Measurement of specific IgA in faecal extracts and intestinal lavage fluid for monitoring of mucosal immune responses

Mechanisms of cellular and humoral immunity through the lens of VLP-based vaccines

INTRODUCTION

Vaccination can be effective defense against many infectious agents and the corresponding diseases. Discoveries elucidating the mechanisms of the immune system have given hopes to developing vaccines against diseases recalcitrant to current treatment/prevention strategies. One such finding is the ability of immunogenic biological nanoparticles to powerfully boost the immunogenicity of poorer antigens conjugated to them with virus-like particle (VLP)-based vaccines as a key example. VLPs take advantage of the well-defined molecular structures associated with sub-unit vaccines and the immunostimulatory nature of conjugate vaccines.

AREAS COVERED

In this review, we will discuss how advances in understanding the immune system can inform VLP-based vaccine design and how VLP-based vaccines have uncovered underlying mechanisms in the immune system.

EXPERT OPINION

As our understanding of mechanisms underlying the immune system increases, that knowledge should inform our vaccine design. Testing of proof-of-concept vaccines in the lab should seek to elucidate the underlying mechanisms of immune responses. The integration of these approaches will allow for VLP-based vaccines to live up to their promise as a powerful plug-and-play platform for next generation vaccine development.

Green tea polyphenol epigallocatechin-3-gallate alleviates nonalcoholic fatty liver disease and ameliorates intestinal immunity in mice fed a high-fat diet

Green tea polyphenol epigallocatechin-3-gallate (EGCG) may help prevent metabolic syndrome and nonalcoholic fatty liver disease (NAFLD). However, the underlying mechanisms of its protective effects are complicated and remain unclear. With the gut-liver axis theory as a foundation, the present study investigated the effects of EGCG on intestinal mucosal immunity in male C57BL/6 mice fed a high-fat Western diet or the diet supplemented with 0.4% dietary EGCG (w/w) for 14 weeks. Dietary EGCG supplementation effectively prevented changes-including excessive accumulation of visceral and hepatic fat, abnormal liver function, and elevated concentrations of serum and liver inflammatory cytokines-known to be caused by high-fat diets. In addition, serum lipopolysaccharide concentrations decreased by 94.3%. RNA sequencing data of differentially expressed genes in ileal samples among three groups indicated that most of the pathways in the Kyoto Encyclopedia of Genes and Genomes in the first 20 enrichment levels were related to immunity and inflammatory reactions. Real-time reverse transcription quantitative polymerase chain reaction was used to determine alterations in expression levels of key genes related to intestinal immune function and inflammatory responses from ileal and colonic samples. Changes in secretory immunoglobulin A in the small intestine, serum, and feces further demonstrated improved intestinal mucosal immunity in the EGCG-treated mice. In conclusion, dietary EGCG effectively prevented the development of NAFLD and significantly improved intestinal mucosal immunity in mice with obesity induced by a high-fat diet. However, whether improved intestinal immune function is the key mechanism underlying the health benefits of dietary EGCG warrants further research.

Gut Microbe-Derived Outer Membrane Vesicles: A Potential Platform to Control Cecal Load of Campylobacter jejuni

Acute diarrheal illness and gastroenteritis caused by Campylobacter jejuni infection remain significant public health risks in developing countries with substantial mortality and morbidity in humans, particularly in children under the age of five. Genetic diversities among Campylobacter jejuni and limited understanding of immunological correlations of host protection remain primary impediments for developing an effective measure to controlCampylobacter infection. Moreover, the lack of a reliable in vivo model to mimic natural infection against Campylobacter jejuni has substantially delayed the vaccine-development process. Given the role of bacterial outer membrane associated proteins in intestinal adherence and invasion as well as modulating dynamic interplay between host and pathogens, bacterial outer-membrane vesicles have emerged as a potential vaccine target against a number of gut pathogens, including Campylobacter jejuni. Here, we describe a mucosal vaccine strategy using chitosan-coated outer-membrane vesicles to induce specific immune responses against Campylobacter jejuni in mice. To overcome the challenges of mucosal delivery of outer membrane vesicles in terms of exposure to variable pH and risk of enzymatic degradation, we preferentially used chitosan as a nontoxic, mucoadhesive polymer. We show that intragastric delivery of chitosan-coated outer-membrane vesicles imparts significant immune protection against Campylobacter jejuni with high level local and systemic antibody production. Further, immunization with the outer membrane vesicles resulted in potent cellular responses with an increased CD4⁺ and CD8⁺ T cell population. Moreover, significant upregulation of IFN-γ and IL-6 gene expression suggests that mucosal delivery of outer membrane vesicles promotes a Th1/Th2 mixed-type immune response. Together, as an acellular and nonreplicating canonical end product of bacterial secretion, mucosal delivery of outer membrane vesicles may represent a promising platform for developing an effective vaccine againstCampylobacter jejuni.

