Oxidative burst mediated by toll like receptors (TLR) and CD14 on avian heterophils stimulated with bacterial toll agonists

Redox Homeostasis in Poultry: Regulatory Roles of NF-κB

Redox biology is a very quickly developing area of modern biological sciences, and roles of redox homeostasis in health and disease have recently received tremendous attention. There are a range of redox pairs in the cells/tissues responsible for redox homeostasis maintenance/regulation. In general, all redox elements are interconnected and regulated by various means, including antioxidant and vitagene networks. The redox status is responsible for maintenance of cell signaling and cell stress adaptation. Physiological roles of redox homeostasis maintenance in avian species, including poultry, have received limited attention and are poorly characterized. However, for the last 5 years, this topic attracted much attention, and a range of publications covered some related aspects. In fact, transcription factor Nrf2 was shown to be a master regulator of antioxidant defenses via activation of various vitagenes and other protective molecules to maintain redox homeostasis in cells/tissues. It was shown that Nrf2 is closely related to another transcription factor, namely, NF-κB, responsible for control of inflammation; however, its roles in poultry have not yet been characterized. Therefore, the aim of this review is to describe a current view on NF-κB functioning in poultry with a specific emphasis to its nutritional modulation under various stress conditions. In particular, on the one hand, it has been shown that, in many stress conditions in poultry, NF-κB activation can lead to increased synthesis of proinflammatory cytokines leading to systemic inflammation. On the other hand, there are a range of nutrients/supplements that can downregulate NF-κB and decrease the negative consequences of stress-related disturbances in redox homeostasis. In general, vitagene-NF-κB interactions in relation to redox balance homeostasis, immunity, and gut health in poultry production await further research.

Host Pathways of Hemostasis that Regulate Group A Streptococcus pyogenes Pathogenicity

A hallmark feature of severe Group A Streptococcus pyogenes (GAS) infection is dysregulated hemostasis. Hemostasis is the primary pathway for regulating blood flow through events that contribute towards clot formation and its dissolution. However, a number of studies have identified components of hemostasis in regulating survival and dissemination of GAS. Several proteins have been identified on the surface of GAS and they serve to either facilitate invasion to host distal sites or regulate inflammatory responses to the pathogen. GAS M-protein, a surface-exposed virulence factor, appears to be a major target for interactions with host hemostasis proteins. These interactions mediate biochemical events both on the surface of GAS and in the solution when M-protein is released into the surrounding environment through shedding or regulated proteolytic processes that dictate the fate of this pathogen. A thorough understanding of the mechanisms associated with these interactions could lead to novel approaches for altering the course of GAS pathogenicity.

Transcriptional analysis of host responses related to immunity in chicken spleen tissues infected with reticuloendotheliosis virus strain SNV

In avian species, the Reticuloendotheliosis virus (REV) causes severe immunosuppression and other symptoms, including avian dwarfing syndrome, and chronic tumors in lymphoid and other tissues. The pathogenesis of REV and its interaction with the host have yet to be fully elucidated with transcriptional studies on the changes in host gene expression after REV infection at the body level. In this study, the Spleen Necrosis Virus (SNV) was used to inoculate the one-day-old specific pathogen free (SPF) chicken to simulate congenital infection. We identified 1507 differentially expressed genes (DEGs) at 7, 14 and 21 dpi using Next Generation Sequencing (NGS) technology. Through the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of these DEGs, it was found that DEGs were mainly involved in the categories of signal transduction, immune system and signaling molecules and interaction. Among them, Pattern recognition receptors (PRRs), chemokine, T cell receptor, JAK-STAT, TNF, and NF-kappa B signaling pathway, and the Hematopoietic cell lineage play an important role in the tumorigenic and immunosuppressive regulation of REV. In addition, a series of DEGs associated with inflammatory factors (CCL4, TNFRSF18, CDKN2), apoptosis (IRF1, PDCD1, WNT5A), innate immunity (TLR, MAD5, TRIM25), and adaptive immunity (LY6E, CD36, LAG3) were also discovered. We further verified 33 selected immune- relevant DEGs using quantitative RT-PCR (qRT-PCR). These findings provide new insights and research directions for revealing the pathogenesis of REV infection and the interaction between REV and the chicken immune system.

