Identification of CpG oligodeoxynucleotide motifs that stimulate nitric oxide and cytokine production in avian macrophage and peripheral blood mononuclear cells

Effects of in ovo supplementation of selenium (Se) and zinc (zn) on hatchability and production performance of broiler chickens

The current research was conducted to assess the effect of in ovo feeding (IOF) of selenium (Se) and zinc (Zn) on hatchability, production performance, liver, intestinal morphology, antioxidant levels and expression levels of immune-related genes in broiler chickens. A total of 400 fertilized eggs were equally divided into four groups: control (non-injected), sham (in ovo injection of 0.75% NaCl), Se (@ 1.5 µg/egg in ovo injection) and Zn (500 µg/egg in ovo injection) groups respectively. On the seventeenth day of incubation, treatment solutions were administered into amniotic fluid of fertilized eggs. The results revealed that Se and Zn supplementation significantly (P < 0.05) enhanced hatchability, post-hatch growth, organ development, and liver antioxidant capability. Histopathological examination revealed a typical hepatocyte morphology, well-arranged cells, and a significant (P < 0.05) decrease in apoptosis in both selenium and zinc groups. Additionally, selenium and zinc produced auspicious effects on intestinal epithelium and villi surface area. Interestingly, our results revealed that IOF of Se and Zn modulated the expression of immune-related genes in comparison to the control and sham groups. Conclusively, IOF of Se and Zn augmented health and productivity by enhancing the cellular immunity in the broiler chickens, thus IOF can be utilized as an effective strategy to promote health and immunity in broiler chickens.

Effects of in ovo injection of bacterial peptides and CpG-ODN on Salmonella enterica serovar Heidelberg infection in specific pathogen-free (SPF) chicks

RESEARCH HIGHLIGHTS

Peptides + CpG-ODN reduced SH in caeca at the first week post-infection.Administered formulations did not reduce SH-faecal excretion.Levels of intestinal IgA were similar between all groups.CpG-ODN improved some parameters associated with chick intestinal health.

Screening of Optimal CpG-Oligodeoxynucleotide for Anti-Inflammatory Responses in the Avian Macrophage Cell Line HD11

CpG-oligodeoxynucleotides (.

CpG-ODNs

) have been shown to possess immunostimulatory features in both mammals and birds. However, compared to their proinflammatory effects, little is known about the anti-inflammatory responses triggered by CpG-ODN in avian cells. Hence, in this study, the anti-inflammatory response in the chicken macrophage cell line HD11 was characterized under stimulation with five types of CpG-ODNs: CpG-A₁₅₈₅, CpG-A_D35, CpG-B₁₅₅₅, CpG-B_K3, and CpG-C₂₃₉₅. Single-stimulus of CpG-B₁₅₅₅, CpG-B_K3, or CpG-C₂₃₉₅ induced interleukin (IL)-10 expression without causing cell injury. The effects of pretreatment with CpG-ODNs before subsequent lipopolysaccharide stimulation were also evaluated. Interestingly, pretreatment with only CpG-C₂₃₉₅ resulted in high expression levels of IL-10 mRNA in the presence of lipopolysaccharide. Finally, gene expression analysis of inflammation-related cytokines and receptors revealed that pre-treatment with CpG-C₂₃₉₅ significantly reduced the mRNA expression of tumor necrosis factor-α, IL-1β, IL-6, and Toll-like receptor 4. Overall, these results shed light on the anti-inflammatory responses triggered by CpG-C₂₃₉₅ stimulation through a comparative analysis of five types of CpG-ODNs in chicken macrophages. These results also offer insights into the use of CpG-ODNs to suppress the expression of proinflammatory cytokines, which may be valuable in the prevention of avian infectious diseases in the poultry industry.

Development of a Nanoparticle Multiepitope DNA Vaccine against Virulent Infectious Bronchitis Virus Challenge

To develop a safe and effective nanoparticle (NP) multiepitope DNA vaccine for controlling infectious bronchitis virus (IBV) infection, we inserted the multiepitope gene expression box SBNT into a eukaryotic expression vector pcDNA3.1(+) to construct a recombinant plasmid pcDNA/SBNT. The NP multiepitope DNA vaccine pcDNA/SBNT-NPs were prepared using chitosan to encapsulate the recombinant plasmid pcDNA/SBNT, with a high encapsulation efficiency of 94.90 ± 1.35%. These spherical pcDNA/SBNT-NPs were 140.9 ± 73.2 nm in diameter, with a mean ζ potential of +16.8 ± 4.3 mV. Our results showed that the chitosan NPs not only protected the plasmid DNA from DNase degradation but also mediated gene transfection in a slow-release manner. Immunization with pcDNA/SBNT-NPs induced a significant IBV-specific immune response and partially protected chickens against homologous IBV challenge. Therefore, the chitosan NPs could be a useful gene delivery system, and NP multiepitope DNA vaccines may be a potential alternative for use in the development of a novel, safe, and effective IBV vaccine.

Broiler Chickens with 1950s Genetics Display a Stable Immune Profile as Measured by Kinome, mRNA Expression, and Metabolism when Stimulated Early in Life with CpG

Significant changes in growth potential and feed conversion have been bred into the modern broiler chicken for well over 60 yr. These metabolic changes have had significant effects on the immune performance as well. To better understand these genetic differences in immunometabolism we studied the immune response of the modern broiler and the Athens Canadian Random Bred (ACRB) heritage broiler strain. We injected newly hatched modern broiler and ACRB chicks intraabdominally with CpG oligonucleotide, an immunostimulatory synthetic oligonucleotide. We conducted species-specific kinome array analysis and gene expression analysis on jejunum and cecal tonsil tissue. We also performed metabolic analysis of blood cells. In the modern birds, there is an initial inflammatory response to the injection at d 3 post-hatch with activation of PI3K-Akt, JAK-STAT, and NF-κB signaling, and IL-1β and IL-6 mRNA expression. By d 15 post-hatch this response changed to deactivation and downregulation of these immune responses in modern but not heritage broilers. Metabolic analysis showed an increase in glycolysis in peripheral blood mononuclear cells from modern birds given CpG, but no difference in ACRB. These results show that the ACRB birds may have a less inflammatory and more stable immune profile in response to immune stimulation than the modern broilers, possibly resulting in a more disease resistant phenotype overall.

Immunomodulatory Potential of Tinospora cordifolia and CpG ODN (TLR21 Agonist) against the Very Virulent, Infectious Bursal Disease Virus in SPF Chicks

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), is characterized by severe immunosuppression in young chicks of 3 to 6 week age group. Although vaccines are available to prevent IBD, outbreaks of disease are still noticed in the field among vaccinated flocks. Further, the birds surviving IBD become susceptible to secondary infections caused by various viral and bacterial agents. This study assessed the immunoprophylactic potential of Cytosine-guanosinedeoxynucleotide (CpG) oligodeoxynucleotides (ODN) and Tinospora cordifolia stem aqueous extract in the specific pathogen free (SPF) chicks, experimentally infected with very virulent IBDV (vvIBDV). Both of these agents (CpG ODN and herbal extract) showed significant increase in the IFN-γ, IL-2, IL-4, and IL-1 levels in the peripheral blood mononuclear cells (PBMCs) (p < 0.05) of chickens in the treatment groups following IBD infection.Further we found significant reduction in mortality rate in vvIBDV infected chicks treated with either, or in combination, compared with the birds of control group. Additionally, the adjuvant or immune enhancing potential of these two immunomodulatory agents with the commercially available IBDV vaccine was determined in chicks. The augmentation of vaccine response in terms of an enhanced antibody titer after vaccination, along with either or a combination of the two agents was noticed. The findings provide a way forward to counter the menace of IBDV in the poultry sector through use of these herbal or synthetic immunomodulatory supplements.

