Gamma/delta T cell response of chickens after oral administration of attenuated and non-attenuated Salmonella typhimurium strains

Chicken γδ T cells proliferate upon IL-2 and IL-12 treatment and show a restricted receptor repertoire in cell culture

In chickens, γδ T cells represent a large fraction of peripheral T cells; however, their function remains largely unknown. Here, we describe the selective in vitro expansion of γδ T cells from total splenocytes by stimulation with the cytokines IL-2 and IL-12. Under these conditions, γδ T cells proliferated preferentially and reached frequencies of >95% within three weeks. Although IL-2 alone also triggered proliferation, an increased proliferation rate was observed in combination with IL-12. Most of the expanded cells were γδ TCR and CD8 double-positive. Splenocytes sorted into TCR1+CD8+, TCR1highCD8-, and TCR1lowCD8- subsets proliferated well upon dual stimulation with IL-2/IL-12, indicating that none of the three γδ T cell subsets require bystander activation for proliferation. TCR1+CD8+ cells maintained CD8 surface expression during stimulation, whereas CD8- subpopulations showed varied levels of CD8 upregulation, with the highest upregulation observed in the TCR1high subset. Changes in the γδ T-cell receptor repertoire during cell culture from day 0 to day 21 were analyzed by next-generation sequencing of the γδ variable regions. Overall, long-term culture led to a restricted γ and δ chain repertoire, characterized by a reduced number of unique variable region clonotypes, and specific V genes were enriched at day 21. On day 0, the δ chain repertoire was highly diverse, and the predominant clonotypes differed between animals, while the most frequent γ-chain clonotypes were shared between animals. However, on day 21, the most frequent clonotypes in both the γ and δ chain repertoires were different between animals, indicating that selective expansion of dominant clonotypes during stimulation seems to be an individual outcome. In conclusion, IL-2 and IL-12 were sufficient to stimulate the in vitro outgrowth of γδ T cells. Analyses of the TCR repertoire indicate that the culture leads to an expansion of individual T cell clones, which may reflect previous in vivo activation. This system will be instrumental in studying γδ T cell function.

The Immunological Basis for Vaccination

Vaccination is crucial for health protection of poultry and therefore important to maintaining high production standards. Proper vaccination requires knowledge of the key players of the well-orchestrated immune system of birds, their interdependence and delicate regulation, and, subsequently, possible modes of stimulation through vaccine antigens and adjuvants. The knowledge about the innate and acquired immune systems of birds has increased significantly during the recent years but open questions remain and have to be elucidated further. Despite similarities between avian and mammalian species in their composition of immune cells and modes of activation, important differences exist, including differences in the innate, but also humoral and cell-mediated immunity with respect to, for example, signaling transduction pathways, antigen presentation, and cell repertoires. For a successful vaccination strategy in birds it always has to be considered that genotype and age of the birds at the time point of immunization as well as their microbiota composition may have an impact and may drive the immune reactions into different directions. Recent achievements in the understanding of the concept of trained immunity will contribute to the advancement of current vaccine types helping to improve protection beyond the specificity of an antigen-driven immune response. The fast developments in new omics technologies will provide insights into protective B- and T-cell epitopes involved in cross-protection, which subsequently will lead to the improvement of vaccine efficacy in poultry.

Loss of αβ but not γδ T cells in chickens causes a severe phenotype

The availability of genetically modified mice has facilitated the study of mammalian T cells. No model has yet been developed to study these cells in chickens, an important livestock species with a high availability of γδ T cells. To investigate the role of γδ and αβ T cell populations in birds, we generated chickens lacking these T cell populations. This was achieved by genomic deletion of the constant region of the T cell receptor γ or β chain, leading to a complete loss of either γδ or αβ T cells. Our results show that a deletion of αβ T cells but not γδ T cells resulted in a severe phenotype in KO chickens. The αβ T cell KO chickens exhibited granulomas associated with inflammation of the spleen and the proventriculus. Immunophenotyping of αβ T cell KO chickens revealed a significant increase in monocytes and expectedly the absence of CD4+ T cells including FoxP3+ regulatory T cells. Surprisingly there was no increase of γδ T cells. In addition, we observed a significant decrease in immunoglobulins, B lymphocytes, and changes in the bursa morphology. Our data reveal the consequences of T cell knockouts in chickens and provide new insights into their function in vertebrates.

Weaning diet supplemented with health-promoting feed additives influences microbiota and immune response in piglets challenged with Salmonella

The aim of this study was to evaluate the potential of micronutrients and feed additives to modulate intestinal microbiota and systemic and mucosal immune responses in weaned pigs infected with Salmonella. At weaning, 32 litters of 12 piglets each were allocated to four dietary treatments: 1) control diet (CTRL), 2) CTRL supplemented with chlortetracycline (ATB), 3) CTRL supplemented with a cocktail of feed additives (CKTL); and 4) CKTL diet containing bovine colostrum in replacement of spray-dry animal plasma (CKTL+COL). The CKTL supplement included cranberry extract, encapsulated carvacrol and yeast-derived products and an enriched selenium and vitamin premix. Three weeks after weaning, four pigs per litter were orally inoculated with Salmonella Typhimurium DT104. Half of them were euthanized 3 days post-infection (dpi) and the other half, 7 dpi. The expression of IL6, TNF, IL8, monocyte chemoattractant protein 1 (MCP1), IFNG, cyclooxygenase 2 (COX2), glutathione peroxidase 2 (GPX2) and β-defensin 2 (DEFB2) showed a peaked response at 3 dpi (P < 0.05). Results also revealed that DEFB2 expression was higher at 3 dpi in CTRL and CKTL groups than in ATB (P = 0.01 and 0.06, respectively) while GPX2 gene was markedly increased at 3 and 7 dpi in pigs fed CKTL or CKTL+COL diet compared to CTRL pigs (P < 0.05). In piglets fed CKTL or CKTL+COL diet, intestinal changes in microbial communities were less pronounced after exposure to Salmonella compared to CTRL and progressed faster toward the status before Salmonella challenge (AMOVA P < 0.01). Furthermore, the relative abundance of several families was either up- or down-regulated in pigs fed CKTL or CKTL+COL diet after Salmonella challenge. In conclusion, weaning diet enriched with bovine colostrum, vitamins and mixture of feed additives mitigated the influence of Salmonella infection on intestinal microbial populations and modulate systemic and intestinal immune defences.