Ulvan Activates Chicken Heterophils and Monocytes Through Toll-Like Receptor 2 and Toll-Like Receptor 4

Responsiveness to invasive pathogens, clearance via the inflammatory response, and activation of appropriate acquired responses are all coordinated by innate host defenses. Toll-like receptor (TLR) ligands are potent immune-modulators with profound effects on the generation of adaptive immune responses. This property is being exploited in TLR-based vaccines and therapeutic agents in chickens. However, for administering the TLR agonist, all previous studies used in ovo, intra-muscular or intra-venous routes that cannot be performed in usual farming conditions, thus highlighting the need for TLR ligands that display systemic immune effects when given orally (per os). Here we have demonstrated that an ulvan extract of Ulva armoricana is able to activate avian heterophils and monocytes in vitro. Using specific inhibitors, we have evidenced that ulvan may be a new ligand for TLR2 and TLR4; and that they regulate heterophil activation in slightly different manner. Moreover, activation of heterophils as well as of monocytes leads to release pro-inflammatory cytokines, including interleukin1-β, interferon α and interferon γ, through pathways that we partly identified. Finally, when given per os to animals ulvan induces heterophils and monocytes to be activated in vivo thus leading to a transient release of pro-inflammatory cytokines with plasma concentrations returning toward baseline levels at day 3.

Toll-like receptor (TLR)4 signalling induces myeloid differentiation primary response gene (MYD) 88 independent pathway in avian species leading to type I interferon production and antiviral response

Engagement of toll-like receptor (TLR)4 ligand, lipopolysaccharide (LPS) with TLR4 in mammals activates two downstream intracellular signaling routes; the myeloid differentiation primary response gene (MyD)88 dependent and independent pathways. However, existence of the later pathway leading to production of type I interferons (IFNs) in avian species has been debated due to conflicting observations. The objective of our study was to investigate whether LPS induces type I IFN production in chicken macrophages leading to antiviral response attributable to type I IFN. We found that LPS elicits type I IFN response dominated by IFN-β production. We also found that reduction in infectious laryngotracheitis virus (ILTV) replication by LPS-mediated antiviral response is attributable to type I IFNs in addition to nitric oxide (NO). Our findings imply that LPS elicits both MyD88 dependent and independent pathways in chicken macrophages consequently eliciting anti-ILTV response attributable to production of both type I IFNs and NO.

Effects of lipopolysaccharide on the histomorphology and expression of toll-like receptor 4 in the chicken trachea and lung

Endotoxin or lipopolysaccharide (LPS) exposure can cause injury to the respiratory airways and in response, the respiratory epithelia express toll-like receptors (TLRs) in many species. However, its role in the innate immunity in the avian respiratory system is poorly understood. The aim of the present study was to evaluate the effects of LPS on the chicken trachea and lung. After intraperitoneal LPS or saline injection, the trachea and lungs were harvested at 0, 12, 36 and 72 h (n = 6 at each time point) and histopathologically analysed using haematoxylin and eosin and periodic acid-Schiff staining, while TLR4 expression was determined by immunohistochemistry and secretory Immunoglobulin A (SIgA) levels by enzyme-linked immunosorbent assay. After LPS stimulation, we observed a remarkable decrease in the number of goblet cells along with obvious disruption and desquamation of the ciliated epithelium in the trachea, blurring of the boundary between pulmonary lobules, narrowed or indistinguishable lumen of the pulmonary atria and leukostasis in the lungs. Following LPS stimulation, TLR4 protein expression was up-regulated in both the trachea and the lungs and was found on the ciliated columnar cells as well as in the submucosa of the trachea, and in the lungs on parenchymal and immune cells. However, SIgA levels were only up-regulated in the trachea at 12 h following LPS stimulation. Hence, this report provides novel information about the effects of LPS on the microstructure of the lower respiratory tract and it is concluded that its intra-peritoneal administration leads to TLR4-mediated destruction of the tracheal epithelium and pulmonary inflammation along with increased SIgA expression in the tracheal mucosa.

