Induction of intestinal IgA and IgG antibodies preventing adhesion of verotoxin-producing Escherichia coli to Caco-2 cells by oral immunization with liposomes

Traffic generated emissions alter the lung microbiota by promoting the expansion of Proteobacteria in C57Bl/6 mice placed on a high-fat diet

Air pollution has been documented to contribute to severe respiratory diseases like asthma and chronic obstructive pulmonary disorder (COPD). Although these diseases demonstrate a shift in the lung microbiota towards Proteobacteria, the effects of traffic generated emissions on lung microbiota profiles have not been well-characterized. Thus, we investigated the hypothesis that exposure to traffic-generated emissions can alter lung microbiota and immune defenses. Since a large population of the Western world consumes a diet rich in fats, we sought to investigate the synergistic effects of mixed vehicle emissions and high-fat diet consumption. We exposed 3-month-old male C57Bl/6 mice placed either on regular chow (LF) or a high-fat (HF: 45% kcal fat) diet to mixed emissions (ME: 30 µg PM/m³ gasoline engine emissions+70 µg PM/m³ diesel engine emissions) or filtered air (FA) for 6 h/d, 7 d/wk for 30 days. Levels of pulmonary immunoglobulins IgA, IgG, and IgM were analyzed by ELISA, and lung microbial profiling was done using qPCR and Illumina 16 S sequencing. We observed a significant decrease in lung IgA in the ME-exposed animals, compared to the FA-exposed animals, both fed a HF diet. Our results also revealed a significant decrease in lung IgG in the ME-exposed animals both on the LF diet and HF diet, in comparison to the FA-exposed animals. We also observed an expansion of Enterobacteriaceae belonging to the Proteobacteria phylum in the ME-exposed groups on the HF diet. Collectively, we show that the combined effects of ME and HF diet result in decreased immune surveillance and lung bacterial dysbiosis, which is of significance in lung diseases.

Modeling Native EHEC Outer Membrane Vesicles by Creating Synthetic Surrogates

Enterohemorrhagic Escherichia coli (EHEC) is a zoonotic pathogen responsible for life-threating diseases such as hemolytic uremic syndrome. While its major virulence factor, the Shiga toxin (Stx), is known to exert its cytotoxic effect on various endothelial and epithelial cells when in its free, soluble form, Stx was also recently found to be associated with EHEC outer membrane vesicles (OMVs). However, depending on the strain background, other toxins can also be associated with native OMVs (nOMVs), and nOMVs are also made up of immunomodulatory agents such as lipopolysaccharides and flagellin. Thus, it is difficult to determine to which extent a single virulence factor in nOMVs, such as Stx, contributes to the molecular pathogenesis of EHEC. To reduce this complexity, we successfully developed a protocol for the preparation of synthetic OMVs (sOMVs) with a defined lipid composition resembling the E. coli outer membrane and loaded with specific proteins, i.e., bovine serum albumin (BSA) as a proxy for functional Stx2a. Using BSA for parameter evaluation, we found that (1) functional sOMVs can be prepared at room temperature instead of potentially detrimental higher temperatures (e.g., 45 °C), (2) a 1:10 ratio of protein to lipid, i.e., 100 µg protein with 1 mg of lipid mixture, yields homogenously sized sOMVs, and (3) long-term storage for up to one year at 4 °C is possible without losing structural integrity. Accordingly, we reproducibly generated Stx2a-loaded sOMVs with an average diameter of 132.4 ± 9.6 nm that preserve Stx2a’s injuring activity, as determined by cytotoxicity assays with Vero cells. Overall, we successfully created sOMVs and loaded them with an EHEC toxin, which opens the door for future studies on the degree of virulence associated with individual toxins from EHEC and other bacterial pathogens.

Cellular and Mucosal Immune Responses Following Vaccination with Inactivated Mutant of Escherichia coli O157:H7

Shiga toxin-producing Escherichia coli O157:H7 (O157) can cause mild to severe gastrointestinal disease in humans. Cattle are the primary reservoir for O157, which colonizes the intestinal tract without inducing any overt clinical symptoms. Parenteral vaccination can reduce O157 shedding in cattle after challenge and limit zoonotic transmission to humans, although the impact of vaccination and vaccine formulation on cellular and mucosal immune responses are undetermined. To better characterize the cattle immune response to O157 vaccination, cattle were vaccinated with either water-in-oil-adjuvanted, formalin-inactivated hha deletion mutant of Shiga toxin 2 negative (stx2^-) O157 (Adj-Vac); non-adjuvanted (NoAdj-Vac); or non-vaccinated (NoAdj-NoVac) and peripheral T cell and mucosal antibody responses assessed. Cattle in Adj-Vac group had a higher percentage of O157-specific IFNγ producing CD4⁺ and γδ⁺ T cells in recall assays compared to the NoAdj-Vac group. Furthermore, O157-specific IgA levels detected in feces of the Adj-Vac group were significantly lower in NoAdj-Vac group. Extracts prepared only from Adj-Vac group feces blocked O157 adherence to epithelial cells. Taken together, these data suggest parenteral administration of adjuvanted, inactivated whole-cell vaccines for O157 can induce O157-specific cellular and mucosal immune responses that may be an important consideration for a successful vaccination scheme.

