Effects of ligands for Toll-like receptors 3, 4, and 21 as adjuvants on the immunogenicity of an avian influenza vaccine in chickens

Safety and efficacy of toll-like receptor agonists as therapeutic agents and vaccine adjuvants for infectious diseases in animals: a systematic review

Introduction

Strengthening global health security relies on adequate protection against infectious diseases through vaccination and treatment. Toll-like receptor (TLR) agonists exhibit properties that can enhance immune responses, making them potential therapeutic agents or vaccine adjuvants.

Methods

We conducted an extensive systematic review to assess the efficacy of TLR agonists as therapeutic agents or vaccine adjuvants for infectious diseases and their safety profile in animals, excluding rodents and cold-blooded animals. We collected qualitative and available quantitative data on the efficacy and safety outcomes of TLR agonists and employed descriptive analysis to summarize the outcomes.

Results

Among 653 screened studies, 51 met the inclusion criteria. In this review, 82% (42/51) of the studies used TLR agonists as adjuvants, while 18% (9/51) applied TLR agonist as therapeutic agents. The predominant TLR agonists utilized in animals against infectious diseases was CpG ODN, acting as a TLR9 agonist in mammals, and TLR21 agonists in chickens. In 90% (46/51) of the studies, TLR agonists were found effective in stimulating specific and robust humoral and cellular immune responses, thereby enhancing the efficacy of vaccines or therapeutics against infectious diseases in animals. Safety outcomes were assessed in 8% (4/51) of the studies, with one reporting adverse effects.

Discussion

Although TLR agonists are efficacious in enhancing immune responses and the protective efficacy of vaccines or therapeutic agents against infectious diseases in animals, a thorough evaluation of their safety is imperative to in-form future clinical applications in animal studies.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=323122.

Evaluation of Adjuvant Effect of Cytosine-Guanosine-Oligodeoxynucleotide in Meat-Type Chickens Coadministered In Ovo with Herpesvirus of Turkey Vaccine

Herpesvirus of turkey (HVT) increases activation of T cells in 1-day-old chickens when administered in ovo. This study evaluated whether adding cytosine-guanosine oligodeoxynucleotides (CpG ODNs) to the HVT vaccine could enhance the adjuvant effect of HVT. We used a CpG ODN dose of 10 μg per egg. The experimental groups were (1) diluent-only control (sham), (2) HVT, (3) HVT+CpG ODN, (4) HVT+non-CpG ODN, (5) CpG ODN, and (6) non-CpG ODN control. Cellular response evaluation included measuring the frequencies of macrophages (KUL01+MHC-II+), gamma delta T cells (γδTCR+MHC-II+), CD4+, and CD8+ T cell subsets, including double-positive (DP) cells. In addition, CD4+ and CD8+ T cell activation was evaluated by measuring the cellular expression of major histocompatibility complex class II (MHC-II), CD44 or CD28 costimulatory molecules. An adjuvant effect was considered when HVT+CpG ODN, but not HVT+non CpG ODN, or CpG ODN, or non-CpG ODN, induced significantly increased effects on any of the immune parameters examined when compared with HVT. The findings showed that (1) HVT vaccination induced significantly higher frequencies of γδ+MHC-II+ and CD4+CD28+ T cells when compared with sham chickens. Frequencies of DP and CD4+CD28+ T cells in HVT-administered birds were significantly higher than those observed in the non-CpG ODN group. (2) Groups receiving HVT+CpG ODN or CpG ODN alone were found to have significantly increased frequencies of activated CD4+ and CD8+ T cells, when compared with HVT. Our results show that CpG ODN administration in ovo with or without HVT significantly increased frequencies of activated CD4+ and CD8+ T cells.

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.

In ovo HVT vaccination enhances cellular responses at hatch and addition of poly I:C offers minimal adjuvant effects

In ovo vaccination with herpesvirus of turkey (HVT) hastens immunocompetence in chickens and the recommended dose (RD) of 6080 plaque-forming-units (PFU) offers the most optimal effects. In previous studies conducted in egg-type chickens, in ovo vaccination with HVT enhanced lymphoproliferation, wing-web thickness with phytohemagglutinin-L (PHA-L), and increased spleen and lung interferon-gamma(IFN-γ) andToll-like receptor 3 (TLR3) transcripts. Here, we evaluated the cellular mechanisms by which HVT-RD can hasten immunocompetence in one-day-old meat-type chickens, and also determined if HVT adjuvantation with a TLR3 agonist, polyinosinic-polycytidylic acid (poly(I:C)), could enhance vaccine-induced responses and provide dose-sparing effects. Compared to sham-inoculated chickens, HVT-RD significantly increased transcription of splenic TLR3 and IFN γ receptor 2 (R2), and lung IFN γ R2, while the splenic IL-13 transcription was found decreased. Additionally, these birds showed increased wing-web thickness following PHA-L inoculation. The thickness was due to an innate inflammatory cell population, CD3⁺ T cells, and edema. In another experiment, HVT-1/2 (3040 PFU) supplemented with 50 μg poly(I:C) [HVT-1/2 + poly(I:C)] was administered in ovo and immune responses were compared with those produced by HVT-RD, HVT-1/2, 50 μg poly(I:C), and sham-inoculated. Immunophenotyping of splenocytes showed HVT-RD induced a significantly higher frequency of CD4⁺, CD4⁺MHC-II⁺, CD8⁺CD44⁺, and CD4⁺CD28⁺ T cells compared to sham-inoculated chickens, and CD8⁺MHC-II⁺, CD4⁺CD8⁺, CD4⁺CD8⁺CD28⁺, and CD4⁺CD8⁺CD44⁺ T cells compared to all groups. Treatment groups, except HVT-1/2 + poly(I:C), had significantly higher frequencies of γδ T cells and all groups induced significantly higher frequencies of activated monocytes/macrophages, compared to sham-inoculated chickens. Poly(I:C)-induced dose-sparing effect was only observed in the frequency of activated monocytes/macrophages. No differences in the humoral responses were observed. Collectively, HVT-RD downregulated IL-13 transcripts (Th2 immune response) and had strong immunopotentiation effects on innate immune responses and the activation of T cells. However addition of poly(I:C) offered a minimal adjuvant/dose-sparing effect.

