Mechanisms of vaccine adjuvanticity at mucosal surfaces

Rapid and Highly Efficient Genetic Transformation and Application of Interleukin-17B Expressed in Duckweed as Mucosal Vaccine Adjuvant

Molecular farming utilizes plants as a platform for producing recombinant biopharmaceuticals. Duckweed, the smallest and fastest growing aquatic plant, is a promising candidate for molecular farming. However, the efficiency of current transformation methods is generally not high in duckweed. Here, we developed a fast and efficient transformation procedure in Lemna minor ZH0403, requiring 7-8 weeks from screening calluses to transgenic plants with a stable transformation efficiency of 88% at the DNA level and 86% at the protein level. We then used this transformation system to produce chicken interleukin-17B (chIL-17B). The plant-produced chIL-17B activated the NF-κB pathway, JAK-STAT pathway, and their downstream cytokines in DF-1 cells. Furthermore, we administrated chIL-17B transgenic duckweed orally as an immunoadjuvant with mucosal vaccine against infectious bronchitis virus (IBV) in chickens. Both IBV-specific antibody titer and the concentration of secretory immunoglobulin A (sIgA) were significantly higher in the group fed with chIL-17B transgenic plant. This indicates that the duckweed-produced chIL-17B enhanced the humoral and mucosal immune responses. Moreover, chickens fed with chIL-17B transgenic plant demonstrated the lowest viral loads in different tissues among all groups. Our work suggests that cytokines are a promising adjuvant for mucosal vaccination through the oral route. Our work also demonstrates the potential of duckweed in molecular farming.

Immunization with recombinant fusion of LTB and linear epitope (40-62) of epsilon toxin elicits protective immune response against the epsilon toxin of Clostridium perfringens type D

Epsilon toxin (Etx) produced by Clostridium perfringens types B and D, a major causative agent of enterotoxaemia causes significant economic losses to animal industry. Conventional vaccines against these pathogens generally employ formalin-inactivated culture supernatants. However, immunization with the culture supernatant and full length toxin subjects the animal to antigenic load and often have adverse effect due to incomplete inactivation of the toxins. In the present study, an epitope-based vaccine against Clostridium perfringens Etx, comprising 40-62 amino acid residues of the toxin in translational fusion with heat labile enterotoxin B subunit (LTB) of E. coli, was evaluated for its protective potential. The ability of the fusion protein rLTB.Etx_40-62 to form pentamers and biologically active holotoxin with LTA of E. coli indicated that the LTB present in the fusion protein retained its biological activity. Antigenicity of both the components in the fusion protein was retained as anti-fusion protein antisera detected both the wild type Etx and LTB in Western blot analysis. Immunization of BALB/c mice with the fusion protein resulted in a significant increase in all isotypes, predominantly IgG1, IgG2a and IgG2b. Anti-fusion protein antisera neutralized the cytotoxicity of epsilon toxin both in vitro and in vivo. Thus, the results demonstrate the potential of rLTB.Etx_40-62 as a candidate vaccine against C. perfringens.

Role of Tumor Necrosis Factor-Producing Mesenchymal Stem Cells on Apoptosis of Chronic B-lymphocytic Tumor Cells Resistant to Fludarabine-based Chemotherapy

BACKGROUND

B-cell chronic lymphocytic leukemia B (B-CLL), the most common type of leukemia, may be caused by apoptosis deficiency in the body. Adipose tissue-derived mesenchymal stem cells (AD-MSCs) as providers of pro-apoptotic molecules such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), can be considered as an effective anti-cancer therapy candidate. Therefore, in this study we assessed the role of tumor necrosis factor-producing mesenchymal stem cells oin apoptosis of B-CLL cells resistant to fludarabine- based chemotherapy.

MATERIALS AND METHODS

In this study, after isolation and culture of AD-MSCs, a lentiviral LeGO-iG2-TRAIL-GFP vector containing a gene producing the ligand pro-apoptotic with plasmid PsPAX2 and PMDG2 virus were transfected into cell-lines to generate T293HEK. Then, T293HEK cell supernatant containing the virus produced after 48 and 72 hours was collected, and these viruses were transduced to reprogram AD-MSCs. Apoptosis rates were separately studied in four groups: group 1, AD-MSCs-TRAIL; group 2, AD-MSCs-GFP; group 3, AD-MSCs; and group 4, CLL.

