Oligodeoxynucleotides containing CpG motifs (CpG-ODN) predominantly induce Th1-type immune response in neonatal chicks

Effects of Synthetic CpG Oligodeoxynucleotide K3 on Immune Response, Behavior, and Physiology in Male Layer Chicks (Gallus gallus)

Unmethylated cytosine-phosphate-guanine (CpG) motifs are often found in bacteria and viruses, but are rare in mammals. In mammals, CpG oligodeoxynucleotides (CpG ODN) stimulate the innate immune system via toll-like receptor 9 (TLR9). However, TLR9 is absent in birds; instead, TLR21 serves as the receptor for CpG ODN. While CpG ODN induce behavioral and physiological changes in mammals, there is limited research on their effects on behavioral and physiological parameters in birds. The aim of the present study was to determine whether intraperitoneal injection of K3, a synthetic class B CpG ODN, affected food intake, voluntary activity, cloacal temperature, blood constituents, and feed passage from the crop in chicks (Gallus gallus). Additionally, the effects of K3 (GC), which contains GpC motifs instead of CpG motifs, were investigated to determine the importance of these CpG motifs. Intraperitoneal injection of K3 significantly increased the mRNA expression of interleukin-1β, interleukin-6, interleukin-8, and interferon-γ in the spleen. These changes were not observed with K3 (GC) administration. Intraperitoneal injection of K3 significantly decreased food intake but did not affect voluntary activity. K3 also significantly increased cloacal temperature, tended to increase plasma glucose and corticosterone concentrations and significantly decreased feed passage from the crop. In contrast, K3 (GC) showed no effects on these parameters. These results demonstrate that class B CpG ODN is associated with anorexia, hyperthermia, and reduced feed passage through the digestive tract in chicks during bacterial and viral infections.

Oligodeoxynucleotides containing CpG motifs upregulate bactericidal activities of heterophils and enhance immunoprotection of neonatal broiler chickens against Salmonella Typhimurium septicemia

In the past, we demonstrated that oligodeoxynucleotides containing CpG motifs (CpG-ODN) mimicking bacterial DNA, stimulate the innate immune system of neonatal broiler chickens and protect them against Escherichia coli and Salmonella Typhimurium (S. Typhimurium) septicemia. The first line of innate immune defense mechanism is formed by heterophils and plays a critical protective role against bacterial septicemia in avian species. Therefore, the objectives of this study were 1) to explore the kinetics of CpG-ODN mediated antibacterial mechanisms of heterophils following single or twice administration of CpG-ODN in neonatal broiler chickens and 2) to investigate the kinetics of the immunoprotective efficacy of single versus twice administration of CpG-ODN against S. Typhimurium septicemia. In this study, we successfully developed and optimized flow cytometry-based assays to measure phagocytosis, oxidative burst, and degranulation activity of heterophils. Birds that received CpG-ODN had significantly increased (p < 0.05) phagocytosis, oxidative burst, and degranulation activity of heterophils as early as 24 h following CpG-ODN administration. Twice administration of CpG-ODN significantly increased the phagocytosis activity of heterophils. In addition, our newly developed CD107a based flow cytometry assay demonstrated a significantly higher degranulation activity of heterophils following twice than single administration of CpG-ODN. However, the oxidative burst activity of heterophils was not significantly different between birds that received CpG-ODN only once or twice. Furthermore, delivery of CpG-ODN twice increased immunoprotection against S. Typhimurium septicemia compared to once but the difference was not statistically significant. In conclusion, we demonstrated enhanced bactericidal activity of heterophils after administration of CpG-ODN to neonatal broiler chickens. Further investigations will be required to identify other activated innate immune cells and the specific molecular pathways associated with the CpG-ODN mediated activation of heterophils.

Induction of trained immunity in broiler chickens following delivery of oligodeoxynucleotide containing CpG motifs to protect against Escherichia coli septicemia

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) can promote antimicrobial immunity in chickens by enriching immune compartments and activating immune cells. Innate memory, or trained immunity, has been demonstrated in humans and mice, featuring the absence of specificity to the initial stimulus and subsequently cross-protection against pathogens. We hypothesize that CpG-ODN can induce trained immunity in chickens. We delivered single or multiple administrations of CpG-ODN to birds and mitochondrial oxidative phosphorylation (OXPHOS) and glycolysis of peripheral blood mononuclear cells were quantified using Seahorse XFp. Next, chickens were administered with CpG-ODN twice at 1 and 4 day of age and challenged with Escherichia coli at 27 days of age. The CpG-ODN administered groups had significantly higher mitochondrial OXPHOS until 21 days of age while cellular glycolysis gradually declined by 14 days of age. The group administered with CpG-ODN twice at 1 and 4 days of age had significantly higher survival, lower clinical score and bacterial load following challenge with E. coli at 27 d of age. This study demonstrated the induction of trained immunity in broiler chickens following administration of CpG-ODN twice during the first 4 days of age to protect birds against E. coli septicemia at 27 days of age.

Efficacy of an inactivated influenza vaccine adjuvanted with Toll-like receptor ligands against transmission of H9N2 avian influenza virus in chickens

Avian influenza viruses (AIV), including the H9N2 subtype, pose a major threat to the poultry industry as well as to human health. Although vaccination provides a protective control measure, its effect on transmission remains uncertain in chickens. The objective of the present study was to investigate the efficacy of beta-propiolactone (BPL) whole inactivated H9N2 virus (WIV) vaccine either alone or in combination with CpG ODN 2007 (CpG), poly(I:C) or AddaVax™ (ADD) to prevent H9N2 AIV transmission in chickens. The seeder chickens (trial 1) and recipient chickens (trial 2) were vaccinated twice with different vaccine formulations. Ten days after secondary vaccination, seeder chickens were infected with H9N2 AIV (trial 1) and co-housed with healthy recipient chickens. In trial 2, the recipient chickens were vaccinated and then exposed to H9N2 AIV-infected seeder chickens. Our results demonstrated that BPL+ CpG and BPL+ poly(I:C) treated chickens exhibited reduced oral and cloacal shedding in both trials post-exposure (PE). The number of H9N2 AIV+ recipient chickens in the BPL+ CpG group (trial 1) was lower than in other vaccinated groups, and the reduction was higher in BPL+ CpG recipient chickens in trial 2. BPL+ CpG vaccinated chickens demonstrated enhanced systemic antibody responses with high IgM and IgY titers with higher rates of seroprotection by day 21 post-primary vaccination (ppv). Additionally, the induction of IFN-γ expression and production was higher in the BPL+ CpG treated chickens. Interleukin (IL)- 2 expression was upregulated in both BPL+ CpG and BPL+ poly(I:C) groups at 12 and 24 hr post-stimulation.