Characterization of Dosage Levels for In Ovo Administration of Innate Immune Stimulants for Prevention of Yolk Sac Infection in Chicks

Innate immune stimulants, especially toll-like receptor (TLR) ligands and agonists, are the main players in the initiation of innate immunity and have been widely studied as alternatives to antibiotics to control infection. In the present study, we characterized the dosage levels of various innate immune stimulants, including unmethylated cytosine-phosphate-guanosine dinucleotide -containing oligodeoxynucleotides (CpG ODN), polyinosinic-polycytidylic acid (poly I:C), cyclic polyphosphazene 75B (CPZ75B), avian beta-defensin 2 (ABD2), and combinations of these reagents given in ovo. Data derived from a series of animal experiments demonstrated that the in ovo administration of 10–50 µg CpG ODN/embryo (on embryonic day 18) is an effective formulation for control of yolk sac infection (YSI) due to avian pathogenic Escherichia coli (E. coli) in young chicks. Amongst the different combinations of innate immune stimulants, the in ovo administration of CpG ODN 10 µg in combination with 15 µg of poly I:C was the most effective combination, offering 100% protection from YSI. It is expected that the introduction of these reagents to management practices at the hatchery level may serve as a potential replacement for antibiotics for the reduction of early chick mortality (ECM) due to YSI/colibacillosis.

Probiotic Lactobacilli Enhance Immunogenicity of an Inactivated H9N2 Influenza Virus Vaccine in Chickens

Avian influenza viruses (AIVs) infect a wide range of hosts, including humans and many avian species. Efforts have been made to control this pathogen in chickens using vaccination programs, but that has been met with varying degrees of success. Therefore, identification of more efficacious vaccination strategies is warranted. This study was undertaken to investigate the potential effects of probiotics on the immunogenicity of a beta-propiolactone-whole inactivated virus (WIV) vaccine of H9N2 subtype adjuvanted with the Toll-like receptor-21 ligand, CpG oligodeoxynucleotides 2007 (CpG). Eighty-four 1-day-old White Leghorn layers were allocated into six groups. Two out of six groups received a mixture of probiotic Lactobacillus spp. (PROB) biweekly from days 1 35 of age. Chickens were intramuscularly vaccinated with WIV either alone or adjuvanted with AddaVax™ (WIV+Add) or CpG (WIV+CpG), and one group received saline (phosphate-buffered saline). Primary and secondary vaccinations occurred at days 14 and 28 of age, respectively. The results revealed that the group that received probiotics and was vaccinated with CpG-adjuvanted WIV H9N2 vaccine had higher hemagglutination inhibition titers than the other treatment groups at days 14 and 21 postprimary vaccination. Probiotics did not induce higher IgM or IgY titers in chickens receiving the WIV vaccine only. Concerning their effect on cell-mediated immune responses, probiotics enhanced interferon-gamma (IFN-γ) gene expression and significantly increased secretion of IFN-γ protein by splenocytes in chickens vaccinated with CpG-adjuvanted WIV H9N2. Together, these findings suggest the use of probiotics to enhance the immunogenicity of CpG-adjuvanted WIV H9N2 vaccines. Additional studies are required to better understand the specific interactions between probiotics and the gut microbiota and different types of cells of the gastrointestinal tract to decipher the underlying mechanisms of how probiotics modulate immune responses to vaccines.

Induction of Robust Immune Responses by CpG-ODN-Loaded Hollow Polymeric Nanoparticles for Antiviral and Vaccine Applications in Chickens

Background

Poultry vaccine has limited choices of adjuvants and is facing severe threat of infectious diseases due to ineffective of widely used commercial vaccines. Thus, development of novel adjuvant that offers safe and effective immunity is of urgent need.

Materials and Methods

The present research engineers a novel chicken adjuvant with potent immune-potentiating capability by incorporating avian toll-like receptor 21 (TLR21) agonist CpG ODN 2007 with a poly(lactic-co-glycolic acid) (PLGA)-based hollow nanoparticle platform (CpG-NP), which subsequently assessed ex vivo and in vivo.