Co-administration of toll-like receptor (TLR)-3 and 4 ligands augments immune response to Newcastle disease virus (NDV) vaccine in chicken

Toll-like receptors (TLRs) are pattern recognition receptors (PRRs) that mediate first line of host defence to pathogens. TLR agonists are potent immunostimulatory agents that help to prime a robust adaptive immune response. In the present study, adjuvant potential of Poly I:C and lipopolysaccharide (LPS) were evaluated with live Newcastle disease virus (NDV) vaccine. Cornish chickens were immunized with live Newcastle disease virus (NDV) vaccine (R2B-mesogenic strain) adjuvanted either with Poly I:C (TLR3 agonist) or LPS-TLR4 agonist and both. Humoral Immune response to ND vaccine was evaluated through haemagglutination inhibition (HI) test and ELISA, while the cellular immune response (CMI) was quantified by lymphocyte transformation test (LTT). IL-1β cytokine mRNA levels in spleen tissue were also quantified by real time PCR. The results suggest that TLR3 and TLR4 agonists are an efficient immune-stimulators separately, as LPS co-administered group has shown significantly higher serum titre on second week post-immunization and Poly I:C group on third week post-immunization both by HI and ELISA (P < 0.01), however, the combined administration of both LPS and Poly I:C did not give any complementary effect on serum titre. There were no significant differences in stimulation indices (SI) and IL-1β cytokine levels between groups at different intervals post-immunization. Hence, TLR agonists LPS followed by Poly I:C could be used as adjuvant to enhance the immune response to NDV vaccine in chicken.

Combination of TLR2 and TLR3 agonists derepress infectious bursal disease virus vaccine-induced immunosuppression in the chicken

Live intermediate plus infectious bursal disease virus (IBDV) vaccines (hot vaccines) are used for protection against the virulent IBDV strains in young chickens. We evaluated the potential of Toll-like receptor (TLR) agonists to alleviate hot vaccine-induced immunosuppression. The combination of Pam3CSK4 and poly I:C synergistically upregulated IFN-β, IFN-γ, IL-12, IL-4, and IL-13 transcripts and cross-inhibited IL-1β, IL-10, and iNOS transcripts in the chicken peripheral blood mononuclear cells (PBMCs) as analyzed by quantitative real-time PCR. Further, four-week old specific pathogen free White Leghorn chickens (n = 60) were randomly divided into six groups and either immunized with hot IBDV vaccine with or without Pam3CSK4 and/or poly I:C or not vaccinated to serve as controls. The results indicated that poly I:C alone and in combination with Pam3CSK4 alleviated vaccine-induced immunosuppression, as evidenced by greater weight gain, increased overall antibody responses to both sheep erythrocytes and live infectious bronchitis virus vaccine, upregulated IFN-γ transcripts and nitric oxide production by PBMCs (P < 0.05), and lower bursal lesion score in the experimental birds. In conclusion, poly I:C alone and its combination with Pam3CSK4 reduced the destruction of B cells as well as bursal damage with restoration of function of T cells and macrophages when used with a hot IBDV vaccine.

Carbon nanotubes significantly enhance the biological activity of CpG ODN in chickens

Synthetic unmethylated cytidine-phosphate-guanosine oligodeoxynucleotides (CpG ODN) is an effective immune stimulant in chicken. To be effective CpG dosage requirement is high. High dosage increases cost of treatment and introduces toxicity. A delivery system using multi-walled carbon nanotubes (MWCNT) is utilized in this study to aid in lowering the effective dose of the immune stimulant. CpG ODNs were attached non-covalently in different ways to multi-walled carbon nanotubes (MWCNT). We assessed and selected an appropriate linking method of CpG ODN with MWCNT followed by cellular uptake studies to establish that MWCNT-conjugated CpG ODNs were delivered better than free CpG ODNs into the cell. It was observed that MWCNT-conjugated CpG ODNs were equally effective in priming the cells in vitro at 1000-fold less concentration than free CpG ODN. In vivo studies revealed that a significantly lower dose of CpG ODN, when given subcutaneously, was enough to protect chickens from a lethal challenge of bacteria. The mechanism of immune stimulation was examined by in vivo cell recruitment and in vitro cytokine production studies. MWCNT-conjugated CpG ODNs are significantly more efficacious and less toxic than free CpG ODN to qualify as a potential immune stimulant.

Resiquimod enhances mucosal and systemic immunity against avian infectious bronchitis virus vaccine in the chicken

Adjuvant enhancing mucosal immune response is preferred in controlling many pathogens at the portal of entry. Earlier, we reported that a toll-like-receptor 7 (TLR7) agonist, resiquimod (R-848), stimulated the systemic immunity when adjuvanted with the inactivated Newcastle disease virus vaccine in the chicken. Here, we report the effect of R-848 when adjuvanted with live or inactivated avian infectious bronchitis virus (IBV) vaccines with special emphasis on mucosal immunity. Specific pathogen free (SPF) chicks (n = 60) were equally divided into six groups at two weeks of age and immunized with either inactivated or live IBV vaccine adjuvanted with or without R-848. Groups that received either PBS or R-848 served as control. A booster was given on 14 days post-immunization (dpi). R-848 enhanced the antigen specific humoral and cellular immune responses when co-administered with the vaccines as evidenced by an increase in the antibody titre in ELISA and stimulation index in lymphocyte transformation test (LTT) till 35 dpi and increased proportion of CD4+ and CD8+ T cells on 21 dpi in the flow cytometry. Interestingly, it potentiated the IgA responses in the tear and intestinal secretions when used with both live and inactivated IBV vaccines. The combination of IBV vaccine with R-848 significantly up-regulated the transforming growth factor beta 4 (TGFβ4) transcripts in the peripheral blood mononuclear cells (PBMCs) than that of the respective vaccine per se. An enhanced secretory IgA response is likely due to the up-regulation of TGFβ4, which is responsible for class switching to IgA. In conclusion, co-administration of R-848 with inactivated or live IBV vaccine enhanced the systemic as well as mucosal immune responses in the chicken.

Synergistic effect of co-stimulation of membrane and endosomal TLRs on chicken innate immune responses

Toll-like receptor (TLR) ligands (TLR-Ls) are critical activators of immunity and are successfully being developed as vaccine adjuvants in both mammals and birds. In this study, we investigated the synergistic effect of co-stimulation of membrane and endosomal TLRs on the innate immune responses using chicken bone marrow-derived macrophages (BMMs), and studied the effect of age on the induction of innate responses. BMMs from 1 and 4-week-old birds were stimulated with Pam3Cys-SK4 (PCSK; TLR2), synthetic monophosphoryl lipid A (MPLA), Di[3-deoxy-d-manno-octulosonyl]-lipid A ammonium salt (KLA; TLR4), Gardiquimod, Resiquimod (R848; TLR7), CpG class B and C (TLR21). Nitric oxide (NO) production and mRNA levels of IL-1β, IL-10 and IL-12p40 showed macrophages from 4-week-old birds showed more sensitive responses compared to 1-week-old birds. The most potent TLR-Ls, PCSK, MPLA and CpG B were used to study the effect of co-stimulation on macrophages. Co-stimulation with TLR21 and TLR4 synergistically up-regulated inflammatory-related genes, as well as NO production. However, incubation of splenocytes with PCSK, MPLA and CpG B did not induce cell proliferation. Moreover, treatment with CpG B led to significant cell death.

In Ovo Administration of CpG ODN Induces Expression of Immune Response Genes in Neonatal Chicken Spleen

Introduction

Due to their immunostimulatory properties TLR ligands are used prophylactically to protect against a variety of viral and bacterial pathogens in mammals. Knowledge of the molecular and functional aspects of TLRs is essential for a better understanding of the immune system and resistance to diseases in birds. For that reason, this study attempted to determine the impact of TLR21 stimulation by its synthetic ligand (CpG ODN, class B) on the chicken immune system.

Material and Methods

Sixty embryonated chicken eggs were randomly allocated into three groups (control and two experimental groups). On day 18 of embryonic development, chickens in one experimental group were administered in ovo a low dose of CpG ODN and the birds of the second experimental group were given a high dose of the ligand. Spleens were collected at 1, 2, 5, and 10 days post-hatching (dph) for analysis of IFN-α, IFN-β, IFN-γ, IL-6, and IL-10 expression using qRT-PCR.