Toll-like Receptor Ligands Enhance Vaccine Efficacy against a Virulent Newcastle Disease Virus Challenge in Chickens

To enhance the efficacy of the current Newcastle disease vaccine, we have selected potential adjuvants that target well-characterized pattern recognition receptors: the toll-like receptors (TLRs). Imiquimod is a small-molecule activator of TLR7, which is a sensor of dsDNA. ODN-1826 is a mimetic of CpG DNA and ligates TLR21 (a chicken homologue of TLR9 in mammals). The activation of TLRs leads to antiviral responses, including the induction of type I interferons (IFNs). In this study, birds were vaccinated intranasally with a live LaSota strain with or without imiquimod or ODN-1826 (50 µg/bird). Two weeks after vaccination, the birds were challenged with a virulent Newcastle disease virus (chicken/CA/212676/2002). Both adjuvants (imiquimod or ODN-1826) induced higher and more uniform antibody titers among vaccinated birds compared with the live vaccine-alone group. In addition, adjuvanted vaccines demonstrated greater protective efficacy in terms of the reduction in virus-shedding titer and the number of birds shedding the challenge virus at 2 and 4 days post-challenge. A differential expression of antiviral and immune-related genes was observed among groups from tissues (Harderian gland, trachea, cecal tonsil, and spleen) collected 1 and 3 days after treatment. These results demonstrate the potential of TLR-targeted adjuvants as mucosal vaccine enhancers and warrant a further characterization of immune correlates and optimization for efficacy.

Determining the Protective Efficacy of Toll-Like Receptor Ligands to Minimize H9N2 Avian Influenza Virus Transmission in Chickens

Low-pathogenicity avian influenza viruses (AIV) of the H9N2 subtype can infect and cause disease in chickens. Little is known about the efficacy of immune-based strategies for reducing the transmission of these viruses. The present study investigated the efficacy of Toll-like receptor (TLR) ligands (CpG ODN 2007 and poly(I:C)) to reduce H9N2 AIV transmission from TLR-treated seeder (trial 1) or inoculated chickens (trial 2) to naive chickens. The results from trial 1 revealed that a low dose of CpG ODN 2007 led to the highest reduction in oral shedding, and a high dose of poly(I:C) was effective at reducing oral and cloacal shedding. Regarding transmission, the recipient chickens exposed to CpG ODN 2007 low-dose-treated seeder chickens showed a maximum reduction in shedding with the lowest number of AIV+ chickens. The results from trial 2 revealed a maximum reduction in oral and cloacal shedding in the poly(I:C) high-dose-treated chickens (recipients), followed by the low-dose CpG ODN 2007 group. In these two groups, the expression of type I interferons (IFNs), protein kinase R (PKR), interferon-induced transmembrane protein 3 (IFITM3), viperin, and (interleukin) IL-1β, IL-8, and 1L-18 was upregulated in the spleen, cecal tonsils and lungs. Hence, TLR ligands can reduce AIV transmission in chickens.

Enhancement of protective efficacy of innate immunostimulant based formulations against yolk sac infection in young chicks

This study was conducted to characterize and compare the protective effects of various innate immune stimulants against yolk sac infection (YSI) caused by an avian pathogenic Escherichia coli in young chicks. The immune stimulants were administered alone or in various combinations of unmethylated CpG oligodeoxynucleotides (CpG), polyinosinic:polycytidylic acid (Poly I:C), and avian antimicrobial peptides (AMPs). Routes included in ovo or in ovo followed by a subcutaneous (S/C) injection. CpG alone and in combination with Poly I:C, truncated avian cathelicidin (CATH)-1(6-26), avian beta defensin (AvBD)1, and CATH-1(6-26) + AvBD1, were administered in ovo to 18-day-old embryonated eggs for gene expression and challenge studies. Next, CpG alone and the potentially effective formulation of CpG + Poly I:C, were administrated via the in ovo route using 40 embryonated eggs. At 1 day post-hatch, half of each group also received their respective treatments via the S/C route. Four hours later, all chicks were challenged using E. coli strain EC317 and mortalities were recorded for 14 d. The first challenge study revealed that amongst the single use and combinations of CpG with different innate immune stimulants, a higher protection and a lower clinical score were offered by the combination of CpG + Poly I:C. The second challenge study showed that this combination (CpG + Poly I:C) provides an even higher level of protection when a second dose is administered via the S/C route at 1 day post-hatch. The current research highlights the efficacy of a combination of CpG + Poly I:C administered either in ovo or in ovo along with a S/C injection and its potential use as an alternative to antibiotics against yolk sac infection in young chicks.

