Construction and immunogenicity of recombinant fowlpox vaccines coexpressing HA of AIV H5N1 and chicken IL18

Advances in Poultry Vaccines: Leveraging Biotechnology for Improving Vaccine Development, Stability, and Delivery

With the rapidly increasing demand for poultry products and the current challenges facing the poultry industry, the application of biotechnology to enhance poultry production has gained growing significance. Biotechnology encompasses all forms of technology that can be harnessed to improve poultry health and production efficiency. Notably, biotechnology-based approaches have fueled rapid advances in biological research, including (a) genetic manipulation in poultry breeding to improve the growth and egg production traits and disease resistance, (b) rapid identification of infectious agents using DNA-based approaches, (c) inclusion of natural and synthetic feed additives to poultry diets to enhance their nutritional value and maximize feed utilization by birds, and (d) production of biological products such as vaccines and various types of immunostimulants to increase the defensive activity of the immune system against pathogenic infection. Indeed, managing both existing and newly emerging infectious diseases presents a challenge for poultry production. However, recent strides in vaccine technology are demonstrating significant promise for disease prevention and control. This review focuses on the evolving applications of biotechnology aimed at enhancing vaccine immunogenicity, efficacy, stability, and delivery.

Poultry Vaccine Technology Platforms

The different technology platforms used to make poultry vaccines are reviewed. Vaccines based on classical technologies are either live attenuated or inactivated vaccines. Genetic engineering is applied to design by deletion, mutation, insertion, or chimerization, genetically modified target microorganisms that are used either as live or inactivated vaccines. Other vaccine platforms are based on one or a few genes of the target pathogen agent coding for proteins that can induce a protective immune response ("protective genes"). These genes can be expressed in vitro to produce subunit vaccines. Alternatively, vectors carrying these genes in their genome or nucleic acid-based vaccines will induce protection by in vivo expression of these genes in the vaccinated host. Properties of these different types of vaccines, including advantages and limitations, are reviewed, focusing mainly on vaccines targeting viral diseases and on technologies that succeeded in market authorization.

Construction and immune protection evaluation of recombinant virus expressing Newcastle disease virus F protein by the largest intergenic region of fowlpox virus NX10

Fowlpox virus (FPV) is used as a vaccine vector to prevent diseases in poultry and mammals. The insertion site is considered as one of the main factors influencing foreign gene expression. Therefore, the identification of insertion sites that can stably and efficiently express foreign genes is crucial for the construction of recombinant vaccines. In this study, we found that the insertion of foreign genes into ORF054 and the ORF161/ORF162 intergenic region of the FPV genome did not affect replication, and that the foreign genes inserted into the intergenic region were more efficiently expressed than when they were inserted into a gene. Based on these results, the recombinant virus rFPVNX10-NDV F-E was constructed and immune protection against virulent FPV and Newcastle disease virus (NDV) was evaluated. Tests for anti-FPV antibodies in the vaccinated chickens were positive within 14 days post-vaccination. After challenge with FPV102, no clinical signs of FP were observed in vaccinated chickens, as compared to that in the control group (unvaccinated), which showed 100% morbidity. Low levels of NDV-specific neutralizing antibodies were detected in vaccinated chickens before challenge. After challenge with NDV ck/CH/LHLJ/01/06, all control chickens died within 4 days post-challenge, whereas 5/15 vaccinated chickens died between 4 and 12 days post-challenge. Vaccination provided an immune protection rate of 66.7%, whereas the control group showed 100% mortality. These results indicate that the ORF161/ORF162 intergenic region of FPVNX10 can be used as a recombination site for foreign gene expression in vivo and in vitro.