Results

Significant differences were observed in mRNA expression levels of all the measured cytokines associated with the modulation and regulation of the immune response at different time points.

Conclusion

The obtained data clearly demonstrate that immune response induction takes place after in ovo administration of class B CpG ODN, and that the ligand has the ability to induce cytokine responses in neonatal chicken spleen.

Identification of new CpG oligodeoxynucleotide motifs that induce expression of interleukin-1β and nitric oxide in avian macrophages

Unmethylated CpG motifs are known to stimulate mammalian toll-like receptor-9 expressing cells such as macrophages. However, the magnitude of immune-stimulation by CpG-motif can be sequence- and host-specific, implying the importance of identifying new immune-stimulatory motifs. This study aimed to determine the frequency distribution of 256 unique hexamers CpG-motifs in the Salmonella genome and to characterize their immune-stimulatory activity in avian host. We synthesized 256 CpG oligodeoxynucleotides (CpG-ODNs) each containing triplicates of a unique hexamer CpG-motif and tested their ability to induce expression of pro-inflammatory cytokine IL-1β in avian macrophages using q-RT PCR in four rounds of screening assays. CpG-ODNs that induced significantly higher IL-1β expression were also subjected to Griess assay to determine their ability to induce nitric oxide (NO) production in avian macrophages. This analysis resulted in identification of 7 CpG-ODNs that consistently induced IL-1β expression and NO production in avian macrophages at a level similar to the expression achieved using commercially available PTO-CpG-ODN 2007 and LPS derived from Salmonella. To the best of our knowledge, this is the first report showing comprehensive screening of all possible unique CpG hexamer (n=256) motifs for their ability to induce IL-1β expression and NO production in avian macrophages. We also show that the newly identified CpG-motifs with high immune-stimulatory activity are widely distributed in Salmonella genome. The CpG-ODNs identified in this study may serve as promising immunoprophylactics to potentiate innate responses in chickens against Salmonella and other infectious agents.

Toll-like receptor (TLR)21 signalling-mediated antiviral response against avian influenza virus infection correlates with macrophage recruitment and nitric oxide production

Cytosine-guanosinedeoxynucleotide (CpG) DNA can be used for the stimulation of the toll-like receptor (TLR)21 signalling pathway in avian species which ultimately leads to up-regulation of gene transcription for pro-inflammatory molecules including nitric oxide and recruitment of innate immune cells. The objective of this study was to determine the antiviral effect of NO, produced in response to in ovo delivery of CpG DNA, against avian influenza virus (AIV) infection. We found that when CpG DNA is delivered at embryo day (ED)18 in ovo and subsequently challenged with H4N6 AIV at ED19 pre-hatch and day 1 post-hatching, CpG DNA reduces H4N6 AIV replication associated with enhanced NO production and macrophage recruitment in lungs. In vitro, we showed that NO originating from macrophages is capable of eliciting an antiviral response against H4N6 AIV infection. This study provides insights into the mechanisms of CpG DNA-mediated antiviral response, particularly against AIV infection in avian species.

Differential Regulation of chTLR3 by Infectious Bursal Disease Viruses with Different Virulence In Vitro and In Vivo

Toll-like receptor 3 (TLR3) is one of the TLRs whose ligand is double-stranded RNA (dsRNA). Infectious bursal disease virus (IBDV) is a dsRNA virus that could be recognized by TLR3. The purpose of this study was to determine the role of the virulence of IBDV on the expression of chicken TLR3 (chTLR3). For this purpose, the levels of chTLR3 expression and its downstream effectors, Interferon β (IFN-β) and Interleukin 8 (IL-8), were detected and analyzed after infection of IBDV field isolates with differential virulence in vitro (chicken embryo fibroblast and/or chicken peripheral blood mononuclear cells) and in vivo (commercial Three-Yellow chicken). The results showed that chTLR3 was activated by IBDV, resulting in the expression of antiviral IFN-β and chemokine IL-8. The expression of chTLR3, IFN-β, and IL-8 correlated well with the virulence of IBDV as the more virulent the IBDV strain that was used, the more pronounced was the expression of chTLR3, IFN-β, and IL-8. These results suggest that chTLR3 is involved in the pathogenesis of IBDV in commercial chickens and its downstream effectors (IFN-β and IL-8) might play an important role in this process.

Activation of toll-like receptor signaling pathways leading to nitric oxide-mediated antiviral responses

Toll-like receptors (TLRs), well-characterized pattern-recognizing receptors of the innate arm of the immune system, are vital in detecting pathogen-associated molecular patterns (PAMPs). The TLR-PAMP interaction initiates an intracellular signaling cascade, predominantly culminating in upregulation of antiviral components, including inducible nitric oxide synthase (iNOS). After activation, various TLR pathways can promote iNOS production via the myeloid differentiation primary response-88 (MyD-88) adapter protein. Subsequently, iNOS facilitates production of nitric oxide (NO), a highly reactive and potent antiviral molecule that can inhibit replication of RNA and DNA viruses. Furthermore, NO can diffuse freely across cell membranes and elicit antiviral mechanisms in various ways, including direct and indirect damage to viral genomes. This review emphasizes current knowledge of NO-mediated antiviral responses elicited after activation of TLR signaling pathways.

Prophylactic potential of resiquimod against very virulent infectious bursal disease virus (vvIBDV) challenge in the chicken

The study evaluated the prophylactic potential of resiquimod (R-848), a synthetic TLR7 agonist, against very virulent infectious bursal disease virus (vvIBDV) infection in chicken. Specific pathogen free White Leghorn chicks of three week age were treated with R-848 (50μg/bird, intramuscular) or PBS (n=26/group). Twenty four hour later, half of the birds from each group were challenged with 10(5) ELD50 of vvIBDV and observed for 10days. To understand the effect of R-848, immune response genes such as interferon (IFN)-β, IFN-γ, IL-1β, IL-4, iNOS and TLR7 were analyzed at 24 and 48h post-challenge in PBMCs ex vivo by real-time PCR (n=6/group). On day 4 post-challenge, representative birds (n=3/group) were sacrificed to study the bursal damage and IBDV antigen clearance. Immunosuppression was assessed by antibody response against live Newcastle disease virus (NDV) vaccine, which was administered on day 10 post-challenge. R-848 pre-treatment significantly upregulated the transcripts of each immune response gene studied (P<0.05). There was 50% mortality on vvIBDV challenge in control birds, while it was only 20% with R-848 group. R-848 pre-treatment reduced the bursal damage as indicated by lower bursal lesion score in histopathology, reduced IBDV antigen signal in immunohistochemistry and improved antigen clearance in agar gel immunodiffusion test. Further, it protected significantly against vvIBDV induced immunosuppression as indicated by HI antibody titre. It is concluded that pre-treatment of R-848 conferred partial protection from mortality and bursal damage while complete protection against immunosuppression in chicken when challenged with vvIBDV, which could be due to the upregulation of immune response genes.

The effects of subcutaneous and intraocular administration of class B ODN CpG in chicken on the expression of TLR21, IFN-γ and IL-1β

The synthetic unmethylated oligodeoxynucleotides with CpG motifs (CpG ODN) were shown to activate Toll-like receptor 21 (TLR21) and stimulate the innate and adaptive immune system. In this study we tested the expression of TLR21, interferon (IFN)-γ and interleukin (IL)-1β mRNA in the blood after subcutaneous and intraocular application of the class B CpG ODN in chicken. The relative expression of mRNA of TLR21, IFN-γ and IL-1β were quantified at 3, 6, 12, 24 and 72 h post-stimulation. The study revealed that IFN-γ mRNA expression was significantly upregulated 12 h after subcutaneous stimulation with a high and low dose of ODN CpG, whereas the IL-1β mRNA expression levels were significantly upregulated 3 and 72 h after subcutaneous administration. After intraocular administration, the IL-1β mRNA levels were the highest at 24 h post-application, albeit not specifically. This data indicates that class B CpG ODN has the ability to induce TLR21 response in blood when administered parenterally in chicken. In contrast, intraocular administration of CpG ODN was not able to produce a significant increase in cytokine mRNA expression in blood. The data suggest that additional stimulus, e.g. the antigen, may be needed on the site of mucosal administration to activate systemic immune response.

