Response of nitric oxide production to CpG oligodeoxynucleotides in turkey and chicken peripheral blood monocytes

Development of innate immunity in chicken embryos and newly hatched chicks: a disease control perspective

Newly hatched chickens are confronted by a wide array of pathogenic microbes because their adaptive immune defences have limited capabilities to control these pathogens. In such circumstances, and within this age group, innate responses provide a degree of protection. Moreover, as the adaptive immune system is relatively naïve to foreign antigens, synergy with innate defences is critical. This review presents knowledge on the ontogeny of innate immunity in chickens pre-hatch and early post-hatch and provides insights into possible interventions to modulate innate responses early in the life of the bird. As in other vertebrate species, the chicken innate immune system which include cellular mediators, cytokine and chemokine repertoires and molecules involved in antigen detection, develop early in life. Comparison of innate immune systems in newly hatched chickens and mature birds has revealed differences in magnitude and quality, but responses in younger chickens can be boosted using innate immune system modulators. Functional expression of pattern recognition receptors and several defence molecules by innate immune system cells of embryos and newly hatched chicks suggests that innate responses can be modulated at this stage of development to combat pathogens. Improved understanding of innate immune system ontogeny and functionality in chickens is critical for the implementation of sound and safe interventions to provide long-term protection against pathogens. Next-generation tools for studying genetic and epigenetic regulation of genes, functional metagenomics and gene knockouts can be used in the future to explore and dissect the contributions of signalling pathways of innate immunity and to devise more efficacious disease control strategies.

Chicken lines divergently selected on feather pecking differ in immune characteristics

It is crucial to identify whether relations between immune characteristics and damaging behaviors in production animals exist, as these behaviors reduce animal welfare and productivity. Feather pecking (FP) is a damaging behavior in chickens, which involves hens pecking and pulling at feathers of conspecifics. To further identify relationships between the immune system and FP we characterized high FP (HFP) and low FP (LFP) selection lines with regard to nitric oxide (NO) production by monocytes, specific antibody (SpAb) titers, natural (auto)antibody (N(A)Ab) titers and immune cell subsets. NO production by monocytes was measured as indicator for innate pro-inflammatory immune functioning, SpAb titers were measured as part of the adaptive immune system and N(A)Ab titers were measured as they play an essential role in both innate and adaptive immunity. Immune cell subsets were measured to identify whether differences in immune characteristics were reflected by differences in the relative abundance of immune cell subsets. Divergent selection on FP affected NO production by monocytes, SpAb and N(A)Ab titers, but did not affect immune cell subsets. The HFP line showed higher NO production by monocytes and higher IgG N(A)Ab titers compared to the LFP line. Furthermore the HFP line tended to have lower IgM NAAb titers, but higher IgM and IgG SpAb titers compared to the LFP line. Thus, divergent selection on FP affects the innate and adaptive immune system, where the HFP line seems to have a more responsive immune system compared to the LFP line. Although causation cannot be established in the present study, it is clear that relationships between the immune system and FP exist. Therefore, it is important to take these relationships into account when selecting on behavioral or immunological traits.

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.

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.

The avian heterophil

Heterophils play an indispensable role in the immune defense of the avian host. To accomplish this defense, heterophils use sophisticated mechanisms to both detect and destroy pathogenic microbes. Detection of pathogens through the toll-like receptors (TLR), FC and complement receptors, and other pathogen recognition receptors has been recently described for the avian heterophil. Upon detection of pathogens, the avian heterophil, through a network of intracellular signaling pathways and the release and response to cytokines and chemokines, responds using a repertoire of microbial killing mechanisms including production of an oxidative burst, cellular degranulation, and production of extracellular matrices of DNA and histones (HETs). In this review, the authors describe the recent advances in our understanding of the avian heterophil, its functions, receptors and signaling, identified antimicrobial products, cytokine and chemokine production, and some of the effects of genetic selection on heterophils and their functional characteristics.

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.