RESULTS

Observed apoptosis rates were: group 1, 42 ± 1.04%; group 2, 21 ± 0.57%; group 3, 19± 2.6%; and group 4, % 0.01 ± 0.01. The highest rate of apoptosis thus occurred ingroup 1 (transduced TRAIL encoding vector). In this group, the average medium-soluble TRAIL was 72.7pg/m and flow cytometry analysis showed a pro-apoptosis rate of 63 ± 1.6%, which was again higher than in other groups.

CONCLUSIONS

In this study we have shown that tumor necrosis factor (TNF) secreted by AD-MSCs may play an effective role in inducing B-CLL cell apoptosis.

Evidence for a common mucosal immune system in the pig

•

There is evidence that the common mucosal immune system exists in pigs.

•

Vaccination at an easily accessible mucosal site may assist in providing protection at other mucosal sites.

•

Local and distal mucosal sites should be sampled after vaccinations to define the optimal dose and formulation which promotes the common mucosal immune system in pigs.

The majority of lymphocytes activated at mucosal sites receive instructions to home back to the local mucosa, but a portion also seed distal mucosa sites. By seeding distal sites with antigen-specific effector or memory lymphocytes, the foundation is laid for the animal's mucosal immune system to respond with a secondary response should to this antigen be encountered at this site in the future. The common mucosal immune system has been studied quite extensively in rodent models but less so in large animal models such as the pig. Reasons for this paucity of reported induction of the common mucosal immune system in this species may be that distal mucosal sites were examined but no induction was observed and therefore it was not reported. However, we suspect that the majority of investigators simply did not sample distal mucosal sites and therefore there is little evidence of immune response induction in the literature. It is our hope that more pig immunologists and infectious disease experts who perform mucosal immunizations or inoculations on pigs will sample distal mucosal sites and report their findings, whether results are positive or negative. In this review, we highlight papers that show that immunization/inoculation using one route triggers mucosal immune system induction locally, systemically, and within at least one distal mucosal site. Only by understanding whether immunizations at one site triggers immunity throughout the common mucosal immune system can we rationally develop vaccines for the pig, and through these works we can gather evidence about the mucosal immune system that may be extrapolated to other livestock species or humans.

Effect of gentle stroking and vocalization on behaviour, mucosal immunity and upper respiratory disease in anxious shelter cats

Emotional, behavioural, and health benefits of gentle stroking and vocalizations, otherwise known as gentling, have been documented for several species, but little is known about the effect of gentling on cats in stressful situations. In this study, 139 cats rated as anxious upon admission to an animal shelter were allocated to either a Gentled or Control group. Cats were gentled four times daily for 10 min over a period of 10 days, with the aid of a tool for cats that were too aggressive to handle. The cats' mood, or persistent emotional state, was rated daily for 10 d as Anxious, Frustrated or Content. Gentled cats were less likely to have negatively valenced moods (Anxious or Frustrated) than Control cats (Incidence Rate Ratio [IRR]=0.61 CI 0.42-0.88, P=0.007). Total secretory immunoglobulin A (S-IgA) was quantified from faeces by enzyme-linked immunosorbent assay. Gentled cats had increased S-IgA (6.9 ± 0.7 logeμg/g) compared to Control cats (5.9 ± 0.5 logeμg/g) (P<0.0001). Within the Gentled group of cats, S-IgA values were higher for cats that responded positively to gentling (7.03 ± 0.6, logeμg/g), compared with those that responded negatively (6.14 ± 0.8, logeμg/g). Combined conjunctival and oropharyngeal swab specimens were tested by quantitative real-time polymerase chain reaction (rPCR) for feline herpesvirus type 1 (FHV-1), feline calicivirus (FCV), Mycoplasma felis, Chlamydophila felis, and Bordetella bronchiseptica. There was a significant increase in shedding over time in Control cats (23%, 35%, 52% on days 1, 4 and 10, respectively), but not in gentled cats (32%, 26%, 30% on days 1, 4 and 10, respectively) (P=0.001). Onset of upper respiratory disease was determined by veterinary staff based on clinical signs, in particular ocular and/or nasal discharge. Control cats were 2.4 (CI: 1.35-4.15) times more likely to develop upper respiratory disease over time than gentled cats (P<0.0001). It is concluded that gentling anxious cats in animal shelters can induce positive affect (contentment), increase production of S-IgA, and reduce the incidence of upper respiratory disease.