Results

CpG-NPs with an average diameter of 164 nm capable of sustained release of CpG for up to 96 hours were successfully prepared. With the ex vivo model of chicken bone marrow-derived dendritic cells (chBMDCs), CpG-NP was engulfed effectively and found to induce DC maturation, promoting dendrite formation and upregulation of CD40, CD80 and CCR7. In addition to enhanced expression of IL-1β, IL-6, IL-12 and IFN-γ, 53/84 immune-related genes were found to be stimulated in CpG-NP-treated chBMDCs, whereas only 39 of such genes were stimulated in free CpG-treated cells. These upregulated genes suggest immune skewing toward T helper cell 1 bias and evidence of improved mucosal immunity upon vaccination with the CpG-NP. The CpG-NP-treated chBMDCs showed protective effects to DF-1 cells against avian influenza virus H6N1 infection. Upon subsequent coupling with infectious bronchitis virus subunit antigen administration, chickens were immunostimulated to acquire higher humoral immune response and protective response against viral challenge.

Conclustion

This work presents a novel hollow CpG-NP formulation, demonstrating effective and long-lasting immunostimulatory ability ex vivo and in vivo for chickens, as systemically compared to free CpG. This enhanced immune stimulation benefits from high stability and controlled release of internal component of nanoparticles that improve cellular delivery, lymphoid organ targeting and sustainable DC activation. CpG-NP has broad application potential in antiviral and vaccine development.

Antiviral responses against chicken respiratory infections: Focus on avian influenza virus and infectious bronchitis virus

Some of the respiratory viral infections in chickens pose a significant threat to the poultry industry and public health. In response to viral infections, host innate responses provide the first line of defense against viruses, which often act even before the establishment of the infection. Host cells sense the presence of viral components through germinal encoded pattern recognition receptors (PRRs). The engagement of PRRs with pathogen-associated molecular patterns leads to the induction of pro-inflammatory and interferon productions. Induced antiviral responses play a critical role in the outcome of the infections. In order to improve current strategies for control of viral infections or to advance new strategies aimed against viral infections, a deep understanding of host-virus interaction and induction of antiviral responses is required. In this review, we summarized recent progress in understanding innate antiviral responses in chickens with a focus on the avian influenza virus and infectious bronchitis virus.

Effect of TLR agonist on infections bronchitis virus replication and cytokine expression in embryonated chicken eggs

Avian infectious bronchitis (IB) is an acute, highly infectious and contagious viral disease of chickens caused by avian infectious bronchitis virus (IBV) belonging to the genus Coronavirus and family Coronaviridae. It can affect all age groups of birds. The toll-like receptors (TLRs) are a major class of innate immune pattern recognition receptors that have a key role in immune response and defense against various infections.The TLRs are essential for initiation of innate immune responses and in the development of adaptive immune responses. An in ovo model was employed to study the antiviral activity of TLR ligands (Pam3CSK4, LPS and CpG ODN) on replication of IBV. It was hypothesized that optimum dose and specific timing of TLR ligands may reduce viral load of IBV in specific pathogen free (SPF) embryonated chicken eggs (ECEs). Further, the mechanism involved in the TLR-mediated antiviral response in chorioallantoic membrane (CAM) of ECEs was investigated. The ECEs of 9-11 days old were treated with different doses (high, intermediate and low) of TLR-2 (Pam3CSK4), TLR-4 (LPS) and TLR-21 (CpG ODN) ligands. In addition, to know the timing of TLR ligand treatment, six time intervals were analyzed viz. 36, 24 and 12 h prior to infection, time of infection (co-administration of TLR ligands and avian IBV) and 12 and 24 h post-IBV infection. For studying the relative expression of immuno-stimulatory genes (IFN-α, IFN-β, IFN-γ, IL-1β, iNOS and OAS) in CAM, TLR ligands were administered through intra-allantoicroute and CAM were collected at 4, 8 and 16 h post treatment. The results demonstrated that intermediate dose of all the three TLR ligands significantly reduced virus titers and used in the present study. However, the LPS reduced virus titer pre- and post-IBV infection but Pam3CSK4 and CpG ODN reduced only pre-IBV infection. Further analysis showed that TLR ligands induced IFN-γ, IL-1β and IFN stimulated genes viz. iNOS and OAS genes in CAM. The present study pointed towards the novel opportunities for rational design of LPS as immuno-stimulatory agent in chickens with reference to IBV. It may be speculated that in ovo administration of these TLR ligands may enhance resistance against viral infection in neonatal chicken and may contribute towards the development of more effective and safer vaccines including in ovo vaccines.

Chicken toll-like receptors and their significance in immune response and disease resistance

Infectious diseases are a major challenge for the poultry industry that causes widespread production losses. Thus, management and control of poultry health and diseases are essential for the viability of the industry. Toll-like receptors are best characterized as membrane-bound receptors that perform a central role in immune homeostasis and disease resistance by recognition of pathogen-associated molecular patterns. In response to pathogen recognition, TLRs initiate both innate and adaptive immune responses which may help to develop immunomodulatory therapeutics for TLR associated diseases. Vaccination produces specific immunity in the animal's body towards pathogens. However, due to certain disadvantages of vaccines, (inactivation of attenuated pathogens into the virulent strains and weak immunogenicity of inactivated vaccines) there is a crucial need to develop the safe and effective therapeutic intervention. TLR ligands have been classified as a potential adjuvant against the infectious diseases in farm animals. TLR adjuvants induce both specific and nonspecific immune responses in chickens to combat several bacterial, viral and parasitic diseases. Therefore, the aim of this review was to explore the chicken TLR4 and their role in immune responses and disease resistance to develop disease resistance poultry breeds in future.