Prospects for understanding immune-endocrine interactions in the chicken

Despite occupying the same habitats as mammals, having similar ranges of body mass and longevity, and facing similar pathogen challenges, birds have a different repertoire of organs, cells, molecules and genes of the immune system when compared to mammals. In other words, birds are not "mice with feathers", at least not in terms of their immune systems. Here we discuss differences between immune gene repertoires of birds and mammals, particularly those known to play a role in immune-endocrine interactions in mammals. If we are to begin to understand immune-endocrine interactions in the chicken, we need to understand these repertoires and also the biological function of the proteins encoded by these genes. We also discuss developments in our ability to understand the function of dendritic cells in the chicken; the function of these professional antigen-presenting cells is affected by stress in mammals. With regard to the endocrine system, we describe relevant chicken pituitary-adrenal hormones, and review recent findings on the expression of their receptors, as these receptors play a crucial role in modulating immune-endocrine interactions. Finally, we review the (albeit limited) work that has been carried out to understand immune-endocrine interactions in the chicken in the post-genome era.

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.

Phosphorothioate oligodeoxyribonucleotides induce in vitro proliferation of chicken B-cells

The study aimed to evaluate short synthetic oligodeoxyribonucleotides (ODN) as inducers of proliferation of chicken peripheral blood mononuclear cells (PBMC) and to identify the proliferating cells. A panel of different ODN; with phosphodiester and/or phosphorothioate backbone, with and without CpG-motifs, was therefore assessed for in vitro induction of proliferation. Six complete phosphorothioate ODN induced proliferation of PBMC while the complete phosphodiester or chimeric phosphodiester/phosphorohiate ODN did not. Moreover, CpG-motifs were not essential for induction of proliferation as responses to CpG-ODN were similar to those of their GpC controls. Two stimulatory phosphorothioate ODN were also used in phosphodiester form. In this comparison, only the phosphorothioate ODN were active despite the identical nucleotide sequences of their phosphodiester counterparts. In order to deliver DNA to the cytoplasm and decrease degradation of ODN by nucleases, stimulating as well as inactive ODN were treated with lipofectin prior to induction. However, proliferative responses were not influenced by lipofectin treatment and in analogy, none of the inactive ODN induced proliferation after lipofectin treatment. Among PBMC, ODN-responding cells were identified as predominantly Bu-1, immunoglobulin and major histocompatibility complex class II expressing cells, while CD3 expressing cells were not responding. Using magnetic cell separation of Bu-1 expressing cells prior to culture it was found that Bu-1 depleted cells did not proliferate upon ODN stimulation while the Bu-1 enriched cells were able to proliferate upon this stimulus. Taken together, among ODN in the present panel, only phosphorothioate ODN induced proliferation of PBMC. Responses were induced regardless of the presence of CpG-motifs and were not influenced by addition of lipofectin. Amid the chicken PBMC, predominantly cells of a B-cell phenotype proliferated in response to ODN stimulation and they were able to respond to this stimulus without the presence of other cell types.

In ovo treatment with CpG oligodeoxynucleotides decreases colonization of Salmonella enteriditis in broiler chickens

Induction of the innate immune response in newly hatched chickens is important for limiting infections with bacteria, such as Salmonella enterica serovar Enteriditis (SE). CpG oligodeoxynucleotides (CpG-ODN) can stimulate the innate immune response of young chickens. Therefore, we examined the effectiveness of CpG-ODN administered in ovo on intestinal colonization by SE and the ability to modulate the function of heterophils in young chickens. Heterophils were isolated from 2-day-old chickens and were stimulated with heat-killed SE (HK-SE) or PMA for oxidative burst and HK-SE or live SE for degranulation assays. CpG-ODN treatment had no effect on heterophil oxidative burst when stimulated with HK-SE or PMA. However, HK-SE and live SE increased degranulation (P<0.01) in heterophils from CpG-ODN-treated birds compared to PBS-treated controls. In a second experiment, chickens were orally infected with SE on day 10 post-hatch and cecal contents were collected 6 days later for assessment of SE intestinal colonization. CpG-ODN treatment reduced SE colonization by greater than 10-fold (P<0.001) compared to PBS-injected control birds. Overall, we show for the first time that CpG-ODN given in ovo stimulates innate immune responsiveness of chicken heterophils and increases resistance of young chickens to SE colonization.