YBX has functional roles in CpG-ODN against cold stress and bacterial infection of Misgurnus anguillicaudatus

Misgurnus anguillicaudatus (M. anguillicaudatus) is a widely cultivated fish. However, in M. anguillicaudatus breeding, the frequent cold stress during daily breeding could induce immune suppression and increase the risk of infection, causing serious economic loss. Based on existing findings, CpG Oligonucleotides (CpG-ODNs) may be an ideal protective agent for low temperature fish breeding, performing anti-infective when faced with cold stress with cold shock proteins Y box binding proteins (YBX). Although YBX has pleiotropic functions, its roles in CpG-ODNs-mediated immunity (especially under cold situations) remain largely unexplored. To clarify the relationship among them, we identified the YBX1/YBX2 in M. anguillicaudatus and analyzed using a series of bioinformatics methods. After that, we immunized the fish with 3 types of CpG-ODNs and challenged with Aeromonas hydrophila (A. hydrophila). Here we showed that the best anti-bacterial effect of CpG-B was accompanied by the significant upregulation of YBX1. And the detection of the YBX1 downstream effectors confirmed that CpG-B induced the YBX1-mediated Th1 oriented responses to A. hydrophila by regulation of the NLRP3 (Caspase-A/-B), IL-1β, IL-12 and IFN-γ. Afterwards, we found that under cold stress, CpG-B can activate the NLRP3 and NF-κB pathways through YBX1, a key mediator of anti-A. hydrophila in CpG-B immunization. In this study, we demonstrated CpG-B protection against infection in low temperature, and its interaction with YBX1, expanded the research of CpG-ODN under cold stress, and provided a new CpG-ODN application for low temperature fish farming.

CpG-ODN induced antimicrobial immunity in neonatal chicks involves a substantial shift in serum metabolic profiles

Synthetic CpG-ODNs can promote antimicrobial immunity in neonatal chicks by enriching immune compartments and activating immune cells. Activated immune cells undergo profound metabolic changes to meet cellular biosynthesis and energy demands and facilitate the signaling processes. We hypothesize that CpG-ODNs induced immune activation can change the host’s metabolic demands in neonatal chicks. Here, we used NMR-based metabolomics to explore the potential of immuno-metabolic interactions in the orchestration of CpG-ODN-induced antimicrobial immunity. We administered CpG-ODNs to day-old broiler chicks via intrapulmonary (IPL) and intramuscular (IM) routes. A negative control group was administered IPL distilled water (DW). In each group (n = 60), chicks (n = 40) were challenged with a lethal dose of Escherichia coli, two days post-CpG-ODN administration. CpG-ODN administered chicks had significantly higher survival (P < 0.05), significantly lower cumulative clinical scores (P < 0.05), and lower bacterial loads (P < 0.05) compared to the DW control group. In parallel experiments, we compared NMR-based serum metabolomic profiles in neonatal chicks (n = 20/group, 24 h post-treatment) treated with IM versus IPL CpG-ODNs or distilled water (DW) control. Serum metabolomics revealed that IM administration of CpG-ODN resulted in a highly significant and consistent decrease in amino acids, purines, betaine, choline, acetate, and a slight decrease in glucose. IPL CpG-ODN treatment resulted in a similar decrease in purines and choline but less extensive decrease in amino acids, a stronger decrease in acetate, and a considerable increase in 2-hydroxybutyrate, 3-hydroxybutyrate, formic acid and a mild increase in TCA cycle intermediates (all P < 0.05 after FDR adjustment). These perturbations in pathways associated with energy production, amino acid metabolism and nucleotide synthesis, most probably reflect increased uptake of nutrients to the cells, to support cell proliferation triggered by the innate immune response. Our study revealed for the first time that CpG-ODNs change the metabolomic landscape to establish antimicrobial immunity in neonatal chicks. The metabolites highlighted in the present study can help future targeted studies to better understand immunometabolic interactions and pinpoint the key molecules or pathways contributing to immunity.

An integrated transcriptomics and metabolomics study of the immune response of newly hatched chicks to the cytosine-phosphate-guanine oligonucleotide stimulation

The immunological immaturity of the innate immune system during the first-week post-hatch enables pathogens to infect chickens, leading to the death of the animals. Current preventive solutions to improve the resistance of chicks to infections include vaccination, breeding, and sanitation. Other prophylactic solutions have been investigated, such as the stimulation of animal health with immunostimulants. Recent studies showed that administration of immune-modulators to one-day-old chicks, or in ovo, significantly reduces mortality in experimental bacterial or viral infection challenge models. Owing to a lack of molecular biomarkers required to evaluate chicken immune responses and assess the efficacy of vaccines or immune-modulators, challenge models are still used. One way to reduce challenge experiments is to define molecular signatures through omics approaches, resulting in new methodologies to rapidly screen candidate molecules or vaccines. This study aims at identifying a dual transcriptomics and metabolomics blood signature after administration of CpG-ODN (cytosine-phosphate-guanine oligodeoxynucleotides), a reference immune-stimulatory molecule. A clinical study was conducted with chicks and transcriptomics and metabolomics analyses were performed on whole-blood and plasma samples, respectively. Differentially expressed genes and metabolites with different abundance were identified in chicks treated with CpG-ODN. The results showed that CpG-ODN activated the innate immune system, within hours after administration, and its effect lasted over time, as metabolomics and transcriptomics profiles still varied 6 D after administration. In conclusion, through an integrated clinical omics approach, we deciphered in part the mode of action of CpG-ODN in post-hatch chicks.

Emerging Role of Mucosal Vaccine in Preventing Infection with Avian Influenza A Viruses

Avian influenza A viruses (AIVs), as a zoonotic agent, dramatically impacts public health and the poultry industry. Although low pathogenic avian influenza virus (LPAIV) incidence and mortality are relatively low, the infected hosts can act as a virus carrier and provide a resource pool for reassortant influenza viruses. At present, vaccination is the most effective way to eradicate AIVs from commercial poultry. The inactivated vaccines can only stimulate humoral immunity, rather than cellular and mucosal immune responses, while failing to effectively inhibit the replication and spread of AIVs in the flock. In recent years, significant progresses have been made in the understanding of the mechanisms underlying the vaccine antigen activities at the mucosal surfaces and the development of safe and efficacious mucosal vaccines that mimic the natural infection route and cut off the AIVs infection route. Here, we discussed the current status and advancement on mucosal immunity, the means of establishing mucosal immunity, and finally a perspective for design of AIVs mucosal vaccines. Hopefully, this review will help to not only understand and predict AIVs infection characteristics in birds but also extrapolate them for distinction or applicability in mammals, including humans.