Advances in swine immunology help move vaccine technology forward

In veterinary animal species, vaccines are the primary tool for disease prevention, a key tool for treatment of infection, and essential for helping maintain animal welfare and productivity. Traditional vaccine development by trial-and-error has achieved many successes. However, effective vaccines that provide solid cross-protective immunity with excellent safety are still needed for many diseases. The path to development of vaccines against difficult pathogens requires recognition of uniquely evolved immunological interactions of individual animal hosts and their specific pathogens. Here, general principles that currently guide veterinary immunology and vaccinology research are reviewed, with an emphasis on examples from swine. Advances in genomics and proteomics now provide the community with powerful tools for elucidation of regulatory and effector mechanisms of protective immunity that provide new opportunities for successful translation of immunological discoveries into safe and effective vaccines.

An Oral Vaccine for TGEV Immunization of Pigs

Transmissible gastroenteritis virus (TGEV) is a commercially important pathogen of hog farms and causes contagious, lethal diarrhea in piglets. While orally and parenterally administered vaccines made from inactivated or attenuated TGEV are commercially available, they require individual administration to piglets, which is time and labor intensive, and run the risk of reversion to pathogenicity. Also, parenteral vaccines produce neutralizing serum antibodies which may be less effective against an orally transmitted pathogen, compared to an oral vaccine that would induce the production of mucosal antibodies. There has been an effort to produce subunit vaccines in an edible form in plants for convenient administration through feed. These efforts towards the expression of the S-antigen of TGEV in maize seed, its effectiveness at inducing neutralizing antibody production in the colostrum of gilts, and its efficacy in protecting piglets against challenge by virulent TGEV are summarized here.

Recognition of Extracellular Bacteria by NLRs and Its Role in the Development of Adaptive Immunity

Innate immune recognition of bacteria is the first requirement for mounting an effective immune response able to control infection. Over the previous decade, the general paradigm was that extracellular bacteria were only sensed by cell surface-expressed Toll-like receptors (TLRs), whereas cytoplasmic sensors, including members of the Nod-like receptor (NLR) family, were specific to pathogens capable of breaching the host cell membrane. It has become apparent, however, that intracellular innate immune molecules, such as the NLRs, play key roles in the sensing of not only intracellular, but also extracellular bacterial pathogens or their components. In this review, we will discuss the various mechanisms used by bacteria to activate NLR signaling in host cells. These mechanisms include bacterial secretion systems, pore-forming toxins, and outer membrane vesicles. We will then focus on the influence of NLR activation on the development of adaptive immune responses in different cell types.

Bursopentine as a novel immunoadjuvant enhances both humoral and cell-mediated immune responses to inactivated H9N2 Avian Influenza virus in chickens

There is an urgent need for identification of a new adjuvant capable of selectively promoting an efficient immune response for use with vaccines and especially subunit vaccines. Our pervious study showed that Bursopentine (BP5) is a novel immunomodulatory peptide and has the ability to significantly stimulate an antigen-specific immune response in mice. In this study, the potential adjuvant activities of BP5 were examined in chickens by coinjection of BP5 and an inactivated avian influenza virus (AIV) (A/Duck/Jiangsu/NJ08/05 [AIV H9N2 subtype]). The results suggested that BP5 markedly elevated serum hemagglutination inhibition (HI) titers and antigen-specific antihemagglutinin (anti-HA) antibody (IgG) levels, induced both Th1 (interleukin 2 [IL-2] and gamma interferon [IFN-γ])- and Th2 (IL-4)-type cytokines, promoted the proliferation of peripheral blood lymphocytes, and increased populations of CD3(+) T cells and their subsets CD4(+) (CD3(+) CD4(+)) T cells and CD8(+) (CD3(+) CD8(+)) T cells. Furthermore, a virus challenge experiment revealed that BP5 contributes to protection against homologous avian influenza virus challenge by reducing viral replication in chicken lungs. This study indicates that the combination of inactivated AIVs and BP5 gives a strong immune response at both the humoral and cellular levels and implies that BP5 is a novel immunoadjuvant suitable for vaccine design.

