Lipopolysaccharide contamination of beta-lactoglobulin affects the immune response against intraperitoneally and orally administered antigen

Protein Concentration Affects the Food Allergen γ-Conglutin Uptake and Bacteria-Induced Cytokine Production in Dendritic Cells

γ-Conglutin (γ-C) from lupin seeds has been identified as a potent allergen with cross reactivity to peanuts. Here, we investigated how γ-C affected the response in bone marrow-derived dendritic cells (DCs) to bacterial stimuli. γ-C enhanced L. acidophilus NCFM (LaNCFM)-induced IL-12, IL-10, and IL-23 dose-dependently. In contrast, together with E. coli Nissle or LPS, γ-C reduced the production of IL-12 but not of IL-23 and IL-10. Enzyme-hydrolyzed γ-C also enhanced LaNCFM-induced IL-12 and IL-23 production. All preparations induced ROS production in the DCs. The mannose receptor ligands mannan and dextran and the clathrin inhibitor monodansylcadaverine partly inhibited the endocytosis of γ-C. Kunitz trypsin inhibitor and the scavenger receptor ligand polyG also enhanced LaNCFM-induced IL-12, indicating the involvement of receptors other than C-type lectin receptors. The endocytosis of labeled γ-C increased dose-dependently by addition of unlabeled γ-C, which coincided with γ-C's tendency to aggregate. Taken together, γ-C aggregation affects endocytosis and affects the cytokine production induced by gram-positive and gram-negative bacteria differently. We suggest that γ-C is taken up by the same mechanism as other food proteins but due to aggregation is present in higher concentration in the DCs. This could influence the resulting T-cell response in a microbial stimuli-dependent way.

Current challenges facing the assessment of the allergenic capacity of food allergens in animal models

Food allergy is a major health problem of increasing concern. The insufficiency of protein sources for human nutrition in a world with a growing population is also a significant problem. The introduction of new protein sources into the diet, such as newly developed innovative foods or foods produced using new technologies and production processes, insects, algae, duckweed, or agricultural products from third countries, creates the opportunity for development of new food allergies, and this in turn has driven the need to develop test methods capable of characterizing the allergenic potential of novel food proteins. There is no doubt that robust and reliable animal models for the identification and characterization of food allergens would be valuable tools for safety assessment. However, although various animal models have been proposed for this purpose, to date, none have been formally validated as predictive and none are currently suitable to test the allergenic potential of new foods. Here, the design of various animal models are reviewed, including among others considerations of species and strain, diet, route of administration, dose and formulation of the test protein, relevant controls and endpoints measured.

The immunomodulatory role of bile acids

Enzymatic oxidation of cholesterol generates numerous distinct bile acids which function both as detergents that facilitate the digestion and absorption of dietary lipids and as hormones that activate five distinct receptors. Activation of these receptors alters gene expression in multiple tissues, leading to changes not only in bile acid metabolism but also in glucose homeostasis, lipid and lipoprotein metabolism, energy expenditure, intestinal motility, bacterial growth, inflammation, and in the liver-gut axis. This review focuses on the present knowledge regarding the physiologic and pathologic role of bile acids and their immunomodulatory role, with particular attention to bacterial lipopolysaccharides (endotoxins) and bile acid and immunological disorders. The specific role that bile acids play in the regulation of innate immunity, various systemic inflammations, inflammatory bowel diseases, allergy, psoriasis, cholestasis, obesity, metabolic syndrome, alcoholic liver disease, and colon cancer will be reviewed.

Exposure to High Doses of Lipopolysaccharide during Ovalbumin Sensitization Prevents the Development of Allergic Th2 Responses to a Dietary Antigen

Food allergies are driven by aberrant T helper (Th) 2 cells. Lipopolysaccharide (LPS) influences the development of Th2-mediated diseases, but its role in food allergy and tolerance remains unclear. To address this issue, we established mouse models presenting allergic or tolerant responses to ovalbumin (OVA). Mice sensitized with crude OVA developed Th2 responses including acute diarrhea, increases in serum OVA-specific IgE, dominant production of serum OVA-specific IgG1, increases in Th2-type cytokines and proliferation of mast cells in duodenal and colonic tissues. Sensitization of mice with crude OVA and LPS abrogated Th2-type responses observed in allergic mice. The level of OVA-specific proliferation in mesenteric lymph node CD4⁺ T cells was comparable in allergic and tolerant mice, indicating that the tolerance is not caused by anergy and apoptosis of antigen-primed T cells. Expression of Th1- and Th2-type cytokines was suppressed in whole spleen cells and/or purified spleen CD4⁺ T cells of tolerant mice, indicating that the tolerance was not caused by the shift from Th2 to Th1. On the other hand, interleukin (IL)-10, a regulatory cytokine produced by regulatory T cells, was upregulated in whole spleen cells and purified spleen CD4⁺ T cells of tolerant mice. Furthermore, spleen CD4⁺ T cells from tolerant mice suppressed the growth of CD4⁺ T cells from DO11.10 mice in co-culture. These results indicate that tolerance is induced in allergic mice by simultaneous exposure to LPS during sensitization with OVA and that a population of T cells producing IL-10 plays an important role in the tolerance induction.