The stimulatory effect of different CpG oligonucleotides on the maturation of chicken bone marrow-derived dendritic cells

CpG oligonucleotide (CpG-ODN) can exert an immunostimulatory effect on different types of immune cells such as dendritic cells (DC). The immunostimulatory activity of CpG-ODN is closely related to its nucleotide sequence and structural characteristics. In this study, we aimed at evaluating the stimulatory effects of different CpG-ODN on the maturation of chicken bone marrow-derived DC (BM-DC) in vitro. First, 4 CpG-ODN were designed. Then chicken bone marrow cells were extracted from tibia and femur and cultured in the RPMI 1640 medium with recombinant chicken granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4. After culture for 6 d, the cells were stimulated by different CpG-ODN or lipopolysaccharide for 24 h. Finally, the effects of different CpG-ODN on the maturation of chicken BM-DC were investigated by morphologic, phenotypic, and functional assays. The results showed that the cultured cells could display the typical DC morphology, and the CpG-ODN could efficiently stimulate the BM-DC to show the mature morphologic characteristics and upregulate the expression of cluster of differentiation (CD) 40 and CD86 molecules. In addition, after stimulation by CpG-ODN, the BM-DC could significantly induce T-cell proliferative response (P < 0.01). Among all the sequences, the stimulatory effect of CpG-ODN F3 with an addition of poly-guanosine strings at the 3' end was the best on the chicken BM-DC. In conclusion, this is the first report to demonstrate that different CpG-ODN have distinct stimulatory effects on the maturation of chicken BM-DC and CpG-ODN F3 with the best stimulatory effect can be a potent stimulant for the maturation of chicken BM-DC.

Enhanced innate immune responses in a brood parasitic cowbird species: Degranulation and oxidative burst

We examined the relative effectiveness of two innate immune responses in two species of New World blackbirds (Passeriformes, Icteridae) that differ in resistance to West Nile virus (WNV). We measured degranulation and oxidative burst, two fundamental components of phagocytosis, and we predicted that the functional effectiveness of these innate immune responses would correspond to the species' relative resistance to WNV. The brown-headed cowbird (Molothrus ater), an obligate brood parasite, had previously shown greater resistance to infection with WNV, lower viremia and faster recovery when infected, and lower subsequent antibody titers than the red-winged blackbird (Agelaius phoeniceus), a close relative that is not a brood parasite. We found that cowbird leukocytes were significantly more functionally efficient than those of the blackbird leukocytes and 50% more effective at killing the challenge bacteria. These results suggest that further examination of innate immunity in the cowbird may provide insight into adaptations that underlie its greater resistance to WNV. These results support an eco-immunological interpretation that species like the cowbird, which inhabit ecological niches with heightened exposure to parasites, experience evolutionary selection for more effective immune responses.

The effects of administration of ligands for Toll-like receptor 4 and 21 against Marek's disease in chickens

Ligands for Toll-like receptors (TLRs) are known to stimulate immune responses, leading to protection against bacterial and viral pathogens. Here, we aimed to examine the effects of various TLR ligands on the development of Marek's disease in chickens. Specific-pathogen free chickens were treated with a series of TLR ligands that interact with TLR3, TLR9 and TLR21. In a pilot study, it was determined that TLR4 and TLR21 ligands are efficacious, in that they could reduce the incidence of Marek's disease tumors in infected birds. Hence, in a subsequent study, chickens were treated with lipopolysaccharide (LPS) as a TLR4 and CpG oligodeoxynucleotides (ODN) as TLR21 agonists before being challenged with the RB1B strain of Marek's disease virus (MDV) via the respiratory route. The results demonstrated that the administration of LPS or CpG ODN, but not PBS or non-CpG ODN, delayed disease onset and reduced MDV genome copy number in the spleens of infected chickens. Taken together, our data demonstrate that TLR4 and 21 agonists modulate anti-virus innate immunity including cytokine responses in MD-infected chicken and this response can only delay, but not inhibit, disease progression.

BacMam virus-based surface display of the infectious bronchitis virus (IBV) S1 glycoprotein confers strong protection against virulent IBV challenge in chickens

Avian infectious bronchitis virus (IBV) is associated with production inefficiencies in domestic fowl, and causes massive economic losses to the poultry industry worldwide. Progress has been made in designing novel and efficient candidate vaccines to control IBV infection. BacMam virus, a modified baculovirus mediating transgene expression under the control of a mammalian promoter, has emerged as a versatile and safe vector during vaccine development. In previous work, we generated the BacMam virus Ac-CMV-S1, which expressed the S1 glycoprotein of IBV-M41. We showed that Ac-CMV-S1 induced excellent cellular immunity, but did not confer adequate protection in chickens compared with the conventional inactivated vaccine. In the current study, we generated an improved BacMam virus, BV-Dual-S1. This virus displayed the S1 glycoprotein on the baculovirus envelope, and was capable of expressing it in mammalian cells. BV-Dual-S1 elicited stronger humoral and cell-mediated immune responses, and showed greater capacity for induction of cytotoxic T lymphocyte responses, compared with Ac-CMV-S1 in specific pathogen-free chickens. A significant difference was not observed for protection rates between chickens immunized with BV-Dual-S1 (83%) or inactivated vaccine (89%) following challenge with virulent IBV-M41. Our findings show that the protective efficacy of BV-Dual-S1 could be significantly enhanced by baculovirus display technology. BacMam virus-based surface display strategies could serve as effective tools in designing vaccines against IB and other infectious diseases.

Impact of CpG oligodeoxynucleotide stimulation on percentage of T and B cells in chicken

TLR stimulation in chickens has been shown to play a role in the initiation and regulation of innate and adaptive immune responses. The aim of this study was to use flow cytometry to establish the percentage of T and B subset in blood and lymphoid organs in chicks after CpG oligodeoxynucleotide (ODN) stimulation. It was demonstrated that the percentages of CD3+, CD4+, TCRgamma delta+ cells and Bu-1+MHC class II+ cells in blood 24 h post-injection were significantly higher than in the control groups. It was also shown that the percentages of CD3+ and CD4+ cells in the spleen at 48 h post-injection were significantly higher than in control groups. The percentage of Bu-1+ cells in the bursa of Fabricius after CpG ODN stimulation (98.38 +/- 0.84) was significantly higher than that found in the non-CpG ODN control group (94.54 +/- 2.51) (p < or = 0.05). The results indicate that class B CpG ODN increases the percentage of both T (especially CD4+ cells) and B cells.

Recombinant flagellin and its cross-talk with lipopolysaccharide--effect on pooled chicken peripheral blood mononuclear cells

Toll-like receptors (TLRs) are one of the types of pattern recognition receptors (PRRs) that recognize conserved pathogen molecules. TLRs link innate and adaptive arms of immune system and are implicated in the development of defense against invading pathogens. Lipopolysaccharide (LPS) and flagellin are recognized by TLR4 and TLR5, respectively. In this study, the effect of flagellin and lipopolysaccharide alone and in combination on chicken peripheral blood mononuclear cells (PBMCs) was investigated. The FliC gene of Salmonella typhimurium was expressed in a prokaryotic expression system and the recombinant flagellin was used to stimulate the chicken PBMCs. A combination of recombinant flagellin and LPS synergistically upregulated nitric oxide production, IL-12 and IL-6 expression but antagonistically down regulated IL-4 expression in comparison to recombinant flagellin alone. The results indicate that these agonists synergistically interact and enhance macrophage function and promote Th1 immune response in chicken PBMCs.