The effects of in ovo administration of encapsulated Toll-like receptor 21 ligand as an adjuvant with Marek's disease vaccine

Marek’s Disease Virus (MDV) is the causative agent of a lymphoproliferative disease, Marek’s disease (MD) in chickens. MD is only controlled by mass vaccination; however, immunity induced by MD vaccines is unable to prevent MDV replication and transmission. The herpesvirus of turkey (HVT) vaccine is one of the most widely used MD vaccines in poultry industry. Vaccines can be adjuvanted with Toll-like receptor ligands (TLR-Ls) to enhance their efficacy. In this study, we examined whether combining TLR-Ls with HVT can boost host immunity against MD and improve its efficacy. Results demonstrated that HVT alone or HVT combined with encapsulated CpG-ODN partially protected chickens from tumor incidence and reduced virus replication compared to the control group. However, encapsulated CpG-ODN only moderately, but not significantly, improved HVT efficacy and reduced tumor incidence from 53% to 33%. Further investigation of cytokine gene profiles in spleen and bursa of Fabricius revealed an inverse association between interleukin (IL)-10 and IL-18 expression and protection conferred by different treatments. In addition, the results of this study raise the possibility that interferon (IFN)-β and IFN-γ induced by the treatments may exert anti-viral responses against MDV replication in the bursa of Fabricius at early stage of MDV infection in chickens.

Characterization of immunogenicity of avian influenza antigens encapsulated in PLGA nanoparticles following mucosal and subcutaneous delivery in chickens

Mucosal vaccine delivery systems have paramount importance for the induction of mucosal antibody responses. Two studies were conducted to evaluate immunogenicity of inactivated AIV antigens encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs). In the first study, seven groups of specific pathogen free (SPF) layer-type chickens were immunized subcutaneously at 7-days of age with different vaccine formulations followed by booster vaccinations two weeks later. Immune responses were profiled by measuring antibody (Ab) responses in sera and lachrymal secretions of vaccinated chickens. The results indicated that inactivated AIV and CpG ODN co-encapsulated in PLGA NPs (2x NanoAI+CpG) produced higher amounts of hemagglutination inhibiting antibodies compared to a group vaccinated with non-adjuvanted AIV encapsulated in PLGA NPs (NanoAI). The tested adjuvanted NPs-based vaccine (2x NanoAI+CpG) resulted in higher IgG responses in the sera and lachrymal secretions at weeks 3, 4 and 5 post-vaccination when immunized subcutaneously. The incorporation of CpG ODN led to an increase in Ab-mediated responses and was found useful to be included both in the prime and booster vaccinations. In the second study, the ability of chitosan and mannan coated PLGA NPs that encapsulated AIV and CpG ODN was evaluated for inducing antibody responses when delivered via nasal and ocular routes in one-week-old SPF layer-type chickens. These PLGA NPs-based and surface modified formulations induced robust AIV-specific antibody responses in sera and lachrymal secretions. Chitosan coated PLGA NPs resulted in the production of large quantities of lachrymal IgA and IgG compared to mannan coated NPs, which also induced detectable amounts of IgA in addition to the induction of IgG in lachrymal secretions. In both mucosal and subcutaneous vaccination approaches, although NPs delivery enhanced Ab-mediated immunity, one booster vaccination was required to generate significant amount of Abs. These results highlight the potential of NPs-based AIV antigens for promoting the induction of both systemic and mucosal immune responses against respiratory pathogens.

A Comparison of Toll-Like Receptor 5 and 21 Ligands as Adjuvants for a Formaldehyde Inactivated H9N2 Avian Influenza Virus Vaccine in Chickens

Low pathogenic avian influenza virus (AIV) infection in chickens can result in economic losses and has impacts on human health. Poultry vaccination is a tool that can be used to decrease infection and transmission of AIVs. Prior research has demonstrated that Toll-like receptor (TLR) ligands can act as vaccine adjuvants and their addition to inactivated AIV vaccines can enhance immune responses elicited in chickens. The objective of this study was to compare the adjuvant capabilities of TLR5 ligand (flagellin) and TLR21 ligand (CpG ODN 2007) administered either alone or in combination with an intramuscular formaldehyde inactivated H9N2 whole virus vaccine in chickens. Along with the inactivated virus, chickens were administered either a single dose of CpG ODN 2007 (2 or 10 μg), flagellin (0.4 or 2 μg), or a combination of both ligands. An additional group received AddaVax™, an oil emulsion style adjuvant. Chickens were vaccinated twice and serum and lachrymal samples were collected weekly following the primary vaccination, and antibody-mediated immune responses were quantified. Results showed that vaccines containing CpG ODN 2007 induce significantly greater systemic and lachrymal antibody responses than vaccines containing flagellin or AddaVax. Combinations of flagellin and CpG ODN 2007 did not demonstrate inhibitory, additive, or synergistic effects on systemic or lachrymal antibody-mediated immune responses. Additionally, for both flagellin and CpG ODN 2007, a fivefold higher dose of each did not induce significantly higher antibody-mediated immune responses compared with the lesser dose. Future studies should examine the induction of cell-mediated immune responses when flagellin, CpG ODN 2007, or other TLR ligands are administered either alone or combined as adjuvants for inactivated H9N2 AIV vaccines.