Salmonella Serovars and Vaccination Effect on the Immune Responses of Male and Female Layers

Salmonella Enteritidis, S. Gallinarum and S. Pullorum are common serovars to infect poultry and cause diseases differently. The antibody production and cellular immune responses of male and female layers were evaluated before and after inoculation. Before inoculation, S. Gallinarum and S. Pullorum could survive and grow in 10% sera from 6-week-old layers, and S. Enteritidis and E. coli were completely eliminated. The weights of the male and female layers were increased the lowest by inoculation with S. Gallinarum, followed by S. Pullorum, and S. Enteritidis. Inoculation with S. Enteritidis, S. Gallinarum and S. Pullorum increased the antibody titer in the males depending on the serovars and maintained same higher antibody level in females. Furthermore, an increased anti-Salmonella IgG titer was associated with bactericidal ability and the level was reduced by serovars and complemente. Despite the vaccination and serovars, the male layers expressed more IgG2a than IgG1, indicating preferential activation of the Th1 pathway. The inoculation number affected the expression level of IFN-γ and IL-12 in the blood not in the secretion of the peripheral blood mononucleated cells (PBMCs) and more inoculations increased the expression of both cytokines. Inoculation increased more reactive oxygen species (ROS) production in polymorphonuclear (PMN) cells, not the PBMCs. ROS production was greater in cells from the males than from the females and greater in the cells treated with S. Enteritidis than S. Gallinarum and S. Pullorum. These three serovars and their vaccinations differed in sera killing and immune responses.

The several elements of intestinal innate immune system at the beginning of the life of broiler chicks

Functional capacity of digestive system and intestinal adaptive immunity are immature at hatching of broiler chicks. Therefore, intestinal innate immunity after hatching is vital to young chicks. The purpose of this study was to investigate expression and tissue distributions of several elements of the innate immune system (i.e., TLR2, TLR4, CD83, and MHC class II expressing cells) in the intestine of one-day-old chicks. For this purpose, ileum and cecum were examined the under different conditions, which included the control and 1, 3, 6, 12, or 24 h after injection of lipopolysaccharide (LPS) and phosphate buffered saline. The findings indicated that regardless of the antigenic stimulation, Toll-like receptor (TLR) 2 and TLR4 expressing cells were present in the intestinal tissues of one-day-old chicks. We noticed that the intestinal segments have different TLR expression levels after LPS stimulation. Dendritic cells were identified, and they left the intestinal tissue after LPS treatment. MHC class II molecules were diffusely present in both the ileum and cecum. This study demonstrates that the intestinal tissue of one-day-old chicks has remarkable defensive material, including histological properties and several elements of the innate immune system. Microsc. Res. Tech. 79:604-614, 2016. © 2016 Wiley Periodicals, Inc.

The effects of environmental enrichment and transport stress on the weights of lymphoid organs, cell-mediated immune response, heterophil functions and antibody production in laying hens

The effects of environmental enrichment and transport stress on the immune system were investigated in laying hens. A total of 48 1-day-old chickens were used, half of the chickens were reared in conventional cages (RCC) and the rest in enriched cages (REC). Transport stress was applied in the 17th week. Liver weight decreased, spleen and bursa of Fabricius weights, white blood cell count, CD4+ and CD8+ cell proportions increased due to the transport. Environmental enrichment significantly increased antibody production and tended to increase monocyte percentage and CD8+ cell proportion. The effect of transport on, heterophil (H) and lymphocyte (L) percentages was not significant in RCC chickens. While heterophil percentage and H:L ratio increased, lymphocyte percentage decreased in REC chickens subjected to transport. Transport stress increased heterophil functions both in REC and RCC chickens, but the increase was higher in REC hens than in RCC hens. In conclusion, although environmental enrichment did not neutralize the effect of transport on lymphoid organs, it activated the non-specific immune system, cellular and the humoral branches of the specific immune system by increasing heterophil functions, CD8+ cells and antibody production, respectively. Therefore, environmental enrichment suggested for improving animal welfare may also be beneficial to improve the immune system of birds exposed to stress.