Combined CpG and poly I:C stimulation of monocytes results in unique signaling activation not observed with the individual ligands

Toll-like receptors (TLRs) bind to components of microbes, activate cellular signal transduction pathways and stimulate innate immune responses. Previously, we have shown in chicken monocytes that the combination of CpG, the ligand for TLR21 (the chicken equivalent of TLR9), and poly I:C, the ligand for TLR3, results in a synergistic immune response. In order to further characterize this synergy, kinome analysis was performed on chicken monocytes stimulated with either unmethylated CpG oligodeoxynucleotides (CpG) and polyinosinic-polycytidylic acid (poly I:C) individually or in combination for either 1h or 4h. The analysis was carried out using chicken species-specific peptide arrays to study the kinase activity induced by the two ligands. The arrays are comprised of kinase target sequences immobilized on an array surface. Active kinases phosphorylate their respective target sequences, and these phosphorylated peptides are then visualized and quantified. A significant number of peptides exhibited altered phosphorylation when CpG and poly I:C were given together, that was not observed when either CpG or poly I:C was given separately. The unique, synergistic TLR agonist affected peptides represent protein members of signaling pathways including calcium signaling pathway, cytokine-cytokine receptor interaction and Endocytosis at the 1h time point. At the 4h time point, TLR agonist synergy influenced pathways included Adipocytokine signaling pathway, cell cycle, calcium signaling pathway, NOD-like receptor signaling pathway and RIG-I-like receptor signaling pathway. Using nitric oxide (NO) production as the readout, TLR ligand synergy was also investigated using signaling protein inhibitors. A number of inhibitors were able to inhibit NO response in cells given CpG alone but not in cells given both CpG and poly I:C, as poly I:C alone does not elicit a significant NO response. The unique peptide phosphorylation induced by the combination of CpG and poly I:C and the unique signaling protein requirements for synergy determined by inhibitor assays both show that synergistic signaling is not a simple addition of TLR pathways. A set of secondary pathways activated by the ligand combination are proposed, leading to the activation of cAMP response element-binding protein (CREB), nuclear factor κB (NFκB) and ultimately of inducible nitric oxide synthase (iNOS). Since many microbes can stimulate more than one TLR, this synergistic influence on cellular signaling may be an important consideration for the study of immune response and what we consider to be the canonical TLR signaling pathways.

Induction of avian β-defensins by CpG oligodeoxynucleotides and proinflammatory cytokines in hen vaginal cells in vitro

Immune function in the vagina of hen oviduct is essential to prevent infection by microorganisms colonizing in the cloaca. The aim of this study was to determine whether CpG oligodeoxynucleotides (CpG-ODN) stimulate the expression of avian β-defensins (AvBDs) in hen vaginal cells. Specific questions were whether CpG-ODN affects the expression of AvBDs and proinflammatory cytokines and whether the cytokines affect AvBDs expression in vaginal cells. The dispersed vaginal cells of White Leghorn laying hens were cultured and stimulated by different doses of lipopolysaccharide (LPS), CpG-ODN, interleukin 1β (IL1B), or IL6. The cultured cell population contained epithelial cells, fibroblast-like cells, and CD45-positive leukocytes. The immunoreactive AvBD3, -10, and -12 were localized in the mucosal epithelium in the section of the vagina. The expression of AvBDs, IL1B, and IL6 was analyzed by quantitative RT-PCR. RT-PCR analysis showed the expression of AvBD1, -3, -4, -5, -10, and -12 in the cultured vaginal cells without stimulation. Toll-like receptors (TLRs) 4 and 21, which recognize LPS and CpG-ODN respectively and IL1 and IL6 receptors (IL1R1 and IL6R) were also expressed in them. The expression of IL1B, IL6, and AvBD10 and -12 was upregulated by LPS, whereas only IL1B and IL6 were upregulated by CpG-ODN. IL1B stimulation upregulated AvBD1 and -3 expression, whereas IL6 stimulation did not cause changes in AvBDs expression. These results suggest that CpG-ODN derived from microbes upregulates the expression of IL1B and IL6 by interaction with TLR21 and then IL1B induces AvBD1 and -3 to prevent infection in the vagina.

A critical role for MAPK signalling pathways in the transcriptional regulation of toll like receptors

Toll-like Receptors (TLR) are phylogenetically conserved transmembrane proteins responsible for detection of pathogens and activation of immune responses in diverse animal species. The stimulation of TLR by pathogen-derived molecules leads to the production of pro-inflammatory mediators including cytokines and nitric oxide. Although TLR-induced events are critical for immune induction, uncontrolled inflammation can be life threatening and regulation is a critical feature of TLR biology. We used an avian macrophage cell line (HD11) to determine the relationship between TLR agonist-induced activation of inflammatory responses and the transcriptional regulation of TLR. Exposure of macrophages to specific TLR agonists induced upregulation of cytokine and nitric oxide pathways that were inhibited by blocking various components of the TLR signalling pathways. TLR activation also led to changes in the levels of mRNA encoding the TLR responsible for recognising the inducing agonist (cognate regulation) and cross-regulation of other TLR (non-cognate regulation). Interestingly, in most cases, regulation of TLR mRNA was independent of NFκB activity but dependent on one or more of the MAPK pathway components. Moreover, the relative importance of ERK, JNK and p38 was dependent upon both the stimulating agonist and the target TLR. These results provide a framework for understanding the complex pathways involved in transcriptional regulation of TLR, immune induction and inflammation. Manipulation of these pathways during vaccination or management of acute inflammatory disease may lead to improved clinical outcome or enhanced vaccine efficacy.

Immunostimulatory properties of Toll-like receptor ligands in chickens

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that have been identified in mammals and avian species. Ligands for TLRs are typically conserved structural motifs of microorganisms termed pathogen-associated molecular patterns (PAMPs). Several TLRs have been detected in many cell subsets, such as in macrophages, heterophils and B cells, where they mediate host-responses to pathogens by promoting cellular activation and the production of cytokines. Importantly, TLR ligands help prime a robust adaptive immune response by promoting the maturation of professional antigen presenting cells. These properties make TLR ligands an attractive approach to enhance host-immunity to pathogens by administering them either prophylactically or in the context of a vaccine adjuvant. In this review, we discuss what is known about the immunostimulatory properties of TLR ligands in chickens, both at the cellular level as well as in vivo. Furthermore, we highlight previous successes in exploiting TLR ligands to protect against several pathogens including avian influenza virus, Salmonella, Escherichia coli, and Newcastle disease Virus.

CpG oligonucleotides and recombinant interferon-γ in combination improve protection in chickens to Salmonella enterica serovar Enteritidis challenge as an adjuvant component, but have no effect in reducing Salmonella carriage in infected chickens

Salmonella enterica serovar Enteritidis is the most common cause of human salmonellosis in many developed nations. It is frequently associated with both poultry meat and eggs. In the present study we have determined whether CpG oligonucleotides that stimulate the immune system via Toll like-receptors 15 and 21 in the chicken can be used as immunomodulatory agents to break carriage of S. Enteritidis in in vitro and in vivo infection models. We also investigated its use as a component in an adjuvant to stimulate cell mediated immunity with a killed vaccine preparation. Following infection of the chicken macrophage-like cell line HD11 with Salmonella enterica serovar Gallinarum, cells were stimulated with an oligonucleotide containing a CpG motif, or with a non-CpG oligonucleotide control at concentrations ranging from 0 to 80 µM. Addition of the CpG oligonucleotide greatly enhanced clearance of S. Enteritidis in dose-dependent manner, whilst the control oligonucleotide had no significant effect. In contrast, stimulation of cells infected with S. Gallinarum had no effect. The CpG or control oligonucleotide with recombinant chicken interferon-γ was administered intramuscularly into chickens experimentally colonized with S. Enteritidis, although neither preparation produced any change in intestinal colonization levels to that in untreated control birds. Finally, CpG oligonucleotides were incorporated with recombinant interferon-γ, double-stranded RNA (Poly I:C) and squalene as a Th1-stimulating combined adjuvant for synergistic activation of cellular immunity (CASAC) together with whole killed Salmonella as the antigen as an experimental vaccine. Following vaccination and challenge of chickens with S. Enteritidis, CASAC gave significant protection to intestinal colonization whereas the same antigen given with a proprietary adjuvant did not. Neither adjuvant increased protection to systemic infection. The data suggest that adjuvants incorporating CpG motifs and interferon-γ may improve protection afforded by killed-Salmonella vaccines.