Induction of immune response in chickens primed in ovo with an inactivated H9N2 avian influenza virus vaccine

Objective

Infection of chickens with low pathogenic avian influenza virus, such as H9N2 virus, culminates in decreased egg production and increased mortality and morbidity if co-infection with other respiratory pathogens occurs. We have previously observed the induction of antibody- and cell-mediated immune responses after intramuscular administration of an H9N2 beta-propiolactone inactivated virus vaccine to chickens. Given the fact that in ovo vaccination represents a practical option for vaccination against H9N2 AIV in chickens, in the current study, we set out to characterize immune responses in chickens against a beta-propiolactone inactivated H9N2 virus vaccine after primary vaccination in ovo on embryonic day 18, and secondary intramuscular vaccination on day 14 post-hatch. We also included the Toll-like receptor 21 ligand, CpG ODN 2007, and an oil emulsion adjuvant, AddaVax™, as adjuvants for the vaccines.

Results

Antibody-mediated immune responses were observed after administering the secondary intramuscular vaccine. Cell-mediated immune responses were observed in chickens that received the beta-propiolactone inactivated H9N2 virus combined with AddaVax™. Our results demonstrate that adaptive immune responses can be induced in chickens after a primary in ovo vaccination and secondary intramuscular vaccination.

Immunosensor Based on Antibody-Functionalized MoS2 for Rapid Detection of Avian Coronavirus on Cotton Thread

Infectious bronchitis virus (IBV), an avian coronavirus, significantly affects the performance of both the egg-laying and meat-type birds causing the foremost of economic loss in poultry industry. This paper aims to develop a rapid, low-cost, and sensitive biosensor for IBV detection by using molybdenum disulfide (MoS₂). MoS₂ is a 2-D nanosheet which has strong high fluorescence-quenching ability when applied to a dye-labeled antibody (Ab). In this paper, we developed an Ab-functionalized MoS₂-based fluorescent immunosensor, which utilized the fluorescence resonance energy transfer (FRET) between the MoS₂ and fluorescence dye during the Ab-antigen interaction. The assay was performed on a low-cost cotton thread-based microfluidic platform due to the good wicking property and flexibility. Upon the optimization of assay conditions, the immunosensor demonstrated remarkable sensitivity of [Formula: see text] EID₅₀ per mL and specificity with a dynamic linear response range of 10²-10⁶ EID₅₀ per mL for IBV standard solutions. The developed immunoassay successfully detected the IBV spiked chicken serum with satisfactory results. The foregoing presents its potential application for on-farm detection.

Examination of the effects of virus inactivation methods on the induction of antibody- and cell-mediated immune responses against whole inactivated H9N2 avian influenza virus vaccines in chickens

Several types of avian influenza virus (AIV) vaccines exist, including live-attenuated, vectored, and whole inactivated virus (WIV) vaccines. Inactivated vaccines offer some advantages compared to other types of vaccines, including ease of production and lack of ability to revert to a virulent state. However, WIV are poorly immunogenic, especially when these vaccines are delivered to mucosal surfaces. There are several factors that contribute to the immunogenicity of vaccines, one of which is the method used to inactivate viruses. Several methods exist for producing influenza WIVs, including formaldehyde, a chemical that affects protein structures leading to virus inactivation. Other methods include treatment with beta-propiolactone (BPL) and the application of gamma radiation, both of which have less effects on protein structures compared to formaldehyde, and instead alter nucleic acids in the virion. Here, we sought to determine the effect of the above inactivation methods on immunogenicity of AIV vaccines. To this end, chickens were vaccinated with three different H9N2 WIVs using formaldehyde, BPL, and gamma radiation for inactivation. In addition to administering these three WIVs alone as vaccines, we also included CpG ODN 2007, a synthetic ligand recognized by Toll-like receptor (TLR)21 in chickens, as an adjuvant for each WIV. Subsequently, antibody- and cell-mediated immune responses were measured following vaccination. Antibody-mediated immune responses were increased in chickens that received the BPL and Gamma WIVs compared to the formaldehyde WIV. CpG ODN 2007 was found to significantly increase antibody responses for each WIV compared to WIV alone. Furthermore, we observed the presence of cell-mediated immune responses in chickens that received the BPL WIV combined with CpG ODN 2007. Based on these results, the BPL WIV + CpG ODN 2007 combination was the most effective vaccine at inducing adaptive immune responses against H9N2 AIV. Future studies should characterize mucosal adaptive immune responses to these vaccines.

