Construction of Lactococcus lactis expressing secreted and anchored Eimeria tenella 3-1E protein and comparison of protective immunity against homologous challenge

Oral vaccination with a recombinant Lactobacillus plantarum expressing the Eimeria tenella rhoptry neck 2 protein elicits protective immunity in broiler chickens infected with Eimeria tenella

BACKGROUND

Chicken coccidiosis is a protozoan disease that leads to considerable economic losses in the poultry industry. Live oocyst vaccination is currently the most effective measure for the prevention of coccidiosis. However, it provides limited protection with several drawbacks, such as poor immunological protection and potential reversion to virulence. Therefore, the development of effective and safe vaccines against chicken coccidiosis is still urgently needed.

METHODS

In this study, a novel oral vaccine against Eimeria tenella was developed by constructing a recombinant Lactobacillus plantarum (NC8) strain expressing the E. tenella RON2 protein. We administered recombinant L. plantarum orally at 3, 4 and 5 days of age and again at 17, 18 and 19 days of age. Meanwhile, each chick in the commercial vaccine group was immunized with 3 × 102 live oocysts of coccidia. A total of 5 × 104 sporulated oocysts of E. tenella were inoculated in each chicken at 30 days. Then, the immunoprotection effect was evaluated after E. tenella infection.

RESULTS

The results showed that the proportion of CD4+ and CD8+ T cells, the proliferative ability of spleen lymphocytes, inflammatory cytokine levels and specific antibody titers of chicks immunized with recombinant L. plantarum were significantly increased (P < 0.05). The relative body weight gains were increased and the number of oocysts per gram (OPG) was decreased after E. tenella challenge. Moreover, the lesion scores and histopathological cecum sections showed that recombinant L. plantarum can significantly relieve pathological damage in the cecum. The ACI was 170.89 in the recombinant L. plantarum group, which was higher than the 150.14 in the commercial vaccine group.

CONCLUSIONS

These above results indicate that L. plantarum expressing RON2 improved humoral and cellular immunity and enhanced immunoprotection against E. tenella. The protective efficacy was superior to that of vaccination with the commercial live oocyst vaccine. This study suggests that recombinant L. plantarum expressing the RON2 protein provides a promising strategy for vaccine development against coccidiosis.

Probiotic Enterococcus faecalis surface-delivering key domain of EtMIC3 proteins: immunoprotective efficacies against Eimeria tenella infection in chickens

IMPORTANCE

Avian coccidiosis caused by Eimeria brings huge economic losses to the poultry industry. Although live vaccines and anti-coccidial drugs were used for a long time, Eimeria infection in chicken farms all over the world commonly occurred. The exploration of novel, effective vaccines has become a research hotspot. Eimeria parasites have complex life cycles, and effective antigens are particularly critical to developing anti-coccidial vaccines. Microneme proteins (MICs), secreted from microneme organelles located at the parasite apex, are considered immunodominant antigens. Eimeria tenella microneme 3 (EtMIC3) contains four conserved repeats (MARc1, MARc2, MARc3, and MARc4) and three divergent repeats (MARa, MARb, and MARd), which play a vital role during the Eimeria invasion. Enterococcus faecalis is a native probiotic in animal intestines and can regulate intestinal flora. In this study, BC1 and C4D domains of EtMIC3, BC1 or C4D fusing to dendritic cells targeting peptides, were surface-displyed by E. faecalis, respectively. Oral immunizations were performed to investigate immune protective effects against Eimeria infection.

Prevention and control of chicken coccidiosis construction of recombinant Lactococcus lactis expressing chicken IL-4 and IL-2 fusion protein and its immune synergistic effect on chicken coccidia live vaccine

