prior works, we obtained a ROM2 sequence of Eimeria maxima (EmROM2). This study was conducted to evaluate the immunogenicity and protective efficacy of EmROM2 recombinant protein (rEmROM2) and EmROM2 DNA (pVAX1-EmROM2) against infection by Eimeria maxima (E. maxima). Firstly, Western blot assay was conducted to analyze the immunogenicity of rEmROM2. The result showed that rEmROM2 was recognized by chicken anti-E. maxima serum. Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assay revealed apparent transcription and expression of EmROM2 at the injection site. qRT-PCR (quantitative real-time PCR), flow cytometry and indirect ELISA indicated that vaccination with rEmROM2 or EmROM2 DNA significantly upregulated the transcription level of cytokines (IFN-γ, IL-2, IL-4, IL-10, IL-17, TGF-β and TNF SF15), the proportion of CD8⁺ and CD4⁺ T lymphocytes and serum IgG antibody response. Ultimately, a vaccination-challenge trial was performed to evaluate the protective efficacy of rEmROM2 and pVAX1-EmROM2 against E. maxima. The result revealed that vaccination with rEmROM2 or pVAX1-EmROM2 significantly alleviated enteric lesions, weight loss, and reduced oocyst output caused by challenge infection of E. maxima, and provided anticoccidial index (ACI) of more than 160, indicating partial protection against E. maxima. In summary, vaccination with rEmROM2 or pVAX1-EmROM2 activated notable humoral and cell-mediated immunity and provided partial protection against E. maxima. These results demonstrated that EmROM2 protein and DNA are promising vaccine candidates against E. maxima infection.

In vitro effects of 5 recombinant antigens of Eimeria maxima on maturation, differentiation, and immunogenic functions of dendritic cells derived from chicken spleen

Eimeria maxima possesses integral families of immunogenic constituents that promote differentiation of immune cells during host-parasite interactions. Dendritic cells (DCs) have an irreplaceable role in the modulation of the host immunity. However, the selection of superlative antigen with immune stimulatory efficacies on host DCs is lacking. In this study, 5 recombinant proteins of E. maxima (Em), including Em14-3-3, rhomboid family domain containing proteins (ROM) EmROM1 and EmROM2, microneme protein 2 (EmMIC2), and Em8 were identified to stimulate chicken splenic derived DCs in vitro. The cultured populations were incubated with recombinant proteins, and typical morphologies of stimulated DCs were obtained. DC-associated markers major histocompatibility complex class II, CD86, CD11c, and CD1.1, showed upregulatory expressions by flow cytometry assay. Immunofluorescence assay revealed that recombinant proteins could bind with the surface of chicken splenic derived DCs. Moreover, quantitative real-time PCR results showed that distinct gene expressions of Toll-like receptors and Wnt signaling pathway were upregulated after the coincubation of recombinant proteins with DCs. The ELISA results indicated that the DCs produced a significant higher level of interleukin (IL)-12 and interferon-γ secretions after incubation with recombinant proteins. While transforming growth factor-β was significantly increased with rEmROM1, rEmROM2, and rEmMIC2 as compared to control groups, and IL-10 did not show significant alteration. Taken together, these results concluded that among 5 potential recombinant antigens, rEm14-3-3 could promote immunogenic functions of chicken splenic derived DCs more efficiently, which might represent an effective molecule for inducing the host Th1-mediated immune response against Eimeria infection.

A Novel Rhoptry Protein as Candidate Vaccine against Eimeria tenella Infection

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

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

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

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

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

Efficacy of a potential DNA vaccine encoding Cryptosporidium baileyi rhomboid protein against homologous challenge in chickens

The parasite Cryptosporidium baileyi can infect the larynx, trachea, bursa and cloaca of poultry, causing high mortality during severe infection and leading to substantial economic losses of the poultry industry. The rhomboid protein is very important in Cryptosporidium infection. In this study, a nucleic acid based vaccine candidate pEGFP-CbROM was constructed. After orally challenging with C. baileyi oocysts, the corresponding immune responses induced were analyzed and the immunoprotective effect evaluated in chickens. Obtained results revealed that this nucleic acid based vaccine could induce antibody responses and peripheral blood T lymphocytes proliferation significantly (P<0.05), while the peripheral blood B lymphocyte proliferation increased significantly (P<0.05) only at a high dose of 100μg of pEGFP-CbROM, compared with the PBS control group. After C. baileyi infection, the duration of oocysts shedding was shortened by 2days in the 100μg pEGFP-CbROM group, and the rate of reduction could reach to around 71.3%. While no significant difference in body weight gain was observed among the immunized groups (P>0.05), the differences between the immunized and the non-immunized groups were found to be significant (P<0.05). Our data provides a useful basis for further work in cryptosporidiosis prevention and treatment.