Differential induction of nitric oxide, degranulation, and oxidative burst activities in response to microbial agonist stimulations in monocytes and heterophils from young commercial turkeys

The toll-like receptors (TLRs) recognize microbial pathogens and pathogen-associated molecular patterns and trigger inflammatory immune responses to control the infection. Here, we examined functional innate immune responses to Salmonella enteritidis (SE, live or formalin-killed) and various TLR agonists including lipoteichoic acid (LTA) and peptidoglycan (PGN) from Staphylococcus aureus and synthetic lipoprotein Pam3CSK4 (PAM), poly I:C (synthetic double-stranded RNA analog), lipopolysaccharide (LPS) from S. enteritidis, flagellin (FGN) from S. typhimurium, loxoribine (LOX) and R837 (synthetic anti-viral compounds), and CpG oligodeoxydinucleotide (CpG ODN)by measuring antimicrobial activities including oxidative burst and degranulation in heterophils and nitric oxide production in peripheral blood monocytes. Our results demonstrate differential nitric oxide responses to TLR agonists in turkey monocytes. LTA and CpG ODN were the most potent stimuli for nitric oxide induction followed by PAM, poly I:C, and LPS, whereas FGN, PGN, LOX, R837, and control ODN stimulated little or no nitric oxide production. Live SE stimulated significantly less NO production than formalin-killed SE (FKSE). Although FKSE induced significant degranulation and oxidative burst, most TLR agonists stimulate little oxidative burst and degranulation responses in turkey heterophils.

Phospholipase C, phosphatidylinositol 3-kinase, and intracellular [Ca(2+)] mediate the activation of chicken HD11 macrophage cells by CpG oligodeoxynucleotide

The activation of phospholipases is one of the earliest key events in receptor-mediated cellular responses to a number of extracellular signaling molecules. Oligodeoxynucleotides containing CpG motifs (CpG ODN) mimic microbial DNA and are immunostimulatory to most vertebrate species. In the present study, we used the production of nitric oxide (NO) as an indicator to evaluate the involvement of the signaling cascades of phospholipases and phosphatidylinositol 3-kinase (PI3K) in the activation of chicken HD11 macrophage cells by CpG ODN. Using selective inhibitors, we have identified the involvement of phosphatidylinositol (PI)-phospholipase C (PI-PLC), but not phosphatidylcholine (PC)-phospholipase C (PC-PLC) and PC-phospholipase D (PC-PLD), in CpG ODN-induced NO production in HD11 cells. Preincubation with PI-PLC selective inhibitors (U-73122) completely abrogated CpG ODN-induced NO production in HD11 cells, whereas PC-PLC inhibitor (D609) and PC-PLD inhibitor (n-butanol) had no inhibitory effects. Additionally, inhibition of PI3K and protein kinase C (PKC) with selective inhibitors and chelation of intracellular [Ca(2+)] also significantly attenuated NO production in CpG ODN-activated HD11 cells. Our results demonstrate that PI-PLC, PI3 K, PKC, and intracellular [Ca(2+)] are important components of the CpG ODN-induced signaling pathway that leads to the production of NO in avian macrophage cells.

In vivo priming heterophil innate immune functions and increasing resistance to Salmonella enteritidis infection in neonatal chickens by immune stimulatory CpG oligodeoxynucleotides

Oligodeoxynucleotides (ODN) containing CpG dinucleotides (CpG-ODN) mimic bacterial DNA and stimulate the innate immune system of vertebrates. Here, we investigated the effects of intraperitoneal (ip) administered CpG-ODN on the innate immune functions of chicken heterophils. Our results demonstrated CpG-ODN-dependent priming of chicken heterophil degranulation and oxidative burst. Heterophils from chickens treated with CpG-ODN exhibited significantly higher (p<0.05) degranulation activity compared to PBS and control ODN (ODN containing no CpG motif) treated groups when stimulated with opsonized Salmonella enterica serovar enteritidis. Similarly, oxidative burst activity, which generates bactericidal reactive oxygen species, was significantly higher (p<0.05) in heterophils from the CpG-ODN treated group than from PBS and control ODN groups when stimulated with formalin-killed S. enteritidis. The priming effects of CpG-ODN on heterophil immune functions continued at least 4 days post-treatment. In the infection study, newly hatched chickens were treated with CpG-ODN, control ODN or PBS for 24h then challenged with oral inoculation of S. enteritidis. A significant reduction (p<0.05) in colonization by S. enteritidis was observed in chickens treated with CpG-ODN. Our study provides evidence that immunostimulatory CpG-ODN potentiates the innate immune responses of heterophils and enhances resistance to infectious pathogens in neonatal chickens.