The Construction and Immunoadjuvant Activities of the Oral Interleukin-17B Expressed by Lactobacillus plantarum NC8 Strain in the Infectious Bronchitis Virus Vaccination of Chickens

Interleukin-17B (IL-17B) is a protective cytokine of the IL-17 family and plays an essential role in the regulation of mucosal inflammation. However, little is known about the role of IL-17B in the control of viral infections. In this study, a recombinant Lactobacillus plantarum, designated as NC8-ChIL17B, was constructed to express the chicken IL-17B (ChIL-17B) gene. The recombinant ChIL17B (rChIL17B) protein was about 14 kDa and was anchored to the surface of NC8 cells. In vitro, it was found that the rChIL17B protein inhibited the proliferation of the infectious bronchitis virus (IBV) through activation of nuclear factor kappa B (NF-κB) and the JAK (Janus kinase)-STAT (signal transducers and activators of transcription) signaling. Moreover, to evaluate the immunoadjuvant activities of NC8-ChIL17B, 40 three-day-old specific pathogen-free (SPF) chickens were divided into four groups. Three groups were orally vaccinated with fresh NC8, NC8-ChIL17B, and phosphate buffered saline (PBS), along with the infectious bronchitis virus vaccine, and the other group was the PBS-negative control. The results of the IBV-specific antibody titer and the concentration of the cytokines IL-2, IL-4, IL-6, and interferon gamma (IFN-γ) in sera, as well as the concentration of secretory immunoglobulin A (sIgA) in the tracheal and small intestinal mucosa, the number of cluster of differentiation 4 positive (CD4⁺) and cluster of differentiation 8 positive (CD8⁺) T cells in the blood, and the expression of immune-related genes all indicated that NC8-ChIL17B efficiently enhanced the humoral and cellular immune responses to IBV vaccine. Moreover, the viral loads in the NC8-ChIL17B- and IBV-vaccinated group were significantly lower than in the control groups, suggesting a significant promotion of the immunoprotection of IBV vaccination against the virulent IBV strain. Therefore, ChIL-17B is a promising, effective adjuvant candidate for chicken virus vaccines.

Inoculation of fowlpox viruses coexpressing avian influenza H5 and chicken IL-15 cytokine gene stimulates diverse host immune responses

Fowlpox virus (FWPV) has been used as a recombinant vaccine vector to express antigens from several important avian pathogens. Attempts have been made to improve vaccine strains induced-host immune responses by coexpressing cytokines. This study describes the construction of recombinant FWPV (rFWPV) strain FP9 and immunological responses in specific-pathogen-free (SPF) chickens, co-expressing avian influenza virus (AIV) H5 of A/Chicken/Malaysia/5858/2004, and chicken IL-15 cytokine genes. Expression of H5 (50 kD) was confirmed by western blotting. Anti-H5 antibodies, which were measured by the haemagglutinin inhibition test, were at the highest levels at Week 3 post-inoculation in both rFWPV/H5- and rFWPV/H5/IL-15-vaccinated chickens, but decreased to undetectable levels from Week 5 onwards. CD3+/CD4+ or CD3+/CD8+T cell populations, assessed using flow cytometry, were significantly increased in both WT FP9- and rFWPV/H5-vaccinated chickens and were also higher than in rFWPV/H5/IL-15- vaccinated chickens, at Week 2. Gene expression analysis using real time quantitative polymerase chain reaction (qPCR) demonstrated upregulation of IL-15 expression in all vaccinated groups with rFWPV/H5/IL-15 having the highest fold change, at day 2 (117±51.53). Despite showing upregulation, fold change values of the IL-18 expression were below 1.00 for all vaccinated groups at day 2, 4 and 6. This study shows successful construction of rFWPV/H5 co-expressing IL-15, with modified immunogenicity upon inoculation into SPF chickens.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Improvement in T helper 1-related immune responses in BALB/c mice immunized with an HIV-1 gag plasmid combined with a chimeric plasmid encoding interleukin-18 and flagellin