Intestinal mucosa injury and loss of weight gain are unavoidable while using live vaccine strain to prevent chicken coccidiosis. In this study, recombinant Lactococcus lactis NZ3900/pNZ8149-IL-4-IL-2, expressing the fusion protein of chicken IL-4 and IL-2, was constructed using food-grade NICE expression system, trying to develop a possible oral immune adjuvant to enhance the immune effect of the live vaccine against chicken coccidiosis and minimize its adverse effects. Chickens were given different doses of recombinant L. lactis together with the live vaccine, then experimently attacked with coccidia virulent strains. Results showed that weight gains of co-immunization groups, given both 1 × 10⁹ or 1 × 10¹⁰ CFU recombinant L. lactis and the live vaccine, were significantly higher than the vaccine-only group (P<0.05), while intestinal lesion scores of duodenum, jejunum, and cecum were significantly lower than the vaccine-only group (P<0.05), so was the oocyst shedding. The anticoccidial indexes (ACI) of the co-immunized groups given 1 × 10⁹ and 1 × 10¹⁰ CFU recombinant L. lactis were 187.85 and 193.33, respectively, higher than 174.61 of the vaccine-only group. In addition, chickens in co-immunization groups gained more body weight than the vaccine-only group before being challenged with the virulent strains (P<0.05). All the results indicated that the constructed recombinant L. lactis NZ3900/ pNZ8149-IL-4-IL-2 exhibited an immune synergistic function to coccidiosis live vaccine, and could alleviate its adverse effect affecting weight gain. The application of the recombinant L. lactis showed the potency to lift the anticoccidial efficiency of the live vaccine from a medium level to a high level.

Construction of a Lactobacillus plantarum-based claudin-3 targeting delivery system for the development of vaccines against Eimeria tenella

Avian coccidiosis causes huge economic losses to the poultry industry worldwide and currently lacks effective live vector vaccines. Achieving efficient antigen delivery to mucosa-associated lymphoid tissue (MALT) is critical for improving the effectiveness of vaccines. Here, chicken claudin-3 (CLDN3), a tight junction protein expressed in MALT, was identified as a target, and the C-terminal region of Clostridium perfringens enterotoxin (C-CPE) was proven to bind to chicken CLDN3. Then, a CLDN3-targeting Lactobacillus plantarum NC8-expressing C-CPE surface display system (NC8/GFP-C-CPE) was constructed to successfully express the heterologous protein on the surface of L. plantarum. The colonization level of NC8/GFP-C-CPE was significantly increased compared to the non-targeting strain and could persist in the intestine for at least 72 h. An oral vaccine strain expressing five EGF domains of Eimeria tenella microneme protein 8 (EtMIC8-EGF) (NC8/EtMIC8-EGF-C-CPE) was constructed to evaluate the protective efficacy against E. tenella infection. The results revealed that CLDN3-targeting L. plantarum induced stronger mucosal immunity in gut-associated lymphoid tissues (GALT) as well as humoral responses and conferred better protection in terms of parasite replication and pathology than the non-targeting strain. Overall, we successfully constructed a CLDN3-targeting L. plantarum NC8 surface display system characterized by MALT-targeting, which is an efficient antigen delivery system to confer enhanced protective efficacy in chickens against E. tenella infection.

Immunomodulatory action of Lactococcuslactis

Fermented foods are gaining popularity due to health-promoting properties with high levels of nutrients, phytochemicals, bioactive compounds, and probiotic microorganisms. Due to its unique fermentation process, Lactococcus lactis plays a key role in the food business, notably in the manufacturing of dairy products. The superior biological activities of L. lactis in these functional foods include anti-inflammatory and immunomodulatory capabilities. L. lactis boosted growth performance, controlled amino acid profiles, intestinal immunology, and microbiota. Besides that, the administration of L. lactis increased the rate of infection clearance. Innate and acquired immune responses would be upregulated in both local and systemic compartments, resulting in these consequences. L. lactis is often employed in the food sector and is currently being exploited as a delivery vehicle for biological research. These bacteria are being eyed as potential candidates for biotechnological applications. With this in mind, we reviewed the immunomodulatory effects of different L. lactis strains.

Combined oral immunization with probiotics Entercoccus faecalis delivering surface-anchored Eimeria tenella proteins provide protective efficacies against homologous infection in chickens

Background and Objectives

Avian coccidiosis is an intestinal parasitic disease exerting a highly negative impact on the global poultry industry. The aim of the present study is to evaluate the immune protective efficacies against Eimeria tenella infection in chickens orally immunized with combined recombinant probiotics Entercoccus faecalis (E. faecalis) delivering surface-anchored E. tenella proteins.

