Antigen-specific lymphocyte proliferation and interleukin production in chickens immunized with killed Salmonella enteritidis vaccine or experimental subunit vaccines

Oral Deliverable Mucoadhesive Chitosan-Salmonella Subunit Nanovaccine for Layer Chickens

PURPOSE

Salmonellosis in poultry is a serious economic burden. A major concern is the public health hazard caused by consumption of Salmonella-contaminated poultry products. Currently used Salmonella vaccines are ineffective in combating poultry Salmonellosis warranting the need of a potent vaccine, especially an oral vaccine that can elicit robust local intestinal immunity.

MATERIALS AND METHODS

A Salmonella subunit chitosan nanoparticles (NPs)-based vaccine was prepared that contained immunogenic outer membrane proteins (OMPs) and -flagellin (F) protein (OMPs-F-CS NPs). OMPs-F-CS NPs were administered as an oral vaccine in layer chickens and the resultant humoral and cell-mediated immune responses and localization of NPs were examined using standard detection methods.

RESULTS

We demonstrated targeting of surface F-protein coated chitosan NPs to immune cells when delivered orally to layer chickens, the particles were localized in ileal Peyer's patches. The OMPs-F-CS NPs vaccinated layer chickens had significantly higher OMPs-specific mucosal IgA production and lymphocyte proliferation response. The candidate vaccine increased the expression of toll-like receptor (TLR)-2, TLR-4, IFN-γ, TGF-ß and IL-4 mRNA expression in chicken cecal tonsils.

CONCLUSION

Our study demonstrated that the chitosan-based oral Salmonella nanovaccine targets immune cells of chickens and induced antigen-specific B and T cell responses. This candidate oral Salmonella nanovaccine has the potential to mitigate Salmonellosis in poultry.

Surface engineered polyanhydride-based oral Salmonella subunit nanovaccine for poultry

PURPOSE

Salmonellosis is a severe economic threat in poultry and a public health concern. Currently available vaccines are ineffective, and thus, developing effective oral Salmonella vaccine is warranted. Especially, a potent oral vaccine such as the mucoadhesive polyanhydride nanoparticle (PNP) protects the vaccine cargo and delivers to intestinal immune sites to elicit robust mucosal immunity and mitigate Salmonella colonization and shedding.

MATERIALS AND METHODS

We designed a Salmonella subunit vaccine using PNP containing immunogenic Salmonella outer membrane proteins (OMPs) and flagellar (F) protein-entrapped and surface F-protein-coated PNPs (OMPs-F-PNPs) using a solvent displacement method. Using high-throughput techniques, we characterized the OMPs-F-PNPs physicochemical properties and analyzed its efficacy in layer birds vaccinated orally.

RESULTS

The candidate vaccine was resistant in acidic microenvironment and had ideal physicochemical properties for oral delivery in terms of particle size, charge, morphology, biocompatibility, and pH stability. In vitro, in vivo, and ex vivo studies showed that F-protein surface-anchored nanoparticles were better targeted to chicken immune cells in peripheral blood and splenocytes and intestinal Peyer's patch sites. In layer chickens inoculated orally with OMPs-F-PNPs, substantially higher OMPs-specific IgG response and secretion of Th1 cytokine IFN-γ in the serum, enhanced CD8+/CD4+ cell ratio in spleen, and increased OMPs-specific lymphocyte proliferation were observed. OMPs-F-PNPs vaccination also upregulated the expression of toll-like receptor (TLR)-2 and -4, TGF-β, and IL-4 cytokines' genes in chicken cecal tonsils (lymphoid tissues). Importantly, OMPs-F-PNPs vaccine cleared Salmonella cecal colonization in 33% of vaccinated birds.

CONCLUSION

This pilot in vivo study demonstrated the targeted delivery of OMPs-F-PNPs to ileum mucosal immune sites of chickens and induced specific immune response to mitigate Salmonella colonization in intestines.