Both flagellin (fliC) and IL-18 (INF-γ-inducing factor) have been developed as adjuvants for improving immunogenicity in DNA-vaccinated hosts. An HIV-1 gag plasmid encodes a protein harboring broad epitopes for cytotoxic T-lymphocytes. In this study, the immunogenicity of BALB/c mice immunized with an HIV-1 gag plasmid (pVAX/gag) combined with a chimeric plasmid encoding IL-18 fused to flagellin (pcDNA3/IL-18_fliC) or a single plasmid encoding IL-18 (pcDNA3/IL-18) and/or flagellin (pcDNA3/fliC) was assessed. Through in vitro transcription and translation, it was demonstrated that both mRNA and protein were appropriately expressed by each construct. The IL-18 and flagellin fusion protein, which could be detected in supernatants from transfected cells, was effective in inducing IFN-γ by lymphocytes. Following i.m. immunization, expressions of flagellin or IL-18 were detected in muscle cells by immunohistochemistry analysis from 72 hr. At 12 weeks post-immunization, both gag-specific IgG in sera and spleen cell proliferation were high in all murine groups. However, the IgG2a/IgG1 ratio, Th1 cytokine (IL-2 and IFN-γ) production and proportion of gag-specific CD3(+) CD8(+) IFN-γ-secreting cells were significantly higher in the murine group co-immunized with pVAX/gag plasmid and pcDNA3/IL-18_fliC than in the mice immunized with pVAX/gag plasmid combined with either pcDNA3/fliC or pcDNA3/IL-18 plasmid or both. These findings suggest that a chimeric plasmid encoding IL-18 fused to flagellin can be used as an adjuvant-like plasmid to improve the Th1 immune response, particularly for induction of CD3(+) CD8(+) IFN-γ-secreting cells in gag plasmid-vaccinated mice.

Characterization of functionally active interleukin-18/eGFP fusion protein expression during cell cycle phases in recombinant chicken DF1 Cells

The dependence of foreign gene expression on cell cycle phases in mammalian cells has been described. In this study, a DF1/chIL-18a cell line that stably expresses the fusion protein chIL-18 was constructed and the enhanced green fluorescence protein connected through a (G4 S)3 linker sequence investigated the relationship between cell cycle phases and fusion protein production. DF1/chIL-18a cells (1 × 10(5) ) were inoculated in 60-mm culture dishes containing 5 mL of media to achieve 50%-60% confluence and were cultured in the presence of the cycle-specific inhibitors 10058-F4, aphidicolin, and colchicine for 24 and 48 h. The percentage of cell density and mean fluorescence intensity in each cell cycle phase were assessed using flow cytometry. The inhibitors effectively arrested cell growth. The fusion protein production rate was higher in the S phase than in the G0/G1 and G2/M phases. When cell cycle progression was blocked in the G0/G1, S, and G2/M phases by the addition of 10058-F4, aphidicolin, and colchicine, respectively, the aphidicolin-induced single cells showed higher fusion protein levels than did the 10058-F4- or colchicine-induced phase cells and the uninduced control cells. Although the cells did not proliferate after the drug additions, the amount of total fusion protein accumulated in aphidicolin-treated cells was similar to that in the untreated cultures. Fusion protein is biologically active because it induces IFN-γ production in splenocyte cultures of chicken. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:581-591, 2016.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Construction and characterization of novel fowlpox virus shuttle vectors

Viral vectors are important vehicles in vaccine research. Avipoxviruses including fowlpox virus (FPV) play major roles in viral vaccine vector development for the prevention and therapy of human and other veterinary diseases due to their immunomodulatory effects and safety profile. Recently, we analyzed the genomic and proteomic backgrounds of the Chinese FPV282E4 strain. Based on analysis of the whole genome of FPV282E4, the FPV150 and FPV193 loci were chosen as insertion sites for foreign genes, and two shuttle vectors with a triple-gene expression cassette were designed and constructed. Homologous recombination between the FPV virus genome and sequences within the shuttle plasmids in infected cells was confirmed. The recombinants were obtained through several rounds of plaque purification using enhanced green fluorescent protein as a reporter and evaluated for the correct expression of foreign genes in vitro using RT-PCR, real-time PCR and Western blotting. Morphogenesis and growth kinetics were assayed via transmission electron microscopy and viral titering, respectively. Results showed that recombinant viruses were generated and correctly expressed foreign genes in CEF, BHK-21 and 293T cells. At least three different exogenous genes could be expressed simultaneously and stably over multiple passages. Additionally, the FPV150 mutation, FPV193 deletion and insertion of foreign genes did not affect the morphogenesis, replication and proliferation of recombinant viruses in cells. Our study contributes to the improvement of FPV vectors for multivalent vaccines.