Lipids are required for the development of Brazil nut allergy: the role of mouse and human iNKT cells

BACKGROUND

Lipids are required for mice sensitization to Ber e 1, Brazil nut major allergen. Here, we characterized different lipid fractions extracted from Brazil nuts and the lipid-binding ability of Ber e 1. Further, we determined their in vivo ability to induce Ber-specific anaphylactic antibodies and the role of invariant natural killer T (iNKT) cells in this process.

METHODS

Wild-type (WT) and iNKT cell-deficient mice were sensitized with Ber e 1 and specific lipid fractions, and anaphylactic antibodies were measured by enzyme-linked immunosorbent assay (ELISA) and passive cutaneous anaphylaxis (PCA). The lipid-binding characteristic of Ber e 1 (Ber) was established by using fluorescent probes and (15) N-labeled NMR. In vitro production of IL-4 was determined in Ber/lipid C-stimulated mouse iNKT cells and human T-cell lines containing NKTs primed with CD1d+C1R transfectants by flow cytometry and ELISA, respectively.

RESULTS

Only one specific lipid fraction (lipid C), containing neutral and common phospholipids, induced Ber anaphylactic antibodies in mice. Ber e 1 has a lipid-binding site, and our results indicated an interaction between Ber e 1 and lipid C. iNKT-deficient mice produced lower levels of anaphylactic antibodies than WT mice. In vitro, Ber/lipid C-stimulated murine iNKT cells produced IL-4 but not IFN-gamma. Human T-cell lines derived from nut-allergic patients produced IL-4 to Ber/lipid C in a CD1d- and dose-dependent manner.

CONCLUSION

Lipid fraction C from Brazil nut presents an essential adjuvant activity to Ber e 1 sensitization, and iNKT cells play a critical role in the development of Brazil nut-allergic response.

Solution structure, copper binding and backbone dynamics of recombinant Ber e 1-the major allergen from Brazil nut

BACKGROUND

The 2S albumin Ber e 1 is the major allergen in Brazil nuts. Previous findings indicated that the protein alone does not cause an allergenic response in mice, but the addition of components from a Brazil nut lipid fraction were required. Structural details of Ber e 1 may contribute to the understanding of the allergenic properties of the protein and its potential interaction partners.

METHODOLOGY/PRINCIPAL FINDINGS

The solution structure of recombinant Ber e 1 was solved using NMR spectroscopy and measurements of the protein back bone dynamics at a residue-specific level were extracted using (15)N-spin relaxation. A hydrophobic cavity was identified in the structure of Ber e 1. Using the paramagnetic relaxation enhancement property of Cu(2+) in conjunction with NMR, it was shown that Ber e 1 is able to specifically interact with the divalent copper ion and the binding site was modeled into the structure. The IgE binding region as well as the copper binding site show increased dynamics on both fast ps-ns timescale as well as slower µs-ms timescale.

CONCLUSIONS/SIGNIFICANCE

The overall fold of Ber e 1 is similar to other 2S albumins, but the hydrophobic cavity resembles that of a homologous non-specific lipid transfer protein. Ber e 1 is the first 2S albumin shown to interact with Cu(2+) ions. This Cu(2+) binding has minimal effect on the electrostatic potential on the surface of the protein, but the charge distribution within the hydrophobic cavity is significantly altered. As the hydrophobic cavity is likely to be involved in a putative lipid interaction the Cu(2+) can in turn affect the interaction that is essential to provoke an allergenic response.

Allergic sensitization can be induced via multiple physiologic routes in an adjuvant-dependent manner

BACKGROUND

Oral exposure to food allergens may be limited in infancy, and the initial site of antigen exposure likely plays an important role in food allergy induction.

OBJECTIVE

To examine the impact of different routes of exposure by using milk allergens, with and without adjuvant, on sensitization.

METHODS

C3H/HeJ mice were repeatedly exposed to the milk allergen α-lactalbumin (ALA), with or without cholera toxin (CT). Sensitization routes used were intragastric, cutaneous, intranasal, and sublingual. Anaphylaxis severity was assessed by symptoms and body temperature in response to oral challenge. Antigen-specific serum antibodies were measured by ELISA. The mechanism of adjuvant activity of cutaneous CT was also determined.

RESULTS

Sensitization to ALA as measured by allergen-specific IgE occurred by all routes of sensitization and was maximal in response to cutaneous exposure. Sensitization was dependent on CT and did not occur to antigen alone by any route. Mucosal, but not cutaneous, exposure resulted in a robust allergen-specific IgA response. Anaphylaxis occurred in all sensitized groups when orally challenged with ALA. Topical CT induced migration of langerin(neg) dermal dendritic cells to the lymph node, resulting in enhanced proliferation and T(H)2 cytokine production from responder T cells.