Particulate delivery systems for vaccination against bioterrorism agents and emerging infectious pathogens

Bioterrorism agents that can be easily transmitted with high mortality rates and cause debilitating diseases pose major threats to national security and public health. The recent Ebola virus outbreak in West Africa and ongoing Zika virus outbreak in Brazil, now spreading throughout Latin America, are case examples of emerging infectious pathogens that have incited widespread fear and economic and social disruption on a global scale. Prophylactic vaccines would provide effective countermeasures against infectious pathogens and biological warfare agents. However, traditional approaches relying on attenuated or inactivated vaccines have been hampered by their unacceptable levels of reactogenicity and safety issues, whereas subunit antigen-based vaccines suffer from suboptimal immunogenicity and efficacy. In contrast, particulate vaccine delivery systems offer key advantages, including efficient and stable delivery of subunit antigens, co-delivery of adjuvant molecules to bolster immune responses, low reactogenicity due to the use of biocompatible biomaterials, and robust efficiency to elicit humoral and cellular immunity in systemic and mucosal tissues. Thus, vaccine nanoparticles and microparticles are promising platforms for clinical development of biodefense vaccines. In this review, we summarize the current status of research efforts to develop particulate vaccine delivery systems against bioterrorism agents and emerging infectious pathogens. WIREs Nanomed Nanobiotechnol 2017, 9:e1403. doi: 10.1002/wnan.1403 For further resources related to this article, please visit the WIREs website.

Mucosal adjuvant activity of oligomannose-coated liposomes for nasal immunization

In the present study, we investigated the effectiveness of liposomes coated with a neoglycolipid consisting of mannotriose and dipalmitoylphosphatidylcholine (Man3-DPPE) as an adjuvant for induction of mucosal immunity. Immunization of BALB/c mice with ovalbumin (OVA)-encapsulated Man3-DPPE-coated liposomes (oligomannose-coated liposomes; OMLs) by a nasal route produced high levels of OVA-specific IgG and IgA antibodies in serum of immunized mice 1 week after the last nasal immunization, whereas no significant serum antibody responses were observed in mice that received OVA in uncoated liposomes or OVA alone. Seven weeks after the last nasal immunization, nasal challenge with an excess amount of OVA in mice that had received OVA/OMLs led to an anamnestic response to the antigen that resulted in 5- to 10-fold increases of antigen-specific serum IgG and IgA antibodies. Only mice immunized nasally with OML/OVA secreted antigen-specific secretory IgA in nasal washes and produced interferon-gamma secreting cells in nasopharyngeal-associated lymphoreticular tissue. Taken together, these results show that nasal administration of OMLs induces mucosal and systemic immunity that are specific for the entrapped antigen in the liposomes. Thus, liposomes coated with synthetic neoglycolipids might be useful as adjuvants for induction of mucosal immunity.

Veterinary vaccines: alternatives to antibiotics?

The prevention of infectious diseases of animals by vaccination has been routinely practiced for decades and has proved to be one of the most cost-effective methods of disease control. However, since the pioneering work of Pasteur in the 1880s, the composition of veterinary vaccines has changed very little from a conceptual perspective and this has, in turn, limited their application in areas such as the control of chronic infectious diseases. New technologies in the areas of vaccine formulation and delivery as well as our increased knowledge of disease pathogenesis and the host responses associated with protection from disease offer promising alternatives for vaccine formulation as well as targets for the prevention of bacterial disease. These new vaccines have the potential to lessen our reliance on antibiotics for disease control, but will only reach their full potential when used in combination with other intervention strategies.

Mannosylated Niosomes as Adjuvant-Carrier System for Oral Mucosal Immunization

The aim of the present study was to develop mannosylated niosomes as oral vaccine delivery carrier and adjuvant for the induction of humoral, cellular, and mucosal immunity. Tetanus toxoid (TT) loaded niosomes composed of sorbiton monostearate (Span 60), cholesterol, and stearylamine were prepared by the reverse-phase evaporation method. They were coated with a modified polysaccharide o-palmitoyl mannan (OPM) to protect them from bile salts caused dissolution and enzymatic degradation in the gastrointestinal tract and to enhance their affinity toward the antigen presenting cells of Peyer's patches. Prepared niosomes were characterized in vitro for their size, shape, entrapment efficiency, ligand binding specificity, and stability in simulated gastric fluid and simulated intestinal fluid. OPM-coated niosomes were found to more stable in simulated gastrointestinal conditions. The immune stimulating activity was studied by measuring serum IgG titer, IgG2a/IgG1 ratio in serum, and sIgA levels in intestinal and salivary secretions following oral administration of niosomal formulations in albino rats. The results were compared with alum-adsorbed TT following oral and intramuscular administration, and it was observed that OPM-coated niosomes produced better IgG levels as compared to plain uncoated niosomes and alum-adsorbed TT upon oral administration. Oral niosomes also elicited a significant mucosal immune response (sIgA levels in mucosal secretions). The developed formulations also elicited a combined serum IgG2a/IgG1 response, suggesting that they were capable of eliciting both humoral and cellular response. The study signifies the potential of OPM-coated niosomes as an oral vaccine delivery carrier and adjuvant. The proposed system is simple, stable, and cost-effective and may be clinically acceptable.