Production of interferon gamma and interleukin 17A in chicken T-cell subpopulations hallmarks the stimulation with live, irradiated and killed avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes colibacillosis with different clinical manifestations. The disease is associated with compromised animal welfare and results in substantial economic losses in poultry production worldwide. So far, immunological mechanisms of protection against colibacillosis are not comprehensively resolved. Therefore, the present study aimed to use an ex vivo model applying chicken mononuclear cells stimulated by live and inactivated APEC. For this purpose, an 8-color flow cytometry panel was set up to target viable chicken immune cells including CD45⁺, CD8α⁺, CD4⁺, TCR-γδ⁺, Bu-1⁺ cells and monocytes/macrophages along with the cytokines interferon gamma (IFN-γ) or interleukin 17A (IL-17A). The 8-color flow cytometry panel was applied to investigate the effect of live and two different types of inactivated APEC (formalin-killed APEC and irradiated APEC) on the cellular immune response. For that, mononuclear cells from spleen, lung and blood of 10-week-old specific pathogen-free layer birds were isolated and stimulated with live, irradiated or killed APEC. Intracellular cytokine staining and RT-qPCR assays were applied for the detection of IFN-γ and IL-17A protein level, as well as at mRNA level for spleenocytes. Ex vivo stimulation of isolated splenocytes, lung and peripheral blood mononuclear cells (PBMCs) from chickens with live, irradiated or killed APEC showed an increasing number of IFN-γ and IL-17A producing cells at protein and mRNA level. Phenotyping of the cells from blood and organs revealed that IFN-γ and IL-17A were mainly produced by CD8α⁺, TCR-γδ⁺ T cells as well as CD4⁺ T cells following stimulation with APEC. Expression level of cytokines were very similar following stimulation with live and irradiated APEC but lower when killed APEC were applied. Consequently, in the present study, an ex vivo model using mononuclear cells of chickens was applied to investigate the cellular immune response against APEC. The results suggest the relevance of IFN-γ and IL-17A production in different immune cells following APEC infection in chickens which needs to be further investigated in APEC primed birds.

Repertoire analysis of γδ T cells in the chicken enables functional annotation of the genomic region revealing highly variable pan-tissue TCR gamma V gene usage as well as identifying public and private repertoires

BACKGROUND

Despite increasing interest in γδ T cells and their non-classical behaviour, most studies focus on animals with low numbers of circulating γδ T cells, such as mice and humans. Arguably, γδ T cell functions might be more prominent in chickens where these cells form a higher proportion of the circulatory T cell compartment. The TCR repertoire defines different subsets of γδ T cells, and such analysis is facilitated by well-annotated TCR loci. γδ T cells are considered at the cusp of innate and adaptive immunity but most functions have been identified in γδ low species. A deeper understanding of TCR repertoire biology in γδ high and γδ low animals is critical for defining the evolution of the function of γδ T cells. Repertoire dynamics will reveal populations that can be classified as innate-like or adaptive-like as well as those that straddle this definition.

RESULTS

Here, a recent discrepancy in the structure of the chicken TCR gamma locus is resolved, demonstrating that tandem duplication events have shaped the evolution of this locus. Importantly, repertoire sequencing revealed large differences in the usage of individual TRGV genes, a pattern conserved across multiple tissues, including thymus, spleen and the gut. A single TRGV gene, TRGV3.3, with a highly diverse private CDR3 repertoire dominated every tissue in all birds. TRGV usage patterns were partly explained by the TRGV-associated recombination signal sequences. Public CDR3 clonotypes represented varying proportions of the repertoire of TCRs utilising different TRGVs, with one TRGV dominated by super-public clones present in all birds.

CONCLUSIONS

The application of repertoire analysis enabled functional annotation of the TCRG locus in a species with a high circulating γδ phenotype. This revealed variable usage of TCRGV genes across multiple tissues, a pattern quite different to that found in γδ low species (human and mouse). Defining the repertoire biology of avian γδ T cells will be key to understanding the evolution and functional diversity of these enigmatic lymphocytes in an animal that is numerically more reliant on them. Practically, this will reveal novel ways in which these cells can be exploited to improve health in medical and veterinary contexts.

Interaction of Salmonella Gallinarum and Salmonella Enteritidis with peripheral leucocytes of hens with different laying performance

Salmonella enterica ssp. enterica serovars Enteritidis (SE) and Gallinarum (SG) cause different diseases in chickens. However, both are able to reach the blood stream where heterophils and monocytes are potentially able to phagocytose and kill the pathogens. Using an ex vivo chicken whole blood infection model, we compared the complex interactions of the differentially host-adapted SE and SG with immune cells in blood samples of two White Leghorn chicken lines showing different laying performance (WLA: high producer; R11: low producer). In order to examine the dynamic interaction between peripheral blood leucocytes and the Salmonella serovars, we performed flow cytometric analyses and survival assays measuring (i) leucocyte numbers, (ii) pathogen association with immune cells, (iii) Salmonella viability and (iv) immune gene transcription in infected whole blood over a four-hour co-culture period. Inoculation of blood from the two chicken lines with Salmonella led primarily to an interaction of the bacteria with monocytes, followed by heterophils and thrombocytes. We found higher proportions of monocytes associated with SE than with SG. In blood samples of high producing chickens, a decrease in the numbers of both heterophils and Salmonella was observed. The Salmonella challenge induced transcription of interleukin-8 (IL-8) which was more pronounced in SG- than SE-inoculated blood of R11. In conclusion, the stronger interaction of monocytes with SE than SG and the better survivability of Salmonella in blood of low-producer chickens shows that the host-pathogen interaction and the strength of the immune defence depend on both the Salmonella serovar and the chicken line.

A Novel Approach against Salmonella: A Review of Polymeric Nanoparticle Vaccines for Broilers and Layers

This work discusses the present-day limitations of current commercial Salmonella vaccines for broilers and layers and explores a novel approach towards poultry vaccination using biodegradable nanoparticle vaccines against Salmonella. With the increasing global population and poultry production and consumption, Salmonella is a potential health risk for humans. The oral administration of killed or inactivated vaccines would provide a better alternative to the currently commercially available Salmonella vaccines for poultry. However, there are currently no commercial oral killed-vaccines against Salmonella for use in broilers or layers. There is a need for novel and effective interventions in the poultry industry. Polymeric nanoparticles could give way to an effective mass-administered mucosal vaccination method for Salmonella. The scope of this work is limited to polymeric nanoparticles against Salmonella for use in broilers and layers. This review is based on the information available at the time of the investigation.