Immunization with intestinal microbiota-derived Staphylococcus aureus and Escherichia coli reduces bacteria-specific recolonization of the intestinal tract

A wide array of microorganisms colonizes distinctive anatomical regions of animals, being the intestine the one that harbors the most abundant and complex microbiota. Phylogenetic analyses indicate that it is composed mainly of bacteria, and that Bacterioidetes and Firmicutes are the most represented phyla (>90% of the total eubacteria) in mice and humans. Intestinal microbiota plays an important role in host physiology, contributing to digestion, epithelial cells metabolism, stimulation of intestinal immune responses, and protection against intestinal pathogens. Changes in its composition may affect intestinal homeostasis, a condition known as dysbiosis, which may lead to non-specific inflammation and disease. The aim of this work was to analyze the effect that a bacteria-specific systemic immune response would have on the intestinal re-colonization by that particular bacterium. Bacteria were isolated and identified from the feces of Balb/c mice, bacterial cell-free extracts were used to immunize the same mice from which bacteria came from. Concurrently with immunization, mice were subjected to a previously described antibiotic-based protocol to eliminate most of their intestinal bacteria. Serum IgG and feces IgA, specific for the immunizing bacteria were determined. After antibiotic treatment was suspended, specific bacteria were orally administered, in an attempt to specifically re-colonize the intestine. Results showed that parenteral immunization with gut-derived bacteria elicited the production of both anti-bacterial IgG and IgA, and that immunization reduces bacteria specific recolonization of the gut. These findings support the idea that the systemic immune response may, at least in part, determine the bacterial composition of the gut.

Variability in gut mucosal secretory IgA in mice along a working day

Objective

To assess the variability of secretory immunoglobulin A (S-IgA) in the lumen and feces of mice along a working day.

Results

Mice were maintained under a 12 h light–dark cycle, light period starting at 8 AM. S-IgA was determined in feces and intestinal content (after one or three washes) at three points along the day: at the beginning, in the middle and at the end of the light period (ELP). Significant reduction in the content of S-IgA in the small intestine fluid and in feces was observed at the end of the light cycle, which coincides with the end of a regular working day (8 PM) in any given animal facility. It was also observed that three washes of the small intestine were more effective than one flush to recover a significant higher amount of S-IgA, with the smallest coefficient of variation observed by the ELP. A smaller CV would imply a reduced number of animals needed to achieve the same meaningful results. The results may be useful when designing animal trials for the selection of probiotic candidates based on their capacity of activating S-IgA, since it would imply a more rational use of experimental animals.

Triggering the adaptive immune system with commensal gut bacteria protects against insulin resistance and dysglycemia

OBJECTIVE

To demonstrate that glycemia and insulin resistance are controlled by a mechanism involving the adaptive immune system and gut microbiota crosstalk.

METHODS

We triggered the immune system with microbial extracts specifically from the intestinal ileum contents of HFD-diabetic mice by the process of immunization. 35 days later, immunized mice were fed a HFD for up to two months in order to challenge the development of metabolic features. The immune responses were quantified. Eventually, adoptive transfer of immune cells from the microbiota-immunized mice to naïve mice was performed to demonstrate the causality of the microbiota-stimulated adaptive immune system on the development of metabolic disease. The gut microbiota of the immunized HFD-fed mice was characterized in order to demonstrate whether the manipulation of the microbiota to immune system interaction reverses the causal deleterious effect of gut microbiota dysbiosis on metabolic disease.

RESULTS

Subcutaneous injection (immunization procedure) of ileum microbial extracts prevented hyperglycemia and insulin resistance in a dose-dependent manner in response to a HFD. The immunization enhanced the proliferation of CD4 and CD8 T cells in lymphoid organs, also increased cytokine production and antibody secretion. As a mechanism explaining the metabolic improvement, the immunization procedure reversed gut microbiota dysbiosis. Finally, adoptive transfer of immune cells from immunized mice improved metabolic features in response to HFD.

CONCLUSIONS

Glycemia and insulin sensitivity can be regulated by triggering the adaptive immunity to microbiota interaction. This reduces the gut microbiota dysbiosis induced by a fat-enriched diet.

Fecal antibody levels as a noninvasive method for measuring immunity to gastrointestinal nematodes in ecological studies

Among‐individual variation in antibody‐associated immunity to gastrointestinal nematode parasites (GIN) is known be associated with life‐history traits and vital rates in wild vertebrate systems. To date, measurement of levels of antibodies against GIN antigens in natural populations has exclusively been based on invasive blood sampling techniques. Previous work in laboratory rodents and ruminant livestock suggests that antibody measures from feces may provide a viable noninvasive approach. We measured total and anti‐GIN antibodies of different isotypes (immunoglobulin (Ig) G, IgA and IgE) from paired samples of plasma and feces from free‐living Soay sheep of different ages and sexes. We tested the correlations among these measures as well as their associations with body mass and Strongyle nematode fecal egg counts (FEC). Significant positive correlations were present among plasma and fecal anti‐GIN antibody levels for IgG and IgA. Generally, correlations between total antibody levels in plasma and feces were weaker and not significant. No significant relationships were found between any antibody measures and body mass; however, fecal anti‐GIN antibody levels were significantly negatively correlated with FEC. Our data clearly demonstrate the feasibility of measuring anti‐GIN antibodies from fecal samples collected in natural populations. Although associations of fecal antibody levels with their plasma counterparts and FEC were relatively weak, the presence of significant correlations in the predicted direction in a relatively small and heterogeneous sample suggests fecal antibody measures could be a useful, noninvasive addition to current eco‐immunological studies.