Molecular cloning, characterization and expression profiles of Annexin family (ANXA1~A6) in yellow catfish (Pelteobagrus fulvidraco) and ANX regulation by CpG ODN responding to bacterial infection

Up to now, many previous reports have emphasized that Annexins (ANX) family played an important role in immune responses. Aeromonas hydrophila (A. hydrophila), the most common zoonotic pathogenic bacteria of yellow catfish (Pelteobagrus fulvidraco), can cause serious economic loss, especially to yellow catfish with high economic value. In our previous work, we demonstrated that synthetic oligodeoxynucleotides containing CpG motifs (CpG ODN) owned powerful immunostimulatory activity. However, the relationship among Pelteobagrus fulvidraco Annexins (Pf_ANX), CpG ODN and A. hydrophila is unknown. Therefore, we cloned Pf_ANX1-6 genes and analyzed its sequences, structures, genetic evolution, post-translation modifications (PTMs), Ca²⁺ ion binding sites and tissue distribution to reveal the relevance. In addition, we investigated the responses of ANXA1-6 and cytokines in intestine and spleen as well as morbidity/survival rate of fish post CpG ODN immunization and/or A. hydrophila infection. The results showed that compared with challenge alone (challenge-CK) group, the CpG immunization following challenge (CpG-challenge) group displayed relatively flat IL-1β level throughout in both organs. Meanwhile, the expression of IFN-γ and morbidity/survival rate of fish in CpG-challenge group showed a great improvement compared with the challenge-CK group. Our results indicated that CpG ODN could improve morbidity/survival by up-regulating Pf_ANXA 1, 2 and 5 in the intestine and spleen to ameliorate inflammatory responses and promote anti-infective responses. Our findings offer some important insights into ANX related to the immunity of fish infection and lay a theoretical basis for the prevention and treatment of fish infections.

Mucosal delivery of CpG-ODN mimicking bacterial DNA via the intrapulmonary route induces systemic antimicrobial immune responses in neonatal chicks

The transition to antibiotic-free poultry production in the face of pathogenic threats is a very challenging task. We recently demonstrated that mucosal delivery of CpG-ODN alone by the intrapulmonary route (IPL) has potential as an effective alternative to antibiotics in neonatal chicks against Escherichia coli septicemia. How exactly mucosal delivery of CpG-ODN elicits, protective antibacterial immunity remained poorly understood. In this study, CpG-ODN or saline was delivered via the intrapulmonary route to day-old chicks (n = 80/group) using a compressor nebulizer in an acrylic chamber (1 mg/mL CpG-ODN for 15 minutes). In the first part of the study, two days after mucosal CpG-ODN delivery, 40 chicks from each group were challenged subcutaneously with 1 × 10⁵ cfu (n = 20) or 1 × 10⁶ cfu (n = 20) of E. coli and the mortality pattern was monitored for seven days. We found significantly higher survival, better clinical conditions and lower bacterial loads in chicks that received mucosal CpG-ODN. To explore the mechanisms behind this protective immunity, we first looked at the kinetics of the cytokine gene expression (three birds/ group/ time for 10 time-points) in the lungs and spleens. Multiplex gene analysis demonstrated a significant elevation of pro-inflammatory cytokine genes mRNA in the CpG-ODN group. Interleukin (IL)-1β robustly upregulated many folds in the lung after CpG-ODN delivery. Lipopolysaccharide-induced tumor necrosis factor (LITAF) and IL-18 showed expression for an extended period in the lungs. Anti-inflammatory cytokine IL-10 was upregulated in both lungs and spleen, whereas IL-4 showed upregulation in the lungs. To investigate the kinetics of immune enrichment in the lungs and spleens, we performed flow cytometry, histology, and immunohistochemistry at 24, 48 and 72 hrs after CpG-ODN delivery. CpG-ODN treated lungs showed a significant enrichment with monocytes/macrophages and CD4⁺ and CD8⁺ T-cell subsets. Macrophages in CpG-ODN treated group demonstrated mature phenotypes (higher CD40 and MHCII expression). Importantly, mucosal delivery of CpG-ODN via the intrapulmonary route significantly enriched immune compartment in the spleen as well, suggesting a systemic effect in neonatal chicks. Altogether, intrapulmonary delivery of aerosolized CpG-ODN orchestrates protective immunity against E. coli septicemia by not only enhancing mucosal immunity but also the systemic immune responses.

Avian Pattern Recognition Receptor Sensing and Signaling

Pattern recognition receptors (PRRs) are a class of immune sensors that play a critical role in detecting and responding to several conserved patterns of microorganisms. As such, they play a major role in the maintenance of immune homeostasis and anti-microbial defense. Fundamental knowledge pertaining to the discovery of PRR functions and their ligands continue to advance the understanding of immune system and disease resistance, which led to the rational design and/or application of various PRR ligands as vaccine adjuvants. In addition, the conserved nature of many PRRs throughout the animal kingdom has enabled the utilization of the comparative genomics approach in PRR identification and the study of evolution, structural features, and functions in many animal species including avian. In the present review, we focused on PRR sensing and signaling functions in the avian species, domestic chicken, mallard, and domestic goose. In addition to summarizing recent advances in the understanding of avian PRR functions, the present review utilized a comparative biology approach to identify additional PRRs, whose functions have been well studied in mammalians but await functional characterization in avian.

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.