A bacterial ghost improves the immunological efficacy of a Newcastle disease virus inactivated vaccine

Newcastle disease (ND) is one of the most common contagious viral infectious diseases of poultry. Vaccination is an effective way to protect chickens from Newcastle disease virus (NDV), and large efforts have been made to acquire not only new vaccines but also new adjuvants to improve the efficiency of existing inactivated vaccines. Here, we observed the adjuvanticity of the bacterial ghost (BG) on the effectiveness of inactivated NDV vaccine in a chicken model. We found that BG, as an adjuvant with inactivated NDV vaccine, substantially strengthened the ND-specific antibody response and protection against lethal challenge in a chicken model, reduced viral shedding, strengthened the time duration of antibody titers, produced an available immunization effect with a low dose of vaccine, and improved serum IL-2 and IFN-γ concentrations. Our results demonstrate that BG significantly improved the immunogenicity of an inactivated NDV vaccine and is a new immune adjuvant candidate.

Chicken mannose-binding lectin function in relation to antibacterial activity towards Salmonella enterica

Mannose-binding lectin (MBL) is a C-type serum lectin of importance in innate immunity. Low serum concentrations of MBL have been associated with greater susceptibility to infections. In this study, binding of purified chicken MBL (cMBL) to Salmonella enterica subsp. enterica (S. enterica) serotypes B, C1 and D was investigated by flow cytometry, and Staphylococcus aureus (S. aureus) was used for comparison. For S. enterica the C1 serotypes were the only group to exhibit binding to cMBL. Furthermore, functional studies of the role of cMBL in phagocytosis and complement activation were performed. Spiking with cMBL had a dose-dependent effect on the HD11 phagocytic activity of S. enterica subsp. enterica serovar Montevideo, and a more pronounced effect in a carbohydrate competitive assay. This cMBL dose dependency of opsonophagocytic activity by HD11 cells was not observed for S. aureus. No difference in complement-dependent bactericidal activity in serum with high or low cMBL concentrations was found for S. Montevideo. On the other hand, serum with high concentrations of cMBL exhibited a greater bactericidal activity to S. aureus than serum with low concentrations of cMBL. The results presented here emphasise that chicken cMBL exhibits functional similarities with its mammalian counterparts, i.e. playing a role in opsonophagocytosis and complement activation.

Molecular cloning, expression and regulation analysis of the interleukin-6 (IL-6) gene in goose adipocytes

1. Interleukin-6 (IL-6) is a multifunctional cytokine involved in lipid metabolism in adipose tissue. The objective of the study was to identify and characterize the IL-6 gene in the goose. 2. A full-length coding sequence (CDS) of the goose (Anser anser) IL-6 gene was cloned that encoded a 234-amino acid peptide containing a 38-amino acid signal peptide, an IL-6/G-CSF/MGF family consensus pattern and four conserved α-helices. The mature goose IL-6 showed 74% and 39% identities to that of chicken and human, respectively. 3. Quantitative real-time PCR analysis showed that the goose IL-6 was predominantly expressed in liver and was up-regulated in adipocytes by lipopolysaccharide (LPS) and oleic acid.

Immunization with outer membrane protein A from Salmonella enterica serovar Enteritidis induces humoral immune response but no protection against homologous challenge in chickens

Vaccination of poultry is one promising strategy to mitigate Salmonella infection in poultry and, in turn, humans as well. We evaluated the efficacy of outer membrane protein A (OmpA) as a novel vaccine candidate against Salmonella in poultry. Native OmpA purified from Salmonella enterica serovar Enteritidis was mixed with adjuvant and administered intramuscularly to 41-d-old chicks. The vaccinated birds showed no decrease in cecal excretion and tissue colonization compared with the unvaccinated birds after oral challenge with 10(9) cfu of the homologous strain at 28 d postimmunization. However, this vaccination induced an increased level of serum anti-OmpA IgG. Similar results were obtained in the replication experiments using a recombinant OmpA with single and double doses. For the development of more effective component vaccines for avian salmonellosis, the vaccine efficacy of outer membrane proteins other than OmpA and route of immunization other than parenteral administration should be evaluated with regard to protection and immune responses, including mucosal IgA.