Chiral MoS2 Quantum Dots: Dual-Mode Detection Approaches for Avian Influenza Viruses

Molybdenum disulfide (MoS2), a type of transition metal dichalcogenide material, has emerged as an important class among 2D systems. When 2D MoS2 materials are reduced to 0D quantum dots (QDs), they introduce new optical properties that point to several potential technological advantages in electronic, magnetic, optical, and catalytic properties. In this study, a simple way to produce chiral MoS2 QDs from MoS2 nanopowder is presented using l(+)-ascorbic acid as a reducing agent. The calculated quantum yield of QDs is 11.06%. Experimental results reveal that the size of QDs is uniformly monodispersed (2-3 nm) and have a blue emissive fluorescence peak and circular dichroism (CD) peak located at 420 and 330 nm, respectively. Furthermore, a dual-mode detection system based on fluorescence and chirality is performed using as-synthesized MoS2 QDs, where QDs are conjugated with anti-hemagglutinin antibodies of avian influenza virus and made into an immunobridge in the presence of target virus and anti-neuraminidase antibodies conjugated magnetic nanoparticles (MNPs). The photoluminescence and CD spectra of unconjugated QDs after separated magnetochirofluorescent (MNPs-QDs) nanohybrids by external magnets enables influenza virus A (H5N1) detection with the limit of detection value of 7.35 and 80.92 pg mL-1, respectively.

Amplified visual immunosensor integrated with nanozyme for ultrasensitive detection of avian influenza virus

Nanomaterial-based artificial enzymes or nanozymes exhibit superior properties such as stability, cost effectiveness and ease of preparation in comparison to conventional enzymes. However, the lower catalytic activity of nanozymes limits their sensitivity and thereby practical applications in the bioanalytical field. To overcome this drawback, herein we propose a very simple but highly sensitive, specific and low-cost dual enhanced colorimetric immunoassay for avian influenza A (H5N1) virus. 3,3´,5,5´- Tetramethylbenzidine (TMBZ) was used as a reducing agent to produce gold nanoparticles (Au NPs) with blue colored solution from a viral target-specific antibody-gold ion mixture at first step. The developed blue color from the sensing design was further amplified through catalytic activity of Au NPs in presence of TMBZ-hydrogen peroxide (H₂O₂) solution in second step. Hence, the developed dual enhanced colorimetric immunosensor enables the detection of avian influenza virus A (H5N1) with a limit of detection (LOD) of 1.11 pg/mL. Our results confirmed that the developed assay has superior sensitivity than the conventional ELISA method, plasmonic-based bioassay and commercial flu diagnostic kits. Proposed sensing method further showed its capability to detect viruses, avian influenza A (H4N6) and A (H9N2) virus, in blood samples with limit of detection of 0.0269 HAU and 0.0331 HAU respectively.

Emerging avian influenza infections: Current understanding of innate immune response and molecular pathogenesis

The highly pathogenic avian influenza viruses (HPAIVs) cause severe disease in gallinaceous poultry species, domestic ducks, various aquatic and terrestrial wild bird species as well as humans. The outcome of the disease is determined by complex interactions of multiple components of the host, the virus, and the environment. While the host-innate immune response plays an important role for clearance of infection, excessive inflammatory immune response (cytokine storm) may contribute to morbidity and mortality of the host. Therefore, innate immunity response in avian influenza infection has two distinct roles. However, the viral pathogenic mechanism varies widely in different avian species, which are not completely understood. In this review, we summarized the current understanding and gaps in host-pathogen interaction of avian influenza infection in birds. In first part of this article, we summarized influenza viral pathogenesis of gallinaceous and non-gallinaceous avian species. Then we discussed innate immune response against influenza infection, cytokine storm, differential host immune responses against different pathotypes, and response in different avian species. Finally, we reviewed the systems biology approach to study host-pathogen interaction in avian species for better characterization of molecular pathogenesis of the disease. Wild aquatic birds act as natural reservoir of AIVs. Better understanding of host-pathogen interaction in natural reservoir is fundamental to understand the properties of AIV infection and development of improved vaccine and therapeutic strategies against influenza.

Self-assembled star-shaped chiroplasmonic gold nanoparticles for an ultrasensitive chiro-immunosensor for viruses

Nanoengineered chiral gold nanoparticles and quantum dots for ultrasensitive chiroptical sensing of viruses in blood samples.

Delivery of an inactivated avian influenza virus vaccine adjuvanted with poly(D,L-lactic-co-glycolic acid) encapsulated CpG ODN induces protective immune responses in chickens

In poultry, systemic administration of commercial vaccines consisting of inactivated avian influenza virus (AIV) requires the simultaneous delivery of an adjuvant (water-in-oil emulsion). These vaccines are often limited in their ability to induce quantitatively better local (mucosal) antibody responses capable of curtailing virus shedding. Therefore, more efficacious adjuvants with the ability to provide enhanced immunogenicity and protective anti-AIV immunity in chickens are needed. While the Toll-like receptor (TLR) 21 agonist, CpG oligodeoxynucleotides (ODNs) has been recognized as a potential vaccine adjuvant in chickens, poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles, successfully tested as vaccine delivery systems in other species, have not been extensively explored. The present study, therefore, assessed both systemic and mucosal antibody-mediated responses following intramuscular vaccination (administered at 7 and 21days post-hatch) of chickens with PLGA encapsulated H9N2 AIV plus encapsulated CpG ODN 2007 (CpG 2007), and nonencapsulated AIV plus PLGA encapsulated CpG 2007 vaccine formulations. Virus challenge was performed at 2weeks post-secondary vaccination using the oculo-nasal route. Our results showed that chickens vaccinated with the nonencapsulated AIV vaccine plus PLGA encapsulated CpG 2007 developed significantly higher systemic IgY and local (mucosal) IgY antibodies as well as haemagglutination inhibition antibody titres compared to PLGA encapsulated AIV plus encapsulated CpG 2007 vaccinated chickens. Furthermore, chickens that received CpG 2007 as an adjuvant in the vaccine formulation had antibodies exhibiting higher avidity indicating that the TLR21-mediated pathway may enhance antibody affinity maturation qualitatively. Collectively, our data indicate that vaccination of chickens with nonencapsulated AIV plus PLGA encapsulated CpG 2007 results in qualitatively and quantitatively augmented antibody responses leading to a reduction in virus shedding compared to the encapsulated AIV plus PLGA encapsulated CpG 2007 formulation.