Methods

Four kinds of novel probiotics vaccines that surface-expressing four Eimeria tenella (E. tenella) proteins EtAMA1, EtIMP1, EtMIC2 and Et3-1E were produced, respectively. The expression of four target proteins on the surface of recombinant bacteria was detected by Western blot and indirect immunofluorescence assay (IFA). Then the four kinds of recombinant E. faecalis were combined to immunize chickens via oral route in different combinations. The immunizations were performed three times at two-week intervals, and each for three consecutive days. After immunizations, chickens in each immunized group were orally challenged with E. tenella sporulated oocysts. The immune responses and protective efficacies against homologous infection were evaluated.

Results

The results showed that three or four live recombinant E. faecalis induced effective antigen-specific humoral, intestinal mucosal immune responses, stimulated peripheral T lymphocytes proliferation, and displayed partial protections against homologous challenge as measured by cecal lesions, oocyst shedding, and body weight gain (BWG). Notably, higher levels of protective efficacies were observed when the four recombinant E. faecalis delivering target proteins were combined.

Conclusion

Chickens orally administrated with three or four, especially the four combined recombinant E. faecalis stimulated specific immune responses, which provided anti-coccidial effects. This study offers an idea for future development of novel vaccines based on multi-antigens delivered by probiotic bacteria.

Probiotics Surface-Delivering Fiber2 Protein of Fowl Adenovirus 4 Stimulate Protective Immunity Against Hepatitis-Hydropericardium Syndrome in Chickens

Background and Objectives

Hepatitis-hydropericardium syndrome (HHS) caused by Fowl adenoviruses serotype 4 (FAdV-4) leads to severe economic losses to the poultry industry. Although various vaccines are available, vaccines that effectively stimulate intestinal mucosal immunity are still deficient. In the present study, novel probiotics that surface-deliver Fiber2 protein, the major virulence determiner and efficient immunogen for FAdV-4, were explored to prevent this fecal–oral-transmitted virus, and the induced protective immunity was evaluated after oral immunization.

Methods

The probiotic Enterococcus faecalis strain MDXEF-1 and Lactococcus lactis NZ9000 were used as host strains to deliver surface-anchoring Fiber2 protein of FAdV-4. Then the constructed live recombinant bacteria were orally vaccinated thrice with chickens at intervals of 2 weeks. Following each immunization, immunoglobulin G (IgG) in sera, secretory immunoglobulin A (sIgA) in jejunum lavage, immune-related cytokines, and T-cell proliferation were detected. Following challenge with the highly virulent FAdV-4, the protective effects of the probiotics surface-delivering Fiber2 protein were evaluated by verifying inflammatory factors, viral load, liver function, and survival rate.

Results

The results demonstrated that probiotics surface-delivering Fiber2 protein stimulated humoral and intestinal mucosal immune responses in chickens, shown by high levels of sIgA and IgG antibodies, substantial rise in mRNA levels of cytokines, increased proliferative ability of T cells in peripheral blood, improved liver function, and reduced viral load in liver. Accordingly, adequate protection against homologous challenges and a significant increase in the overall survival rate were observed. Notably, chickens orally immunized with E. faecalis/DCpep-Fiber2-CWA were completely protected from the FAdV-4 challenge, which is better than L. lactis/DCpep-Fiber2-CWA.

Conclusion

The recombinant probiotics surface-expressing Fiber2 protein could evoke remarkable humoral and cellular immune responses, relieve injury, and functionally damage target organs. The current study indicates a promising method used for preventing FAdV-4 infection in chickens.

An Eimeria maxima Antigen: Its Functions on Stimulating Th1 Cytokines and Protective Efficacy Against Coccidiosis