In ovo delivery of Toll-like receptor 2 ligand, lipoteichoic acid induces pro-inflammatory mediators reducing post-hatch infectious laryngotracheitis virus infection

Toll-like receptor (TLR) ligands are pathogen associated molecular patterns (PAMPs) recognized by the TLRs resulting in induction of host innate immune responses. One of the PAMPs that binds to TLR2 and cluster of differentiation (CD) 14 is lipotechoic acid (LTA), which activates downstream signals culminating in the release of pro-inflammatory cytokines. In this study, we investigated whether in ovo LTA delivery leads to the induction of antiviral responses against post-hatch infectious laryngotracheitis virus (ILTV) infection. We first delivered the LTA into embryo day (ED)18 eggs via in ovo route so that the compound is available at the respiratory mucosa. Then the LTA treated and control ED18 eggs were allowed to hatch and the hatched chicken was infected with ILTV intratracheally on the day of hatch. We found that in ovo delivered LTA reduces ILTV infection post-hatch. We also found that in ovo delivery of LTA significantly increases mRNA expression of pro-inflammatory mediators in pre-hatch embryo lungs as well as mononuclear cell infiltration, predominantly macrophages, in lung of post-hatch chickens. Altogether, the data suggest that in ovo delivered LTA could be used to reduce ILTV infection in newly hatched chickens.

Toll-like receptor 2 ligand, lipoteichoic acid is inhibitory against infectious laryngotracheitis virus infection in vitro and in vivo

Lipoteichoic acid (LTA) is one of the pathogen associated molecular patterns (PAMPs) that activates toll-like receptor (TLR)2-cluster of differentiation (CD)14 signalling pathway. This recognition elicits antiviral responses that have been recorded against viruses of mammals although such responses have not been characterized adequately against avian viruses. In this investigation, we characterized the LTA induced antiviral responses against infectious laryntotracheitis virus (ILTV) infection in vitro and in vivo. We found that LTA is capable of up regulating mRNA expression of innate proteins in macrophages such as MyD88, iNOS and IL-1β and reduces the ILTV plaques in vitro. Similarly, we found that LTA treatment of embryonic day 18 (ED18) eggs can lead to the antiviral response against pre-hatch ILTV infection in vivo and is associated with expansion of macrophage populations and expression of IL-1β and MyD88 in the lung. The data highlight that LTA can be a potential innate immune stimulant that can be used against ILTV infection in chickens.

Effect of supplementing direct-fed microbials on broiler performance, nutrient digestibilities, and immune responses

Direct-fed microbials (DFM) are used to improve livestock health and performance. The effects of 2 DFM products, a blend of 3 Bacillus strains (DFMB) and a Propionibacteriumspp. (DFMP), on broiler performance, nutrient utilization, and immune responses were investigated. Day-old (n = 120) male broilers were divided into 24 groups of 5 birds and fed 3 wheat-based diets in mash form (8 groups per diet) from d 1 to 22. The control diet was fed without or with 7.5 × 10(4) cfu/g of either DFMB or DFMP. From d 19 to 21 fecal samples were collected for determination of total tract apparent retention (TTAR) of nutrients and AMEn. On d 21, feed intake and BW were determined. On d 22, 5 birds per treatment were killed by cervical dislocation to collect jejunal and ileal contents for determination of digesta viscosity and apparent ileal digestibility (AID) of nutrients, respectively, and ileum, cecal tonsil, and spleen tissues for Toll-like receptors (TLR) and cytokine expressions. Compared with the control, DFM did not affect BW gain and feed intake but DFMP reduced G:F (P < 0.01). Compared with the control (2,875 kcal/kg), birds fed on DFMB and DFMP had higher AMEn (2,979 and 2,916 kcal/kg, respectively; P < 0.05), whereas both DFM reduced the AID of DM (P < 0.001) and CP (P < 0.01). Furthermore, DFMP reduced TTAR of NDF (29.0 vs. 18.4%; P < 0.001), whereas both DFM increased TTAR of DM and fat (P < 0.001). Supplementing DFMP downregulated ileal expression of TLR-2b, IL-2, IL-4, IL-6, IL-10, and IL-13, whereas DFMB downregulated TLR-2b, IL-2, IL-4, and IL-6 in all 3 tissues, IL-10 in the spleen, and upregulated IL-13 in the spleen. In conclusion, the DFM did not improve performance but increased the AMEn of diet by possibly increasing DM and fat retention. Overall, both DFM showed an antiinflammatory effect in the ileum, but DFMB had more effects on local and systemic immunity than DFMP.