Influence of environmental enrichment on circulating white blood cell counts and behavior of female turkeys

Under commercial conditions turkeys are housed in large groups in poorly structured environments. This leads to stress and subsequently to pecking and cannibalism. Environmental enrichment is suggested to reduce stress and feather pecking, thus leading to an increase of the overall flock health. However, the effect of increasing age on the use of enrichment elements and on the behavior repertoire as well as its correlation with health parameters has scarcely been studied. Therefore, our objective was to investigate the influence of environmental enrichment on the behavioral repertoire and on health parameters of turkeys. In 3 consecutive trials, female turkeys were housed up to 12 wk either in an unstructured (control group) or enriched environment (EE group) featuring elevated plateaus at different levels (“turkey tree”). Behavior parameters, clinical health, and immune parameters were determined at selected time points. The percentage of birds using the turkey tree increased with age up to 55 to 77% at 22 to 30 d post hatch (dph). Thereafter, the number of birds located on the turkey tree decreased to 25 to 32% at 73 to 79 dph. Feather pecking and fighting was significantly lower in the EE group compared to the control group in 2 and 3 trials, respectively (P < 0.05). The integrity of feathers and integument, scored in the head/neck, wing, and tail regions was repeatedly better in the EE birds compared to control birds at most investigated time points (P < 0.05), suggesting a reduction in stress related aggression by the use of the turkey tree. Head pecking, running and flying activity, foraging, and preening were overall comparable between the EE and the control group (P > 0.05). Humoral immunity as determined by vaccination-induced anti-Newcastle disease virus antibody titers was not affected by the turkey tree use. The flow cytometric evaluation of blood monocyte and T-lymphocyte numbers showed no repeatable difference between control and EE groups. Interestingly, compared to the control groups, EE birds displayed significantly higher numbers of circulating MHC class II⁺ lymphocytes and lower numbers of thrombocytes at various time points compared to controls (P < 0.05). This study provides clear evidence that environmental enrichment with plateaus not only leads to an altered behavioral repertoire but also modifies some of the investigated immune parameters, implying that EE may have a modulatory effect on turkeys’ immunity and overall fitness. Further studies are needed to understand the correlation between behavior and health parameters in birds more closely.

Bacterial vaccines in poultry

BACKGROUND

Poultry bacterial pathogens are mainly controlled by using high-cost sanitary measures and medical treatment. However, the drug-resistant strains of pathogens continuously emerge, and medical treatments are often ineffective. Moreover, there is increasing public objections to drug residues in poultry products. The other important type of control is the vaccination which depends on immunity. This immunological control is the major practical alternative to chemotherapy. Success of vaccines in combating poultry diseases depends mainly on the choice of the proper type of vaccines, correct time of its usage, and method of administration.The types of vaccines include attenuated live vaccines, and these vaccines were shown to be effective in inducing protection. The second type is killed vaccine or whole bacteria extracts which is less successful in providing protection compared to live vaccines. The metabolic product vaccine (toxoids) is the third type of vaccine. The recombinant DNA technique was adopted to produce the protective antigens in a sufficient amount and in cost-effective ways.

CONCLUSIONS

Protection studies against bacterial diseases were performed by using several trials: living vaccines (live attenuated vaccines; live, non-pathogenic microorganisms; live, low virulence microorganism), inactivated (killed) vaccines (heat-inactivated, chemical inactivates, radiation), metabolic product vaccines (toxoids), subunit vaccines (whole cell proteins, outer membrane proteins, purified flagellar proteins (flagellin), fimbrial proteins, pilus proteins, lipopolysaccharides), vaccines produced by recombinant deoxyribonucleic acid (DNA) technology, and DNA vaccines.

Translating 'big data': better understanding of host-pathogen interactions to control bacterial foodborne pathogens in poultry

Recent technological advances has led to the generation, storage, and sharing of colossal sets of information ('big data'), and the expansion of 'omics' in science. To date, genomics/metagenomics, transcriptomics, proteomics, and metabolomics are arguably the most ground breaking approaches in food and public safety. Here we review some of the recent studies of foodborne pathogens (Campylobacter spp., Salmonella spp., and Escherichia coli) in poultry using big data. Genomic/metagenomic approaches have reveal the importance of the gut microbiota in health and disease. They have also been used to identify, monitor, and understand the epidemiology of antibiotic-resistance mechanisms and provide concrete evidence about the role of poultry in human infections. Transcriptomics studies have increased our understanding of the pathophysiology and immunopathology of foodborne pathogens in poultry and have led to the identification of host-resistance mechanisms. Proteomic/metabolomic approaches have aided in identifying biomarkers and the rapid detection of low levels of foodborne pathogens. Overall, 'omics' approaches complement each other and may provide, at least in part, a solution to our current food-safety issues by facilitating the development of new rapid diagnostics, therapeutic drugs, and vaccines to control foodborne pathogens in poultry. However, at this time most 'omics' approaches still remain underutilized due to their high cost and the high level of technical skills required.

Emerging role of γδ T cells in vaccine-mediated protection from infectious diseases

γδ T cells are fascinating cells that bridge the innate and adaptive immune systems. They have long been known to proliferate rapidly following infection; however, the identity of the specific γδ T cell subsets proliferating and the role of this expansion in protection from disease have only been explored more recently. Several recent studies have investigated γδ T‐cell responses to vaccines targeting infections such as Mycobacterium, Plasmodium and influenza, and studies in animal models have provided further insight into the association of these responses with improved clinical outcomes. In this review, we examine the evidence for a role for γδ T cells in vaccine‐induced protection against various bacterial, protozoan and viral infections. We further discuss results suggesting potential mechanisms for protection, including cytokine‐mediated direct and indirect killing of infected cells, and highlight remaining open questions in the field. Finally, building on current efforts to integrate strategies targeting γδ T cells into immunotherapies for cancer, we discuss potential approaches to improve vaccines for infectious diseases by inducing γδ T‐cell activation and cytotoxicity.

Effect of High Dietary Manganese on the Immune Responses of Broilers Following Oral Salmonella typhimurium Inoculation

Manganese (Mn) is an essential nutrient for both host and pathogen. Recent studies have demonstrated the nutritional immunity of Mn against Salmonella infection in mammals. To investigate the effect of high dietary Mn on immune responses of broilers following Salmonella challenge, 144 1-day-old male broilers were fed a basal diet (containing 20.04 mg Mn/kg) plus an additional 40 (the control group) or 400 mg Mn/kg (the H-Mn group) for 7 days. The 72 broilers in each group were then orally inoculated with 5 × 10⁷ CFUs of Salmonella typhimurium (ATCC#14028) or phosphate-buffered saline. Peripheral blood, spleens, cecal tonsils, and bursa of Fabricius were collected from Salmonella-inoculated and Salmonella-noninoculated broilers (n = 6) at 2 days post inoculation (2 DPI) and 7 days post inoculation (7 DPI). Peripheral blood lymphocyte subpopulations were determined by flow cytometry. The messenger RNA (mRNA) abundance of genes was determined by quantitative real-time polymerase chain reaction. Salmonella counts were higher (P < 0.05) in the H-Mn group than that in the control group at 2 DPI in the cecal contents of Salmonella-inoculated broilers. High dietary Mn increased CD3⁺CD4⁺ and CD3⁺CD8⁺ percentages in the peripheral blood of Salmonella-inoculated broilers at 2 DPI. Salmonella inoculation increased interleukin (IL)-6 mRNA expression in spleens and bursa of Fabricius at 2 DPI and increased IL-1β and IL-6 mRNA expression in cecal tonsils at 7 DPI in the H-Mn group. These changes were not observed in the control group. High dietary Mn increased interferon-γ (IFN-γ) in spleens and decreased IFN-γ and IL-12 mRNA expression in cecal tonsils of Salmonella-inoculated broilers at 2 DPI. High dietary Mn decreased IL-17 mRNA expression in the bursa of Fabricius at 7 DPI, but increased this expression in cecal tonsils at 2 and 7 DPI in Salmonella-inoculated broilers. These results suggested that dietary Mn level affected T helper (Th) 1-cytokine reaction in spleens and cecal tonsils, and Th17-mediated immunity in cecal tonsils and the bursa of Fabricius of broilers when challenged with Salmonella.