Specific faecal antibody responses in sheep infected with Mycobacterium avium subspecies paratuberculosis

Many studies have examined the serum antibody response to Mycobacterium avium subspecies paratuberculosis (MAP) infection in cases of Johne's disease (JD), but there are no reports on the mucosal antibody response. Faecal immunoglobulin (Ig) G and IgA ELISA responses were examined from sheep experimentally inoculated with MAP for up to 23 months post inoculation (PI). Corresponding serum IgG responses and the presence of viable MAP shed in faeces were also examined. The sheep were divided into three groups: (i) "un-inoculated controls" (n=10), (ii) "clinical cases" (n=8) which were inoculated animals that developed clinical disease and had moderate to high levels of MAP shedding and (iii) "survivors" (n=11) which were inoculated animals from which MAP could not be cultured from tissues at the conclusion of the trial. Serum IgG responses gradually increased in all inoculated animals, peaking at 12-16 months PI. A significant increase in the levels of MAP-specific faecal IgG and IgA was measured in the survivors at 16 and 17 months PI, while levels in the un-inoculated controls and clinical cases remained at baseline levels. The detection of faecal Ig in the survivors coincided with the removal of sheep that developed clinical disease. The data suggest that some sheep produced MAP-specific IgG and IgA in the intestinal mucosa, which was released into their faeces. We hypothesise that the survivors produced faecal Ig as a direct response to ingestion of MAP associated with environmental contamination from clinical cases. Thus MAP specific mucosal antibodies may play a previously unreported role as part of a protective response triggered by environmental exposure.

Investigation of 3D ordered macroporous carbon with different polymer coatings and their application as an oral vaccine carrier

3-D ordered macroporous carbon with different polymer coatings were developed as new oral vaccine immunological systems. Poly dimethyl diallyl ammonium (PDDA), polyethyleneimine (PEI) and chitosan (CTS), three different polymers with electropositive or adsorption-promoting properties, were chosen as the coating materials to endow the vaccine delivery systems with different surface properties. The bovine serum albumin (BSA) was used as a model vaccine. The three different polymer coated systems exhibited similar release rate which minimized the influence of release rate. The measured value of immunoglobulin G (IgG) titers suggested that the sustained release rate of BSA from polymer coated systems exhibited no strengthened effect on the immune response but could delay the appearance of the peak of the IgG titers compared with uncoated system. The electrostatic attraction between the mucosal and positively charged carrier would be useful during the whole immune experiment. In addition, using the coating material with the ability of enhancing mucosal adsorption was important in the mid-late period of immune. The immunoglobulin A (IgA) titers induced by the polymer coated systems were significantly higher than that induced by the oral BSA solution or i.m. BSA with Freund's complete adjuvant (FCA) which suggested the successful mucosal immune response of the three different coated systems. Overall, this work provides valuable information for the development of oral vaccine delivery system.

Purification and functional characterization of mucosal IgA from vaccinated and SIV-infected rhesus macaques

Vaccine-induced mucosal antibodies are often evaluated using small volumes of secretory fluids. However, fecal matter containing mucosal IgA is abundant. We purified fecal IgA from five SIV-vaccinated and five SIV-infected rhesus macaques by sequential affinity chromatography. The purified IgA was dimeric by native PAGE, contained secretory component, and was analogous to IgA in colostrum and vaginal fluid by western blot. IgA from one infected and four vaccinated animals neutralized H9-derived SIV(mac)251 with IC(50)s as low as 1 μg/mL. Purified IgAs inhibited transcytosis and exhibited phagocytic activity, the latter significantly correlated with SIV(mac)251 Env-specific IgA in the purified samples. Among different affinity resins, peptide M was optimal compared to jacalin, anti-monkey IgA and SSL7 for IgA purification, as confirmed using tandem peptide M/anti-monkey IgA columns. Fecal IgA provided material sufficient for several assays relevant to protective efficacy, and was shown to be multifunctional. Our approach is potentially applicable to human clinical studies.

An alphavirus-based adjuvant enhances serum and mucosal antibodies, T cells, and protective immunity to influenza virus in neonatal mice

Neonatal immune responses to infection and vaccination are biased toward TH2 at the cost of proinflammatory TH1 responses needed to combat intracellular pathogens. However, upon appropriate stimulation, the neonatal immune system can induce adult-like TH1 responses. Here we report that a new class of vaccine adjuvant is especially well suited to enhance early life immunity. The GVI3000 adjuvant is a safe, nonpropagating, truncated derivative of Venezuelan equine encephalitis virus that targets dendritic cells (DCs) in the draining lymph node (DLN) and produces intracellular viral RNA without propagating to other cells. RNA synthesis strongly activates the innate immune response so that in adult animals, codelivery of soluble protein antigens induces robust humoral, cellular, and mucosal responses. The adjuvant properties of GVI3000 were tested in a neonatal BALB/c mouse model using inactivated influenza virus (iFlu). After a single immunization, mice immunized with iFlu with the GVI3000 adjuvant (GVI3000-adjuvanted iFlu) had significantly higher and sustained influenza virus-specific IgG antibodies, mainly IgG2a (TH1), compared to the mice immunized with antigen only. GVI3000 significantly increased antigen-specific CD4(+) and CD8(+) T cells, primed mucosal immune responses, and enhanced protection from lethal challenge. As seen in adult mice, the GVI3000 adjuvant increased the DC population in the DLNs, caused activation and maturation of DCs, and induced proinflammatory cytokines and chemokines in the DLNs soon after immunization, including gamma interferon (IFN-γ), tumor necrosis factor alpha (TNF-α), granulocyte colony-stimulating factor (G-CSF), and interleukin 6 (IL-6). In summary, the GVI3000 adjuvant induced an adult-like adjuvant effect with an influenza vaccine and has the potential to improve the immunogenicity and protective efficacy of new and existing neonatal vaccines.