In Ovo Administration of Innate Immune Stimulants and Protection from Early Chick Mortalities due to Yolk Sac Infection

Omphalitis or yolk sac infection (YSI) and colibacillosis are the most common infectious diseases that lead to high rates of early chick mortalities (ECMs) in young chicks. Out of numerous microbial causes, avian pathogenic Escherichia coli (APEC) or extraintestinal pathogenic E. coli infections are considered the most common cause of these conditions. YSI causes deterioration and decomposition of yolk, leading to deficiency of necessary nutrients and maternal antibodies, retarded growth, poor carcass quality, and increased susceptibility to other infections, including omphalitis, colibacillosis, and respiratory tract infection. Presently, in ovo injection of antibiotics, heavy culling, or after hatch use of antibiotics is practiced to manage ECM. However, increased antibiotic resistance and emergence of "super bugs" associated with use or misuse of antibiotics in the animal industry have raised serious concerns. These concerns urgently require a focus on host-driven nonantibiotic approaches for stimulation of protective antimicrobial immunity. Using an experimental YSI model in newborn chicks, we evaluated the prophylactic potential of three in ovo-administered innate immune stimulants and immune adjuvants for protection from ECM due to YSI. Our data have shown >80%, 65%, and 60% survival with in ovo use of cytosine-phosphodiester-guanine (CpG) oligodeoxynucleotides (ODN), polyinosinic:polycytidylic acid, and polyphosphazene, respectively. In conclusion, data from these studies suggest that in ovo administration of CpG ODN may serve as a potential candidate for replacement of antibiotics for the prevention and control of ECM due to YSI in young chicks.

Intrapulmonary Delivery of CpG-ODN Microdroplets Provides Protection Against Escherichia coli Septicemia in Neonatal Broiler Chickens

Synthetic oligodeoxynucleotides (ODN) containing unmethylated cytosine phosphodiester guanine (CpG) motifs (CpG-ODN) are effective immunostimulatory agents against a variety of viral, bacterial, and protozoan diseases in different animals including poultry. We have recently demonstrated that in ovo injection of CpG-ODN confers protection in neonatal chickens against bacterial septicemias. The objective of this study was to investigate the effectiveness of needle-free intrapulmonary (IPL) delivery of CpG-ODN microdroplets against Escherichia coli infection in neonatal chicks. In the present study, we used 880 chicks in total keeping 40 chicks per group. Chicks were delivered CpG-ODN or saline by IPL at the day 1 of hatch. Three days later, chicks were challenged with two doses (1 × 10⁴ CFU, n = 20 or 1 × 10⁵ CFU, n = 20) of E. coli. Chicks treated with CpG-ODN by the IPL route had significantly lower clinical signs and bacterial load compared to the group treated with saline ( P < 0.05). CpG-ODN-treated groups were significantly protected against E. coli septicemia. We observed dose- and exposure time-dependent immunoprotective effects of IPL CpG-ODN in chicks. We found that IPL delivery of CpG-ODN can induce protective immunity as early as 6 hr that remains effective at least until day 5 post-treatment. Moreover, there were no adverse effects of IPL delivery of CpG-ODN on growth or mortality up to 42 days of age. Based on these findings, it can be suggested that CpG-ODN delivery by IPL route can be a promising alternative to antibiotics for inducing protective immunity in chicks during the critical first week of neonatal life.

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.

Immunostimulatory Activities of CpG-Oligodeoxynucleotides in Teleosts: Toll-Like Receptors 9 and 21

Toll-like receptors (TLRs) are pattern-recognition receptors that detect a wide variety of microbial pathogens for the initiation of host defense immunological responses. Thirteen TLRs have been identified in mammals, and teleosts contain 22 mammalian or non-mammalian TLRs. Of these, TLR9 and TLR21 are the cytosine-phosphate-guanosine-oligodeoxynucleotides (CpG-ODNs) recognition TLRs in teleosts. TLR9 is a mammalian TLR expressed in teleost but not in the avian species. TLR21 is a non-mammalian TLR expressed in both teleost and the avian species. Synthetic CpG-ODNs are potent immunostimulants that are being studied for their application against tumors, allergies, and infectious diseases, and as a vaccine adjuvant in humans. The immunostimulatory effects of CpG-ODNs as vaccine adjuvants and their antimicrobial function in domestic animals and teleosts are also being investigated. Most of our current knowledge about the molecular basis for the immunostimulatory activity of CpG-ODNs comes from earlier studies of the interaction between CpG-ODN and TLR9. More recent studies indicate that in addition to TLR9, TLR21 is another receptor for CpG-ODN recognition in teleosts to initiate immune responses. Whether these two receptors have differential functions in mediating the immunostimulatory activity of CpG-ODN in teleost has not been well-studied. Nevertheless, the existence of two recognition TLRs suggests that the molecular basis for the immunostimulatory activity of CpG-ODN in teleosts is different and more complex than in mammals. This article reviews the current knowledge of TLR9 and TLR21 activation by CpG-ODNs. The key points that need to be considered for CpG-ODNs as immunostimulants with maximum effectiveness in activation of immune responses in teleosts are discussed. This includes the structure/activity relationship of CpG-ODN activities for TLR9 and TLR21, the structure/functional relationship of these two TLRs, and differential expression levels and tissue distributions for these two TLRs.

Synthetic CpG-ODN rapidly enriches immune compartments in neonatal chicks to induce protective immunity against bacterial infections

Oligodeoxynucleotides containing CpG motifs (CpG-ODN) induce innate immunity against bacterial infections. Despite recent advances, how CpG-ODN alone protects against bacterial infections remained elusive. Here, we report for the first time, to our knowledge, that CpG-ODN orchestrates anti-microbial protective immunity by inducing a rapid enrichment of various immune compartments in chickens. In this study, eighteen-day-old embryonated eggs were injected with either 50 µg of CpG-ODN or saline (~n = 90 per group). In the first experiment, four days after CpG-ODN treatment, chicks were challenged subcutaneously with a virulent strain of Escherichia coli (E. coli) and mortality was monitored for 8 days. We found significant protection, and reduced clinical scores in CpG-ODN treated chicks. To gain insights into mechanisms of protection induced by CpG-ODN, first we investigated cytokine expression kinetics elicited by CpG-ODN. The spleen and lung were collected from embryos or chicks (n = 3-4 per group) at 10 time points post-CpG-ODN inoculation. Multiplex gene analysis (interleukin (IL)-1, IL-4, IL-6, IL-10, IL-18, interferon (IFN)-γ, IFN-α, and lipopolysaccharide induced tumor necrosis factor (LITAF), revealed a significantly higher expression of pro-inflammatory cytokines following CpG-ODN treatment compared to the saline controls. In our study, LITAF stands out in the cytokine profiles of spleen and lungs, underscoring its role in CpG-ODN-induced protection. The third experiment was designed to examine the effects of CpG-ODN on immune cell populations in spleen, lungs, and thymus. Flow cytometry analysis was conducted at 24, 48 and 72 hrs (thymus only collected at 72 hr) after CpG-ODN administration to examine the changes in CD4⁺ and CD8⁺ T-cell subsets, monocyte/macrophage cell populations and their expression of maturation markers (CD40 and CD86). Flow cytometry data indicated a significant enrichment of macrophages, CD4⁺ and CD8⁺ T-cell subsets in both spleen and lungs of CpG-ODN treated embryos and chicks. Macrophages in spleen and lungs showed an upregulation of CD40 but not CD86, whereas thymocytes revealed significantly high CD4 and CD8 expression. Overall, the present study has demonstrated that CpG-ODN provides protection in neonatal chicks against E. coli infection not only by eliciting cytokine responses and stimulating immune cells but also through enriching immunological niches in spleen and lungs.