Different roles of CD4, CD8 and γδ T-lymphocytes in naive and vaccinated chickens during Salmonella Enteritidis infection

Lymphocytes represent the key antigen-specific leukocyte subpopulation. Despite their importance in mounting an immune response, an unbiased description of proteins expressed by chicken lymphocytes has not been presented. In this study, we therefore intravenously infected chickens with Salmonella Enteritidis, sorted CD4, CD8 and γδ T-lymphocytes from the spleen by flow cytometry and determined the proteome of each population by LC-MS/MS. CD4 T-lymphocyte characteristic proteins included ubiquitin SUMO-like domain and BAR domain containing proteins. CD8 T-lymphocyte specific proteins were characterized by purine ribonucleoside triphosphate binding and were involved in cell differentiation, cell activation and regulation of programmed cell death. γδ T-lymphocyte specific proteins exhibited enrichment of small GTPase of Rab type and GTP binding. Following infection, inducible proteins in CD4 lymphocytes included ribosomal proteins and downregulated proteins localized to the lysosome. CD8 T-lymphocytes induced MCM complex proteins, proteins required for DNA replication and machinery for protein processing in the endoplasmic reticulum. Proteins inducible in γδ T-lymphocytes belonged to immune system response, oxidative phosphorylation and the spliceosome. In this study, we predicted the likely events in lymphocyte response to systemic bacterial infection and identified proteins which can be used as markers specific for each lymphocyte subpopulation.

Evaluation of blood monocyte and lymphocyte population in broiler chicken after vaccination and experimental challenge with Newcastle disease virus

In the present study, after vaccination and challenge with Newcastle disease virus, changes in the population of blood monocytes and lymphocytes of broiler chickens were evaluated using flow cytometry. 300 apparently healthy 1-day-old Cobb broiler chicks were divided randomly into four experimental groups (n=75). At 20days of age the chicks in group 1 and 2 were vaccinated with live B1 ND vaccine. Those in group 2 were additionally injected with a killed vaccine simultaneously and group 3 chicks received only the adjuvant of the killed vaccine. The birds in groups 1, 2 and 3 were challenged with a velogenic ND virus and those in group 4 were treated as control. Sampling was done on days 1,2,3,7 after vaccination and also on 1, 2, 3,7,14, 21 post challenge days. In this study percentage of B cell population was increased after vaccination and challenge in vaccinated birds, but CD3+ cells were decreased after vaccination and challenge, which showed B cells have more expansion than T cells. The CD4+ cell percentage in vaccinated birds was always lower than control birds. However, the percentage of CD8+ cells in vaccinated birds was increased. Results indicate increased CMI with the live NDV vaccination. In this study CD4/CD8 ratio in control birds was about 1.5 at 30days of age and it was slightly lower in vaccinated and challenged birds. The percentage of monocytes in vaccinated birds was significantly higher than control birds from 3days post vaccination to the end of the experiment.

In vitro and in vivo generation of heterophil extracellular traps after Salmonella exposure

The release of extracellular traps (ETs) by granulocytes is a unique strategy to stop the dissemination of microbial pathogens. This study was undertaken to elucidate the potential of avian granulocytes (heterophils) to form ETs that can arrest and kill Salmonella organisms. After in vitro exposure of isolated heterophils and in vivo infection of day-old chicks with Salmonella enterica subsp. enterica serovars Infantis (SI) or Enteritidis (SE), the generation of ETs as well as the trapping and survivability of Salmonella organisms in the ET meshwork were determined by means of microscopy and spectrophotometry. In vitro, heterophils were able to form ETs within 15min after SE and SI inoculation. At 120min and with a multiplicity of infection of 1 and 5, SI induced significantly more ETs and DNA release than SE. Both SE and SI were found to be associated with the ET structures. Live-dead staining showed most of the microorganisms within the extracellular scaffold alive. In vivo, heterophils were detected in cecal lumen of SE-, but not SI-infected chicks. In cecum of the SE-exposed chicks, ET formations were scarcely detected whereas intact heterophils with phagocytosed bacteria were frequently found. The results evidence the capability of heterophils to generate ETs after SE and SI exposure in vitro. However, an infection of chicks with Salmonella did not significantly induce the formation of ET structures in cecum. Thus, the process to form ETs (ETosis) seems not to be of special relevance for Salmonella defense within the cecal lumen of young chicks.

Prevention of egg contamination by Salmonella Enteritidis after oral vaccination of laying hens with Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC mutants

Vaccination of laying hens has been successfully used to reduce egg contamination by Salmonella Enteritidis, decreasing human salmonellosis cases worldwide. Currently used vaccines for layers are either inactivated vaccines or live attenuated strains produced by mutagenesis. Targeted gene deletion mutants hold promise for future vaccines, because specific bacterial functions can be removed that may improve safety and allow differentiation from field strains. In this study, the efficacy of Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains in laying hens as live vaccines was evaluated. The mutants are deficient in either the membrane channel TolC (ΔtolC) or the multi-drug efflux systems acrAB, acrEF and mdtABC (ΔacrABacrEFmdtABC). These strains have a decreased ability for gut and tissue colonization and are unable to survive in egg white, the latter preventing transmission of the vaccine strains to humans. Two groups of 30 laying hens were orally inoculated at day 1, 6 weeks and 16 weeks of age with 10⁸ cfu of either vaccine strain, while a third group was left unvaccinated. At 24 weeks of age, the birds were intravenously challenged with 5 × 10⁷ cfu Salmonella Enteritidis PT4 S1400/94. The vaccine strains were not shed or detected in the gut, internal organs or eggs, 2 weeks after the third vaccination. The strains significantly protected against gut and internal organ colonization, and completely prevented egg contamination by Salmonella Enteritidis under the conditions of this study. This indicates that Salmonella Enteritidis ΔtolC and ΔacrABacrEFmdtABC strains might be valuable strains for vaccination of layers against Salmonella Enteritidis.