CONCLUSIONS

Sensitization can occur via all physiologic routes when adjuvant is present. The skin is a potent and likely important physiologic route of sensitization whereby adjuvant induces an efflux of antigen-bearing dermal dendritic cells to the lymph node that generate a proallergic T(H)2 response.

Sensitization with 7S globulins from peanut, hazelnut, soy or pea induces IgE with different biological activities which are modified by soy tolerance

BACKGROUND

It is not known why some foods sensitizing via the gastrointestinal tract are prevalent allergenic foods and others are not. Eating habits, processing, and the food matrix have been suggested to influence the allergenicity of a given food. Factors related to protein structure, such as stability to digestion, have also been suggested. 7S globulins from peanut, hazelnut, soy, and pea were studied to determine whether related proteins would induce a similar sensitization when removed from their 'normal' matrix.

METHODS

Brown Norway rats (soy tolerant or nontolerant) were immunized i.p. 3 times with 100 μg purified peanut, hazelnut, soy, or pea 7S without adjuvant. Sera were analyzed for specific antibodies by different ELISAs (IgG1, IgG2a, and IgE), inhibition ELISA, and rat basophilic leukemia cell assay.

RESULTS

The 4 related 7S globulins induced a response with an almost identical level of specific antibodies, but peanut 7S induced IgE of higher avidity than hazelnut and pea 7S which, again, had a higher avidity than IgE induced by soy 7S. Soy tolerance reduced the functionality of IgE without influencing antibody titers.

CONCLUSIONS

Although the 4 7S globulins are structurally related allergens, they induce antibodies with different antigen-binding characteristics. Peanut 7S induces IgE of a higher avidity than hazelnut and pea 7S which, again, has a higher avidity than IgE induced by soy 7S. We also show that soy tolerance influences the function of antibodies to peanut 7S. These findings may help explain how antibodies of different clinical significances can develop in different individuals sensitized to the same allergen.

Allergen specific responses in cord and adult blood are differentially modulated in the presence of endotoxins

Background

Endotoxins are common contaminants in allergen preparations and affect antigen-specific cellular responses. Distinct effects of endotoxin on cells in human umbilical cord and adult blood are poorly defined.

Objectives

To examine the effect of endotoxins in allergen preparations on cellular responses in human cord and peripheral blood (PB).

Methods

The endotoxin content in β lactoglobulin (BLG), the peanut allergen Ara h 1 and the major birch pollen allergen Bet v 1 was assessed. Proliferation and cytokine response of mononuclear cells towards contaminated and lipopolysaccharide (LPS)-free allergens were evaluated at different time-points. Fractions of contaminated BLG were generated and assayed on their immuno-stimulatory capacity. The involvement of toll-like receptor (TLR) 2 and 4 was investigated by blocking antibodies and TLR-transfected human embryonic kidney cells.

Results

The proliferative response of cord blood (CB)-derived mononuclear cells towards allergen-preparations at day 3 was related to the level of LPS contamination. At day 7, proliferation was also detected in the absence of endotoxin. Cytokine production in CB was strongly affected by the content of endotoxin, TLR-4 dependent and not related to the allergen content. Allergen- and endotoxin-induced proliferative responses were generally significantly higher in CB than in adult blood.

Conclusion

Endotoxins in allergen preparations confound allergen-specific cellular responses. The impact of these contaminations varies with the blood source (CB vs. PB), the type of allergen and is time- and dose-dependent.

Cite this as: T. Eiwegger, E. Mayer, S. Brix, I. Schabussova, E. Dehlink, B. Bohle, V. Barkholt and Z. Szépfalusi, Clinical and Experimental Allergy, 2008 (38) 1627–1634.

The effect of the food matrix on in vivo immune responses to purified peanut allergens

There is little knowledge about the factors that determine the allergenicity of food proteins. One aspect that remains to be elucidated is the effect of the food matrix on immune responses to food proteins. To study the intrinsic immunogenicity of allergens and the influence of the food matrix, purified peanut allergens (Ara h 1, Ara h 2, Ara h 3, or Ara h 6) and a whole peanut extract (PE) were tested in the popliteal lymph node assay (PLNA) and in an oral model of peanut hypersensitivity. In the PLNA, peanut proteins were injected into the hind footpad of BALB/c mice; in the oral exposure experiments C3H/HeOuJ mice were gavaged weekly with PE or allergens in the presence of cholera toxin (CT). Upon footpad injection, none of the allergens induced significant immune activation. In contrast, PE induced an increase in cell number, cytokine production, and activation of antigen-presenting cells. Furthermore, the presence of a food matrix enhanced the immune response to the individual allergens. Oral exposure to the purified allergens in the presence of CT induced specific IgE responses, irrespective of the presence of a food matrix. These results suggest that purified peanut allergens possess little intrinsic immune-stimulating capacity in contrast to a whole PE. Moreover, the data indicate that the food matrix can influence responses to individual proteins and, therefore, the food matrix must be taken into account when developing models for allergenic potential assessment.