Local Innate Responses to TLR Ligands in the Chicken Trachea

The chicken upper respiratory tract is the portal of entry for respiratory pathogens, such as avian influenza virus (AIV). The presence of microorganisms is sensed by pathogen recognition receptors (such as Toll-like receptors (TLRs)) of the innate immune defenses. Innate responses are essential for subsequent induction of potent adaptive immune responses, but little information is available about innate antiviral responses of the chicken trachea. We hypothesized that TLR ligands induce innate antiviral responses in the chicken trachea. Tracheal organ cultures (TOC) were used to investigate localized innate responses to TLR ligands. Expression of candidate genes, which play a role in antiviral responses, was quantified. To confirm the antiviral responses of stimulated TOC, chicken macrophages were treated with supernatants from stimulated TOC, prior to infection with AIV. The results demonstrated that TLR ligands induced the expression of pro-inflammatory cytokines, type I interferons and interferon stimulated genes in the chicken trachea. In conclusion, TLR ligands induce functional antiviral responses in the chicken trachea, which may act against some pathogens, such as AIV.

Characterization of Immune Responses to an Inactivated Avian Influenza Virus Vaccine Adjuvanted with Nanoparticles Containing CpG ODN

Avian influenza virus (AIV), a mucosal pathogen, gains entry into host chickens through respiratory and gastrointestinal routes. Most commercial AIV vaccines for poultry consist of inactivated, whole virus with adjuvant, delivered by parenteral administration. Recent advances in vaccine development have led to the application of nanoparticle emulsion delivery systems, such as poly (d,l-lactic-co-glycolic acid) (PLGA) nanoparticles to enhance antigen-specific immune responses. In chickens, the Toll-like receptor 21 ligand, CpG oligodeoxynucleotides (ODNs), have been demonstrated to be immunostimulatory. The objective of this study was to compare the adjuvant potential of CpG ODN 2007 encapsulated in PLGA nanoparticles with nonencapsulated CpG ODN 2007 when combined with a formalin-inactivated H9N2 virus, through intramuscular and aerosol delivery routes. Chickens were vaccinated at days 7 and 21 posthatch for the intramuscular route and at days 7, 21, and 35 for the aerosol route. Antibody-mediated responses were evaluated weekly in sera and lacrimal secretions in specific pathogen-free chickens. The results indicate that nonencapsulated CpG ODN 2007 in inactivated AIV vaccines administered by the intramuscular route generated higher antibody responses compared to the encapsulated CpG ODN 2007 formulation by the same route. Additionally, encapsulated CpG ODN 2007 in AIV vaccines administered by the aerosol route elicited higher mucosal responses compared to nonencapsulated CpG ODN 2007. Future studies may be aimed at evaluating protective immune responses induced with PLGA encapsulation of AIV and adjuvants.

Reduction of avian influenza virus shedding by administration of Toll-like receptor ligands to chickens

Avian influenza viruses (AIV) are of concern to the poultry industry. Outbreaks of AIV highlight the urgent need for effective control measures. Prophylactic strategies should be explored that rapidly elicit immunity against the virus. Toll-like receptors (TLRs) are innate immune molecules that can induce anti-viral responses, therefore the application of TLR ligands as prophylactic agents in chickens is gaining more attention. We hypothesized that treatment of chickens with TLR ligands reduces the shedding of AIV from infected birds. In addition, the effects of TLR ligand dose and route of administration on the efficiency of TLR ligands to reduce AIV shedding were examined. Chickens were treated with TLR2, 4, 7 and 21 ligands using different doses and routes of administration, 18h before AIV infection. Moreover, the expression of several candidate genes, such as type I interferons, PKR, OAS, viperin and IFITM3 was quantified at 3, 8 and 18h post-treatment with TLR ligands. The results revealed that route of administration and dosage affect the efficacy of TLR ligands to reduce virus shedding. Furthermore, varying effects were observed when different ligands were applied. Our results demonstrated that all TLR ligand treatments reduced AIV shedding, with the CpG-ODN 1826 being the most efficacious to reduce oral virus shedding, whereas LPS from Escherichia coli 026:B6 resulted in the largest reduction in cloacal virus shedding. Moreover, TLR ligands induced the expression of genes involved in antiviral responses such as type I interferons and interferon-stimulated genes in chicken trachea and cecal tonsils. These results raise the possibility of treatment of chickens with TLR ligands as anti-viral agents.