A consensus is that the Th1 immune response plays a predominant role against avian coccidiosis. Therefore, an antigen with the ability to induce Th1 cytokine responses is an ideal candidate for the development of coccidiosis vaccines. In our previous study, EmARM-β, a Th1 cytokines-stimulating antigen, was screened from the cDNA expression library of Eimeria maxima (E. maxima). Herein, we verified its stimulative effects on Th1 cytokine productions and evaluated its protective efficacy against E. maxima infection. Recombinant EmARM-β protein was expressed, and eukaryotic expression plasmid pVAX1-EmARM-β was also constructed for the immunization of birds. An immunofluorescence assay was performed to detect the native form of EmARM-β protein in the stage of sporozoites. Expressions of specific transcription factors and cytokines in immunized chickens were measured using qPCR and ELISA to verify its stimulating function on Th1 cytokines. Specific IgG antibody levels and T lymphocyte subpopulation in the immunized chickens were detected using ELISA and indirect flow cytometry to determine induced immune responses. The results showed that EmARM-β native protein is massively expressed in the sporozoites stage of E. maxima. Effective stimulation from the EmARM-β antigen to T-bet and Th1 cytokines (IL-2 and IFN-γ) was observed in vivo. After being immunized with rEmARM-β or pVAX1-EmARM-β, significant promotion to the proportion of CD4+ and CD8+ T cells and the level of antigen-specific IgG antibodies in immunized chickens was also observed. Furthermore, vaccination with rEmARM-β antigen or pVAX1-EmARM-β resulted in alleviated weight loss and enteric lesion, reduced oocyst output, and higher anticoccidial index (ACI) in challenged birds. These results indicate that EmARM-β antigen can effectively stimulate the expression of Th1 cytokines and initiate host immune responses, providing moderate protective efficacy against E. maxima. Notably, EmARM-β protein is a promising candidate for developing a novel anticoccidial vaccine.

Protective Efficacy of Rhomboid-Like Protein 3 as a Candidate Antigen Against Eimeria maxima in Chickens

Avian coccidiosis brings tremendous economic loss to the poultry industry worldwide. The third generation vaccine, including subunit and DNA vaccines, exhibited promising developmental prospects. In a previous study, we found rhomboid-like protein 3 of Eimeria maxima (EmROM3) was involved in infections by Eimeria species. However, the protective efficacy of EmROM3 against Eimeria maxima (E. maxima) remains unknown. In this study, chickens were intramuscularly immunized with the recombinant protein EmROM3 (rEmROM3) or pVAX1-EmROM3 to determine the EmROM3-induced immune response. The induced humoral immune response was determined by measuring serum IgG antibody levels in immunized chickens. The induced cellular immune response was detected by measuring the transcription level of immune related cytokines and the proportion of T cell subsets of the immunized chickens. Finally, the protective efficacy of the EmROM3 vaccine against E. maxima was evaluated by immunization-challenge trials. Results revealed that the purified rEmROM3 reacted with chicken anti-E. maxima serum. The recombinant plasmid of pVAX1-EmROM3 was transcribed and translated in the injected muscle from the vaccinated chickens. In experimental groups, the IgG titers, proportions of CD4⁺ and CD8⁺ T cells, and transcription level of splenic cytokines were significantly increased compared with the control groups. The immunization-challenge trial revealed that immunization with rEmROM3 or pVAX1-EmROM3 led to restored weight gain, alleviated enteric lesion, decreased oocyst output as well as the higher anticoccidial index (ACI), indicating partial protection against E. maxima. These results indicate that EmROM3 is an effective candidate antigen for developing novel vaccines against infection by E. maxima.

Oral Immunization of Recombinant Lactococcus lactis and Enterococcus faecalis Expressing Dendritic Cell Targeting Peptide and Hexon Protein of Fowl Adenovirus 4 Induces Protective Immunity Against Homologous Infection

Hepatitis-hydropericardium syndrome (HPS) causes severe economic losses in the global poultry industry. The present study aims to explore oral immunization of recombinant Lactococcus lactis and Enterococcus faecalis expressing Hexon protein of fowl adenovirus 4 (FAdV-4). The bacteria L. lactis NZ9000 and E. faecalis MDXEF-1 were, respectively, modified as host strain to deliver truncated Hexon protein (ΔHexon) or ΔHexon protein fusing with dendritic cell (DC) targeting peptide (DC-ΔHexon) on the surface of bacteria. The expression of target protein in L. lactis NZ9000 and E. faecalis MDXEF-1 were detected by western blot. To evaluate the immune responses and protective efficacies provided by the live recombinant bacteria, chickens were immunized with the constructed ΔHexon-expressing bacteria three times at 2-week intervals, then experimentally challenged with hypervirulent FAdV-4/GX01. The results showed that oral immunizations with the four ΔHexon-expressing bacteria (NZ9000/ΔHexon-CWA, NZ9000/DC-ΔHexon-CWA, MDXEF-1/ΔHexon-CWA, and MDXEF-1/DC-ΔHexon-CWA), especially the two bacteria carrying DC-targeting peptide, stimulated higher levels of ΔHexon-specific sera IgG and secretory IgA (sIgA) in jejunal lavage fluid, higher proliferation of peripheral blood lymphocytes (PBLs) and higher levels of Th1/Th2-type cytokines, along with significantly decreased virus loads in liver and more offered protective efficacies against FAdV infection compared with PBS and empty vector control groups (p < 0.01). For chickens in the group MDXEF-1/DC-ΔHexon-CWA, the levels of aspartate transaminase (AST), alanine transaminase (ALT) and lactate dehydrogenase (LDH) in sera, and the virus loads in livers were significantly decreased vs. the other three ΔHexon-expressing bacteria (p < 0.01). The pathological changes in the hearts, livers, spleens and kidneys of chickens in MDXEF-1/DC-ΔHexon-CWA group were relatively slight compared to infection control group and other three ΔHexon-expressing bacteria groups. The rate of protection in MDXEF-1/DC-ΔHexon-CWA group was 90%. The present work demonstrated that cell surface-displayed target protein and immune enhancers in L. lactis and E. faecalis might be a promising approach to enhance immunity and immune efficacy against pathogen FAdV-4 infection.