IMPORTANCE

The suboptimal immune responses in early life constitute a significant challenge for vaccine design. Here we report that a new class of adjuvant is safe and effective for early life immunization and demonstrate its ability to significantly improve the protective efficacy of an inactivated influenza virus vaccine in a neonatal mouse model. The GVI3000 adjuvant delivers a truncated, self-replicating viral RNA into dendritic cells in the draining lymph node. Intracellular RNA replication activates a strong innate immune response that significantly enhances adaptive antibody and cellular immune responses to codelivered antigens. A significant increase in protection results from a single immunization. Importantly, this adjuvant also primed a mucosal IgA response, which is likely to be critical for protection during many early life infections.

Isolation, identification and characterisation of three novel probiotic strains (Lactobacillus paracasei CNCM I-4034, Bifidobacterium breve CNCM I-4035 and Lactobacillus rhamnosus CNCM I-4036) from the faeces of exclusively breast-fed infants

The aim of the present study was to isolate, identify and characterise novel strains of lactic acid bacteria and bifidobacteria with probiotic properties from the faeces of exclusively breast-fed infants. Of the 4680 isolated colonies, 758 exhibited resistance to low pH and tolerance to high concentrations of bile salts; of these, only forty-two exhibited a strong ability to adhere to enterocytes in vitro. The identities of the isolates were confirmed by 16S ribosomal RNA (rRNA) sequencing, which permitted the grouping of the forty-two bacteria into three different strains that showed more than 99 % sequence identity with Lactobacillus paracasei, Lactobacillus rhamnosus and Bifidobacterium breve, respectively. The strain identification was confirmed by sequencing the 16S-23S rRNA intergenic spacer regions. Strains were assayed for enzymatic activity and carbohydrate utilisation, and they were deposited in the Collection Nationale de Cultures de Microorganismes (CNCM) of the Institute Pasteur and named L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036. The strains were susceptible to antibiotics and did not produce undesirable metabolites, and their safety was assessed by acute ingestion in immunocompetent and immunosuppressed BALB/c mouse models. The three novel strains inhibited in vitro the meningitis aetiological agent Listeria monocytogenes and human rotavirus infections. B. breve CNCM I-4035 led to a higher IgA concentration in faeces and plasma of mice. Overall, these results suggest that L. paracasei CNCM I-4034, B. breve CNCM I-4035 and L. rhamnosus CNCM I-4036 should be considered as probiotic strains, and their human health benefits should be further evaluated.

Enhanced mucosal and systemic immune responses obtained by porous silica nanoparticles used as an oral vaccine adjuvant: effect of silica architecture on immunological properties

Three different kinds of silica (S2, S1 and SBA-15) with different particle sizes (130, 430 nm and 1-2 μm) and different pore characteristics (i.e. pore size and shape) were developed as oral vaccine immunological adjuvants and the relationship between the silica architecture and immunological properties was investigated. The silica particles were characterized using SEM, TEM and nitrogen adsorption. Model antigen bovine serum albumin (BSA) was successfully entrapped into the silica pores to produce a sustained release vaccine delivery system. Compared with the responsiveness induced by parenteral administration of BSA emulsified in Freund's complete adjuvant (FCA), oral immunization with the silica/BSA formulation produced a stimulated humoral and mucosal (sIgA) response. The IgG and IgA titers induced by loading BSA was as follows: S1>S2>SBA-15. The highest IgG and IgA titers of S1 were attributed to its large honeycombed pores and the optimal particle diameter of 430 nm. The corresponding IgG1 and IgG2a titers were also investigated to confirm that BSA loaded in nanoparticles by oral immunization can induce both T-helper 1- and T-helper 2- (Th1 or Th2) mediated responses. We believe that the results of our research will open up new avenues for the formulation of oral vaccines.

Synthesis of a novel kind of carbon nanoparticle with large mesopores and macropores and its application as an oral vaccine adjuvant

The purpose of this study is to develop a novel kind of adjuvant for oral vaccine delivery. In order to effectively prevent the degradation of antigens in the gastrointestinal tract and optimize the uptake for M cells, a novel kind of hydrophobic carbon nanoparticle (C1) with the size of 470nm was synthesized by taking silica as a template and sucrose as a carbon source. Notably, there were large mesopores and macropores mainly of 40-60nm, which made it to be excellent candidate as an antigen carrier. C1 was characterized using SEM, TEM and nitrogen adsorption. Following oral immunization with BSA loaded in C1, the IgG titer reached to a level almost equal to that of parenteral administration of antigen emulsified in Freund's complete adjuvant (FCA). Mucosal IgA was also detected in intestinal, salivary and vaginal secretions, suggesting an effective stimulation of mucosal immune response. Besides, both T-helper 1 and T-helper 2 (Th1 or Th2) mediated responses were induced. We believe that the research will help in the design of novel vaccine adjuvant for improvement their potential on modulation of immune response.

Outer membrane protein A (OmpA) of Shigella flexneri 2a, induces protective immune response in a mouse model

Background

In our earlier studies 34 kDa outer membrane protein (OMP) of Shigella flexneri 2a has been identified as an efficient immunostimulant.

Key Results

In the present study MALDI-TOF MS analysis of the purified 34 kDa OMP of Shigella flexneri 2a shows considerable sequence homology (Identity 65%) with the OmpA of S. flexneri 2a. By using the specific primers, the gene of interest has been amplified from S. flexneri 2a (N.Y-962/92) genomic DNA, cloned in pET100/D-TOPO® vector and expressed using induction with isopropyl thiogalactoside (IPTG) for the first time. Immunogenicity and protective efficacy of the recombinant OmpA has been evaluated in an intranasally immunized murine pulmonary model. The recombinant protein induces significantly enhanced protein specific IgG and IgA Abs in both mucosal and systemic compartments and IgA secreting cells in the systemic compartment (spleen). The mice immunized with OmpA have been protected completely from systemic challenge with a lethal dose of virulent S. flexneri 2a. Immunization with the protein causes mild polymorphonuclear neutrophil infiltration in the lung, without inducing the release of large amounts of proinflammatory cytokines.