Tissue colonization and circulating T lymphocytes in laying hens upon oral challenge with Salmonella enterica serovars

Evaluating the potential of Salmonella serovars for tissue colonization and egg contamination in laying hens is critical due to widespread consumption of poultry and egg-containing products. The 2009 FDA Egg Rule was implemented to target the eradication of Salmonella enterica Enteritidis (SE) from layers; however, other Salmonella serovars, such as Heidelberg (SH) and Typhimurium (ST), have also been associated with poultry-related outbreaks. We conducted this study to see if serovars other than SE could colonize in laying hens, cause egg contamination, and modulate circulating T-cell populations. Laying hens were orally gavaged with 10⁷ colony forming units (CFU) of SE, SH, or ST and assessed for colonization in spleen, ovaries, and oviduct 10 d postchallenge. Splenic colonization was similar for all the serovars; however, colonization of ovaries and oviducts was significantly higher with SH compared to SE and ST. Furthermore, SH challenge resulted in egg contamination, while SE and ST did not result in contaminated eggs. Phenotypic evaluation of peripheral blood lymphocytes showed significant reduction in CD4 cells in SH-challenged birds and lower CD8α and CD8β cells in SE-challenged birds compared to controls. Our data showed that non-SE serovars have equal or higher potential to colonize reproductive tissues of laying hens and may be accompanied by altered lymphocyte populations.

Avaliação da resposta imunológica da mucosa intestinal de frangos de corte desafiados com diferentes sorovares de Salmonella

Objetivou-se com o presente estudo comparar o efeito de diferentes sorovares de Salmonella na resposta imune local da mucosa do intestino de frangos de corte. Aos sete dias de idade, as aves foram desafiadas com os sorovares S. Enteritidis, S. Typhimurium, S. Senftenberg, S. Mbandaka e S. Minnesota. Foi observado que todos os sorovares testados foram capazes de colonizar o intestino das aves sendo possível o isolamento de Salmonella em suabes de cloaca, 48 h após inoculação. De maneira geral, as aves do grupo controle negativo, que não foram desafiados apresentaram quantidade significativamente menor de células imunológicas na mucosa intestinal do que as aves desafiadas. Porém, verificou-se que os sorovares de Salmonella, utilizados neste estudo, apresentaram diferentes efeitos sobre a dinâmica celular da mucosa do íleo e ceco e afetaram de modo diferente o ganho de peso e ganho médio diário das aves demonstrando distintos graus de patogenicidade. Os sorovares Enteritidis e Typhimurium apresentaram um efeito mais intenso tanto no desempenho quanto na mobilização de células imunológicas na mucosa intestinal de frangos de corte

Gene expression in the chicken caecum in response to infections with non-typhoid Salmonella

Chickens can be infected with Salmonella enterica at any time during their life. However, infections within the first hours and days of their life are epidemiologically the most important, as newly hatched chickens are highly sensitive to Salmonella infection. Salmonella is initially recognized in the chicken caecum by TLR receptors and this recognition is followed by induction of chemokines, cytokines and many effector genes. This results in infiltration of heterophils, macrophages, B- and T-lymphocytes and changes in total gene expression in the caecal lamina propria. The highest induction in expression is observed for matrix metalloproteinase 7 (MMP7). Expression of this gene is increased in the chicken caecum over 4000 fold during the first 10 days after the infection of newly hatched chickens. Additional highly inducible genes in the caecum following S. Enteritidis infection include immune responsive gene 1 (IRG1), serum amyloid A (SAA), extracellular fatty acid binding protein (ExFABP), serine protease inhibitor (SERPINB10), trappin 6-like (TRAP6), calprotectin (MRP126), mitochondrial ES1 protein homolog (ES1), interferon-induced protein with tetratricopeptide repeats 5 (IFIT5), avidin (AVD) and transglutaminase 4 (TGM4). The induction of expression of these proteins exceeds a factor of 50. Similar induction rates are also observed for chemokines and cytokines such as IL1β, IL6, IL8, IL17, IL18, IL22, IFNγ, AH221 or iNOS. Once the infection is under control, which happens approx. 2 weeks after infection, expression of IgY and IgA increases to facilitate Salmonella elimination from the gut lumen. This review outlines the function of individual proteins expressed in chickens after infection with non-typhoid Salmonella serovars.

Salmonella enterica in the Chicken: How it has Helped Our Understanding of Immunology in a Non-Biomedical Model Species

Salmonella infection of the chicken is important both as a source of foodborne human salmonellosis and as a source of disease in the chicken itself. Vaccination and other control strategies require an understanding of the immune response and as such have been important in understanding both mucosal immunity and more generally the response to bacterial infection. In this review, we discuss the contribution the study of avian salmonellosis has made to understanding innate immunity including the function of phagocytic cells, pattern recognition receptors, and defensins. The mucosal response to Salmonella infection and its regulation and the contribution this makes in protection against infection and persistence within the gut and future directions in better understanding the role of TH17 and Tregs in this response. Finally, we discuss the role of the immune system and its modulation in persistent infection and infection of the reproductive tract. We also outline key areas of research required to fully understand the interaction between the chicken immune system and Salmonella and how infection is maintained in the absence of substantive gastrointestinal disease.

Cytokines Expression and Nitric Oxide Production under Induced Infection to Salmonella Typhimurium in Chicken Lines Divergently Selected for Cutaneous Hypersensitivity

In the present study, the impact of Salmonella Typhimurium on cell-mediated immunity (CMI) was investigated in 5 week-old immuno divergent broiler lines selected for the high and low response to phytohemagglutinin-P. The immune response was assessed in peripheral-blood mononuclear cells (PBMCs) induced with Salmonella Typhimurium at different time intervals (0 h, 0.5 h, 2 h, 4 h, 6 h, 12 h and 24 h). The differential mRNA expression patterns of IFN-γ, IL-2 and iNOS were evaluated by quantitative real time PCR. In-vitro production of nitric oxide (NO) was also estimated in the culture supernatant and correlated with iNOS mRNA expression. Present study showed higher production of NO in the high cell-mediated line (HCMI) as compared to the low cell-mediated line (LCMI) upon stimulation with Salmonella Typhimurium. Correspondingly, higher mRNA expression of iNOS and IFN-γ were observed in high response birds (HCMI); but IL-2 was down regulated in this line compared to the low response birds (LCMI). Significantly (p<0.05) higher expression of iNOS, IFN-γ and higher production of NO in high line indicated that the selection for PHA-P response might be employed for increasing the immune competence against Salmonella Typhimurium in chicken flocks.