Immunogenicity of recombinant GP5 protein of porcine reproductive and respiratory syndrome virus expressed in tobacco plant

The aim of the study was to evaluate the immunogenicity of the ORF5-encoded major envelop glycoprotein 5 (GP5) of porcine reproductive and respiratory syndrome virus (PRRSV) expressed in tobacco plant as a potential pig oral vaccine in protection against PRRSV infection. Six-week-old PRRSV-free pigs were fed four times orally with 50g of chopped fresh GP5 transgenic tobacco leaves (GP5-T) (GP5 reaching 0.011% of total soluble protein) or wild-type tobacco leaves (W-T) each on days 0, 14, 28, and 42. Samples of serum, saliva, and peripheral blood mononuclear cells (PBMCs) were collected on days -1, 6, 13, 20, 27, 34, 41, and 48 after the initial oral vaccination. A similar vaccination-dependent gradual increase in the responses of serum and saliva anti-PRRSV total IgG and IgA, respectively, and in the levels of PRRSV-specific blastogenic response of PBMCs was seen in GP5-T-treated pigs; all statistically significant elevations occurred after the 2nd vaccination and were revealed after 20 days post-initial oral vaccination (DPIOV). Pigs fed on GP5-T also developed serum neutralizing antibodies to PRRSV at a titer of 1:4-1:8 after the 4th vaccination by 48 DPIOV. No detectable anti-PRRSV antibody responses and PRRSV-specific blastogenic response were seen in W-T-treated pigs. The present study has demonstrated that pigs fed on GP5-T could develop specific mucosal as well as systemic humoral and cellular immune responses against PRRSV. The results also support that transgenic plant as GP5-T can be an effective system for oral delivery of recombinant subunit vaccines in pigs.

Mouse models for the study of mucosal vaccination against otitis media

Otitis media (OM) is one of the most common infectious diseases in humans. The pathogenesis of OM involves nasopharyngeal (NP) colonization and retrograde ascension of the pathogen up the Eustachian tube into the middle ear (ME). Due to increasing rates of antibiotic resistance, there is an urgent need for vaccines to prevent infections caused by the most common causes of bacterial OM, including nontypeable Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis. Current vaccine strategies aim to diminish bacterial NP carriage, thereby reducing the likelihood of developing acute OM. To be effective, vaccination should induce local mucosal immunity both in the ME and in the NP. Studies in animal models have demonstrated that the intranasal route of vaccination is particularly effective at inducing immune responses in the nasal passage and ME for protection against OM. The mouse is increasingly used in these models, because of the availability of murine reagents and the existence of technology to manipulate murine models of disease immunologically and genetically. Previous studies confirmed the suitability of the mouse as a model for inflammatory processes in acute OM. Here, we discuss various murine models of OM and review the applicability of these models to assess the efficacy of mucosal vaccination and the mechanisms responsible for protection. In addition, we discuss various mucosal vaccine antigens, mucosal adjuvants and mucosal delivery systems.

Leptospirosis vaccines

Leptospirosis is a serious infection disease caused by pathogenic strains of the Leptospira spirochetes, which affects not only humans but also animals. It has long been expected to find an effective vaccine to prevent leptospirosis through immunization of high risk humans or animals. Although some leptospirosis vaccines have been obtained, the vaccination is relatively unsuccessful in clinical application despite decades of research and millions of dollars spent. In this review, the recent advancements of recombinant outer membrane protein (OMP) vaccines, lipopolysaccharide (LPS) vaccines, inactivated vaccines, attenuated vaccines and DNA vaccines against leptospirosis are reviewed. A comparison of these vaccines may lead to development of new potential methods to combat leptospirosis and facilitate the leptospirosis vaccine research. Moreover, a vaccine ontology database was built for the scientists working on the leptospirosis vaccines as a starting tool.