Conclusion

These results suggest that the OmpA of S. flexneri 2a can be an efficacious mucosal immunogen inducing protective immune responses. Our findings also demonstrate that antibodies and Th1 immune response may be associated with the marked protective efficacy of immunized mice after intranasal shigellae infection.

Degree of polymerization of inulin-type fructans differentially affects number of lactic acid bacteria, intestinal immune functions, and immunoglobulin A secretion in the rat cecum

This study examined the role of degree of polymerization (DP) of inulin-fructans in modulating the interaction between lactic acid bacteria and IgA cecal secretion. Rats were fed a control diet or a diet containing one of the fructans with different DP. Consuming fructans increased the cecal IgA concentrations in the order DP4 > DP8 > DP16. Cecal lactobacilli counts were higher in DP4, DP8, and DP16, whereas bifidobacteria were higher in DP8, DP16, and DP23. Cecal IgA concentrations were correlated with cecal lactobacilli counts (P < 0.01). DP4, DP8, and DP16, but not DP23, significantly increased IgA-producing plasma cells in the cecal mucosa. IFN-γ and IL-10 production in the cecal CD4(+) T cells was enhanced solely in DP4. The results show that fructans with lower DP enhance cecal IgA secretion and increase the plasma cells and suggest that the increased lactobacilli may contribute to the stimulation of cecal IgA secretion.

Longitudinal analysis of the prevalence, maintenance, and IgA response to species of the order Bacteroidales in the human gut

Bacteroidales species are the most abundant Gram-negative bacteria of the human intestinal microbiota. These bacteria evolved to synthesize numerous capsular polysaccharides (PS) that are subject to phase variation. In Bacteroides fragilis, PS synthesis is regulated so that only one of the eight PS biosynthesis loci is transcribed at a time in each bacterium. To determine if the bacteria evolved this unusual property to evade a host IgA response, we directly studied the human fecal ecosystem. We performed a longitudinal analysis of the abundant Bacteroidales species from 15 healthy adults at four intervals over a year. For this study, we used bacterial culture to perform analyses not accurate with DNA-based methods, including quantification of total viable Bacteroidales bacteria, strain maintenance, and IgA responses. Abundant Bacteroidales isolates were identified to the species level using multiplex PCR and 16S rRNA gene sequencing. Arbitrarily primed PCR was used for strain typing. IgA responses to endogenous strains carried over the year were analyzed, and the orientations of the invertible PS locus promoters from the ecosystem were quantified. Subjects consistently harbored from 5 × 10(8) to 8 × 10(10) Bacteroidales bacteria/g of feces. Within the cohort, 20 different Bacteroidales species were detected at high concentrations. Bacteroides uniformis was the most prevalent; however, abundant Bacteroidales species varied between subjects. Strains could be maintained over the year within the ecosystem at high density. IgA responses were often not induced and did not correlate with the elimination of a strain or major changes in the orientations of the capsular PS locus promoters.

Short-chain inulin-like fructans reduce endotoxin and bacterial translocations and attenuate development of TNBS-induced colitis in rats

Anti-inflammatory effects of short-chain inulin-like fructans (SCF) on trinitrobenzene sulfonic acid (TNBS)-induced colitis were investigated in rats, focusing specifically on endotoxin and bacterial translocations. SCF with degrees of polymerization (DP) of 4 and 8 were used. Rats were fed either control diet or diets including 60 g DP4 or DP8 per kilogram for 7 days, and then received intracolonic TNBS and were fed the respective diets for a further 10 days. DP4 and DP8 significantly reduced colonic injuries as assessed by damage score, but the reduction of colonic myeloperoxidase activity was manifest solely with DP8. At 3 days after colitis induction, bacterial translocation to the mesenteric lymph node was significantly lower in the DP4 and DP8 groups, but significant reduction in the portal endotoxin concentration was achieved solely in the DP8 group. Immediately prior to colitis induction, cecal immunoglobulin A and mucin concentrations were higher in the DP4 and DP8 groups, but these changes were abolished at 10 days post colitis induction. The data suggest that SCF exert prophylactic effects against TNBS colitis, presumably as a result of inhibitory effects on endotoxin and bacterial translocations.

Intestinal mucosal immune response in ducklings following oral immunisation with an attenuated Duck enteritis virus vaccine

To investigate the intestinal mucosal immune responses in ducklings orally inoculated with attenuated Duck enteritis virus (DEV), the kinetics of the viral load, the specific humoral immune responses, and the distribution of immunoglobulin (Ig)A-secreting cells in the intestine were evaluated. Oral inoculation with attenuated DEV stimulated an IgA-dominant response in intestinal secretions and a IgY-dominant response in the serum. The dramatic increase in virus-specific mucosal IgA 15 days after inoculation was accompanied by reductions in the DEV intestinal load, suggesting that the IgA response has a role in controlling viral replication. The kinetics of virus-specific IgA production closely correlated with the presence of IgA+ plasma cells in the intestinal lamina propria.