Performance, histomorphology, and toll-like receptor, chemokine, and cytokine profile locally and systemically in broiler chickens fed diets supplemented with yeast-derived macromolecules

The turnover of intestinal epithelial cells is a dynamic process that includes adequate cell proliferation and maturation in the presence of microbiota and migration and seeding of immune cells in early gut development in chickens. We studied the effect of yeast-derived macromolecules (YDM) on performance, gut health, and immune system gene expression in the intestine of broiler chickens. One thousand eighty 1-d-old birds, with 60 birds per pen and 6 pens per treatment, were randomly assigned to 3 treatment diets; a diet containing monensin (control), control diet supplemented with bacitracin methylene disalycylate (BMD), and BMD diet supplemented with YDM. Feed intake, BW, mortality, ileum histomorphology, and gene expression of Toll-like receptors (TLR2b, TLR4, and TLR21), cytokines [interferon (IFN)-γ, IFN-β, IL-12p35, IL-1β, IL-6, IL-10, IL-8, IL-2, IL-4, and transforming growth factor (TGF)-β4], and cluster of differentiation (CD)40 in the ileum, cecal tonsil, bursa of Fabricius, and spleen were assessed. No significant overall difference in performance in terms of feed intake, BW gain, and G:F was observed among treatments (P > 0.05). The YDM diet resulted in significantly higher villi height and villi height:crypt depth ratio compared with BMD and control diets (P < 0.05). A significantly lower mortality was observed in the YDM treatment compared with both control and BMD treatments. Compared with the control, gene expression analysis in YDM treatment showed no major change in response in the ileum, whereas higher CD40, IFN-β, IL-β, IL-6, TGF-β4, IL-2, and IL-4 in the cecal tonsil; TLR2b, TLR4, TLR21, and TGF-β4 in the bursa of Fabricius; and TLR4, IL-12p35, IFN-γ, TGF-β4, and IL-4 in the spleen was observed (P < 0.05). In conclusion, supplementation of YDM supports pro- and anti-inflammatory cytokine production via T helper type 1 and 2 (Th1 and Th2) cell-associated pathways both locally and systemically with a stronger additive effect in the cecal tonsil in the presence of BMD in the diet of chickens.

Induction of Toll-like receptor 4 signaling in avian macrophages inhibits infectious laryngotracheitis virus replication in a nitric oxide dependent way

LPS is one of the pathogen associated molecular patterns that activates Toll-like receptor 4 (TLR4) signaling pathway eliciting antiviral host responses in mammals although information on such responses in avian species is scarce. Our objectives were to characterize the LPS induced innate responses particularly the expression of LPS receptors (TLR4, CD14) in avian macrophages and observe whether TLR4 mediated induction of NO can elicit antiviral response against infectious laryngotracheitis virus (ILTV) replication. We found that LPS was capable of inducing the expression of TLR4, CD14 and NO production but not the type 1 interferons in an avian macrophage cell line, MQ-NCSU. We also showed that TLR4 mediated NO production can lead to antiviral response against ILTV replication when MQ-NCSU cells were treated with LPS and the resultant supernatant was then transferred to ILTV replicating cells to assess antiviral activity. Antiviral activity of NO was blocked by a selective inhibitor, S-methylisothiourea sulfate that inhibits inducible NO synthase. This observation confirms that the antiviral activity is positively correlated with NO production. The data show that LPS can be a potential innate immune stimulant that can be used against ILTV infection in chickens that require further evaluation in vivo.

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.

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.

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.

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.