[Fowl plague and avian influenza A viruses of poultry and birds. Diagnosis, control measures and practical experiences]

The causes of the notifiable fowl plague are high and low pathogenic avian influenza A viruses of the haemagglutinin subtypes H5 and H7 but also other haemagglutinin subtypes If the intravenous pathogenicity index is greater than 1.2. The German fowl plague order (Geflügelpest-Verordnung) differentiates between highly pathogenic influenza A viruses of the subtypes H5 and H7, if multiple basic amino acids at the cleavage site of the haemagglutinin molecules are detected by virus isolation, antigen or genome determination and low pathogenic avian influenza A viruses of the subtypes H5 and H7 if either the intravenous pathogenicity index is lower than 1.2 or no basic amino acids are present at the cleavage site of the haemagglutinin molecule. Aspects of diagnosis, control including culling, therapy and vaccination are reviewed. The currently available means and their limitations of a therapy of fowl plague by oral administration of neuraminidase inhibitors (e. g. oseltamivir) are described. Following granted permission, individually marked valuable zoo and pet birds may be vaccinated using licensed inactivated vaccines. Vector vaccines have not been used in Germany so far. Avian influenza A viruses of other haemagglutinin subtypes (H1-H4, H6, H8-H18) may also cause infections and severe disease. These subtypes are not subject to governmental interventions and disease can be prevented by timely use of inactivated vaccines.

Prevalence and control of H7 avian influenza viruses in birds and humans

The H7 subtype HA gene has been found in combination with all nine NA subtype genes. Most exhibit low pathogenicity and only rarely high pathogenicity in poultry (and humans). During the past few years infections of poultry and humans with H7 subtypes have increased markedly. This review summarizes the emergence of avian influenza virus H7 subtypes in birds and humans, and the possibilities of its control in poultry. All H7Nx combinations were reported from wild birds, the natural reservoir of the virus. Geographically, the most prevalent subtype is H7N7, which is endemic in wild birds in Europe and was frequently reported in domestic poultry, whereas subtype H7N3 is mostly isolated from the Americas. In humans, mild to fatal infections were caused by subtypes H7N2, H7N3, H7N7 and H7N9. While infections of humans have been associated mostly with exposure to domestic poultry, infections of poultry have been linked to wild birds or live-bird markets. Generally, depopulation of infected poultry was the main control tool; however, inactivated vaccines were also used. In contrast to recent cases caused by subtype H7N9, human infections were usually self-limiting and rarely required antiviral medication. Close genetic and antigenic relatedness of H7 viruses of different origins may be helpful in development of universal vaccines and diagnostics for both animals and humans. Due to the wide spread of H7 viruses and their zoonotic importance more research is required to better understand the epidemiology, pathobiology and virulence determinants of these viruses and to develop improved control tools.

Insight into alternative approaches for control of avian influenza in poultry, with emphasis on highly pathogenic H5N1

Highly pathogenic avian influenza virus (HPAIV) of subtype H5N1 causes a devastating disease in poultry but when it accidentally infects humans it can cause death. Therefore, decrease the incidence of H5N1 in humans needs to focus on prevention and control of poultry infections. Conventional control strategies in poultry based on surveillance, stamping out, movement restriction and enforcement of biosecurity measures did not prevent the virus spreading, particularly in developing countries. Several challenges limit efficiency of the vaccines to prevent outbreaks of HPAIV H5N1 in endemic countries. Alternative and complementary approaches to reduce the current burden of H5N1 epidemics in poultry should be encouraged. The use of antiviral chemotherapy and natural compounds, avian-cytokines, RNA interference, genetic breeding and/or development of transgenic poultry warrant further evaluation as integrated intervention strategies for control of HPAIV H5N1 in poultry.