Toll-like receptor ligands induce the expression of interferon-gamma and interleukin-17 in chicken CD4+ T cells

Background

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that mediate host responses to pathogens. To date, at least 10 different TLRs have been identified in chickens including TLR2, which binds lipopeptides and other similar ligands such as Pam3CSK4, TLR3, which binds double stranded RNA as well as synthetic molecules such as poly I:C, TLR4, which binds lipopolysaccharide (LPS), and TLR21, which binds CpG DNA motifs. In mammals, TLRs have been detected on CD4+ T cells where they mediate cellular survival, proliferation and the production of cytokines. However, the TLR-mediated responses in chicken CD4+ T cells remain to be determined. As such, the objective of the present study was to elucidate the kinetics of cytokine response to several different TLR ligands in chicken CD4+ T cells.

Results

The results suggest that these cells express TLRs 2, 3, 4 and 21 at the transcript level, and treatment with ligands for these TLRs significantly influenced the expression of the cytokines interferon (IFN)-γ and interleukin (IL)-17, but not IL-4, IL-10 and IL-13. Specifically, treatment with Pam3CSK4, poly I:C and LPS up-regulated IFN-γ transcripts, while CpG ODN significantly down-regulated them. In contrast, at least one dose of each of the TLR ligands, except for Pam3CSK4, significantly down-regulated IL-17 transcripts.

Conclusion

Chicken CD4+ T cells respond to ligands for TLRs 2, 3, 4 and 21 by up-regulating or down-regulating cytokine transcripts. Future studies may consider exploring how these TLR ligands may modulate other effector functions in chicken CD4+ T cells, as well as in other T cell subsets such as CD8+ T cells.

Gene Expression Analysis of Toll-Like Receptor Pathways in Heterophils from Genetic Chicken Lines that Differ in Their Susceptibility to Salmonella enteritidis

Previously conducted studies using two chicken lines (A and B) show that line A birds have increased resistance to a number of bacterial and protozoan challenges and that heterophils isolated from line A birds are functionally more responsive. Furthermore, when stimulated with Toll-like receptor (TLR) agonists, heterophils from line A expressed a totally different cytokine and chemokine mRNA expression pattern than heterophils from line B. A large-scale gene expression profile using an Agilent 44K microarray on heterophils isolated from line A and line B also revealed significantly differential expression in many immune-related genes following Salmonella enteritidis (SE) stimulation, which included genes involved in the TLR pathway. Therefore, we hypothesize the differences between the lines result from distinctive TLR pathway signaling cascades that mediate heterophil function and, thus, innate immune responsiveness to SE. Using quantitative RT-PCR on mRNA from heterophils isolated from control and SE-stimulated heterophils of each line, we profiled the expression of all chicken homologous genes identified in a reference TLR pathway. Several differentially expressed genes found were involved in the TLR-induced My88-dependent pathway, showing higher gene expression in line A than line B heterophils following SE stimulation. These genes included the TLR genes TLR4, TLR15, TLR21, MD-2, the adaptor proteins Toll-interleukin 1 receptor domain-containing adaptor protein (TIRAP), Tumor necrosis factor-receptor associated factor 3 (TRAF3), the IκB kinases transforming growth factor-β-activating kinase 1 (TAK1), IKKε and IKKα, the transcription factors NFkB2 and interferon regulatory factor 7, phosphatidylinositol-3 kinase (PI-3K), and the mitogen-activated protein kinase p38. These results indicate that higher expression of TLR signaling activation of both MyD88-dependent and TRIF-dependent pathways are more beneficial to avian heterophil-mediated innate immunity and a complicated regulation of downstream adaptors is involved in stronger induction of a TLR-mediated innate response in the resistant line A. These findings identify new targets for genetic selection of chickens to increase resistance to bacterial infections.

Co-stimulation with TLR3 and TLR21 ligands synergistically up-regulates Th1-cytokine IFN-γ and regulatory cytokine IL-10 expression in chicken monocytes

Toll-like receptors (TLRs) are pattern recognition receptors of the innate immune system for various conserved pathogen-associated molecular motifs. Chicken TLR3 and TLR21 (avian equivalent to mammalian TLR9) recognize poly I:C (double-stranded RNA) and CpG-ODN (a CpG-motif containing oligodeoxydinucleotide), respectively. Interaction between TLR3 and TLR21 agonists poly I:C and CpG-ODN has been reported to synergize in expression of proinflammatory cytokines and chemokines and the production of nitric oxide in chicken monocytes. However, the interaction between poly I:C and CpG-ODN on the expression of interferons (IFNs) and Th1/Th2 cytokines remains unknown. The objective of the present study was to investigate the effect of the interaction between poly I:C and CpG-ODN on the mRNA expression levels of IFN-α and IFN-β, Th1 cytokines IFN-γ and IL-12, Th2 cytokine IL-4, and regulatory IL-10 in chicken monocytes. When stimulated with either agonist alone, CpG-ODN significantly up-regulated the expression of INF-γ, IL-10, and IL-12p40, but not IFN-α and IFN-β; whereas poly I:C induced the expression of INF-γ, IFN-α, IFN-β, and IL-10; but not IL-12p40. However, stimulation with a combinatory CpG-ODN and poly I:C further synergistically increased the expression of IFN-γ and IL-10 mRNA. Our results provide strong evidence supporting the critical role of TLR3 and TLR21 in avian innate immunity against both viral and bacterial infections; and the synergistic interaction between the TLR3 and TLR21 pathways produces a stronger Th1-biased immune response in chicken monocytes. Our result also suggest a potential use of poly I:C and CpG-ODN together as a more efficient adjuvant for poultry vaccine development.

Cytokine production and proliferation upon in vitro oligodeoxyribonucleotide stimulation of equine peripheral blood mononuclear cells

Synthetic oligodeoxyribonucleotides (ODN) may prove useful immune modulators in equine medicine. It is however important to assess the effects of each specific ODN in the species it is intended to be used in. The present study therefore aimed to evaluate some ODN for induction of cytokine production; i.e. type I interferons (IFN), IFN-γ, tumor necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β), and proliferation of equine peripheral blood mononuclear cells (PBMC). A panel of four ODN containing unmethylated cytosine-guanosine sequences (CpG) was used: ODN 1 and ODN 8 representing A-class; ODN 2006 representing B-class and ODN 2395 representing C-class-ODN. In addition, two ODN where CpG-motifs were reversed to GpC were included; ODN 2137 otherwise identical to ODN 2006 and ODN 5328 otherwise identical to ODN 2395. Cytokine concentrations were measured in cell culture supernatants after 24h of induction and proliferation was determined after 72 h of induction. Each ODN was tested with PBMC from at least 5 individual horses with and without the addition of lipofectin to cell cultures. Type I IFN, IFN-γ and TNF-α production was readily induced by ODN 1, ODN 2006 and ODN 2395 both in the presence and absence of lipofectin and all three types of ODN induced similar levels of cytokines. Proliferation of PBMC was clearly induced by ODN 2006 and ODN 2395 while ODN 1 only induced low-level proliferation. The levels of proliferation induced were not influenced by the presence of lipofectin. TGF-β production was not induced by any of the tested ODN. ODN 8, ODN 2137 and ODN 5328 were largely inactive in all assays. Thus, responses seemed dependent on or increased by CpG-motifs but presence of CpG-motifs did not necessarily confer activity since ODN 8 was inactive despite its CpG-motifs. Taken together, with equine PBMC distinctions in induction of different leukocyte functions between A-, B-, and C-class ODN were less obvious than what has been observed for human cells. These observations further stress the presence of species differences in ODN-induced responses.