Characterization of a novel inactivated Salmonella enterica serovar Enteritidis vaccine candidate generated using a modified cI857/λ PR/gene E expression system

A new strategy to develop an effective vaccine is essential to control food-borne Salmonella enterica serovar Enteritidis infections. Bacterial ghosts (BGs), which are nonliving, Gram-negative bacterial cell envelopes, are generated by expulsion of the cytoplasmic contents from bacterial cells through controlled expression using the modified cI857/λ P(R)/gene E expression system. In the present study, the pJHL99 lysis plasmid carrying the mutated lambda pR37-cI857 repressor and PhiX174 lysis gene E was constructed and transformed in S. Enteritidis to produce a BG. Temperature induction of the lysis gene cassette at 42°C revealed quantitative killing of S. Enteritidis. The S. Enteritidis ghost was characterized using scanning and transmission electron microscopy to visualize the transmembrane tunnel structure and loss of cytoplasmic materials, respectively. The efficacy of the BG as a vaccine candidate was evaluated in a chicken model using 60 10-day-old chickens, which were divided into four groups (n = 15), A, B, C, and D. Group A was designated as the nonimmunized control group, whereas the birds in groups B, C, and D were immunized via the intramuscular, subcutaneous, and oral routes, respectively. The chickens from all immunized groups showed significant increases in plasma IgG and intestinal secretory IgA levels. The lymphocyte proliferation response and CD3(+) CD4(+) and CD3(+) CD8(+) T cell subpopulations were also significantly increased in all immunized groups. The data indicate that both humoral and cell-mediated immune responses are robustly stimulated. Based on an examination of the protection efficacy measured by observations of gross lesions in the organs and bacterial recovery, the candidate vaccine can provide efficient protection against virulent challenge.

Abundance of IFN-α and IFN-γ gene transcripts and absence of IL-2 transcripts in the blood of chickens vaccinated with live or inactivated NDV

As immune responses to live and inactivated vaccines might differ, temporal responses of broiler chickens to vaccination were examined on the basis of the abundance in the circulating blood of gene transcripts of IFN-α, IFN-γ and IL-2, critical cytokines for immune responses. Blood samples were collected 6, 12 and 24 hours, and 7 and 14 days following vaccination with either live or inactivated Newcastle disease virus, La Sota strain, at 14 days of age, and the abundance of transcripts for each cytokine was assayed by real-time RT-PCR. Physiological saline and vaccine emulsion without viral antigen were administered to control groups for live and inactivated vaccine groups, respectively. The abundance of IFN-γ transcripts was elevated during the early times following vaccination and had reached baseline by the seventh day but the abundance of IFN-α transcripts remained elevated. Transcripts for neither IFN gene were detected in the control birds. The abundance of transcripts for each IFN was not different between the two vaccinated groups at any time. Transcripts for IL-2 were detected only in spleens from chicken embryos that had been inoculated with the live virus. The results show that cells stimulated to produce IFN-α and IFN-γ enter the circulating blood but those stimulated to produce IL-2 do not, or in very low number, and the IFN responses to both vaccines are the same.

Importance of the major Fli C antigenic site of Salmonella enteritidis as a subunit vaccine antigen

Our previous study indicated that the antibody against the major antigenic site of SE Fli C (g.m. region) is characteristically produced after the application of SE bacterin, however, the antibody is not produced in chickens after SE infection. In the present study, we determined histologically if the major antigenic site could be a candidate antigen for SE subunit vaccine. When Layermune SE, a commercial SE bacterin, was injected subcutaneously into the shoulder region as a positive control, the following histological changes were observed: formation of epithelioid granuloma with epithelioid cells and multinuclear giant cells surrounding necrotic sites and oil cysts (Indicator 1); a perivascular accumulation of lymphocytes near the granulation tissue (Indicator 2); peripheral fibroplasia encapsulating the granulation tissue (Indicator 3). On the other hand, at the injection site from the incomplete Freund adjuvant as a negative control antigen, there was only hyperplasia of the connective tissues around oil cysts. By using these indicators, the histological changes induced by injection of major antigenic site (SEp9) of Fli C, Fli C, and SE somatic antigen were evaluated. Histological changes after the injection with SEp9 demonstrated Indicators 2 and 3. The injection with SE Fli C demonstrated all three indicators. Contrarily, de-flagellated SE antigen injection induced only Indicator 3. The present results suggest that the antigen g.m. site of SE Fli C (SEp9) may play an important role as a subunit vaccine not only for including continuous immunological reaction in SE infection in chickens but also for antigen presentation.