Rectal and vaginal immunization of mice with human papillomavirus L1 virus-like particles

Human papillomavirus (HPV) vaccines based on L1 virus-like particle (VLP) can prevent genital HPV infection and associated lesions after three intramuscular injections. Needle-free administration might facilitate vaccine implementation, especially in developing countries. Here we have investigated rectal and vaginal administration of HPV16 L1 VLPs in mice and their ability to induce anti-VLP and HPV16-neutralizing antibodies in serum and in genital, rectal and oral secretions. Rectal and vaginal immunizations were not effective in the absence of adjuvant. Cholera toxin was able to enhance systemic and mucosal anti-VLPs responses after rectal immunization, but not after vaginal immunization. Rectal immunization with Resiquimod and to a lesser extent Imiquimod, but not monophosphoryl lipid A, induced anti-HPV16 VLP antibodies in serum and secretions. Vaginal immunization was immunogenic only if administered in mice treated with nonoxynol-9, a disrupter of the cervico-vaginal epithelium. Our findings show that rectal and vaginal administration of VLPs can induce significant HPV16-neutralizing antibody levels in secretions, despite the fact that low titers are induced in serum. Imidazoquinolines, largely used to treat genital and anal warts, and nonoxonol-9, used as genital microbicide/spermicide were identified as adjuvants that could be safely used by the rectal or vaginal route, respectively.

Chitosan Microparticles as Oral Delivery System for Tetanus Toxoid

Systemic and local immune response against Chitosan encapsulated tetanus toxoid (CS-TT) microparticles is studied, prepared by ionic cross-linking using Sodium Tripolyphosphate (STPP). Final formulation was evaluated in terms of release of TT in 0.1 N HCl and PBS (pH 7.4), sedimentation profile and stability. CS-TT microparticles, TT in PBS and plain CS microparticles were orally administered to mice and TT (adsorbed) was administered through intramuscular route. Sera were analyzed for anti-TT IgG and intestinal lavage, faeces, intestinal washings for anti-TT IgA levels using an ELISA. Entrapment efficiency of about 100% was obtained. A dose dependent immune response was observed in mice vaccinated with Chitosan-TT microparticles. A strong enhancement of the systemic and local immune response against TT were found when compared with oral feeding of TT in PBS. The study shows the efficacy of chitosan microparticle suspension system, containing a high molecular protein (TT), in inducing the IgA in intestine and IgG in systemic circulation. This demonstrates that chitosan microparticles can prove to be a promising oral vaccine delivery system for mucosal and systemic immunity.

Differential immunogenicity of vaccinia and HIV-1 components of a human recombinant vaccine in mucosal and blood compartments

Mucosal immune responses induced by HIV-1 vaccines are likely critical for prevention. We report a Phase 1 safety and immunogenicity trial in eight participants using the vaccinia-based TBC-3B vaccine given subcutaneously to determine the relationship between HIV-1 specific systemic and gastrointestinal mucosal responses. Across all subjects, detectable levels of blood vaccinia- and HIV-1-specific antibodies were elicited but none were seen mucosally. While the vaccinia component was immunogenic for CD8(+) T lymphocyte (CTL) responses in both blood and mucosa, it was greater in blood. The HIV-1 component of the vaccine was poorly immunogenic in both blood and mucosa. Although only eight volunteers were studied intensively, the discordance between mucosal and blood responses may highlight mechanisms contributing to recent vaccine failures.

Colonic antigen administration induces significantly higher humoral levels of colonic and vaginal IgA, and serum IgG compared to oral administration

It was hypothesised that different immune responses would be obtained following oral and colonic antigen administration, due to the significant differences in the immune environments of the colon and that of the small intestine. Antigen administration to the mouse colon (via the rectum) was found to generate different profiles of immune responses compared to oral administration (by gavage). Serum IgG and IgA levels in faecal and colonic extracts and in the vaginal wash were significantly higher following colonic administration of soluble (plus cholera toxin B subunit adjuvant) or encapsulated (in microspheres) antigen while smaller differences were seen in the small intestinal IgA levels. This reflects the compartmentalisation within the common mucosal immune system and suggests that the colon may be an appropriate vaccination target for diseases of the colon, and for sexually and vertically transmitted diseases. Antigen was also administered rectally and intramuscularly as controls. Colonic administration was superior to rectal administration, possibly due to the greater amounts of lymphoid tissue in the colon, although the immune response profiles were similar.

Systemic but not mucosal immunity induced by AVA prevents inhalational anthrax

Improved vaccines and adjuvants are being developed to reduce the threat posed by a terrorist attack involving aerosolized anthrax spores. Nevertheless, uncertainty persists concerning the relative benefits of inducing mucosal vs systemic immunity to host survival following inhalational exposure to anthrax spores. This work examines the effect of delivering the licensed human vaccine (anthrax vaccine adsorbed, AVA) combined with a CpG oligodeoxynucleotide (ODN) adjuvant intraperitoneally or intranasally to A/J mice. Results indicate that protection from inhalational anthrax correlates with the induction of a strong systemic rather than mucosal immune response, and demonstrate that protection is significantly improved and accelerated by the addition of CpG ODN.