Effects of avian triggering receptor expressed on myeloid cells (TREM-A1) activation on heterophil functional activities

A class of innate receptors called the triggering receptors expressed on myeloid cells (TREM) has been discovered and shown to be involved in innate inflammatory responses. The TREM family has been found in the chicken genome and consists of one activating gene (TREM-A1) and two inhibitory genes (TREM-B1 and TREM-B2). However, to date, there have been no reports on the effects of activating the TREM molecules on the functional activity of the primary avian polymorphonuclear cell, the heterophil. To characterize the activation of avian heterophils, we evaluated the effect of receptor ligation on heterophil effector functions. A specific agonistic antibody (Ab) was generated against the peptide sequence of chicken TREM-A1 38-51aa (YNPRQQRWREKSWC). To study TREM-A1 mediated activation, purified peripheral blood heterophils were incubated with various concentrations of the anti-TREM-A1 Ab or control Ab against an irrelevant antigen. Activation via TREM-A1 induces a significant increase in phagocytosis of Salmonella enteritidis, a rapid degranulation, and a dramatic up-regulation in gene expression of the pro-inflammatory cytokine, IL-6, and the inflammatory chemokine, CXCLi2. However, we found no direct TREM-A1 stimulation of the heterophil oxidative burst. Like mammalian TREM, avian TREM-A1 ligation synergizes with the activation of Toll-like receptor-4 (TLR4) ligand, LPS. In addition, the synergistic activity of LPS and TREM-A1 resulted in a significantly (p⩽0.05) increased production of an oxidative burst. Taken together, these results suggest, unlike in mammalian neutrophils, TREM-A1 engagement activates a differential functional activation of avian heterophils, but like mammalian neutrophils, acts in synergy with TLR agonists. These results provide evidence of the function of TREM-A1 in heterophil biology and avian innate immunity.

Bacterial toll-like receptor agonists induce sequential NF-κB-mediated leukotriene B4 and prostaglandin E2 production in chicken heterophils

Studies of the response of the primary avian polymorphonuclear leukocyte, the heterophil, to microbe associated molecular patterns (MAMPs) through toll-like receptors (TLR) has concentrated on the activation of the respiratory burst, release of intracellular granules, and the induction of cytokine and chemokine expression. Virtually no studies have been described on the role of lipid mediators, leukotrienes and prostaglandins, as effectors of the avian inflammatory response. We have previously shown that flagellin (FLG), the bacterial lipoprotein mimic palmitoly-3-cysteine-serine-lysine-4 (PAM), and unmethylated CpG motifs of bacteria DNA (CpG) are all potent activators of the avian innate immune system. In the present studies, we hypothesized that FLG, PAM, and CpG are also capable of eliciting the production of these lipid mediators of inflammation by avian heterophils. Compared to non-stimulated control heterophils, all three TLR agonists were potent inducers (3-5-fold increase) of a rapid production (30 min) of leukotriene B(4) (LTB(4)) followed by a later release (60-120 min) of prostaglandin (PGE(2)) by the heterophils. LTB(4) and PGE(2) production were derived from lipoxygenase-5 (5-LO) and cyclooxygenase-2 (COX-2) enzymatic activities, respectively, as the selective 5-LO (caffeic acid) and COX-2 (NS-398) inhibitors eliminated LTB(4) and PGE(2) production from the MAMP-stimulated heterophils. These results demonstrate that both the lipoxygenase and cycloxygenase pathways are operational in avian heterophils in response to bacterial MAMPs. Treatment of heterophils with either FLG, PAM, or CpG also induced a significant increase in DNA binding by NF-κB family members' p50, c-Rel, and RelB. Additionally, the production of LTB(4) and PGE(2) were inhibited following treatment of heterophils with the specific pharmacologic inhibitor of NF-κB (Bay 11-7086), thus suggesting that TLR pathway activation of NF-κB controls LTB(4) and PGE(2) production. This the first report of the production of lipid mediators of inflammation by avian heterophils in response to PAMPs. Since FLG, lipoproteins, and bacterial CpG DNA are abundant during bacterial infections, these data support their role in the inflammatory response mediated by avian heterophils.

In vivo administration of ligands for chicken toll-like receptors 4 and 21 induces the expression of immune system genes in the spleen

Toll-like receptors (TLRs) are a group of conserved proteins that play an important role in pathogen recognition in addition to the initiation and regulation of innate and adaptive immune responses. To date, several TLRs have been identified in chickens, each recognizing different ligands. TLR stimulation in chickens has been shown to play a role in host-responses to pathogens. However, the mechanisms through which TLRs modulate the chicken immune system have not been well examined. The present study was conducted to characterize the kinetics of responses to TLR4 and TLR21 stimulation in chickens following intramuscular injections of their corresponding ligands, lipopolysaccharide (LPS) and CpG oligodeoxynucleotides (ODNs), respectively. To this end, relative expression of cytokine genes in the spleen was determined at 2, 6, 12 and 24 h after injection of TLR ligands. The results indicated that LPS strongly induced the up-regulation of some immune system genes early on in the response to treatment, including interferon (IFN)-γ, interleukin (IL)-10, and IL-1β. Furthermore, treatment with CpG ODN promoted the up-regulation of major histocompatibility complex (MHC)-II, IFN-γ and IL-10. The response to CpG ODN appeared to be somewhat delayed compared to the response to LPS. Moreover, we found a significant increase in IFN-α gene expression in response to LPS but not CpG ODNs. Future studies may be aimed to further characterize the molecular mechanisms of TLR activation in chickens or to exploit TLR agonists as vaccine adjuvants.

Avian-specific TLRs and downstream effector responses to CpG-induction in chicken macrophages

Chickens possess toll-like receptor (TLR15), a pattern recognition receptor (PRR) absent in mammals. We characterized the regulation and mechanism of CpG responsiveness via TLRs in chicken macrophage HD11 cells. TLR15 was significantly upregulated after induction with B- and C-type CpG oligonucleotides (ODN), tripalmitoylated lipopeptide (PAM3CSK4), Escherichia coli- and Salmonella enteritidis-derived lipopolysaccharide (LPS). In response to CpG-ODN inhibitor, TLR15 and IL1B were downregulated, but TLR21 was upregulated. IL1B was upregulated with CpG-ODN and downregulated after inhibitor treatment. The results suggest that responsiveness to different types of CpG-ODN in chicken macrophages requires multiple receptors, each with unique variation in expression. We utilized RNA interference (RNAi) technology to examine myeloid differentiation primary response gene (MyD88) dependency of TLR15 and TLR21. HD11 macrophages transfected with multiple MyD88-target siRNAs exhibited 70% decrease in MyD88 mRNA expression. IL1B was upregulated with CpG induction in cells with no reduction of MyD88 mRNA levels, but not in cells with 70% MyD88 reduction. Therefore, induction through TLR15 in response to CpG-ODN operates via the MyD88-dependent pathway in chicken macrophages.

Cell invasion of poultry-associated Salmonella enterica serovar Enteritidis isolates is associated with pathogenicity, motility and proteins secreted by the type III secretion system

Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major cause of food-borne gastroenteritis in humans worldwide. Poultry and poultry products are considered the major vehicles of transmission to humans. Using cell invasiveness as a surrogate marker for pathogenicity, we tested the invasiveness of 53 poultry-associated isolates of S. Enteritidis in a well-differentiated intestinal epithelial cell model (Caco-2). The method allowed classification of the isolates into low (n = 7), medium (n = 18) and high (n = 30) invasiveness categories. Cell invasiveness of the isolates did not correlate with the presence of the virulence-associated gene spvB or the ability of the isolates to form biofilms. Testing of representative isolates with high and low invasiveness in a mouse model revealed that the former were more invasive in vivo and caused more and earlier mortalities, whereas the latter were significantly less invasive in vivo, causing few or no mortalities. Further characterization of representative isolates with low and high invasiveness showed that most of the isolates with low invasiveness had impaired motility and impaired secretion of either flagella-associated proteins (FlgK, FljB and FlgL) or type III secretion system (TTSS)-secreted proteins (SipA and SipD) encoded on Salmonella pathogenicity island-1. In addition, isolates with low invasiveness had impaired ability to invade and/or survive within chicken macrophages. These data suggest that not all isolates of S. Enteritidis recovered from poultry may be equally pathogenic, and that the pathogenicity of S. Enteritidis isolates is associated, in part, with both motility and secretion of TTSS effector proteins.