CpG oligodeoxynucleotide-specific duck TLR21 mediates activation of NF-κB signaling pathway and plays an important role in the host defence of DPV infection

TLR21 can recognize unmethylated cytosine-phosphate-guanine oligodeoxynucleotides (CpG-ODN) and activates NF-κB immune signaling pathway. However, the function of TLR21 in duck remains largely unclear. Here, the complete duck TLR21 (duTLR21) cDNA was cloned from Cherry Valley duck for the first time, and its immune response was preliminarily studied. Tissue specificity analysis showed duTLR21 was higher expressed in the peripheral blood, spleen, bursa of Fabricius and cecum. The expression of duTLR21 was significantly upregulated after stimulation with CpG-ODN or duck plague virus (DPV), but not Tembusu virus (TMUV), LPS or Poly (I:C). In addition, the transfection of DEF with duTLR21 stimulated by CpG-ODN activated NF-κB, through this signal pathway, the transcription of IL-1β, IL-6 and IFN-α were promoted, whereas knockdown of duTLR21 impaired the transcription of these genes. Furthermore, the overexpression of duTLR21 inhibited the replication of the DPV and the knockdown of duTLR21 by shRNA significantly promoted DPV replication in vitro. Altogether, these results indicate that duTLR21 can be activated by CpG-ODN, which mediates activation of NF-κB signaling pathway, and plays an important role in the host defence of DPV infection.

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.

Protection of Neonatal Broiler Chickens Following in ovo Delivery of Oligodeoxynucleotides Containing CpG Motifs (CpG-ODN) Formulated with Carbon Nanotubes or Liposomes

Unformulated oligodeoxynucleotides (ODN) containing CpG motifs (CpG-ODN) have been shown to stimulate the innate immune system against a variety of bacterial, viral, and protozoan infections in a variety of vertebrate species. We have previously shown that in ovo delivery of unformulated CpG-ODN was able to significantly protect neonatal broiler chickens against Escherichia coli or Salmonella Typhimurium infections. The objectives of this study were to examine the safety and immunoprotective effects of CpG-ODN formulated with 2 types of carbon nanotubes (CNTs) or 2 types of lipid-surfactant (LSC) delivery systems in neonatal broilers against E. coli septicemia. Embryonated eggs, which had been incubated for 18 days, received either 50 μg of CNT-CpG-ODN, 50 μg of LSC-CpG-ODN, 50 μg of unformulated CpG-ODN, or saline. Four days after exposure to CpG-ODN (day 1 posthatch), 1 x 10(4) or 1 x 10(5) colony-forming units of a virulent strain of E. coli isolated from a turkey with septicemia were inoculated subcutaneously in the neck. Clinical signs, pathology, bacterial isolations from the air sacs, and mortality were observed for 8 days following challenge with E. coli. Bacterial isolations and pathologic observations were conducted immediately after birds were dead or euthanatized. The survival rate of birds in groups receiving saline following E. coli infection was 20% to 30%. In contrast, birds receiving CpG-ODN formulations had a significantly higher survival rate of 60% to 80% (P < 0.01). Bacterial loads and clinical scores were significantly lower (P < 0.05) in groups treated with CNT- or LSC-CpG-ODN compared to the groups receiving CpG-ODN or saline. Moreover, there is no evidence of any adverse effects of these formulations in any organs or in growth rates of birds until 42 days of age. This is the first time that CpG-ODN formulated with CNT and LSC have been demonstrated to have an immunomodulatory effect against an E. coli infection in neonatal broiler chickens following in ovo delivery.

Immune responses associated with homologous protection conferred by commercial vaccines for control of avian pathogenic Escherichia coli in turkeys

Avian pathogenic Escherichia coli (APEC) infections are a serious impediment to sustainable poultry production worldwide. Licensed vaccines are available, but the immunological basis of protection is ill-defined and a need exists to extend cross-serotype efficacy. Here, we analysed innate and adaptive responses induced by commercial vaccines in turkeys. Both a live-attenuated APEC O78 ΔaroA vaccine (Poulvac® E. coli) and a formalin-inactivated APEC O78 bacterin conferred significant protection against homologous intra-airsac challenge in a model of acute colibacillosis. Analysis of expression levels of signature cytokine mRNAs indicated that both vaccines induced a predominantly Th2 response in the spleen. Both vaccines resulted in increased levels of serum O78-specific IgY detected by ELISA and significant splenocyte recall responses to soluble APEC antigens at post-vaccination and post-challenge periods. Supplementing a non-adjuvanted inactivated vaccine with Th2-biasing (Titermax® Gold or aluminium hydroxide) or Th1-biasing (CASAC or CpG motifs) adjuvants, suggested that Th2-biasing adjuvants may give more protection. However, all adjuvants tested augmented humoral responses and protection relative to controls. Our data highlight the importance of both cell-mediated and antibody responses in APEC vaccine-mediated protection toward the control of a key avian endemic disease.