Immunostimulatory effects of oriental plum (Prunus salicina Lindl.)

The fruit of the plum tree (Prunus salicina Lindl.) has been used as a traditional medicinal food in humans to enhance immunity against infectious agents and to treat cancers. However, limited information exists on the mechanisms responsible for its immune enhancing properties. In this study, the immunostimulatory effects of a methanol extract of plum fruit following methanol evaporation and dissolving in PBS were assessed by in vitro lymphocyte proliferation, tumor cell cytotoxicity, and nitric oxide (NO) production. The crude methanol extract stimulated spleen lymphocyte proliferation and NO production by cultured macrophages, and inhibited the viability of tumor cells, significantly greater than media controls. Sequential gel filtration chromatographic separation of the extract on Sephadex G-25 and Sephacryl S-200 gel filtration columns resulted in a more purified preparation that retained the ability to induce lymphoproliferation, tumor killing, and NO production. These results suggest that Prunus salicina contains immunostimulatory components that potentially may be useful in human and veterinary medicine.

Immunogenomic approaches to study host immunity to enteric pathogens

With increasing consumer demands for safe poultry products, effective control of disease-causing pathogens is becoming a major challenge to the poultry industry. Many chicken pathogens enter the host through the gastrointestinal tract, and over the past few decades, in-feed antibiotics and active vaccination have been the 2 main mechanisms of disease control. However, increasing public concerns are prompting government regulations on the use of growth-promoting drugs in animal production, and the ability of current vaccines to protect against emerging hypervirulent strains of pathogens is becoming an issue. Therefore, there is a need to develop alternative control strategies against poultry pathogens of economic importance as well as to carry out basic research to enhance understanding of host-pathogen interactions at local sites of infection. Effective control strategies against pathogens can only be accomplished by comprehensive analysis of the basic immunobiology of host-pathogen interactions. Recent sequencing of the poultry genome and the availability of several tissue-specific cDNA microarrays are facilitating the rapid application of functional immunogenomic technologies to poultry disease research. Studies using functional genomic, immunology, and bioinformatic approaches have provided novel insights into disease processes and protective immunity to chicken pathogens. In this review, we summarize recent published literature concerning the host response to Eimeria and Salmonella infections with emphasis on our studies using immunogenomic tools to investigate and characterize the mechanisms of avian immunity to these mucosal pathogens. The results clearly indicate that this immunogenomic approach will lead to increased understanding of immune responses to infectious agents that will enable the development of effective prevention strategies against mucosal pathogens.

Comparative evaluation of a bivalent killed Salmonella vaccine to prevent egg contamination with Salmonella enterica serovars Enteritidis, Typhimurium, and Gallinarum biovar Pullorum, using 4 different challenge models

We evaluated a newly developed commercial bivalent killed Salmonella vaccine Oilvax SET for its ability to decrease contamination with Salmonella enterica serovars Enteritidis and Typhimurium in layer chickens. In either an oral or intravaginal challenge model, the fecal shedding was decreased in vaccinated hens, but egg contamination was not evaluated due to scarcity of contaminated eggs even in the unvaccinated control groups. In contrast, an intravenous and an intraperitoneal challenge resulted in the relatively high level of egg contamination in unvaccinated chickens, which was significantly reduced in vaccinated chickens. In a second experiment, 2 strains of Salmonella serovar Gallinarum biovar Pullorum, which has the common O9 antigen with SE and transmits vertically into eggs, were used to test the efficacy of the Oilvax SET against egg transmission. Vertical egg transmission by the Pullorum strain was significantly reduced in the vaccinated groups of hens. The Oilvax SET can be a useful tool in the control of Salmonella egg contamination in laying hens.