Induction of antiviral responses against avian influenza virus in embryonated chicken eggs with toll-like receptor ligands

Early responses against viruses, such as avian influenza virus (AIV), may be induced by Toll-like receptor (TLR) pathways. In the present study, an in ovo model was employed to study the antiviral activities of TLR ligands. It was hypothesized that administration of TLR ligands in ovo at the appropriate dose and time can reduce AIV titer in embryonated chicken eggs. Moreover, the study aimed to determine the mechanisms involved in the TLR-mediated antiviral responses in the chorioallantoic membrane (CAM). Embryonated eggs (10-14 day old) were treated with TLR2, 4, 7, and 21 ligands using different doses and times pre- and post-AIV infection. The results revealed that treatment of embryonated chicken eggs with TLR ligands reduced AIV replication. Further analysis showed that TLR ligands induced interferon (IFN)-γ and IFN stimulatory genes in the CAM, which may have played a role in the reduction of the AIV titer. The timing and dose of TLR ligands administration had significant impacts on the outcome of the treated eggs. In conclusion, the present study demonstrated that the in ovo route may be employed to determine the antiviral characteristics of TLR ligands against AIV.

Efficient vaccine against pandemic influenza: combining DNA vaccination and targeted delivery to MHC class II molecules

There are two major limitations to vaccine preparedness in the event of devastating influenza pandemics: the time needed to generate a vaccine and rapid generation of sufficient amounts. DNA vaccination could represent a solution to these problems, but efficacy needs to be enhanced. In a separate line of research, it has been established that targeting of vaccine molecules to antigen-presenting cells enhances immune responses. We have combined the two principles by constructing DNA vaccines that encode bivalent fusion proteins; these target hemagglutinin to MHC class II molecules on antigen-presenting cells. Such DNA vaccines rapidly induce hemagglutinin-specific antibodies and T cell responses in immunized mice. Responses are long-lasting and protect mice against challenge with influenza virus. In a pandemic situation, targeted DNA vaccines could be produced and tested within a month. The novel DNA vaccines could represent a solution to pandemic preparedness in the advent of novel influenza pandemics.

Poly I:C adjuvanted inactivated swine influenza vaccine induces heterologous protective immunity in pigs

•

Intranasal administration of Poly I:C adjuvanted bivalent swine influenza vaccine induced challenge virus-specific HI antibodies.

•

Poly I:C adjuvanted vaccine also induced IgA and IgG antibodies in the lungs.

•

Poly I:C adjuvanted vaccine provided protection against antigenic variant and heterologous swine influenza viruses.

Swine influenza is widely prevalent in swine herds in North America and Europe causing enormous economic losses and a public health threat. Pigs can be infected by both avian and mammalian influenza viruses and are sources of generation of reassortant influenza viruses capable of causing pandemics in humans. Current commercial vaccines provide satisfactory immunity against homologous viruses; however, protection against heterologous viruses is not adequate. In this study, we evaluated the protective efficacy of an intranasal Poly I:C adjuvanted UV inactivated bivalent swine influenza vaccine consisting of Swine/OH/24366/07 H1N1 and Swine/CO/99 H3N2, referred as PAV, in maternal antibody positive pigs against an antigenic variant and a heterologous swine influenza virus challenge. Groups of three-week-old commercial-grade pigs were immunized intranasally with PAV or a commercial vaccine (CV) twice at 2 weeks intervals. Three weeks after the second immunization, pigs were challenged with the antigenic variant Swine/MN/08 H1N1 (MN08) and the heterologous Swine/NC/10 H1N2 (NC10) influenza virus. Antibodies in serum and respiratory tract, lung lesions, virus shedding in nasal secretions and virus load in lungs were assessed. Intranasal administration of PAV induced challenge viruses specific-hemagglutination inhibition- and IgG antibodies in the serum and IgA and IgG antibodies in the respiratory tract. Importantly, intranasal administration of PAV provided protection against the antigenic variant MN08 and the heterologous NC10 swine influenza viruses as evidenced by significant reductions in lung virus load, gross lung lesions and significantly reduced shedding of challenge viruses in nasal secretions. These results indicate that Poly I:C or its homologues may be effective as vaccine adjuvants capable of generating cross-protective immunity against antigenic variants/heterologous swine influenza viruses in pigs.

Toll-like receptor-based adjuvants: enhancing the immune response to vaccines against infectious diseases of chicken

Huge productivity loss due to infectious diseases in chickens is a major problem and, hence, robust development of the poultry industry requires control of poultry health. Immunization using vaccines is routine practice; however, to combat infectious diseases, conventional vaccines as well as new-generation recombinant vaccines alone, due to relatively weak immunogenicity, may not be effective enough to provide optimum immunity. With this in mind, there is a need to incorporate better and more suitable adjuvants in the vaccines to elicit the elevated immune response in the host. Over last few decades, with the increase in the knowledge of innate immune functioning, efforts have been made to enhance vaccine potency using novel adjuvants like Toll-like receptor based adjuvant systems. In this review, we will discuss the potential use of toll-like receptor ligands as an adjuvant in vaccines against the infectious diseases of chickens.