Preparation of recombinant vaccines

Vaccination is one of the most efficient ways to eradicate some infectious diseases in humans and animals. The material traditionally used as vaccines is attenuated or inactivated pathogens. This approach is sometimes limited by the fact that the material for vaccination is not efficient, not available, or generating deleterious side effects. A possible theoretical alternative is the use of recombinant proteins from the pathogens. This implies that the proteins having the capacity to vaccinate have been identified and that they can be produced in sufficient quantity at a low cost. Genetically modified organisms harboring pathogen genes can fulfil these conditions. Microorganisms, animal cells as well as transgenic plants and animals can be the source of recombinant vaccines. Each of these systems that are all getting improved has advantages and limits. Adjuvants must generally be added to the recombinant proteins to enhance their vaccinating capacity. This implies that the proteins used to vaccinate have been purified to avoid any immunization against the contaminants. The efficiency of a recombinant vaccine is poorly predictable. Multiple proteins and various modes of administration must therefore be empirically evaluated on a case-by-case basis. The structure of the recombinant proteins, the composition of the adjuvants and the mode of administration of the vaccines have a strong and not fully predictable impact on the immune response as well as the protection level against pathogens. Recombinant proteins can theoretically also be used as carriers for epitopes from other pathogens. The increasing knowledge of pathogen genomes and the availability of efficient systems to prepare large amounts of recombinant proteins greatly facilitate the potential use of recombinant proteins as vaccines. The present review is a critical analysis of the state of the art in this field.

Genomic dissection of mucosal immunobiology in the porcine small intestine

The enteric immune system of swine protects against infectious and noninfectious environmental insults and discriminates ingested nutrients, food, and commensal microflora from pathogenic agents. The molecular and cellular elements of the immune system have been selected over evolutionary time in response to the specific environment of pigs. Thus, models of immune function based on mouse and human need to be applied cautiously in the pig. To better understand how the mucosal immune system of the small intestine accomplishes the conflicting functions of food tolerance and immunity to enteric infection, we used a genomic approach to profile gene expression in the Peyer's patch. More than 40% of mRNA enriched by differential subtraction for Peyer's patch-specific expressed sequences represented genes of unknown function or had no match in GenBank. Microarray analysis and radiation hybrid mapping validated their porcine origin and provided additional insights into putative functions. The abundance of expressed genes of unknown function indicates that a substantial fraction of the immunological and physiological processes of the Peyer's patch remains to be discovered. It further suggests that swine have evolved specialized biochemical and immunological processes in the small intestine. Further elucidation of these processes are expected to provide novel insights into swine enteric mucosal immune function.

The ovine nasal mucosa: an alternative tissue site for mucosal immunization

The ovine nasal mucosal environment has histological and ultrastructural features that resemble well-known inductive sites of mucosa-associated lymphoid tissue. In the present study, the nasal mucosa was assessed as a potential mucosal tissue site for delivering vaccines to sheep. Sheep were immunized by either injection with the model antigen, Keyhole Limpet Haemocyanin (KLH), and aluminium hydroxide gel (alum) or by aerosol spray with KLH with and without cholera toxin (CT). Sheep immunized by injection with KLH/alum and aerosol spray with KLH/CT induced strong anti-KLH IgG and IgA serum antibody responses as well as specific T cell memory. Anti-KLH IgG1 responses were significantly higher following immunization by injection and no significant differences in anti-KLH IgG2 responses were detected between groups. Sheep immunized with KLH by aerosol spray without CT did not produce serum antibody and T cell memory responses. Antibody-secreting cells were present in the parotid lymph nodes (draining lymph nodes) of sheep immunized with KLH/alum and KLH/CT, but secreted only Ag-specific IgG1, and not IgG2 or IgA. These results suggest that aerosolization of soluble antigen formulations with CT may provide an alternative method of delivering nasal vaccines to sheep and other large animal species, and that further improvements in antigen penetration of nasal tissues may dramatically improve the strength of the immune response.