Role of Hsp90 in CpG ODN mediated immunostimulation in avian macrophages

In mammals, CpG mediated immune activation is initiated through toll-like receptor (TLR) 9 and Hsp90 via activation of MAPK/ERK and PI3K/AKT pathways. However, in the absence of TLR9 ortholog in chicken genome, the role of Hsp90 and kinase (MAPK/ERK and PI3K/AKT) pathways in initiating CpG ODN(2007) induced immune activation in chicken is not clear. Using electrophoretic mobility shift assay (EMSA) and selective inhibitors of signal transduction pathways, we determined the role of these pathways in the production of Th1 cytokines/chemokines and nitric oxide (NO) in CpG ODN(2007) treated avian macrophage cells. Hsp90alpha but not Hsp90beta is bound to CpG ODN(2007). Inhibition of Hsp90 with geldanamycin resulted in the inactivation of MAPK/ERK and PI3K/AKT pathways leading to significantly reduced levels of IFN-gamma, IL-6 and NO mRNAs in CpG ODN(2007) stimulated cells. Moreover, inhibition of ERK1/2 and PI3/AKT kinase pathways with PD985009 and LY294002, respectively, suppresses the phosphorylation of ERK2 and AKT leading to the production of decreased amounts of IFN-gamma, IL-6 and NO mRNAs in CpG ODN(2007) stimulated cells. Our results demonstrate that binding of CpG ODN(2007) to Hsp90 induces activation of ERK2 and AKT phosphorylation leading to the production of high levels of IFN-gamma, IL-6, MIP-3alpha and nitric oxide (NO). In contrast to mammals, our results suggest that Hsp90alpha but not Hsp90beta binds with the CpG ODN(2007) and may play a major role in CpG ODN(2007) induced immunoactivation in avian macrophage cells. To our knowledge, this is the first report evaluating the involvement of Hsp90 and kinase (MAPK/ERK and PI3K/AKT) pathways in CpG mediated immunostimulation in avian macrophage cells.

CpG oligodeoxynucleotide and double-stranded RNA synergize to enhance nitric oxide production and mRNA expression of inducible nitric oxide synthase, pro-inflammatory cytokines and chemokines in chicken monocytes

Toll-like receptors (TLRs) recognize microbial components and initiate the innate immune responses that control microbial infections. The interaction between ligands of TLR3 and TLR9, poly I:C (an analog of viral double-stranded RNA) and CpG-ODN (a CpG-motif containing oligodeoxydinucleotide) on the inflammatory immune responses, including the production of nitric oxide (NO) and the expression of inducible NO synthase (iNOS), pro-inflammatory cytokines interleukin (IL)-1β and IL-6, and chemokines IL-8 and macrophage inflammatory protein (MIP)-1β, were investigated in chicken monocytes. The NO production was significantly higher when stimulated with a combination of CpG-ODN and poly I:C than with either CpG-ODN or poly I:C alone. Similarly, a significant synergistic effect by CpG-ODN and poly I:C was observed in the up-regulation of iNOS and IL-8 mRNA after 2 h and persisted up to 24 h. Although the combinatory treatment of CpG-ODN and poly I:C enhanced the expression of IL-1β, IL-6, and MIP-1β(3 after 2 h stimulation, the synergism in the up-regulation of IL-1β and IL-6 mRNA was observed after 8-h and 24-h stimulation, respectively, whereas there was no synergistic effect on MIP-1β. Our results demonstrate that CpG-ODN synergizes with poly I:C to induce pro-inflammatory immune response in chicken monocytes.

Activation of human and chicken toll-like receptors by Campylobacter spp

Campylobacter infection in humans is accompanied by severe inflammation of the intestinal mucosa, in contrast to colonization of chicken. The basis for the differential host response is unknown. Toll-like receptors (TLRs) sense and respond to microbes in the body and participate in the induction of an inflammatory response. Thus far, the interaction of Campylobacter with chicken TLRs has not been studied. Here, we investigated the potential of four Campylobacter strains to activate human TLR1/2/6, TLR4, TLR5, and TLR9 and chicken TLR2t2/16, TLR4, TLR5, and TLR21. Live bacteria showed no or very limited potential to activate TLR2, TLR4, and TLR5 of both the human and chicken species, with minor but significant differences between Campylobacter strains. In contrast, lysed bacteria induced strong NF-kappaB activation through human TLR1/2/6 and TLR4 and chicken TLR2t2/16 and TLR4 but not via TLR5 of either species. Interestingly, C. jejuni induced TLR4-mediated beta interferon in human but not chicken cells. Furthermore, isolated chromosomal Campylobacter DNA was unable to activate human TLR9 in our system, whereas chicken TLR21 was activated by DNA from all of the campylobacters tested. Our data are the first comparison of TLR-induced immune responses in humans and chickens. The results suggest that differences in bacterial cell wall integrity and in TLR responses to Campylobacter LOS and/or DNA may contribute to the distinct clinical manifestation between the species.

Chicken TLR21 acts as a functional homologue to mammalian TLR9 in the recognition of CpG oligodeoxynucleotides

Similar to mammalian species, chickens show marked immunological responses to CpG oligodeoxynucleotides (ODNs) both in vivo and in vitro. In mammals, the receptor for ODNs has been demonstrated to be TLR9; however, an orthologue to mammalian TLR9 is absent in the chicken genome. In this study, chicken TLRs 7, 15 and 21 were expressed in mammalian HEK-293T cells; expression of TLR21 but not TLR7 or 15 resulted in marked NF-kappaB activation upon stimulation with exogenous ODN. This activation was not observed when cells were stimulated by TLR agonists other than ODNs. In addition, responsiveness of the ectopically expressed TLR21 demonstrated similar kinetics of activation as reported for mammalian TLR9 and was dependent on the nucleotide sequence of the ODN. The same ODN specificity was observed for chicken HD11 macrophage when ODN mediated activation was monitored by up-regulation of IL1, IL6 and iNOS transcripts. Furthermore, when TLR21, but not TLR15, was partially silenced in HD11 cells by RNA interference, ODN mediated responses were reduced. TLR21-mediated NF-kappaB activation in HEK-293T cells was inhibited by bafilomycin A suggesting that endosomal maturation is required for TLR21 activation and observations by confocal microscopy and digestion with endoglycosidase H suggest TLR21 localizes to the endoplasmic reticulum (ER) of resting cells. Expression of TLR21 transcripts was found in all chicken tissues examined but was significantly less in the lung and small intestine of newly hatched birds. Two of the leucine rich repeat regions (LRRs) of TLR21 showed homology with a LRR conserved within mammalian TLR9 and implicated in ligand binding. We hypothesize that avian TLR21 plays a similar role to that of mammalian TLR9 and enables recognition of microbial DNA as a danger signal resulting in downstream innate and adaptive immune responses.

The in vitro and in ovo responses of chickens to TLR9 subfamily ligands

Although Toll-like receptors (TLRs) have been well characterised in mammals, less work has been carried out in non-mammalian species, such as chickens. In this study the response of chicken cells to the TLR9 subfamily of ligands was characterised in vitro and in ovo. It was found that even though chickens appear to have only one functional receptor to represent the TLR9 subfamily, stimulation of chicken splenocytes with TLR7 and TLR9 ligands induced proinflammatory cytokine production and cell proliferation, similar to that observed when the homologous mammalian receptors are stimulated. Furthermore, we demonstrated that the in ovo administration of these TLR ligands elicits a response, such as cytokine production, that can be detected post-hatch. The current knowledge of the action of TLR ligands in mammals, in conjunction with their immunomodulating ability shown in this study, draws attention to their potential use as therapeutic agents for the poultry industry.