Enhancement of Th1-biased protective immunity against avian influenza H9N2 virus via oral co-administration of attenuated Salmonella enterica serovar Typhimurium expressing chicken interferon-α and interleukin-18 along with an inactivated vaccine

Background

Control of currently circulating re-assorted low-pathogenicity avian influenza (LPAI) H9N2 is a major concern for both animal and human health. Thus, an improved LPAI H9N2 vaccination strategy is needed to induce complete immunity in chickens against LPAI H9N2 virus strains. Cytokines play a crucial role in mounting both the type and extent of an immune response generated following infection with a pathogen or after vaccination. To improve the efficacy of inactivated LPAI H9N2 vaccine, attenuated Salmonella enterica serovar Typhimurium was used for oral co-administration of chicken interferon-α (chIFN-α) and chicken interleukin-18 (chIL-18) as natural immunomodulators.

Results

Oral co-administration of S. enterica serovar Typhimurium expressing chIFN-α and chIL-18, prior to vaccination with inactivated AI H9N2 vaccine, modulated the immune response of chickens against the vaccine antigen through enhanced humoral and Th1-biased cell-mediated immunity, compared to chickens that received single administration of S. enterica serovar Typhimurium expressing either chIFN-α or chIL-18. To further test the protective efficacy of this improved vaccination regimen, immunized chickens were intra-tracheally challenged with a high dose of LPAI H9N2 virus. Combined administration of S. enterica serovar Typhimurium expressing chIFN-α and chIL-18 showed markedly enhanced protection compared to single administration of the construct, as determined by mortality, clinical severity, and feed and water intake. This enhancement of protective immunity was further confirmed by reduced rectal shedding and replication of AIV H9N2 in different tissues of challenged chickens.

Conclusions

Our results indicate the value of combined administration of chIFN-α and chIL-18 using a Salmonella vaccine strain to generate an effective immunization strategy in chickens against LPAI H9N2.

Innate immune recognition of poxviral vaccine vectors

The study of poxviruses pioneered the field of vaccinology after Jenner's remarkable discovery that 'vaccination' with the phylogenetically related cowpox virus conferred immunity to the devastating disease of smallpox. The study of poxviruses continues to enrich the field of virology because the global eradication of smallpox provides a unique example of the potency of effective immunization. Other poxviruses have since been developed as vaccine vectors for clinical and veterinary applications and include modified vaccinia virus strains such as modified vaccinia Ankara and NYVAC as well as the avipox viruses, fowlpox virus and canarypox virus. Despite the empirical development of poxvirus-based vectored vaccines, it is only now becoming apparent that we need to better understand how the innate arm of the immune system drives adaptive immunity to poxviruses, and how this information is relevant to vaccine design strategies, which are the topics addressed in this article.

Oral co-administration of live attenuated Salmonella enterica serovar Typhimurium expressing chicken interferon-α and interleukin-18 enhances the alleviation of clinical signs caused by respiratory infection with avian influenza virus H9N2