Body temperature responses of Pekin ducks (Anas platyrhynchos domesticus) exposed to different pathogens

Poultry, like mammals and other birds, develop fever when exposed to compounds from gram-negative bacteria. Mammals also develop fever when exposed to the constituents of viruses or gram-positive bacteria, and the fevers stimulated by these different pathogenic classes have discrete characteristics. It is not known whether birds develop fever when infected by viruses or gram-positive bacteria. Therefore, we injected Pekin ducks with muramyl dipeptide, the cell walls of heat-killed Staphylococcus aureus, or the viral mimic polyinosinic:polycytidylic acid and monitored their body temperature (T(b)). For comparative purposes we also injected a group of ducks with lipopolysaccharide, the only known pyrogen in birds. We then compared the T(b) invoked by each injection with the T(b) after an injection of saline. Muramyl dipeptide did not affect T(b). The cell walls of heat-killed S. aureus invoked long-lasting, dose-dependent fevers with relatively low magnitudes. Polyinosinic:polycytidylic acid invoked dose-dependent fevers with high febrile peaks. Fever is a well-known clinical sign of infection in mammals, and the results of this study indicate that the pattern of increase in T(b) could serve as an indicator for diverse pathogenic diseases in birds.

Antigen presenting cells in a non-mammalian model system, the chicken

The chicken has a different repertoire of tissues, cells and genes of the immune response compared to mammals, yet generally survives infection with viral, bacterial, protozoal and fungal pathogens, and also worms and ectoparasites, just like mammals. Poultry are also probably the most heavily vaccinated group of farmed animals. Antigen presentation to the adaptive immune response therefore obviously normally occurs efficiently in birds. Although comparatively much is known about macrophages and B cells in the chicken, there is as yet little work on the other, professional, antigen-presenting cells, the dendritic cells (DC). Birds also have at least two other sets of phagocytic cells, heterophils and thrombocytes, which may also have the ability to present antigen. Here we review the current state of knowledge about antigen presenting cells in the chicken, concentrating mainly on recent advances in our knowledge of DC.

Genetic control of chicken heterophil function in advanced intercross lines: associations with novel and with known Salmonella resistance loci and a likely mechanism for cell death in extracellular trap production

Heterophils, the avian polymorphonuclear leukocyte and the counterpart of mammalian neutrophils, generate the primary innate response to pathogens in chickens. Heterophil performance against pathogens is associated with host disease resistance, and heterophil gene expression and function are under genetic control. To characterize the genomic basis of heterophil function, heterophils from F₁₃ advanced intercross chicken lines (broiler × Leghorn and broiler × Fayoumi) were assayed for phagocytosis and killing of Salmonella enteritidis, oxidative burst, and extracellular trap production. A whole-genome association analysis of single nucleotide polymorphisms at 57,636 loci identified genomic locations controlling these functional phenotypes. Genomic analysis revealed a significant association of extracellular trap production with the SAL1 locus and the SLC11A1 gene, which have both been previously associated with resistance to S. enteritidis. Fine mapping supports SIVA1 as a candidate gene controlling SAL1-mediated resistance and indicates that the proposed cell-death mechanism associated with extracellular trap production, ETosis, likely functions through the CD27/Siva-1-mediated apoptotic pathway. The SLC11A1 gene was also associated with phagocytosis of S. enteritidis, suggesting that the Slc11a1 protein may play an additional role in immune response beyond depleting metal ions to inhibit intracellular bacterial growth. A region of chromosome 6 with no characterized genes was also associated with extracellular trap production. Further characterization of these novel genes in chickens and other species is needed to understand their role in polymorphonuclear leukocyte function and host resistance to disease.

Advances in avian immunology--prospects for disease control: a review

In order to develop novel solutions to avian disease problems, including novel vaccines and/or vaccine adjuvants, and the identification of disease resistance genes which can feed into conventional breeding programmes, it is necessary to gain a more thorough understanding of the avian immune response and how pathogens can subvert that response. Birds occupy the same habitats as mammals, have similar ranges of longevity and body mass, and face similar pathogen challenges, yet birds have a different repertoire of organs, cells, molecules and genes of the immune system compared to mammals. This review summarises the current state of knowledge of the chicken's immune response, highlighting differences in the bird compared to mammals, and discusses how the availability of the chicken genome sequence and the associated postgenomics technologies are contributing to theses studies and also to the development of novel intervention strategies againts avian and zoonotic disease.