Alteration in lymphocytes responses, cytokine and chemokine profiles in laying hens infected with Salmonella Typhimurium

Salmonella Typhimurium has been reported to contaminate egg production across the world, but the exact nature of the immune mechanisms protective against Salmonella infection in laying hens has not been characterized at the molecular level. The experiment was conducted to determine Salmonella colonization and lymphocytes subpopulation in the ileum and spleen, and the mRNA expression of pro-inflammatory cytokines [interleukin (IL)-1β and IL-6], chemokine IL-8, and T helper (Th)1/Th2 cytokines [Interferon (IFN)-γ, IL-12 and IL-18; IL-4 and IL-10 respectively] in the cecal tonsil and spleen of Salmonella challenged hens. Forty Salmonella-free laying hens were challenged orally with Salmonella Typhimurium or phosphate-buffered saline (PBS; control). The Salmonella challenged or non-challenged hens (n=10) were sacrificed at 2 and 7 days post-infection (DPI). The lymphocyte subpopulation was determined via flow cytometric analysis in the ileum and spleen. The cecal tonsil and spleen samples were collected for mRNA expression through quantitative-RT-PCR. The Salmonella counts were higher (P<0.05) in the ileum than that in the spleen at 2 and 7DPI, and were higher (P<0.05) at 7DPI than that at 2DPI in the spleen. Salmonella challenge increased (P<0.05) ileal CD4+ and CD8α+ cells ratios at 2 and 7DPI, whereas it increased (P<0.05) splenic CD8α+ cells ratio only at 7DPI. The magnitude of increase in ileal CD8α+ cells ratio was higher (P<0.05) than that in CD4+ cells ratio. The mRNA expression of IL-1β, IL-6, IL-8, IFN-γ, IL-12 and IL-18 were significantly up-regulated in the cecal tonsil of Salmonella challenged hens, and the magnitude of increases in IL-6, IL-8 and IL-12 were significantly higher at 7DPI than that at 2DPI. However, Salmonella challenge increased (P<0.05) the mRNA expression of IL-1β, IL-10 and IL-18 at 2 and 7DPI, and IL-8 and IFN-γ mRNA only at 7DPI in the spleen. These findings demonstrated that there appeared the induction of cellular immune responses, and a Th1-cytokines reaction in the intestine and spleen of laying hens infected with Salmonella Typhimurium.

Construction of a recombinant-attenuated Salmonella Enteritidis strain secreting Escherichia coli heat-labile enterotoxin B subunit protein and its immunogenicity and protection efficacy against salmonellosis in chickens

A live attenuated Salmonella Enteritidis (SE) strain secreting Escherichia coli heat-labile enterotoxin B subunit (LTB) protein was constructed as a new vaccine candidate. The comparative effect of this vaccine candidate was evaluated with a previously reported SE vaccine, JOL919. An asd+, p15A ori plasmid containing eltB-encoding LTB was introduced into a ΔlonΔcpxRΔasd SE strain, and designated as JOL1364. In a single immunization experiment, group A chickens were orally inoculated with phosphate-buffered saline as a control, group B chickens were orally immunized with JOL919, and group C chickens were orally immunized with JOL1364. The immunized groups B and C showed significantly higher systemic, mucosal and cellular immune responses as compared to those of the control group. In addition, the immunized group C showed significantly higher mucosal and cellular immune responses as compared to those of the immunized group B at the 1st week post-immunization. In the examination of protection efficacy, the immunized groups B and C showed lower gross lesion scores in the liver and spleen, and lower bacterial counts of SE challenge strain in the liver, spleen, and caeca as compared to those of the control group. The number of SE-positive birds was significantly lower in the immunized group C as compared to that of the control group at the 14th day post-challenge. In addition, the number of birds carrying the challenge strain in the caeca was significantly lower in the immunized group C than those in the immunized group B and control group at the 7th and 14th day post-challenge. These results indicate that immunization with the JOL1364 vaccine candidate can induce higher mucosal and cellular immune responses than those of the JOL919 for efficient protection against salmonellosis.

Immunity to bacterial infection in the chicken

Bacterial infections remain important to the poultry industry both in terms of animal and public health, the latter due to the importance of poultry as a source of foodborne bacterial zoonoses such as Salmonella and Campylobacter. As such, much focus of research to the immune response to bacterial infection has been to Salmonella. In this review we will focus on how research on avian salmonellosis has developed our understanding of immunity to bacteria in the chicken from understanding the role of TLRs in recognition of bacterial pathogens, through the role of heterophils, macrophages and γδ lymphocytes in innate immunity and activation of adaptive responses to the role of cellular and humoral immunity in immune clearance and protection. What is known of the immune response to other bacterial infections and in particular infections that have emerged recently as major problems in poultry production including Campylobacter jejuni, Avian Pathogenic Escherichia coli, Ornithobacterium rhinotracheale and Clostridium perfringens are discussed.

Dynamics of the systemic components of the chicken (Gallus gallus domesticus) immune system following activation by Escherichia coli; implications for the costs of immunity

The immune response is thought to be costly and deters from growth and reproduction, but the magnitude and sources of these costs are unknown. Thus, we quantified the changes in mass of leukocytes (CD4(+) and CD8(+) T cells, Bu1(+) IgM(+) and Bu1(+) IgG(+) B cells, monocytes/macrophages, heterophils and thrombocytes) and protective plasma proteins in systemic (non-mucosal) components of adult chickens injected intravenously with dead Escherichia coli. During the first day after E. coli injection most types of blood leukocytes decreased and α-1-acid glycoprotein increased. Specific IgM, specific IgY, total IgM, Bu1(+) lymphocytes in the spleen and bone marrow and thymic CD8(+) lymphocytes increased at 5d post-injection. Quantitatively, the increases in the weight of cells and antibodies due to E. coli were dwarfed by the increase in the weight of the liver and acute phase proteins. Thus the acute phase response was markedly more costly than the subsequent adaptive response. The weight of the cells and proteins of the systemic immune system prior to challenge was 0.14% of body weight. Following E. coli injection, the additional weight of the immune components and the hypertrophy of the liver resulted in a 3.6-fold increase in weight which is equivalent to 18.5% of a large egg.

A mathematical model representing cellular immune development and response to Salmonella of chicken intestinal tissue

The aim of this study was to create a dynamic mathematical model of the development of the cellular branch of the intestinal immune system of poultry during the first 42 days of life and of its response towards an oral infection with Salmonella enterica serovar Enteritidis. The system elements were grouped in five important classes consisting of intra- and extracellular S. Enteritidis bacteria, macrophages, CD4+, and CD8+ cells. Twelve model variables were described by ordinary differential equations, including 50 parameters. Parameter values were estimated from literature or from own immunohistochemistry data. The model described the immune development in non-infected birds with an average R² of 0.87. The model showed less accuracy in reproducing the immune response to S. Enteritidis infection, with an average R² of 0.51, although model response did follow observed trends in time. Evaluation of the model against independent data derived from several infection trials showed strong/significant deviations from observed values. Nevertheless, it was shown that the model could be used to simulate the effect of varying input parameters on system elements response, such as the number of immune cells at hatch. Model simulations allowed one to study the sensitivity of the model outcome for varying model inputs. The initial number of immune cells at hatch was shown to have a profound impact on the predicted development in the number of systemic S. Enteritidis bacteria after infection. The theoretical contribution of this work is the identification of responses in system elements of the developing intestinal immune system of poultry obtaining a mathematical representation which allows one to explore the relationships between these elements under contrasting environmental conditions during different stages of intestinal development.