Development of a subunit vaccine containing recombinant Riemerella anatipestifer outer membrane protein A and CpG ODN adjuvant

Riemerella anatipestifer, a Gram-negative bacillus, causes septicemia that can result in high mortality for ducklings. In this study, we evaluated the immune response and protective efficacy provided by a subunit vaccine containing recombinant outer membrane protein A (rOmpA) and plasmid constructs containing CpG oligodeoxynucleotides (ODN). Results showed that CpG ODN enhanced both humoral and cell-mediated immunity elicited by rOmpA as early as two weeks after primary immunization. When compared to ducks immunized with rOmpA, ducks immunized with rOmpA+CpG ODN showed higher levels (p<0.05) of antibody titer, T cell proliferation, and percentages of CD4(+) and CD8(+) T cell in peripheral blood mononuclear cells (PBMCs). The relative fold inductions of mRNA expression of Th1-type (IFN-γ and IL-12), and Th2-type (IL-6) cytokines in PBMCs isolated from ducks immunized with rOmpA+CpG ODN were significantly higher than those of the rOmpA group. Homologous challenge result showed that the rOmpA+CpG ODN vaccine reduced the pathological score by 90% in comparison with the saline control. In conclusion, our study found that CpG ODN can enhance both humoral and cellular immunity elicited by a rOmpA vaccine. The rOmpA+CpG ODN vaccine can be further developed as a subunit vaccine against R. anatipestifer.

Class B CpG ODN stimulation upregulates expression of TLR21 and IFN-γ in chicken Harderian gland cells

This study aimed to evaluate the response of Harderian gland (HG) cells after in vitro stimulation with class B synthetic oligodeoxyribonucleotides (ODN) containing CpG motifs. This knowledge is of importance for the development of mucosal vaccines for poultry, such as eye-drop or spray vaccines, to determine if class B CpG ODN can act as an vaccine adjuvant or as a prophylactic treatment mainly against respiratory disease viruses. The relative expression of Toll-like receptor 21 (TLR21), interferon (IFN)-γ, interleukin (IL)-1β and IL-10 genes were quantified at 1, 3, 6 and 18 h post-stimulation of HG cells from 5-week-old birds. In addition, it was also investigated if expression of these genes was affected by the age of the birds (differences between 5- and 12-week-old birds), concentrations of ODN or cell preparation method used. Class B CpG ODN induced upregulation of TLR21 and IFN-γ mRNA expression levels at 1h post-stimulation depending on concentration of ODN used but only in HG cells isolated from young birds.

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.

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.

Sinonasal epithelial cell expression of Toll-like receptor 9 is elevated in cystic fibrosis-associated chronic rhinosinusitis

BACKGROUND

Cystic fibrosis (CF) patients frequently suffer from chronic rhinosinusitis (CRS). The extent to which alterations in sinonasal innate immunity contribute to this disease process is unknown. Activation of sinonasal epithelial cell (SNEC) Toll-like receptors (TLRs), an important component of the innate immune system, may be associated with the hyperinflammatory state observed in sinonasal mucosa of CF patients with CRS. This study compares expression of Toll-like receptor 9 (TLR9), in SNRCs collected from CF subjects with CRS to that of normal control subjects.

METHODS

This was a prospective study measuring TLR9 on SNECs collected via endoscopic-guided middle meatal brushings from 8 adult controls and 14 adult subjects with CF-associated CRS.

RESULTS

TLR9 expression was significantly elevated in CF subjects at 91% ± 6% when compared with 76% ± 10% in normal controls (p = 0.001).

CONCLUSION

The significantly greater expression of sinonasal epithelial TLR9 in CF likely reflects increased antimicrobial innate immune activity in chronically colonized and frequently infected CF individuals. However, this finding contrasts with previously reported decreased epithelial TLR9 expression in eosinophilic CRS with nasal polyposis and may indicate differential modulation of innate immunity in Th1-predominent CF versus Th2-dominated CRS with nasal polyps, despite both being diseases of sinonasal mucosal inflammation.

Characterization of responses initiated by different Toll-like receptor 2 ligands in chicken spleen cells

Toll-like receptors (TLRs) are pattern recognition receptors that mediate host responses to pathogens by promoting cellular activation and the production of cytokines. Ligands for TLRs are conserved structural motifs of pathogens termed pathogen-associated molecular patterns. In the case of TLR2, these ligands include peptidoglycan, lipomannan and lipopeptides. In mammals, it has been shown that different TLR2 ligands induce distinct cytokine responses. However, whether a similar phenomenon occurs in chickens remains to be determined. To this end, chicken splenocytes were stimulated with three different TLR2 ligands: Pam3CSK4, FSL-1 and lipomannan, and the relative gene expression of several cytokines was quantified at 2, 6 and 18h post-stimulation. The results suggest that Pam3 and FSL-1 modulate the kinetics of the pro-inflammatory cytokine response differently, as Pam3 induced a robust interleukin (IL)-1β response, while FSL-1 induced an early and prolonged up-regulation of IL-8. Furthermore, it appears that all three TLR2 ligands induce a mixed T-helper (TH) 1 and 2-like response, as characterized by the up-regulation of IFN-γ, IL-12, IL-4 and IL-13. In conclusion, we have demonstrated that different TLR2 ligands may induce different cytokine responses in chicken splenocytes. Future studies may be aimed at examining the immunomodulating effects of these ligands in vivo.

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.

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.

Treatment with ligands for toll-like receptors 2 and 5 induces a mixed T-helper 1- and 2-like response in chicken splenocytes

Toll-like receptors (TLRs) play an important role in the induction of host responses to pathogens. Interactions between TLRs and their ligands result in the production of cytokines that modulate the adaptive immune response through polarizing CD4+ T cells into either T-helper (T(H))1 or T(H)2 phenotypes. In this regard, TLR2 and TLR5 ligands have been shown to induce responses in mammals that are biased toward T(H)1 or T(H)2 phenotypes. However, whether a similar phenomenon occurs in chickens remains to be elucidated. To this end, chicken splenocytes were stimulated with the TLR2 ligand Pam3CSK4 and the TLR5 ligand flagellin, and the relative expression of several cytokines and transcription factors was quantified at 1, 3, 8, and 18 h poststimulation. The results suggest that both TLR ligands induce a mixed T(H)1- and T(H)2-like response, as characterized by the upregulation of both the T(H)1-associated cytokine interferon-γ and the T(H)1-inducing cytokine interleukin (IL)-12, in addition to the T(H)2-associated cytokine IL-4, and in the case of flagellin, IL-13 as well. Future studies may be aimed at assessing the adjuvant potential of these ligands.