The differential evolutionary dynamics of avian cytokine and TLR gene classes

The potential for investigating immune gene diversity has been greatly enhanced by recent advances in sequencing power. In this study, variation at two categories of avian immune genes with differing functional roles, pathogen detection and mediation of immune mechanisms, was examined using high-throughput sequencing. TLRs identify and alert the immune system by detecting molecular motifs that are conserved among pathogenic microorganisms, whereas cytokines act as mediators of resulting inflammation and immunity. Nine genes from each class were resequenced in a panel of domestic chickens and wild jungle fowl (JF). Tests on population-wide genetic variation between the gene classes indicated that allele frequency spectra at each group were distinctive. TLRs showed evidence pointing toward directional selection, whereas cytokines had signals more suggestive of frequency-dependent selection. This difference persisted between the distributions considering only coding sites, suggesting functional relevance. The unique patterns of variation at each gene class may be constrained by their different functional roles in the immune response. TLRs identify a relatively limited number of exogeneous pathogenic-related patterns and would be required to adapt quickly in response to evolving novel microbes encountered in new environmental niches. In contrast, cytokines interact with many molecules in mediating the power of immune mechanisms, and accordingly respond to the selective stimuli of many infectious diseases. Analyses also indicated that a general pattern of high variability has been enhanced by widespread genetic exchange between chicken and red JF, and possibly between chicken and gray JF at TLR1LA and TLR2A.

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.

Genetic lines differ in Toll-like receptor gene expression in spleens of chicks inoculated with Salmonella enterica serovar Enteritidis

Toll-like receptors (TLR) recognize evolutionarily conserved molecular motifs (pathogen-associated molecular patterns) of infectious microbes and initiate innate immune response upon activation with relevant pathogens. This study investigated the acute effect of Salmonella Enteritidis challenge on TLR mRNA expression in cecum and spleen of birds from 3 distinct genetic lines. Chicks from broiler, Leghorn, and Fayoumi lines were inoculated or mock-inoculated with Salmonella Enteritidis. The mRNA expression levels of TLR2, TLR4, and TLR5 genes were assessed by quantitative reverse transcription-PCR of cecum and spleen tissue harvested at 2 or 18 h postinoculation (PI). There were no significant genetic line effects on TLR mRNA expression in spleen or cecum of mock-infected birds, or in the cecum of infected birds. Genetic line effect was significant (P < 0.05) on TLR mRNA expression in the spleen of Salmonella Enteritidis-infected birds. The Fayoumi line had higher TLR2 and TLR4 expression than Leghorn, higher TLR2 mRNA expression than broiler, and the broiler line had higher TLR5 expression than Leghorn and Fayoumi. In Salmonella Enteritidis-infected birds, the TLR2 expression in both cecum and spleen and TLR4 expression in spleen were significantly higher at 18 h PI than 2 h PI. The results demonstrate a significant genetic line effect on TLR expression in the spleen of Salmonella Enteritidis-infected birds, which may partly explain genetic variability in immune response to Salmonella Enteritidis.

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.

Pathogen-induced defense and innate immunity in macroalgae

Animals and vascular plants are known to defend themselves facultatively against pathogens, with innate receptors mediating their resistance. Macroalgal defense against microorganisms, in contrast, has until recently been regarded mainly as constitutive. Indeed, many macroalgae appear to be chemically defended at constantly high levels, and this is possibly one of the reasons why the first evidence of pathogen-aroused resistance in a macroalga was detected only a decade ago. Here, I summarize the results of studies that indicate the existence of pathogen-activated or pathogen-induced macroalgal defense. Most indications so far come from molecular investigations, which revealed major functional similarities among the defense systems of distant macroalgal clades and the innate immune systems of vascular plants and metazoans. Homologies exist in the primary and secondary defense-activating signals, as well as in the enzymes that are involved and the cellular responses that are activated. This strongly suggests that innate immunity also exists in relatively distinct macroalgal clades. However, a macroalgal receptor still needs to be isolated and characterized, and the molecular concept of macroalgal receptor-mediated immunity needs to be complemented with an ecological perspective on pathogen-induced defense, to develop a joint neuroecological perspective on seaweed-microbe interactions.

The avian immune genome – a glass half-full or half-empty?