Distinct intensity of host-pathogen interactions in Chlamydia psittaci- and Chlamydia abortus-infected chicken embryos

Factors and mechanisms determining the differences in virulence and host specificity between the zoonotic agents Chlamydia psittaci and Chlamydia abortus are still largely unknown. In the present study, two strains were compared for their invasiveness, virulence, and capability of eliciting an immune response in chicken embryos. On breeding day 10, embryonated chicken eggs were inoculated with 5 × 10(4) inclusion-forming units. As shown by immunohistochemistry and quantitative real-time PCR, C. psittaci displayed a significantly better capability of disseminating in the chorioallantoic membrane (CAM) and internal organs than C. abortus. The higher infectious potential of C. psittaci in birds was underlined by significantly higher mRNA expression rates of essential chlamydial genes, such as incA, groEL (in CAM, liver, and spleen), cpaf, and ftsW (in CAM). Although the immune responses to both pathogens were similar, C. psittaci elicited higher macrophage numbers and a stronger expression of a subset of immune-related proteins. The data imply that invasiveness of Chlamydia spp. and propagation in the host are not solely dependent on the level of host immune response but, even to a greater extent, on the expression of bacterial factors related to virulence. The fact that C. psittaci has coped far better than C. abortus with the avian embryo's response by upregulating essential genes may be a key to understanding the mechanisms underlying host adaptation and etiopathology.

Immune markers and correlates of protection for vaccine induced immune responses

Vaccines have been a major innovation in the history of mankind and still have the potential to address the challenges posed by chronic intracellular infections including tuberculosis, HIV and malaria which are leading causes of high morbidity and mortality across the world. Markers of an appropriate humoral response currently remain the best validated correlates of protective immunity after vaccination. Despite advancements in the field of immunology over the past few decades currently there are, however, no sufficiently validated immune correlates of vaccine induced protection against chronic infections in neither human nor veterinary medicine. Technological and conceptual advancements within cell-mediated immunology have led to a number of new immunological read-outs with the potential to emerge as correlates of vaccine induced protection. For T(H)1 type responses, antigen-specific production of interferon-gamma (IFN-γ) has been promoted as a quantitative marker of protective cell-mediated immune responses over the past couple of decades. More recently, however, evidence from several infections has pointed towards the quality of the immune response, measured through increased levels of antigen-specific polyfunctional T cells capable of producing a triad of relevant cytokines, as a better correlate of sustained protective immunity against this type of infections. Also the possibilities to measure antigen-specific cytotoxic T cells (CTL) during infection or in response to vaccination, through recombinant major histocompatibility complex (MHC) class I tetramers loaded with relevant peptides, has opened a new vista to include CTL responses in the evaluation of protective immune responses. Here, we review different immune markers and new candidates for correlates of a protective vaccine induced immune response against chronic infections and how successful they have been in defining the protective immunity in human and veterinary medicine.

Cytokine signaling in splenic leukocytes from vaccinated and non-vaccinated chickens after intravenous infection with Salmonella enteritidis

In order to design a new Salmonella enterica vaccine, one needs to understand how naive and immune chickens interact differently when exposed to S. enterica. In this study we therefore determined the immune response of vaccinated and non-vaccinated chickens after intravenous infection with Salmonella enterica serovar Enteritidis (S. Enteritidis). Using flow cytometry we showed that 4 days post infection (DPI), counts of CD4 and B-lymphocytes did not change, CD8 and γδ T-lymphocytes decreased and macrophages and heterophils increased in the spleen. When vaccinated and non-vaccinated chickens were compared, only macrophages and heterophils were found in significantly higher counts in the spleens of the non-vaccinated chickens. The non-vaccinated chickens also expressed higher anti-LPS antibodies than the vaccinated chickens. The expression of interleukin (IL)1β, IL6, IL8, IL18, LITAF, IFNγ and iNOS did not exhibit any clear pattern in the cells sorted from the spleens of vaccinated or non-vaccinated chickens. Only IL17 and IL22 showed a differential expression in the CD4 T-lymphocytes of the vaccinated and non-vaccinated chickens at 4 DPI, both being expressed at a higher level in the non-vaccinated chickens. Due to a similar IFNγ expression in the CD4 T-lymphocytes in both the vaccinated and non-vaccinated chickens, and a variable IL17 expression oscillating around IFNγ expression levels, the IL17∶IFNγ ratio in CD4 T-lymphocytes was found to be central for the outcome of the immune response. When IL17 was expressed at higher levels than IFNγ in the non-vaccinated chickens, the Th17 immune response with a higher macrophage and heterophil infiltration in the spleen dominated. However, when the expression of IL17 was lower than that of IFNγ as in the vaccinated chickens, the Th1 response with a higher resistance to S. Enteritidis infection dominated.

Immunogenicity of a Salmonella Enteritidis mutant as vaccine candidate and its protective efficacy against salmonellosis in chickens

A novel Salmonella Enteritidis (SE) vaccine candidate strain, JOL919 was constructed by deleting the lon and cpxR genes from a wild-type SE using an allelic exchange method. The study was carried out to evaluate the strain as a vaccine candidate against salmonellosis. The strain showed the enhanced macrophage invasion, early bacterial clearance and higher immune responses as compared to the other mutants, JOL917 (Δlon) and JOL918 (ΔcpxR), and the wild type. In further analysis, the chickens immunized with JOL919 showed a significant increase in plasma IgG and intestinal secretory IgA levels, which was an indication of robust humoral and mucosal immune responses induced by the candidate. The lymphocyte proliferation response and CD45(+)CD3(+) T cells, associated with an activation of T helper and cytotoxic cells, were also significantly increased in the immunized group, which indicated that the candidate also induced cellular immune responses. The immune cell influx into caecal tissues analyzed by immunohistochemistry showed that CD8(+) T cells were predominated in the immunized group, suggesting that the candidate can clear the invaded pathogen in the intestines by a more direct way involving cytotoxic activity. By the examination of the protection efficacy measured by observations of gross lesions in the organs and bacterial recovery, the candidate can provide an efficient protection upon virulent challenge.

Characterization of avian γδ T-cell subsets after Salmonella enterica serovar Typhimurium infection of chicks

Avian γδ T lymphocytes are frequently found in blood and organs and are assumed to be crucial to the immune defense against Salmonella infections of chicks. To elucidate the so-far-unknown immunological features of subpopulations of avian γδ T cells in the course of infection, day-old chicks were infected orally with Salmonella enterica serovar Typhimurium. Until 11 days after infection, the occurrence as well as transcription of the CD8 antigen and immunologically relevant protein genes of CD8α(-) and CD8α(+high) (CD8αα(+) CD8αβ(+)) γδ cells were analyzed using flow cytometry and quantitative real-time reverse transcription-PCR (RT-PCR) with blood, spleen, thymus, and cecum samples. After infection, an increased percentage of CD8α(+high) γδ T lymphocytes was found in blood, in spleen, and, with the highest values and most rapidly, in cecum. Within the CD8α(+high) subset, a significant rise in the number of CD8αα(+) cells was accompanied by enhanced CD8α antigen expression and reduced gene transcription of the CD8β chain. CD8αα(+) and CD8αβ(+) cells showed elevated transcription for Fas, Fas ligand (FasL), interleukin-2 receptor α (IL-2Rα), and gamma interferon (IFN-γ). While the highest fold changes in mRNA levels were observed in CD8αβ(+) cells, the mRNA expression rates of CD8αβ(+) cells never significantly exceeded those of the CD8αα(+) cells. In conclusion, both CD8α(+high) γδ T-cell subpopulations (CD8αα(+) and CD8αβ(+)) might be a potential source of IFN-γ in Salmonella-infected chicks. However, due to their prominent frequency in blood and organs after infection, the avian CD8αα(+) γδ T-cell subset seems to be unique and of importance in the course of Salmonella Typhimurium infection of very young chicks.