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

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

Plasmid Replicons for the Production of Pharmaceutical-Grade pDNA, Proteins and Antigens by Lactococcus lactis Cell Factories

The Lactococcus lactis bacterium found in different natural environments is traditionally associated with the fermented food industry. But recently, its applications have been spreading to the pharmaceutical industry, which has exploited its probiotic characteristics and is moving towards its use as cell factories for the production of added-value recombinant proteins and plasmid DNA (pDNA) for DNA vaccination, as a safer and industrially profitable alternative to the traditional Escherichia coli host. Additionally, due to its food-grade and generally recognized safe status, there have been an increasing number of studies about its use in live mucosal vaccination. In this review, we critically systematize the plasmid replicons available for the production of pharmaceutical-grade pDNA and recombinant proteins by L. lactis. A plasmid vector is an easily customized component when the goal is to engineer bacteria in order to produce a heterologous compound in industrially significant amounts, as an alternative to genomic DNA modifications. The additional burden to the cell depends on plasmid copy number and on the expression level, targeting location and type of protein expressed. For live mucosal vaccination applications, besides the presence of the necessary regulatory sequences, it is imperative that cells produce the antigen of interest in sufficient yields. The cell wall anchored antigens had shown more promising results in live mucosal vaccination studies, when compared with intracellular or secreted antigens. On the other side, engineering L. lactis to express membrane proteins, especially if they have a eukaryotic background, increases the overall cellular burden. The different alternative replicons for live mucosal vaccination, using L. lactis as the DNA vaccine carrier or the antigen producer, are critically reviewed, as a starting platform to choose or engineer the best vector for each application.

Activation of ChTLR15/ChNF-κB-ChNLRP3/ChIL-1β signaling transduction pathway mediated inflammatory responses to E. tenella infection

Avian coccidiosis caused by Eimeria leads to severe economic losses in the global poultry industry. Although chicken Toll-like receptor 15 (ChTLR15) was reported to be involved in Eimeria infection, the detailed mechanism underlying its role in the inflammatory response remains to be discovered. The present study demonstrated that the mRNA expression levels of ChTLR15, ChMyD88, ChNF-κB, ChNLRP3, ChCaspase-1, ChIL-18 and ChIL-1β and the protein levels of ChTLR15 and ChNLRP3 in cecal tissues of Eimeria-infected chickens were significantly elevated at 4, 12, and 24 h compared with those in noninfected control chickens (p < 0.01). Moreover, the mRNA levels of molecules in the ChTLR15/ChNF-κB and ChNLRP3/ChIL-1β pathways and the protein levels of ChTLR15 and ChNLRP3 in chicken embryo fibroblast cells (DF-1) stimulated by E. tenella sporozoites were consistent with those in Eimeria-infected chickens. Furthermore, overexpression of ChTLR15 in DF1 cells augmented activation of the ChTLR15/ChNF-κB and ChNLRP3/ChIL-1β pathways when stimulated with E. tenella sporozoites, while knockdown of ChTLR15 in DF1 cells showed inverse effects. Taken together, the present study provides evidence that E. tenella sporozoites specifically activate ChTLR15 and then trigger activation of the ChNLRP3/ChIL-1β pathway, which partially mediates inflammatory responses to Eimeria infection.