Isotype-specific antibody responses against Escherichia coli O157:H7 locus of enterocyte effacement proteins in adult beef cattle following experimental infection

Escherichia coli O157:H7 is an important food-borne pathogen and cause of hemorrhagic colitis and hemolytic uremic syndrome in humans. Cattle are an important reservoir of E. coli O157:H7, in which the organism colonizes the intestinal tract and is shed in the feces. Vaccination of cattle has significant potential as a pre-harvest intervention strategy for E. coli O157:H7; however, basic information about the bovine immune responses to important bacterial colonization factors resulting from infection has not been reported. The serum and fecal IgG and IgA antibody responses of adult cattle to E. coli O157:H7 intimin, translocated intimin receptor (Tir), E. coli-secreted proteins (Esp)A, EspB and O157 lipopolysaccharide (LPS) in response to infection were determined. All animals were seropositive for all five antigens prior to inoculation, with antibody titers to EspB and O157 LPS significantly higher (P<0.05) than those to Tir, intimin and EspA. After inoculation, the cattle became colonized and developed significant increases in their serum antibody titers to intimin, Tir, EspB, EspA and O157 LPS (P<0.05); however, by 42 days post-inoculation the titers to all except EspB were on the decline. In contrast, pre- and post-inoculation fecal IgG and IgA antibodies to these same antigens were not detected (<1:5). These results indicate that cattle respond serologically to E. coli O157:H7 type III secreted proteins, intimin and O157 LPS during the course of infection and the response is correlated with the extent of fecal shedding.

Mucosal immunisation of mice with malaria protein on lactic acid bacterial cell walls

Mice were orally and nasally immunised with a malaria parasite protein, MSA2, expressed in Lactococcus lactis, covalently attached to the peptidoglycan (MSA2cP), or non-covalently rebound to L. lactis cell walls, live Lactobacillus reuteri and Lb. salivarius (MSA2cA). Although there was marked variation within mice of the same inbred strain, the data suggest that the characteristics of serum IgG antibodies formed against MSA2 are influenced by the mouse strain and mode of MSA2 presentation. MSA2-specific IgA antibodies in sera and faecal pellets, and IFNgamma-secreting spleen cells were detectable in some immunised animals. MSA2cA on lactobacilli, although not effective in eliciting serum IgG antibodies, showed a potential for eliciting IgA antibodies in the gut. The presence of MSA2 in L. lactis tended to divert the antibody response from lactococcal antigens. The data suggest that anti-MSA2 and anti-lactococcal antibody responses are not necessarily associated in the mice. The findings are related to the use of lactic acid bacteria expressing heterologous proteins for therapy and vaccination.

Vaccine potential for inactivated shigellae

We used human monocyte-derived dendritic cells (DC) and Balb/c mice as models to establish the immunogenic and protective potential of formalin-inactivated Shigella spp. Incubation of DC with inactivated or live bacteria induced DC maturation and cytokine release. Mice immunized orally or intranasally with killed S. flexneri, S. sonnei, or S. dysenteriae developed IgG and fecal IgA titers to the homologous LPS. Following respiratory challenge with the live homologous organisms, 80-100% survival was seen in all vaccinated groups compared to negligible survival in mice given PBS. Oral or intranasal immunization with an inactivated S. flexneri 2a strain (CVD1203) expressing the CFA/I and CS3 antigens of enterotoxigenic Escherichia coli induced IgG responses to both heterologous antigens. These in vivo and in vitro data indicate that inactivated shigellae retain the ability to interact effectively with key antigen presenting cells and induce protective immune responses in mice.

Delivery systems and adjuvants for oral vaccines

The oral route is the ideal means of delivering prophylactic and therapeutic vaccines, offering significant advantages over systemic delivery. Most notably, oral delivery is associated with simple administration and improved safety. In addition, unlike systemic immunisation, oral delivery can induce mucosal immune responses. However, the oral route of vaccine delivery is the most difficult because of the numerous barriers posed by the gastrointestinal tract. To facilitate effective immunisation with peptide and protein vaccines, antigens must be protected, uptake enhanced and the innate immune response activated. Numerous delivery systems and adjuvants have been evaluated for oral vaccine delivery, including live vectors, inert particles and bacterial toxins. Although developments in oral vaccines have been disappointing so far, in terms of the generation of products, the availability of a range of novel delivery systems offers much greater hope for the future development of improved oral vaccines.

Development of a fecal sample collection strategy for extraction and quantification of fecal immunoglobulin A in dogs

OBJECTIVE

To develop a fecal sample collection strategy and quantification method for measurement of fecal IgA concentrations in dogs.

SAMPLE POPULATION

Fecal samples from 23 healthy pet dogs of various breeds.

PROCEDURES

Immunoglobulin A was extracted from fecal samples. An ELISA for the measurement of fecal IgA concentrations was established and analytically validated. Intraindividual variation of fecal IgA was determined by calculation of coefficients of variation. A sample collection strategy was developed on the basis of results of intraindividual variation of fecal IgA concentrations. A reference range for fecal IgA concentrations was determined.

RESULTS

The method for extraction and quantification of fecal IgA was determined to be sufficiently sensitive, reproducible, accurate, and precise. On the basis of the intraindividual variability of our results, the determined fecal sample collection strategy required analysis of a total of 4 fecal samples/dog, with each fecal sample collected on 2 consecutive days with 28 days between sample collection periods (ie, days 1 and 2 followed by days 28 and 29). Reference range values for fecal IgA concentration were 0.22 to 3.24 mg/g of feces.

CONCLUSIONS AND CLINICAL RELEVANCE

Methods of fecal IgA extraction and quantification used in our study allow for identification of dogs with consistently low fecal IgA concentrations. Use of these techniques will enable future investigations into possible associations between low fecal IgA concentrations and signs of gastrointestinal disease in dogs.