Immune response induced by ppGpp-defective Salmonella enterica serovar Gallinarum in chickens

To protect chickens from typhoid caused by Salmonella enterica serovar Gallinarum (S. Gallinarum), the attenuated 9R strain has been used in the field as a vaccine. However, safety concerns have been raised because the mutations in 9R are undefined while its efficacy is still a question under debate. A global regulator, ppGpp, synthesized by RelA and SpoT, has been shown to induce various virulence genes in S. Gallinarum (Jeong et al., 2008). In this study, two mutant strains defective in ppGpp-synthesis were constructed in wild-type S. Gallinarum (ΔppGpp) and 9R strain (9R-ΔppGpp) backgrounds and tested as live vaccines in chickens. After oral inoculation, the LD(50) values of ΔppGpp and 9R-ΔppGpp were approximately 5×10(10) colony forming unit (CFU) similarly as 9R strain, which was ∼10(5)-fold higher than that of the wildtype S. Gallinarum strain. Immunological analyses revealed immunization with either of the two attenuated ppGpp-defective strains induced significant antibody responses, the production of antibody-secreting B cells in blood, proliferation of CD4+ and CD8+ T cells in the spleen, and splenic expression of proinflammatory cytokines, such as IFN-γ and TGF-β4, at levels comparable to the 9R strain. Chickens immunized with the mutants (1×10(8) CFU) were 80% protected against oral challenge with 1×10(9) wild-type virulent bacteria (4,000-fold LD(50) dose), similar to the level of protection achieved by 9R immunization. Based on these data, live attenuated ΔppGpp-defective strains may serve as novel vaccines to control fowl typhoid in chickens.

Salmonella enteritidis ghost vaccine induces effective protection against lethal challenge in specific-pathogen-free chicks

Bacterial ghosts (BGs) are empty bacterial envelopes generated by expulsion of the bacterial genome and cytoplasmic contents from bacterial cells, and the process is mediated by lysis protein E encoded on bacteriophage PhiX174. BGs represent a new approach in vaccine development and have been applied to a variety of gram-negative bacterial vaccine candidates. In this study, a BG vaccine generated from Salmonella enteritidis (S. enteritidis) strain DH091 was prepared using the highly efficient plasmid, pBV-mE. The efficacy of the BG vaccine was tested using 75 chicks (Gallus gallus) kept under specific pathogen-free (SPF) conditions. A comprehensive evaluation of the immune response, including humoral and cellular immune responses, interferon-γ (IFN-γ) and interleukin-4 (IL-4) production, and histopathology of various tissues, was performed in BG-vaccinated animals subsequently challenged with S. enteritidis. The results were compared with animals that were immunized with the inactivated vaccine. S. enteritidis ghosts not only promoted the generation of high titer antibodies and IFN-γ and IL-4 production but also stimulated a significant increase in CD8(+) and CD4(+) T lymphocytes. In particular, the dramatic increase in CD8(+) T cells indicated that the vaccine was able to induce clearance of intracellular Salmonella. The protective effects of BG vaccination in SPF chicks against 5×10(9) colony forming units of S. enteritidis were a result of the induction of a more effective immune response than that observed with the inactivated vaccine. These findings demonstrate the potential of S. enteritidis ghosts to be used as effective vaccines.

Induction of a homologous and heterologous invasion-inhibition effect after administration of Salmonella strains to newly hatched chicks

Administration of live Salmonella strains to day-old chicks provides protection against infection within hours by intestinal colonisation-inhibition. However, the extent to which the oral application of live Salmonella wild-type or vaccine strains may induce an early invasion-inhibition effect is unknown. Potentially protective pre-treatment strains of Salmonella Enteritidis and Infantis were examined for their ability (i) to colonise the caeca, to invade the liver, to induce an influx of granulocytes in caecal mucosa and, (ii) for their capacity to inhibit the systemic invasion of homologous and heterologous Salmonella challenge organisms. The highly invasive strain Salmonella Enteritidis induced a strong influx of heterophils in the caecal mucosa followed by a complete invasion-inhibition of both homologous and heterologous Salmonella challenge organisms administered 24h later. Pre-treatment with a less invasive Salmonella Infantis resulted in a lower influx of granulocytes in the caecal tissue followed by a complete invasion-inhibition of the homologous serovar Infantis but only an incomplete invasion-inhibition of heterologous serovars. This invasion-inhibition effect has not been described previously in chickens and should be considered in the development of novel live Salmonella vaccines to prevent an early invasion of extra-intestinal organs by Salmonella challenge organisms in young chicks.

Flow cytometric assessment of antigen-specific proliferation in peripheral chicken T cells by CFSE dilution

Carboxyfluorescein succinimidyl ester (CFSE) dilution is a well established method for analysis of dividing cells by flow cytometry. In other species the method has been extensively used in the study of antigen-specific T cells. The purpose of this study was to apply the method to chicken peripheral mononuclear blood cells (PBMC) and to evaluate and optimize its performance in relation to detection of vaccine-induced chicken T cells specific for Newcastle disease virus (NDV). The method was based on analysis of CFSE dilution upon ex vivo recall stimulation with whole vaccine antigen. Analysis of proliferation was combined with the use of monoclonal antibodies directed against the lymphocyte surface markers CD4 and CD8 in order to phenotype the responding cells. Problems with nonspecific background proliferation especially in the CD8 compartment were significantly reduced by replacing medium containing fetal calf serum with serum-free medium. It was rendered probable that antigen-specific cellular immunity can be assessed by this method as NDV-vaccinated chickens showed a significantly higher proliferative capacity than age-matched naïve controls. Furthermore it was shown that the recall stimulation lead to a proliferative response in T cells expressing αβ-type TCRs but also those expressing the γδ-type. In summary, the method was found challenging but nevertheless useful to quantify the proliferative response of chicken antigen-specific T cells. Further investigations though, are needed in order to prove what cell subsets are true antigen-specific responders and what cells are bystander activated. Nevertheless, the method is expected to be a valuable tool to evaluate and quantify vaccine responses to current and new chicken vaccines in the future.