Pichia pastoris expressed EtMic2 protein as a potential vaccine against chicken coccidiosis

Chicken coccidiosis caused by Eimeria species leads to tremendous economic losses to the avian industry worldwide. Identification of parasite life cycle specific antigens is a critical step in recombinant protein vaccine development against Eimeria infections. In the present study, we amplified and cloned the microneme-2 (EtMIC2) gene from Eimeria tenella wild type strain SD-01, and expressed the EtMic2 protein using Pichia pastoris and Escherichia coli expression systems, respectively. The EtMic2 proteins expressed by P. pastoris and E. coli were used as vaccines to immunize chickens and their protective efficacies were compared and evaluated. The results indicated that both P. pastoris and E. coli expressed EtMic2 proteins exhibited good immunogenicity in stimulating host immune responses and the Pichia expressed EtMic2 provided better protection than the E. coli expressed EtMic2 did by significantly increasing growth rate, inducing high specific antibody response, reducing the oocyst output and cecal lesions. Particularly, the Pichia expressed EtMic2 protein exhibited much better ability in inducing cell mediated immune response than the E. coli expressed EtMic2.

Protective efficacy in chickens of recombinant plasmid pET32a(+)-ADF-3-1E of Eimeria acervulina

This experiment was conducted to study the protective efficacy of recombinant plasmid pET32a(+)-ADF-3-1E in coccidian-infected breeding chickens. The 7-day-old chickens were randomly divided into five groups: a recombinant plasmid pET32a(+)-ADF-3-1E group, a pET32a(+)-ADF group, a pET32a(+)-3-1E group, a control group, and an infection control group. The chickens were immunized intramuscularly with recombinant plasmid DNA in a dose of 200 μg, respectively, and a booster vaccination was given at the same dosage 1 week later. The peripheral blood T lymphocyte proliferation, serum IgG antibody response, and levels of interleukin 2 (IL-2) and interferon gamma (IFN-γ) were detected, respectively. The chickens were inoculated with 4 × 10(6) Eimeria acervulina-sporulated oocysts (Baoding strain) on the seventh day after the last immunization to evaluate the protective efficiency of the recombinant plasmid DNA. The results showed that the lymphocyte proliferation, serum IgG antibody, and IL-2 and IFN-γ levels in recombinant plasmid DNA group were significantly higher than those in control group (P < 0.01). The lymphocyte proliferation, serum IgG antibody, and IL-2 and IFN-γ levels in pET32a(+)-ADF-3-1E group were significantly higher than those in pET32a(+)-3-1E group and pET32a(+)-ADF group, respectively (P < 0.05). It indicated that the pET32a(+)-ADF-3-1E could produce stronger immune responses. The relative body weight gain rate in pET32a(+)-ADF-3-1E group was 88.36 %, which was significantly higher than that in control group (P < 0.05) and infection control group (P < 0.01). The reductions of oocyst production and lesion scores in pET32a(+)-ADF-3-1E group were 67.88 and 67.13 %, respectively. The oocyst excretion and the lesion score of chickens in pET32a(+)-ADF-3-1E group were lower than those in infection control group, respectively. Anticoccidial index (ACI) value in group immunized with pET32a(+)-ADF-3-1E was 169.82. ACI value of 160-179 was considered as effective. These results demonstrated that the pET32a(+)-ADF-3-1E recombinant plasmid DNA could effectively improve the cellular responses and humoral immune responses of the chickens, and it might provide protection against coccidiosis in chickens.

