Mucosal tolerance in type I allergy

Research project P 14634 Mucosal tolerance in type I allergy Ursula WIEDERMANN-SCHMIDT 09.10.2000 Based on the fact that type I allergies are frequently elicited by airborne allergens, we have established a murine model of allergic asthma, leading to allergen-specific Th-2 responses in vivo and in vitro, eosinophilic lung infiltration and airway hyperresponsiveness. Using this model our studies focus on modulating the allergic immune response via the mucosal route. Immunoniodulation has been performed in the naive as well as the sensitized animal by the use of mucosal adjuvants (such as cholera toxin or the B subunit of cholera toxin conjugated to antigen) or by induction of oral/mucosal tolerance with unconjugated allergens. We noted opposite effects on the immune responses with respect to the nature of the mucosally applied antigen. Mucosal application of ovalbumin, a dietary allergen, conjugated to the B subunit of Cholera toxin (CTB), led to suppression of Th2 responses, while application of the inhalant allergen Bet v 1, conjuagted to CTB, induced aggravation of the allergic immune responses. In unconjugated form, mucosal application of ovalbumin did not significantly suppress, but Bet vI inhibited allergic sensitization. This indicated that successful tolerance induction is dependent on the nature of an antigen/allergen per se. In our birch pollen model we detected that tolerance induction was associated with markedly enhanced production of TGF-P, a well known anti-inflammatory and inummosuppressive cytokine. - Since TGF-P has been lately described to be produced by a third subset of T he lper cells, related to oral tolerance induction, i.e.regulatory Tr cells or Th3 cells, we propose that these cells may play a centrale role in tolerance induction in our model. In the present project two main issues shall be focused on: 1. We plan to investigate the influence of possible intrinsic differences of frequently, recognized allergens on tolerance induction and seek for possible candiates for mucosal vaccines against allergy. For this purpose (i) different recombinant tree and grass pollen, food and latex allergens, co-expressed in a plant expression system with mucosal adjuvants, (ii) hypoallergenic molecules, defined by a low IgE binding capacity but retained T- cell stimulating activity, (iii) chimeric proteins, containing the inummodominant T cell epitopes of two or more allergens, will be tested for their efficacy to modulate or inhibit allergic sensitization when administered by the mucosal route. 2. Analysis of the mechanisms leading to tolerance induction, in particular the role of regulatory T cells shall be investigated in our model system. Kinetic studies shall evaluate the duration of tolerance with respect to the applied antigen. Moreover, we plan`to establish allergen-specific T cell clones, which should then lead to establishment of transgenic, (tg) mouse models for tree-, grass pollen and latex allergy. The Tg mouse model would provide an important tool to investigate not only the effector - but also the inductive sites of tolerance induction. The ultimate aim of this project is to evaluate whether mucosal tolerance induction offers an effective, safe and convenient alternative to conventional immuntherapy. With studies on the regulatory mechanisms this project shall contribute to a better understanding of mucosal tolerance induction, essential for presenting mucosal vaccines as a prospective treatment strategy of allergic diseases.

Today the treatment of choice for allergic diseases is specific immunotherapy. The disadvantage of this treatment is that allergens have to be injected in weekly or monthly intervals and that this treatment lasts up to 3 years, which often leads to a reduced compliance of the patients. Moreover, for many patients that are allergic to several allergens (such as birch pollen, grass pollen, house dust mite or allergens of animal dander origin) this treatment can not be applied. Therefore the aim of the present study was to develop a treatment strategy via the mucosal route (i.e. nasal or oral application), which is easy to apply and will be accepted by a broader group of patients, in particular by children. Furthermore, we aimed to develop a mucosal vaccine that can be used for patients that are allergic to several allergens. Mucosal (oral or nasal) application of an antigen/allergen can lead to suppression of systemic immune responses. This phenomenon is called mucosal tolerance. By using a mouse model of type I allergy we established a treatment protocol, by applying specific allergens via the nasal route to allergic mice. This treatment reduced all allergic symptoms/parameters in mice. More importantly, we demonstrated that three intranasal allergen applications inhibited the allergic responses for more than one year, demonstrating that this treatment is very effective and long lasting. In order to minimize the allergic side reactions during the treatment we used so called hypo-allergenic variants. Hypoallergenic variants are allergens that have a reduced capacity to elicit allergic reactions, because IgE antibodies, which are typical for allergic responses, can not bind to these molecules. Applying such molecules via the mucosa leads to a comparable strong capacity suppression of the allergic responses as the whole allergen molecules. In order to study whether it is possible to induce tolerance with more than one allergen, a mixture of common birch and grass pollen allergens were intranasally applied, showing that a mixture of peptides could be used for successful tolerance induction to the respective allergens. The mechanisms behind successful tolerance induction differed with respect to the nature of the allergen. Mucosal application of single or whole allergens leads to suppression due to development of so called regulatory cells, that produce substances with suppressive capacities, whereas short molecules, such as peptides, rather induce immunosuppression by direct interaction with immunocompedent cells, a mechanism that is called anergy. Taken together our studies demonstrate that mucosal tolerance induction - i.e. intranasal or oral application of allergens or hypoallergenic variants thereof - may represent a safe and convenient alternative treatment to specifc immunotherapy, in particular in patients that are allergic to more than one allergen.