The combined use of cytokines has shown synergistic and/or additive effects in controlling several viral infections of livestock animals. However, little is known concerning the practical use of chicken cytokine combinations to control avian diseases. Here, we investigated the antiviral efficacy of oral co-administration of chicken interferon-α (chIFN-α) and chicken interleukin-18 (chIL-18) using attenuated Salmonella enterica serovar Typhimurium in chickens infected with avian influenza virus (AIV) H9N2. Our results demonstrate that oral co-administration of S. enterica serovar Typhimurium expressing chIFN-α and chIL-18 produced a greater alleviation of clinical signs caused by respiratory infection with AIV H9N2 in chickens, when compared to administration of S. enterica serovar Typhimurium expressing either chIFN-α or chIL-18 alone. Mortality, clinical symptom severity, and feed and water intake were used to access treatment effectiveness. This enhancement of antiviral immunity was further confirmed by evidence of reduced rectal shedding and decreased replication of AIV H9N2 in several different tissues of challenged chickens including trachea, lung, cecal tonsil, and brain. Furthermore, oral co-administration of chIFN-α and chIL-18 more efficiently modulated the immune responses of chickens against AIV H9N2 by enhancing both humoral and Th1-biased cell-mediated immunity, compared to single administration of either construct. Therefore, our results suggest that the combined administration of two chicken cytokines, chIFN-α and chIL-18, using attenuated S. enterica serovar Typhimurium as an oral carrier, provides an effective means for controlling respiratory disease caused by AIV H9N2 infection.

Expression of HA of HPAI H5N1 virus at US2 gene insertion site of turkey herpesvirus induced better protection than that at US10 gene insertion site

Herpesvirus of turkey (HVT) is being widely used as a vector for development of recombinant vaccines and US2 and US10 genes are often chosen as insertion sites for targeted gene expression. However, the different effects of the two genes for generation of recombinant HVT vaccines were unknown. In order to compare the effects of inserted genes in the two sites on the efficacy of the recombinant vaccines, host-protective haemagglutinin (HA) gene of the highly pathogenic avian influenza virus (HPAIV) H5N1 was inserted into either US2 or US10 gene locus of the HVT. The resulting US2 (rHVT-US2-HA) or US10 (rHVT-US10-HA) recombinant HVT viruses were used to infect chicken embryo fibroblasts. Plaques and the growth kinetics of rHVT-US2-HA-infected chicken embryo fibroblasts were similar to those of parental HVT whereas rHVT-US10-HA infected chicken embryo fibroblasts had different growth kinetics and plaque formation. The viremia levels in rHVT-US10-HA virus-infected chickens were significantly lower than those of rHVT-US2-HA group on 28 days post infection. The vaccine efficacy of the two recombinant viruses against H5N1 HPAIV and virulent Marek's disease virus was also evaluated in 1-day-old vaccinated chickens. rHVT-US2-HA-vaccinated chickens were better protected with reduced mortality than rHVT-US10-HA-vaccinated animals following HPAIV challenge. Furthermore, the overall hemaglutination inhibition antibody titers of rHVT-US2-HA-vaccinated chickens were higher than those of rHVT-US10-HA-vaccinated chickens. Protection levels against Marek's disease virus challenge following vaccination with either rHVT-US2-HA or rHVT-US10-HA, however, were similar to those of the parental HVT virus. These results, for the first time, indicate that US2 gene provides a favorable foreign gene insertion site for generation of recombinant HVT vaccines.

Immune responses of chickens inoculated with a recombinant fowlpox vaccine coexpressing HA of H9N2 avain influenza virus and chicken IL-18

Control of the circulation of H9N2 avian influenza virus (AIV) is a major concern for both animal and public health, and H9N2 AIV poses a major threat to the chicken industry worldwide. Here, we developed a recombinant fowlpox virus (rFPV-HA) expressing the haemagglutinin (HA) gene of the A/CH/JY/1/05 (H9N2) influenza virus and a recombinant fowlpox virus (rFPV-HA/IL18) expressing the HA gene and chicken interleukin-18 (IL-18) gene. Recombinant plasmid pSY-HA/IL18 was constructed by cloning chicken IL-18 expression cassette into recombinant plasmid pSY-HA containing the HA gene. Two rFPVs were generated by transfecting two recombinant plasmids into the chicken embryo fibroblast cells pre-infected with S-FPV-017, and assessed for their immunological efficacy on one-day-old White Leghorn specific-pathogen-free chickens challenged with the A/CH/JY/1/05 (H9N2) strain. There was a significant difference in HI antibody levels (P<0.05) elicited by either rFPV-HA or rFPV-HA/IL18. The level of splenocyte proliferation response in the rFPV-HA/IL18-vaccinated group was significantly higher (P<0.05) than that in the rFPV-HA group. After challenge with 10(6.5)ELD(50) H9N2 AIV 43days after immunization, rFPVs vaccinated groups could prevent virus shedding and replication in multiple organs in response to H9N2 AIV infection, and rFPV-HA/IL18 vaccinated group had better inhibition of viruses than rFPV-HA vaccinated group. Our results show that the protective efficacy of the rFPV-HA vaccine could be enhanced significantly by simultaneous expression of IL-18.