Eimeria maxima: efficacy of recombinant Mycobacterium bovis BCG expressing apical membrane antigen1 against homologous infection

Coccidiosis is one of the most important protozoan diseases and inflicts severe economic losses on the poultry industry. The aim of this study was to evaluate the capacity of Bacillus Calmette-Guerin (BCG) to deliver apical membrane antigen1 (AMA1) of Eimeria maxima to stimulate specific cellular and humoral immune responses in chickens. Day-old birds were immunized twice with rBCG/pMV261-AMA1, rBCG/pMV361-AMA1, or BCG via oral, intranasal, and subcutaneous routes and then orally challenged with homologous E. maxima sporulated oocysts. Gain of body weight, fecal oocyst output, lesion scores, serum antibody responses, numbers of splenocyte CD4(+) and CD8(+) T cells, and gut cytokine transcript levels were assessed as measures of protective immunity. Challenge experiments demonstrated that rBCG vaccination via intranasal or subcutaneous routes could increase weight gain, decrease intestinal lesions, and reduce fecal oocyst shedding, and the subcutaneous and intranasal routes were superior to the oral route based on the immune effects. Furthermore, intranasal rBCG immunization could also lead to a significant increase in serum antibody, the percentage of CD4+ and CD8+ T lymphocyte cells, and the levels of IL-1β, IFN-γ, IL-15, and IL-10 mRNAs compared with the control group. These results suggested that intranasal rBCG immunization could induce a strong humoral and cellular response directed against homologous E. maxima infection. This study provides data for the use of rBCG to develop a prophylactic vaccine against coccidiosis.

Immunization with Eimeria ninakohlyakimovae-live attenuated oocysts protect goat kids from clinical coccidiosis

Caprine coccidiosis, affecting mainly young goat kids around the weaning period, is worldwide the most important disease in the goat industry. Control of caprine coccidiosis is increasingly hampered by resistances developed against coccidiostatic drugs leading to an enhanced need for anticoccidial vaccines. In the current study we conducted an oral immunization trial with live attenuated sporulated Eimeria ninakohlyakimovae oocysts. Sporulated E. ninakohlyakimovae oocysts were attenuated by X-irradiation technique. The experimental design included a total of 18 goat kids divided into the following groups: (i) animals immunized with attenuated E. ninakohlyakimovae oocysts at 5 weeks of age and challenged 3 weeks later with non-irradiated homologous oocysts (group 1); (ii) animals infected with non-attenuated E. ninakohlyakimovae oocysts at 5 weeks of age and challenged 3 weeks later with non-attenuated homologous oocysts (group 2); (iii) animals primary-infected with untreated E. ninakohlyakimovae oocysts at 8 weeks of age (control of the challenge infection, group 3); (iv) non-infected control animals (group 4). Goat kids immunized with live attenuated E. ninakohlyakimovae oocysts (group 1) excreted significantly less oocysts in the faeces (95.3% reduction) than kids infected with non-attenuated ones (group 2). Furthermore, immunization with live but attenuated oocysts resulted in ameliorated clinical coccidiosis compared to goat kids infected with untreated oocysts (group 2) and resulted in equally reduced signs of coccidiosis after challenge infection compared to acquired immunity driven by non-attenuated oocysts. Overall, the present study demonstrates for the first time that live attenuated E. ninakohlyakimovae oocysts orally administered showed almost no pathogenicity but enough immunogenicity in terms of immunoprotection. Importantly, vaccinated animals still shed low amounts of oocysts, guaranteeing environmental contamination and consecutive booster infections to sustain ongoing immunity.

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.

Protective immunity induced by a DNA vaccine encoding Eimeria tenella rhomboid against homologous challenge

Rhomboid protein in Apicomplexa was associated with the process of host cell invasion. To evaluate the potential of the protein in eliciting protective immunity against challenge, a DNA vaccine pVAX1-Rho encoding Eimeria tenella rhomboid was constructed. Recombinant protein was expressed in Hela cells and verified by indirect immunofluorescence and western blotting analysis. In vivo experiments, 1-week-old chickens were randomly divided into three groups. Experimental group of chickens were immunized with DNA vaccines while control group of chickens were injected with pVAX1 plasmid alone or sterile water. Two weeks following the booster dose, all chickens were inoculated orally with 5 × 10(4) sporulated oocysts of E. tenella. The host immunity and protective efficacy of this vaccine against E. tenella challenge in broilers were evaluated. Results showed that specific antibody, the levels of interleukin-2 (IL-2), interferon-γ (IFN-γ), and the percentages of CD4(+) and CD8(+) T lymphocyte cells were significantly increased in the pVAX1-Rho group. Challenge experiments demonstrated that pVAX1-Rho vaccination could reduce oocyst excretion, decrease cecal lesion, increase bodyweight gains and provide chickens with oocysts decrease ratio around 75.8 %. These results suggest that the pVAX1-Rho was able to induce humoral and cellular responses and generate protective immunity against E. tenella infection.

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.