Oral tolerance is not influenced by oral application of oil-emulsified proteins

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

BACKGROUND

Microbial components in the environment are potent activators of the immune system with capacity to shift the active immune response towards priming of Th1 and/or Th2 cells. Lipopolysaccharide (LPS), a cell-wall component of Gram-negative bacteria, is extensively present in food products like cow's milk. It is not well established, however, how this presence of LPS affects oral tolerance induction.

METHODS

We studied the effect of LPS contamination in a commercial preparation of the cow milk protein beta-lactoglobulin (beta-LG) on antigen-specific immune responses. IgG1/IgG2a production upon intraperitoneal immunization without adjuvant was measured, and oral tolerance induction against beta-LG after administration of either an aqueous solution or water-in-oil (w/o) emulsion of beta-LG was evaluated.

RESULTS

LPS contamination of beta-LG provoked a beta-LG-specific IgG2a response, as well as an enhanced beta-LG-specific IgG1 response upon intraperitoneal immunization. Oral tolerance induction to beta-LG was induced by aqueous solutions of beta-LG with and without LPS administration. Conversely, oral administration of w/o-emulsified beta-LG prevented oral tolerance to beta-LG only when the beta-LG was contaminated with LPS.

CONCLUSIONS

LPS contamination of an aqueous protein solution does not affect oral tolerance induction, whereas LPS present in emulsion prevents oral tolerance induction towards the food protein.

Association complexes between ovalbumin and cyclodextrins have no effect on the immunological properties of ovalbumin

Delivery systems are designed to deliver necessary amounts of drugs without modifying their biological features. Cyclodextrins (CD) are potential candidates for such a role due to their ability to alter physical and chemical properties of guest molecules by the formation of inclusion/association complexes. They have already been used to stabilize and solubilize peptides and proteins of biological importance. However, no systematic study has been reported on their immunological effects upon coupling to such proteins. Herein, we prepared and characterized the association complexes between alpha-, beta- and hydroxypropyl-beta-cyclodextrin and ovalbumin (Ova). Afterward we tested the effect of CD coupling in the Ova antigenicity and the immunological effects of CD coupling on Ova oral and subcutaneous administration. Our results clearly show that CD-coupled Ova elicits the same immunological activities as uncoupled Ova. Therefore, we conclude that CDs are immunologically safe for use as delivery systems in animals.

Oral tolerance for treating uveitis - new hope for an old immunological mechanism

Oral tolerance induction has evolved as an attractive approach for the treatment of autoimmune uveitis. This approach is effective and generally void of the side effects associated with conventional immunosuppression. Following uptake of soluble antigen via the gut mucosa a specific systemic tolerance is generated. Experimental autoimmune diseases such as uveitis can efficiently be treated when autoantigens are fed to animals. The immunological mechanisms of oral tolerance are not well understood but are thought to involve the recognition of tolerogenic epitopes, generation of suppressor T cells and altered regulation of selected cytokines. The dose, purity of the antigen (tissue extract vs. single peptide) and concomitant treatment with cytokines were evaluated with the aim to enhance oral tolerance. Immunomodulatory drugs can abrogate oral tolerance. This requires careful evaluation with respect to therapeutic approaches in patients. The first clinical trials for treatment of uveitis with oral retinal autoantigen or an HLA-peptide crossreactive with S-Antigen show a promising therapeutic effect and confirmed the safety of this approach.

Enhancing effect of dietary oil emulsions on immune responses to protein antigens fed to mice

Repeated intragastric administration of beta-lactoglobulin (beta-Lg) with emulsified soybean oil elicited an antigen-specific, systemic humoral immune response in different strains of mice. The antibody response was enhanced as the dose of oil was increased and the particle size of emulsions was decreased. Feeding of aqueous beta-Lg could induce the antibody response only when emulsified oil was fed almost simultaneously. However, the emulsion-driven humoral immune response was not observed when mice were treated with anti-CD40 ligand antibody or in athymic mice. It is likely that the intestinal coexistence of emulsified oil with dietary antigens modulates the immune system to crucially support B cell response. A practical application of the present results to the prevention of cow's milk protein sensitization in infants is proposed.

Immune response to orally consumed antigens and probiotic bacteria

The gut mucosal system must fulfil conflicting roles in suppressing immune responses against orally fed antigens (tolerance) while still retaining the ability to respond to potential enteric pathogens. It must also, to a large degree, not mount an immune response against commensal enteric bacteria and the administration of large numbers of probiotic bacteria formulated as dietary supplements in food products. Contrary to this dogma, it has been found that feeding ovalbumin as a marker antigen, in association with selected probiotic bacteria, appears to prime for an intestinal immune response that is further augmented by skin vaccination. Skin immunization is known to stimulate a strong innate, humoral and cellular immune response. Such dominant immunogenic signals appear to override tolerogenic signals engendered by oral feeding of antigen. High-dose antigen feeding stimulated a strong Th2-dependent antibody response to skin vaccination but completely suppressed cytotoxic T cell responses. This was true even when ovalbumin was administered in conjunction with various selected probiotic bacteria. However, while yeast appeared to be better at priming for an enhanced humoral response, Lactobacillus fermentum and Staphylococcus carnosus were more effective in enhancing the postvaccinal lymphoproliferative response against ovalbumin.

The influence of initial exposure timing to beta-lactoglobulin on oral tolerance induction

BACKGROUND

Although a number of studies have investigated the induction of oral tolerance to several proteins, relatively little is known about the induction of oral tolerance to beta-lactoglobulin, one of the major antigenic proteins in milk.

OBJECTIVE

We investigated the influence of the timing of the initial beta-lactoglobulin exposure on oral tolerance induction and examined some characteristics of the tolerogenic immune response.

METHODS

BALB/c mice were given beta-lactoglobulin prenatally or from the third or fifth postnatal week, bred for 17 weeks, and compared with unexposed control mice. Specific plasma anti-beta-lactoglobulin antibodies (total IgG, IgG subclasses, IgM, and IgE), antigen-specific splenocyte responses, frequencies of antibody-producing cells, and cytokine production by splenocytes, intestinal mucosal lymphocytes, and Peyer's patches were analyzed.

RESULTS

Differences were observed among the 4 groups of mice in changes of plasma anti-beta-lactoglobulin antibody titers, antigen-specific T-cell proliferation, and frequencies of antibody-producing splenocytes, intestinal mucosal lymphocytes, and Peyer's patch cells after the first exposure to beta-lactoglobulin. The onset and duration of the immunologic responses were found to be dependent on the timing of antigen exposure. Prenatal exposure to antigen facilitated the induction of oral tolerance to beta-lactoglobulin, whereas delayed antigen exposure retarded tolerance. The induction of oral tolerance was associated with increased IL-4 and/or IL-10 production and decreased IL-12 production.

CONCLUSION

Our results suggest that the timing of initial antigen exposure greatly influences the induction of oral tolerance to beta-lactoglobulin and that altered secretion of regulatory cytokines may be responsible for the differences in antibody production and oral tolerance induction.