Expression, antibody generation, and biological analysis of chicken interleukin-18

The gene encoding mature chicken interleukin-18 (ChIL-18) was cloned into prokaryotic expression vector pET-30a(+), resulting in a recombinant plasmid pET-30a-ChIL-18. After pET-30a-ChIL-18 was transformed into Escherichia coli Rosseta, the expression of ChIL-18 induced by 1 mM IPTG at 37°C was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The expressed fusion protein of 26 kDa was purified with a Ni-NTA affinity column and used to generate a hyperimmune antiserum in a rabbit. The specificity and titer of anti-ChIL-18 serum were analyzed by the enzyme-linked immunosorbent assay. Western blot and immunofluorescence assays indicated that the anti-ChIL-18 antibody specifically reacted with the ChIL-18 expressed from E. coli or ChIL-18-transfected eukaryotic cells. Moreover, the renatured ChIL-18 stimulated the production of nitric oxide (NO) from macrophages via eliciting the secreting of IFN-γ from lymphocytes.

Cloning, in vitro expression, and bioactivity of interleukin-18 isolated from a domestic porcine breed found in Henan

To evaluate the effects of recombinant porcine interleukin-18 (rpIL-18) on the replication of viruses in host cells and proliferation of lymphocytes, porcine IL-18 (pIL-18) isolated from a domestic big-white porcine breed found in the Henan province (HN) was cloned using a reverse transcriptase-PCR. The cloned HN pIL-18 contained an ORF of 579 base pairs encoding a 192-amino-acid precursor protein. The amino acid sequence of HN pIL-18 was compared with all the other pIL-18 amino acid sequences and varied by at least one amino acid to the consensus of all the others available. HN pIL-18 mature protein gene was inserted into a prokaryotic vector pGEX-4T-1 and expressed in Escherichia coli BL21. The expression of glutathione-S-transferase-pIL18 fusion protein was confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and Western blot analysis. The rpIL-18 induced in vitro proliferation of concanavalin-A-stimulated porcine splenocytes, as revealed by the MTT assay. We studied the antiviral activities of the rpIL-18 on the replication of porcine reproductive and respiratory syndrome virus (PRRSV), pseudorabies virus (PRV), and porcine parvovirus (PPV) cultured in two homologous cell lines. The results suggested that rpIL-18 can stimulate the proliferation of lymphocytes and inhibit viral pathogens infecting the porcine population.

Construction and immunogenicity of a DNA vaccine containing clumping factor A of Staphylococcus aureus and bovine IL18

Selection of potent cytokine adjuvants is important for the development of Staphylococcus aureus DNA vaccines. Several potential cytokines have been proven to induce enhanced immune responses in animal models and clinical tests. There is still no reported use of IL18 as an adjuvant to design DNA vaccines against S. aureus. In this study, we cloned the main fibronectin binding protein gene (a fragment from clumping factor A, ClfA(221-550)) of S. aureus and bovine interleukin 18 (bIL18). Then recombinant plasmids were constructed based on the eukaryotic expression vector pVAX1 with or without bIL18. Indirect immunofluorescence assays in transfected HeLa cells indicated that the recombinant DNAs (rDNAs) could be expressed correctly and had antigenicity. BALB/c mice were used as experimental models to examine the immunogenicity of rDNAs in vivo. The ClfA(221-550) rDNA provoked antibody production. The bIL18 rDNA induced production of the Th1 type cytokines IL2 and IFNgamma, and ClfA(221-550) and bIL18 synergistically stimulated T-lymphocyte proliferation. The data demonstrated that bIL18 is a potent adjuvant that could be used to enhance cellular immunity.