Although in broad terms the avian immune response is remarkably similar to that of mammals, when one looks at specifics birds have a different repertoire of immune organs, cells and molecules compared to those characterized in mammals. Birds lack organized lymph nodes, yet have the Bursa of Fabricius. Birds lack neutrophils and functional eosinophils, yet have a distinct group of polymorphonuclear granulocytes known as heterophils. Birds also have a different repertoire of cytokines, chemokines, Toll-like receptors, defensins and integrins, as detailed in this review.

The Central Leucine-Rich Repeat Region of Chicken TLR16 Dictates Unique Ligand Specificity and Species-Specific Interaction with TLR2

The ligand specificity of human TLR (hTLR) 2 is determined through the formation of functional heterodimers with either hTLR1 or hTLR6. The chicken carries two TLR (chTLR) 2 isoforms, type 1 and type 2 (chTLR2t1 and chTLR2t2), and one putative TLR1/6/10 homologue (chTLR16) of unknown function. In this study, we report that transfection of HeLa cells with the various chicken receptors yields potent NF-kappaB activation for the receptor combination of chTLR2t2 and chTLR16 only. The sensitivity of this complex was strongly enhanced by human CD14. The functional chTLR16/chTLR2t2 complex responded toward both the hTLR2/6-specific diacylated peptide S-(2,3-bispalmitoyloxypropyl)-Cys-Gly-Asp-Pro-Lys-His-Pro-Lys-Ser-Phe (FSL-1) and the hTLR2/1 specific triacylated peptide tripalmitoyl-S-(bis(palmitoyloxy)propyl)-Cys-Ser-(Lys)(3)-Lys (Pam(3)CSK(4)), indicating that chTLR16 covers the functions of both mammalian TLR1 and TLR6. Dissection of the species specificity of TLR2 and its coreceptors showed functional chTLR16 complex formation with chTLR2t2 but not hTLR2. Conversely, chTLR2t2 did not function in combination with hTLR1 or hTLR6. The use of constructed chimeric receptors in which the defined domains of chTLR16 and hTLR1 or hTLR6 had been exchanged revealed that the transfer of leucine-rich repeats (LRR) 6-16 of chTLR16 into hTLR6 was sufficient to confer dual ligand specificity to the human receptor and to establish species-specific interaction with chTLR2t2. Collectively, our data indicate that diversification of the central LRR region of the TLR2 coreceptors during evolution has put constraints on both their ligand specificity and their ability to form functional complexes with TLR2.

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.

Synergy of CpG oligodeoxynucleotide and double-stranded RNA (poly I:C) on nitric oxide induction in chicken peripheral blood monocytes

Toll-like receptors (TLRs) recognize microbial components and initiate the innate immune responses that control microbial infections. We have investigated the innate immune response of chicken monocytes to ligands of TLR3 and TLR9, poly I:C (an analog of viral double-stranded RNA) and CpG-ODN (a CpG-motif containing oligodeoxydinucleotide) by measuring the induction of nitric oxide (NO) synthesis in chicken monocytes. Our results show that poly I:C and CpG-ODN synergized the induction of NO. When stimulated separately, CpG-ODN induced significant NO production in the chicken monocytes; whereas, poly I:C stimulated very little NO production. In combination, CpG-ODN and poly I:C induced significantly higher level of NO in chicken monocytes than either agonist alone. The addition of poly I:C prior to or simultaneously with CpG-ODN was required for the synergy. No synergistic effects on NO production were observed when monocytes were stimulated with combinations of CpG-ODN or poly I:C with other TLR agonists. Unlike chicken monocytes, cells of a chicken macrophage cell line, HD11, were readily stimulated to produce NO by both CpG-ODN and poly I:C with no synergism on NO induction when HD11 cells were stimulated by a combination of CpG-ODN and poly I:C. Using a pharmacological inhibitor, we also demonstrated that double-stranded RNA-dependent protein kinase (PKR) is indispensable for stimulation of NO production by CpG-ODN alone or in combination with poly I:C in both chicken peripheral blood monocytes and HD11 macrophage cells. Our results show that a combination of bacterial DNA and dsRNA induces an enhanced inflammatory immune response that has both antiviral and antibacterial activity in primary chicken monocytes.