Prophylactic treatment with Toll-like receptor ligands enhances host immunity to avian influenza virus in chickens

Avian influenza viruses (AIV) pose a threat towards the health of both poultry and humans. To interrupt the transmission of the virus, novel prophylactic strategies must be considered which may reduce the shedding of AIV. One potential is the prophylactic use of Toll-like receptor (TLR) ligands. Many cells of the immune system express TLRs, and cellular responses to TLR stimulation include activation and the production of cytokines. TLR ligands have been employed as prophylactic treatments to enhance host resistance to pathogens both in mammals and chickens. Therefore, the present study was conducted to determine whether TLR ligands may be used prophylactically in chickens to enhance host immunity to AIV. Chickens received intramuscular injections of either low or high doses of the TLR ligands poly I:C, lipopolysaccharide (LPS) and CpG ODN. Twenty-four hours post-treatment, chickens were infected with the low pathogenic avian influenza virus H4N6, and both oropharyngeal and cloacal virus shedding were assessed on days 4 and 7 post-infection. To identify potential correlates of immunity, spleen and lungs were collected on days 2, 4 and 7 post-infection for RNA extraction. The results suggested that all of the TLR ligand treatments induced a significant reduction in virus shedding, with the TLR3 ligand poly I:C conferring the greatest AIV immunity compared to control birds, followed by CpG ODN and LPS. Furthermore, transcriptional analysis of gene expression in the spleen and lungs suggest IFN-α and IL-8 as correlates of immunity conferred by poly I:C, and IFN-γ for CpG ODN and LPS. In conclusion, TLR ligands, have the ability to enhance host immunity against AIV, and future studies should consider exploring the combinatory effects of poly I:C and CpG ODN prophylaxis in conjunction with AIV vaccination.

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.

Expression of Toll-like receptors 2, 4 and 9 in patients with Guillain-Barré syndrome

OBJECTIVE

A myriad of transcription factors and inflammatory cytokines have been described to participate in the pathogenesis of Guillain-Barré syndrome (GBS). However, the innate immunity components--Toll-like receptors (TLRs)--have never been explored in this disease. We therefore investigated the expression of TLR2, 4 and 9 in the peripheral circulation of GBS patients as well as healthy controls.

METHODS

Twenty-one GBS patients and 21 healthy donors participated in this study. Peripheral blood mononuclear cells were used for mRNA and protein analysis of TLR-related molecules. Also, peripheral blood mononuclear cells from different subjects were incubated with different TLR agonists and the subsequent IFN-γ secretion was determined.

RESULTS

Expression of TLR2, 4 and 9 as well as their related signaling molecules were higher in GBS patients compared to healthy controls. Disability scores of GBS patients had a strong positive correlation with the high levels of expression of TLR2, 4 and 9.

CONCLUSIONS

The TLR signaling pathway may be involved in the pathogenesis of GBS.

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.

Inactivation of TLR9 by a suppressive oligodeoxynucleotides can ameliorate the clinical signs of EAN

Susceptible-strain animals immunized with P2 peptide could generate the disease of experimental autoimmune neuritis (EAN) with inflammation and demyelination of peripheral nerve. A myriad of transcription factors and inflammatory cytokines have been found to participate in this process; however, the roles of toll-like receptors (TLRs) are poorly understood in EAN. The aim of this study is to explore the role of TLR9 in the pathogenesis of EAN. The EAN was induced in Lewis rat by immunization with P2(53-78) and complete Freund's adjuvant. CpG oligodeoxynucleotides (ODN) (cODN), a suppressive ODN (sODN) and a control non-specific ODN (nODN) were respectively administered to explore the role of TLR9 in EAN both in vivo and vitro. Following immunization up to the peak phase of EAN, EAN rats inoculated with sODN had remarkably better clinical score of EAN and expressed a significantly inhibited TLR9 signaling pathway. Our study suggests that TLR9 may be involved in the pathogenesis of EAN.

CpG oligodeoxynucleotides containing GACGTT motifs enhance the immune responses elicited by a goose parvovirus vaccine in ducks

Recombinant parvovirus VP2 (rVP2) was formulated with different types of adjuvant, including aluminum adjuvant and CpG oligodeoxynucleotides (ODNs), and the immunological responses after vaccination in ducks were examined. In comparison with the control group, production of rVP2-specific antibodies, expression of cytokines in peripheral blood mononuclear cells (PBMC) stimulated by rVP2, and percentage of CD4(+)/CD8(+) cells in PBMC were significantly increased in ducks immunized with rVP2 formulated with CpG ODNs containing 3 copies of GACGTT motif. CpG ODNs with GACGTT motifs might be used to improve the efficacy of vaccines for ducks.

An Assay in Microtitre Plates for Absolute Abundance of Chicken Interferon Alpha Transcripts

Immunosuppression of commercial chickens is a serious animal health and economic problem in the poultry industry. The major causes of the immunosuppression are viruses that suppress transcription of interferon genes, especially interferon alpha. There is a need for monitoring immunosuppression in commercially bred chickens. For this purpose, the absolute abundance of interferon alpha transcripts can be measured in blood of chickens by a suitable assay. Such an assay was used to estimate abundance of chicken interferon alpha in a sample of splenic cells induced with polyinosinic polycytidylic acid. The abundance measured was 29 ± 2 attomoles/µg total RNA. This assay can be performed in microtitre plates using samples collected from chickens in poultry houses.

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.

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.

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.