Confronting potential influenza A (H5N1) pandemic with better vaccines

Better understanding of host-virus interaction is essential to produce effective vaccines against influenza (H5N1) viruses.

Influenza A (H5N1) viruses are strong candidates for causing the next influenza pandemic if they acquire the ability for efficient human-to-human transmission. A major public health goal is to make efficacious vaccines against these viruses by using novel approaches, including cell-culture system, reverse genetics, and adjuvant development. Important consideration for the strategy includes preparation of vaccines from a currently circulating strain to induce broad-spectrum immunity toward newly emerged human H5 strains. This strategy would be a good solution early in a pandemic until an antigenically matched and approved vaccine is produced. The concept of therapeutic vaccines (e.g., antidisease vaccine) directed at diminishing the cytokine storm frequently seen in subtype H5N1–infected persons is underscored. Better understanding of host–virus interaction is essential to identify tools to produce effective vaccines against influenza (H5N1).

Immune responses of swine inoculated with a recombinant fowlpox virus co-expressing P12A and 3C of FMDV and swine IL-18

Two recombinant fowlpox viruses (rFPV-P1 and rFPV-IL18-2AP12A) containing foot-and-mouth disease virus (FMDV) capsid polypeptide, 3C coding regions of O/NY00 were evaluated to determine their abilities to induce humoral and cellular responses in the presence or absence of swine IL-18 as genetic adjuvant. The ability to protect swine against homologous virus challenge was examined. All swine were given booster vaccinations at 21 days after the initial inoculation and were challenged 10 days after the booster vaccination. Control groups were inoculated with wild-type fowlpox virus (wtFPV). All animals vaccinated with rFPV-P12A and rFPV-IL18-P12A developed specific anti-FMDV ELISA antibody and neutralizing antibody and T-lymphocyte proliferation was observed. Cellular immune function was evaluated via examination of IFN-gamma production in swine peripheral blood serum. The results demonstrate the potential viability of a fowlpox virus-based recombinant vaccine in the control and prevention of FMDV infections.

Immune responses of pigs inoculated with a recombinant fowlpox virus coexpressing GP5/GP3 of porcine reproductive and respiratory syndrome virus and swine IL-18

Two recombinant fowlpox viruses (rFPV-ORF5-ORF3 and rFPV-IL-18-ORF5-ORF3) containing the ORF5/ORF3 cDNAs of PRRSV (strain Chang Chun) and IL-18 of swine were constructed and evaluated for theirs abilities to induce humoral and cellular responses in piglets. In addition, their abilities to protect piglets against homologous virus challenge were examined. All piglets were given booster vaccinations at 21 days after the initial inoculation, and all piglets were challenged at 60 after the initial inoculation. Control groups were inoculated with wild-type fowlpox virus (wtFPV). All animals vaccinated with rFPV-ORF5-ORF3 and rFPV-IL-18-ORF5-ORF3 developed specific anti-PRRSV ELISA antibody and neutralizing antibody, as well as T-lymphocyte proliferation response. To evaluate the cellular immune function, IFN-gamma production in pigs serum and T-lymphocytes (CD4 and CD8 T cells) in peripheral blood were examined. Following challenge with a pathogenic strain of PRRSV (strain Chang Chun), piglets inoculated with recombinant fowlpox virus (rFPV) showed lower (P<0.05) temperature, viremia and virus load in bronchial lymph nodes than control animals, suggesting the establishment of partial protection against PRRSV infection. The results demonstrated the potential use of a fowlpox virus-based recombinant vaccine in the control and prevention of PRRSV infections.