The use of a systemic prime/mucosal boost strategy with an equine influenza ISCOM vaccine to induce protective immunity in horses

In horses, natural infection confers long lasting protective immunity characterised by mucosal IgA and humoral IgGa and IgGb responses. In order to investigate the potential of locally administered vaccine to induce a protective IgA response, responses generated by vaccination with an immunostimulating complex (ISCOM)-based vaccine for equine influenza (EQUIP F) containing A/eq/Newmarket/77 (H7N7), A/eq/Borlänge/91 (H3N8) and A/eq/Kentucky/98 (H3N8) using a systemic prime/mucosal boost strategy were studied. Seven ponies in the vaccine group received EQUIP F vaccine intranasally 6 weeks after an initial intramuscular immunisation. Following intranasal boosting a transient increase in virus-specific IgA was detected in nasal wash secretions. Aerosol challenge with the A/eq/Newmarket/1/93 reference strain 4 weeks after the intranasal booster resulted in clinical signs of infection and viral shedding in seven of seven influenza-naive control animals whereas the seven vaccinated ponies had statistically significantly reduced clinical signs and duration of virus excretion. Furthermore, following this challenge, significantly enhanced levels of virus-specific IgA were detected in the nasal washes from vaccinated ponies compared with the unvaccinated control animals. These data indicate that the intranasal administration of EQUIP F vaccine primes the mucosal system for an enhanced IgA response following exposure to live influenza virus.

Oral immunization induces local and distant mucosal immunity in swine

Transmission of porcine reproductive and respiratory syndrome virus (PRRSV) in semen and reproductive disease in pregnant swine might be reduced by vaccines that induce mucosal immunity in the reproductive tract. Cholera toxin (CT), when delivered orally, is a potent mucosal adjuvant and immunogen in swine. To determine if oral immunization additionally elicits immunity at distant mucosal surfaces, we examined antibody responses to CT-B subunit in the reproductive tract and oral cavity. Orally administered CT induced distant mucosal immunity, as measured by antibodies to CT-B subunit in saliva and vaginal secretions. Presentation of PRRSV nucleocapsid as a genetic fusion with CT resulted in local mucosal antibody production, but no response was observed in vaginal secretions. The results demonstrate the feasibility of using orally administered CT for the induction of immunity to reproductive pathogens in swine. However, effective induction of PRRSV-specific immune responses in the reproductive tract requires a better understanding of the mechanisms of antigenicity and adjuvanticity at distant mucosal sites.

Cytokines as adjuvants for avian vaccines

The worldwide trend towards a reduced reliance on in-feed antibiotics has increased the pressure to develop alternative strategies to manage infectious diseases in poultry. With this in mind, there is a great emphasis on vaccine use and the enhancement of existing vaccines to provide long-term protection. Currently existing adjuvants for poultry can have deleterious side-effects, such as inflammation, resulting in the down-grading of meat quality and a subsequent reduction in profits. Therefore, to enhance the use of vaccination, alternative adjuvants must be developed. The use of recombinant cytokines as adjuvants in poultry is attracting considerable attention, and their potential role as such has been addressed by several studies. The recent identification of a number of chicken cytokine genes has provided the possibility to study their effectiveness in enhancing the immune response during infection and vaccination. This review focuses on the recent studies involving the assessment of cytokines as vaccine adjuvants.

Improvement of the systemic prime/oral boost strategy for systemic and local responses

This paper describes oral boost immunisations of primed animals as an alternative oral vaccination strategy. Mice were primed orally (PO), intranasally (IN), subcutaneously (SC), or intraperitoneally (IP) with ovalbumin (OVA) with or without adjuvant. Boost immunisations were given orally with or without cholera toxin (CT) as adjuvant. Prime immunisations induced variable IgA and IgG(1) titres in serum depending on the route. A subsequent oral boost increased these titres. Use of an adjuvant in the priming significantly increased serum IgA and, to a lesser extend, IgG(1). Oral boost immunisation induced significantly higher serum IgA titres in animals primed via the SC, IP and the IN route compared to the PO route. This was independent of the use of CT. Three oral boosts with OVA plus 5 microg CT given in 5 days to primed mice revealed higher IgA titres compared to single oral boosts and anti-OVA IgA titres in faeces were also detected. Finally, we put together our findings and propose a systemic priming/oral boost strategy in which mice were primed via the SC route with 100 microg OVA plus 50 microg Butyl16-p(AA), and subsequently orally boosted with three doses of 300 microg OVA plus 5 microg CT each. We concluded that oral immunisation is more effective in IN, SC, or IP primed mice than in PO primed mice, and that the IgA antibody response in serum and faeces can be improved by increasing the immunisation frequency and the use of appropriate adjuvants in primary and boost immunisation. The here-formulated strategy improves the probability of success of oral vaccination. The results are discussed in the light of the development of edible vaccines.