Monoclonal antibodies against chicken interleukin-6

Monoclonal antibodies (mAb) were produced against a recombinant (r) chicken interleukin-6 (IL-6). Eight mAbs produced were tested for isotype; ability to inhibit recombinant forms of chicken (ch), human (h) and murine (m) IL-6; and recognition of rchIL-6 by Western immunoblotting. The mAb isotypes were represented by IgG1 (one), IgG2a (six) and IgG2b (one). In a mouse B9 hybridoma cell bioassay with rmIL-6, four mAbs effectively inhibited activity of rmIL-6. Further bioassays with the four mAbs at varying concentrations showed that two of these mAbs (1.20.7 and 1.26.4) were quite effective at inhibiting rmIL-6. Recombinant forms of ch, h and mIL-6 were all tested in a bioassay with the most potent inhibiting mAb (1.26.4), and this mAb was effective in inhibiting all three recombinant IL-6 proteins. Western immunoblotting revealed identification of the original IL-6 immunogen used for mAb production. Based upon inhibition of IL-6 activity in a standard bioassay and IL-6 recognition by Western immunoblotting, mAb 1.26.4 was judged the most useful antibody for future studies and applications.

Effects of Nonimmunized Egg Yolk Powder–Supplemented Feed on Salmonella Enteritidis Prevention and Elimination in Broilers

Chicken consumption is a newly identified risk factor in Salmonella enterica serovar Enteritidis (SE) infection in humans. SE is widely distributed in commercial chicken flocks and high levels of cecal carriage and shedding may lead to broiler meat contamination. In the present study, the preventive and eliminative effect of nonimmunized freeze-dried egg yolk powder (EYP) on SE in broilers was investigated. In the prevention trial, reduced SE counts were observed in liver (P < or = 0.05), cecal contents, and fecal shedding (P < or = 0.05) in birds fed 10% or 5% EYP. Histological examination of cecal wall and cecal tonsils at 23 days postinfection indicated a lesser degree of intestinal pathology. In the elimination trial, a significantly lower (P < or = 0.05) number of SE reached the liver and spleen, and a reduction in cecal carriage and fecal shedding was observed. The histological changes in the cecal mucosa and cecal tonsils reflected an apparent inflammation and mucosal repair and also suggested that the infection had not completely resolved, confirming SE bacterial isolations in the cecal tissue. The present study indicates that supplementing the diets of broilers with 5% nonimmunized EYP, at the early stages of the growing period, reduces preharvest Salmonella load with a minimal degree of intestinal pathology.

Differential responses of macrophages to Salmonella enterica serovars Enteritidis and Typhimurium

Macrophages are major effectors against Salmonella infection, and also transport bacteria between host tissues and provide a protected site for intracellular bacterial replication. We hypothesized that differences in chicken macrophage responses to Salmonella enterica serovar Enteritidis (SE) and serovar Typhimurium (ST) played a role in preferential infection of eggs by SE compared with ST. To test this hypothesis, we determined bacterial phagocytosis and intracellular viability and macrophage nitric oxide (NO) production following in vitro infection with SE or ST in the presence or absence of interferon-gamma (IFN-gamma). The effects of bacterial components, lipopolysaccharide (LPS), outer membrane proteins (OMP) and flagella, on NO production were also assessed. Our results showed: (1) in the presence or absence of IFN-gamma, the percentage macrophages phagocytizing SE and ST was similar; (2) the number of intracellular viable SE was significantly reduced compared with ST in the presence or absence of IFN-gamma; (3) increased macrophage necrosis was seen in the presence of IFN-gamma and ST; (4) Salmonella infection acted synergistically with IFN-gamma in induction of nitric oxide production; and (5) in the absence of IFN-gamma, macrophages produced significantly greater NO following treatment with SE outer membrane protein or flagella compared with ST OMP or flagella, while in the presence of IFN-gamma significantly less NO was produced following treatment with SE-LPS compared with ST-LPS. These results suggest that differential responses of chicken macrophages to SE versus ST may result in increased macrophage death with ST, which could result in an increased inflammatory response as compared to SE.