Eimeria tenella: IMP1 protein delivered by Lactococcus lactis induces immune responses against homologous challenge in chickens

Avian coccidiosis leads to severe economic losses on the global poultry industry. Immune mapped protein-1 (IMP1) is a novel membrane protein, and was reported to be a candidate protective antigen. However, production and utilization modes of IMP1 using Lactococcus lactis as delivery vector were not reported untill now. In the present study, Eimeria tenella IMP1 (EtIMP1) protein was expressed in L. lactis under the nisin-inducible promoter, and EtIMP1 protein was produced in cytoplasmic, cell wall-anchored and secreted forms. Each chicken was orally immunized with one of the three live EtIMP1-expressing lactococci three times at 2 weeks intervals (immunized group), or with live bacteria harboring empty vector (immunized control group). Chickens in immunized and immunized control group were challenged with E. tenella sporulated oocysts to assess the immune responses. The results showed that proliferative responses of peripheral blood T lymphocytes, mRNA expression levels of IL-2, IL-4, IL-10 and IFN-γ in spleen tissues, levels of serum IgG and secretory IgA (sIgA) in cecal lavage fluids from chickens in immunized group were all significantly elevated compared to that in immunized control group. All three the live EtIMP1-expressing lactococci significantly decreased oocyst shedding, alleviated pathological damage in cecum and improved weight gain compared with bacteria harboring empty vector. These results suggested EtIMP1 protein delivered by L. lactis might be a promising candidate in developing novel vaccines against Eimeria infection.

A potential vaccine candidate towards chicken coccidiosis mediated by recombinant Lactobacillus plantarum with surface displayed EtMIC2 protein

Eimeria tenella (E. tenella) has caused severe economic loss in chicken production, especially after the forbidden use of antibiotics in feed. Considering the drug resistant problem caused by misuse of chemoprophylaxis and live oocyst vaccines can affect the productivity of chickens, also it has the risk to reversion of virulence, the development of efficacious, convenient and safe vaccines is still deeply needed. In this study, the EtMic2 protein of E. tenella was anchored on the surface of Lactobacillus plantarum (L. plantarum) NC8 strain. The newly constructed strain was then used to immunize chickens, followed by E. tenella challenge. The results demonstrated that the recombinant strain could provide efficient protection against E. tenella, shown by increased relative body weight gains, percentages of CD4⁺ and CD8⁺ T cells, humoral immune response and inflammatory cytokines. In addition, decreased cecum lesion scores and fecal oocyst shedding were also observed during the experiment. In conclusion, this study proves the possibility to use L. plantarum as a vessel to deliver protective antigen to protect chickens against coccidiosis.

Immune response and protective efficacy of recombinant Enterococcus faecalis displaying dendritic cell-targeting peptide fused with Eimeria tenella 3-1E protein

Avian coccidiosis causes significant economic losses on the global poultry breeding industry. Exploration of new-concept vaccines against coccidiosis has gradually become a research hotspot. In this study, an Enterococcus faecalis strain (MDXEF-1) showing excellent performance isolated from chicken intestinal tract was used as a vector to deliver Eimeria target protein. The plasmid pTX8048-SP-DCpep-NAΔ3-1E-CWA harboring dendritic cell–targeting peptide (DCpep) fusion with Eimeria tenella NAΔ3-1E gene (3-1E protein–coding gene without start codon ATG and terminator codon TAA) was electrotransformed into MDXEF-1 to generate the recombinant bacteria MDXEF-1/pTX8048-SP-DCpep-NAΔ3-1E-CWA in which NAΔ3-1E protein was covalently anchored to the surface of bacteria cells by cell wall anchor (CWA) sequence. The expression of target fusion protein DCpep-NAΔ3-1E-CWA was detected by Western blot. Each chicken was immunized 3 times at 2-wk intervals with live E. faecalis expressing DCpep-NAΔ3-1E fusion protein (DCpep-NAΔ3-1E group), live E. faecalis expressing NAΔ3-1E protein (NAΔ3-1E group), and live E. faecalis containing empty vector only. The 3 immunized groups were then challenged with homologous E. tenella sporulated oocyst after immunizations, and the immune response and protective efficacy in each group were evaluated. The results showed that serum IgG levels, secretory IgA levels in cecal lavage, proportion of CD4+ and CD8α+ cells in peripheral blood, and mRNA expression levels of IL-2 and IFN-γ in the spleen were significantly higher in chickens in the DCpep-NAΔ3-1E group than in chickens of the NAΔ3-1E group (P < 0.05). Oral immunization to chickens with live E. faecalis expressing DCpep-NAΔ3-1E offered more protective efficacy against homologous challenge including significant improved body weight gain, increased oocyst decrease ratio, and reduced average lesion scores in cecum compared with chickens with live E. faecalis expressing NAΔ3-1E protein. These results suggest that recombinant E. faecalis expressing dendritic cell–targeting peptide fusion with E. tenella 3-1E protein could be a potential approach for prevention of Eimeria infection.