Adjuvant danger signals increase the immune response to porcine reproductive and respiratory syndrome virus

The immune response of swine to vaccination with a live, attenuated PRRSV was assessed in the presence and absence of cytokine adjuvants or cholera toxin (CT) to address the hypothesis that adjuvant danger signals, that is, inflammatory cytokines and bacterial extoxin, stimulate a more robust immune response. Animals received four injections of recombinant porcine IL-1 and IL-6, IL-12 alone, or CT alone within 1 week of intramuscular administration of a vaccine strain of PRRSV, Ingelvac MLV. Serological and cell-mediated responses were monitored for 42 days after vaccination and for a further 10 days after challenge with the virulent VR2332 strain of PRRSV. First, the principal observation was an enhancing effect of IL-12 on the interferon gamma response to PRRSV, with a more rapid and heightened PRRSV-specific interferon gamma ELISPOT response in peripheral blood mononuclear cells. The more rapid and robust development of a cell-mediated immune response, as determined by this assay, suggests that IL-12 may influence the induction of antigen-specific T cell responses. Second, animals that received CT adjuvant displayed a more robust antibody response to GP5, the major envelope glycoprotein. Anti-GP5 titers peaked at 21 days after vaccination at more than twice the level of any other treatment, for which the peak response was at 28 days. Third, there was no evidence of PRRSV immunosuppression of immunity to unrelated antigens, including circovirus. CT is a potent mucosal adjuvant, particularly for antibody responses. It acts in part through the production of IL-1 in macrophages, but its effect was not replaced by combination treatment with IL-1 and IL-6. In sum, the results suggest that cytokine adjuvants, particularly IL-12, and CT have the potential to enhance immune responses to live viral vaccines.

Salmonella vaccines for use in humans: present and future perspectives

In recent years there has been significant progress in the development of attenuated Salmonella enterica serovar Typhi strains as candidate typhoid fever vaccines. In clinical trials these vaccines have been shown to be well tolerated and immunogenic. For example, the attenuated S. enterica var. Typhi strains CVD 908-htrA (aroC aroD htrA), Ty800 (phoP phoQ) and chi4073 (cya crp cdt) are all promising candidate typhoid vaccines. In addition, clinical trials have demonstrated that S. enterica var. Typhi vaccines expressing heterologous antigens, such as the tetanus toxin fragment C, can induce immunity to the expressed antigens in human volunteers. In many cases, the problems associated with expression of antigens in Salmonella have been successfully addressed and the future of Salmonella vaccine development is very promising.

Inflammatory cytokines and antigen presenting cell activation

Immune responses are stimulated in response to threats against health. In animals, defense against infectious agents, particularly rapidly growing viruses and bacteria, requires an immediate response to limit growth and dissemination, and then stimulation of a more prolonged, specific immunity to prevent re-infection. The process by which animals meet the dual needs of an immediate response to danger and initiation of long-term protection is substantially influenced by inflammatory cytokines produced primarily by macrophages and professional antigen presenting cells (APCs). Inflammatory cytokines mobilize the immune system in response to danger and increase the efficiency of an immune response as effectors of APC function. Here we review the evidence for the involvement of inflammatory cytokines in immune induction and as mediators of APC activity, with a particular emphasis on swine and on the induction of immunity at mucosal surfaces. The vast majority of infections occur at mucosal surfaces of the enteric, respiratory and reproductive tracts, and induction of protective immunity at these sites is particularly challenging. Induction of immunity at mucosal surfaces of the small intestine is greatly facilitated by the oral adjuvant, cholera toxin (CT). CT potentiates inflammatory cytokine and costimulatory molecule expression in macrophages, and stimulates humoral and cell-mediated immune responses both locally and systemically. These observations are consistent with the hypothesis that activation of APCs is a key step in the induction of antigen-specific immunity, and that inflammatory cytokine expression is a hallmark of activated APC function. The efficacy of vaccine adjuvants, particularly in the context of mucosal immunity, may be determined by their ability to induce a controlled inflammatory response in gut-associated lymphoid tissue, characterized by the expression of various costimulatory molecules and inflammatory cytokines. Thus, elucidation of the patterns of inflammatory cytokine expression and features of APC activation will help to facilitate the rational development of more efficacious vaccines.