Immunogenicity of a malaria parasite antigen displayed by Lactococcus lactis in oral immunisations

A putative protective protein from Plasmodium falciparum merozoites, MSA2, was expressed in two different ways on the cell surface of the Gram-positive food-grade bacterium, Lactococcus lactis. The first display format exploits an LPXTG-type anchoring motif of the lactococcal proteinase PrtP to covalently anchor MSA2 to the genetically modified producer cells. In a second display format, MSA2 was fused to the peptidoglycan-binding domain (Protein Anchor) of the lactococcal cell wall hydrolase AcmA and was non-covalently rebound to the surface of non-genetically modified, non-living high-binder L. lactis cells, termed Gram-positive enhancer matrix (GEM) particles. The L. lactis recombinants carrying covalently bound MSA2 were used to immunise rabbits through nasal and oral routes. The highest levels of IgG antibodies reacting with near-native MSA2 on merozoites was elicited by oral administration. Intestinal antibodies to MSA2 were produced only after oral immunisation. MSA2-specific T(h)-cell activation could be demonstrated. Based on these results, the immunogenicity in oral immunisations of MSA2, bound non-covalently to non-genetically modified L. lactis GEM particles, was compared with MSA2 that was bound covalently to genetically modified L. lactis. These two forms elicited similar titres of serum antibodies. The results illustrate the potential of using non-genetically modified L. lactis as a safe vaccine delivery vehicle to elicit systemic antibodies, thereby avoiding the dissemination of recombinant DNA into the environment.

Ingestion of resistant starch protects endotoxin influx from the intestinal tract and reduces D-galactosamine-induced liver injury in rats

BACKGROUND AND AIMS

The aim of the present study was to examine the protective effect of a dietary high-amylose cornstarch (HAS) against D-galactosamine (D-GalN)-induced liver injury, focusing specifically on intestinal endotoxin translocation.

METHODS

Male Wistar rats fed a HAS-free basal diet or a 30% HAS-supplemented diet were injected intraperitoneally with D-GalN. Serum transaminase activities, serum concentrations of tumor necrosis factor (TNF)-alpha, and portal venous endotoxin concentrations were determined at various time points. Ileal mucosal proliferation, small intestinal immunoglobulin (Ig)A and mucin, and the size of the cecal short-chain fatty acids (SCFA) pool were also determined.

RESULTS

High-amylose cornstarch ingestion significantly reduced the increase in serum transaminase activities at 22 h after the injection of D-GalN. Rats fed the HAS diet showed a greater cecal SCFA production as measured by pool size than those fed the basal diet. Luminal IgA and mucin content were significantly greater in rats fed the HAS diet. Protein, DNA and RNA contents in the ileal mucosa were also higher in rats fed the 30% HAS diet. In a further experiment, portal venous endotoxin concentrations in rats fed the basal diet reached 72 ng/L at 4 h after D-GalN administration, but endotoxin was not detected in rats fed the HAS diet. At this time, portal endotoxin concentrations were significantly and positively correlated with the serum concentrations of TNF-alpha and serum alanine aminotransferase activities.

CONCLUSION

These data support the view that HAS ingestion may reduce D-GalN-induced liver injury as a result of an inhibitory effect on endotoxin influx from the intestinal tract, at least in part as a result of alterations in the mucosal barrier functions.

Intestinal and systemic immune responses to an oral cholera toxoid B subunit whole-cell vaccine administered during zinc supplementation

Zinc plays a critical role in the normal functioning of the immune system. We investigated whether zinc sulfate administered orally to adult zinc-replete volunteers modulates systemic and intestinal immune responses to an oral killed cholera toxoid B subunit (CTB) whole-cell cholera vaccine. The 30 participants were immunized twice, with a 17-day interval. The vaccinees in the intervention group ingested 45 mg of elemental zinc thrice daily for 9 days starting 2 days before each vaccine dose. The median serum anti-CTB immunoglobulin A (IgA) and IgG responses from day 0 to day 30, i.e. after two vaccine doses, were 13-fold lower (P value for identical distribution, <0.005) in the zinc-supplemented compared to the nonsupplemented vaccinees. The median serum vibriocidal responses from baseline to after one (day 0 to day 17) and two (day 0 to day 30) vaccine doses were at least sixfold (P = 0.033) and fourfold (P = 0.091) higher, while the median fecal anti-CTB IgA response after two doses was estimated to be fourfold higher (P = 0.084) in the zinc-supplemented vaccinees. These observations show that zinc reduces the antitoxin and may enhance the antibacterial responses in serum. Zinc may also improve the intestinal antitoxin immune response. Oral zinc administration has the potential to modify critical immune responses to antigens applied to mucosal surfaces.

Development of a time-resolved immunofluorometric assay for quantitation of mucosal and systemic antibody responses

We developed a solid phase immunoassay that measured mucosal and systemic antibody responses from mice inoculated with either a staphylococcal enterotoxin B vaccine (SEBv) or noninfectious virus-like particles (VLP) of lentiviral origin. The assay used time-resolved fluorescence (TRF) with affinity-purified goat anti-mouse IgA and IgG conjugated to samarium and europium chelates, respectively. By employing these fluorogenic conjugates with different spectral emissions, IgA and IgG specific for SEB or VLP were readily detected in serum and saliva from mice inoculated intranasally. The TRF assay detected antigen-specific IgA in saliva 10 min after the addition of enhancement solution, while a conventional alkaline phosphatase-based assay for salivary IgA required 18 h after substrate addition. The TRF assay also provided a significantly higher signal-to-noise ratio and exhibited greater sensitivity. TRF assays detected both IgA and IgG in the same well, thereby reducing sample and reagent requirements.