Protective effects of a food-grade recombinant Lactobacillus plantarum with surface displayed AMA1 and EtMIC2 proteins of Eimeria tenella in broiler chickens

Background

Avian coccidiosis posts a severe threat to poultry production. In addition to commercial attenuated vaccines, other strategies to combat coccidiosis are urgently needed. Lactobacillus plantarum has been frequently used for expression of foreign proteins as an oral vaccine delivery system using traditional erythromycin resistance gene (erm). However, antibiotic selection markers were often used during protein expression and they pose a risk of transferring antibiotic resistance genes to the environment, and significantly restricting the application in field production. Therefore, a food-grade recombinant L. plantarum vaccine candidate would dramatically improve its application potential in the poultry industry.

Results

In this study, we firstly replaced the erythromycin resistance gene (erm) of the pLp_1261Inv-derived expression vector with a non-antibiotic, asd-alr fusion gene, yielding a series of non-antibiotic and reliable, food grade expression vectors. In addition, we designed a dual-expression vector that displayed two foreign proteins on the surface of L. plantarum using the anchoring sequences from either a truncated poly-γ-glutamic acid synthetase A (pgsA′) from Bacillus subtilis or the L. acidophilus surface layer protein (SlpA). EGFP and mCherry were used as marker proteins to evaluate the surface displayed properties of recombinant L. plantarum strains and were inspected by western blot, flow cytometry and fluorescence microscopy. To further determine its application as oral vaccine candidate, the AMA1 and EtMIC2 genes of E. tenella were anchored on the surface of L. plantarum strain. After oral immunization in chickens, the recombinant L. plantarum strain was able to induce antigen specific humoral, mucosal, and T cell-mediated immune responses, providing efficient protection against coccidiosis challenge.

Conclusions

The novel constructed food grade recombinant L. plantarum strain with double surface displayed antigens provides a potential efficient oral vaccine candidate for coccidiosis.

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

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

Live recombinant Lactococcuslactis expressing avian hepatitis virus ORF2 protein: Immunoprotection against homologous virus challenge in chickens

Avian hepatitis E virus (aHEV) is a pathogen associated with hepatitis-splenomegaly syndrome in chickens. To date, no commercial vaccine is available for preventing aHEV infection. In this study, three recombinant LactococcuslactisNZ9000experimental live vaccines expressing cytoplasmic, secreted, and cell wall-anchored forms of aHEV truncated ORF2 protein spanning amino acids 249-606 (ΔORF2) were constructed using pTX8048 vector and characterized. Each chicken was immunized three times at two-week intervals with one of the three live aHEV ORF2 vaccines (experimental group) or with live vaccine containing empty vector only (control group). Both groups were then challenged with aHEV and evaluated to compare immune responses and immunogenic effects. Serum IgG levels, secretory IgA (sIgA) levels in bile and jejunal lavage fluid, and mRNA expression levels ofIL-2 and IFN-γ in liver and spleen were significantly higher in experimental chickens than in controls. Meanwhile, post-challenge serum and fecal virus loads were significantly lower in experimental chickens versus controls. Moreover, on day 7 post infection (PI), serum lactose dehydrogenase (LDH) levels were significantly higher in controls than experimental chickens. Furthermore, at day 28 PI, obvious gross pathological lesions and histopathological changes typical for aHEV infection were observed in control livers and spleens, with only moderate pathological changes observed in the experimental group. The results of this study collectively demonstrate that an oral vaccineusing L.lactisNZ9000 as a delivery vector for aHEV immunogenic antigen could effectively control aHEV infection of chickens.

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

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