Oral vaccination: where we are?

As early as 900 years ago, the Bedouins of the Negev desert were reported to kill a rabid dog, roast its liver and feed it to a dog-bitten person for three to five days according to the size and number of bites [1] . In sixteenth century China, physicians routinely prescribed pills made from the fleas collected from sick cows, which purportedly prevented smallpox. One may dismiss the wisdom of the Bedouins or Chinese but the Nobel laureate, Charles Richet, demonstrated in 1900 that feeding raw meat can cure tuberculous dogs - an approach he termed zomotherapy. Despite historical clues indicating the feasibility of oral vaccination, this particular field is notoriously infamous for the abundance of dead-end leads. Today, most commercial vaccines are delivered by injection, which has the principal limitation that recipients do not like needles. In the last few years, there has been a sharp increase in interest in needle-free vaccine delivery; new data emerges almost daily in the literature. So far, there are very few licensed oral vaccines, but many more vaccine candidates are in development. Vaccines delivered orally have the potential to take immunization to a fundamentally new level. In this review, the authors summarize the recent progress in the area of oral vaccines.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

Recombinant Shiga toxin B-subunit-keyhole limpet hemocyanin conjugate vaccine protects mice from Shigatoxemia

Enterohemorrhagic Escherichia coli (EHEC) causes hemorrhagic colitis in humans and, in a subgroup of infected subjects, a more serious condition called hemolytic-uremic syndrome (HUS). These conditions arise because EHEC produces two antigenically distinct forms of Shiga toxin (Stx), called Stx1 and Stx2. Despite this, the production of Stx2 by virtually all EHEC serotypes and the documented role this toxin plays in HUS make it an attractive vaccine candidate. Previously, we assessed the potential of a purified recombinant Stx2 B-subunit preparation to prevent Shigatoxemia in rabbits. This study revealed that effective immunization could be achieved only if endotoxin was included with the vaccine antigen. Since the presence of endotoxin would be unacceptable in a human vaccine, the object of the studies described herein was to investigate ways to safely augment, in mice, the immunogenicity of the recombinant Stx2 B subunit containing <1 endotoxin unit per ml. The study revealed that sera from mice immunized with such a preparation, conjugated to keyhole limpet hemocyanin and administered with the Ribi adjuvant system, displayed the highest Shiga toxin 2 B-subunit-specific immunoglobulin G1 (IgG1) and IgG2a enzyme-linked immunosorbent assay titers and cytotoxicity-neutralizing activities in Ramos B cells. As well, 100% of the mice vaccinated with this preparation were subsequently protected from a lethal dose of Stx2 holotoxin. These results support further evaluation of a Stx2 B-subunit-based human EHEC vaccine.

Extracts of Haematoxylon brasiletto inhibit growth, verotoxin production, and adhesion of enterohemorrhagic Escherichia coli O157:H7 to HeLa cells

The extracts of 33 plants were evaluated for their effects on growth of Escherichia coli O157:H7 (EHEC). The extract of Haematoxylon brasiletto was the only one that effectively inhibited bacterial growth. The effects of ethanolic extracts of this plant on growth, verotoxin production, and adhesion of E. coli O157:H7 to HeLa cells were determined. The MBC for growth was 4 mg/ml. No verotoxin formation was detected at 1, 2, or 3 mg/ml. Preexposing bacteria and HeLa cells to various concentrations of extracts affected the adhesion between non-EHEC and HeLa cells. Partial purification of the active fraction suggested that polyphenols might play a role in the antimicrobial activity exhibited by H. brasiletto extracts.

Mucosal adjuvants

Induction of immune responses following oral immunization is frequently dependent upon the co-administration of appropriate adjuvants that can initiate and support the transition from innate to adaptive immunity. The three bacterial products with the greatest potential to function as mucosal adjuvants are the ADP-ribosylating enterotoxins (cholera toxin and the heat-labile enterotoxin of Escherichia coli), synthetic oligodeoxynucleotides containing unmethylated CpG dinucleotides (CpG ODN), and monophosphoryl lipid A (MPL). The mechanism of adjuvanticity of the ADP-ribosylating enterotoxins is the subject of considerable debate. Our own view is that adjuvanticity is an outcome and not an event. It is likely that these molecules exert their adjuvant function by interacting with a variety of cell types, including epithelial cells, dendritic cells, macrophages, and possibly B- and T-lymphocytes. The adjuvant activities of CpG and MPL are due to several different effects they have on innate and adaptive immune responses and both MPL and CpG act through MyD88-dependent and -independent pathways. This presentation will summarize the probable mechanisms of action of these diverse mucosal adjuvants and discuss potential synergy between these molecules for use in conjunction with plant-derived vaccines.