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Assessment of allergen specific response in humans

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Universitat de Barcelona. Facultat de Medicina

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[spa]  Las alergias están aumentando por razones que aun son desconocidas. Los alérgenos, pueden actuar al nivel de IgE como al nivel de células T. Generalmente, los pacientes alérgicos están polysensitizados a distintas especies que contienen alérgenos debido a su relación filogenética. Aunque la reactividad cruzada ha sido estudiada a nivel de IgE, la misma ha sido poco estudiada a nivel de células T. En este estudio utilizamos tetrámeros de clase II para estudiar este fenómeno en dos modelos: uno de gramíneas y otro de frutos secos. Para el primero encontramos que un sistema de especies múltiples debería de ser utilizado, debido a que células que mínimamente reactivas están presentes con fenotipos, frecuencias y funcionalidad a la de la gramínea Timothy. Para los frutos secos encontramos que los clones de células T derivados de anacardos reconocen y tienen capacidades funcionales hacia pistacho y almendra pero no a la nuez. Evitar estos alimentos debería de ser estrictamente sugerido. Finalmente, nuestro estudio que se baso en la caracterización de células T especificas contra alimentos fue enfocado en la alergia a la nuez. Encontramos que los pacientes alérgicos contienen una variedad heterogenia en la respuesta celular T, caracterizada por respuestas TH2, TH2/TH17 y TH17, mientras que los pacientes no alérgicos tenían una frecuencia de células T baja o ausente y un fenotipo TH1. Además, la mayoría de las células tienen un fenotipo de memoria central. El entendimiento de esta heterogeneidad debería de ser aplicado para la mejora de tratamientos.

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[eng]  Allergies are emerging as a major public health concern in the westernized world as they are increasing for reasons that remain poorly understood. Allergies involving polysensitization and multiple organ involvement result in decreased quality of life, increased morbidity and mortality. Allergic subjects can be poly-sensitized to different allergens due to phylogenetic relatedness; several species contain shared allergenic epitopes. This phenomenon occurs both at the IgE as the T cell level. While IgE cross-reactivity has been well documented, T-cell cross-reactivity has not been thoroughly studied. Well-designed studies that underlie the T-cell mechanisms that accompany allergic inflammation are highly useful in future design for successful immunotherapy as T-cells play a crucial role in the perpetuating cycle of allergic response. Cross-reactivity at the T-cell level was studied with the use of HLA class II Tetramers in two distinct models: grass-pollen and tree nut allergy. In the first study, grass pollen from the Pooideae subfamily was studied. We identified that Timothy grass derived epitopes did not cross-reacted with all homologous epitopes from distinct grass-pollen species indicating that timothy grass alone does not cover the whole set of epitopes. Moreover, these minimally cross-reactive epitopes were detected with comparable frequency, phenotype and functionality to Phl p-specific T-cells, suggest that a multiple allergen system should be considered for immunotherapy instead of a mono allergen system. In the tree nut allergy model, we used cashew as a model to study tree-nut cross-reactivity against hazelnut, pistachio and walnut at the T-cell level. T-cell-clones specific to 7 out of 12 were generated to assess cross-reactivity by tetramer co-staining and proliferation experiments. TCC specific to cashew derived epitopes could readily proliferate with hazelnut and pistachio but not walnut peptides. This study leads to the conclusion that exposure to other tree nut allergens can trigger cashew-specific T-cell responses in these cashew allergic subjects. Strict avoidance of other tree nuts should be recommended in cashew allergic subjects. Food allergies have become a major public health concern as they can cause severe and sometimes fatal reactions. Nonetheless, food allergy-specific T-cell epitopes remain unidentified and uncharacterized. In the food allergy characterization study, we examined walnut allergen-specific T-cells. T-cell reactivity towards Jug r 1 and Jug r 2, as their corresponding allergens in peanut, 2S albumin (Ara h 2) and 7S vicilin-like seed storage protein (Ara h 1) respectively, are highly immunogenic in peanut allergic subjects. Jug r 3 was also studied since we have a small cohort of samples from Spain, where LTP is the major plant food allergen. We initially investigated Jug r 1 Jug r 2 and Jug r 3-specific T-cell responses using CD154 activation assay. Jug r 2, but neither Jug r 1 nor Jug r 3, elicited dominant T-cell responses in allergic subjects. Several Jug r 2 derived epitopes were then identified by using tetramer-guided epitope mapping (TGEM). The magnitude and phenotype of the response of Jug r 2-specific CD4+ T-cells in allergic and non-allergic subjects were determined directly ex-vivo. The predominant phenotype for Jug r 2 reactive T-cells is central memory phenotype. Results show that allergic subjects have a predominant TH2 phenotype, however, TH17 responses in some individuals were also observed. T-cells with CCR4+CD27+, CCR4+CD27-, CCR4+CCR6+ and CCR4+CCR6- surface phenotypes were detected in allergic subjects. T-cells from non-allergic subjects have a TH1 and TH1/TR1 phenotypes characterized by surface expression of CXCR3. Similar observations were observed in the cashew model. Both Cashew and Walnut-specific T-cells with TH2, TH17 and TH2/TH17 phenotypes could be detected in non-asthmatic and asthmatic walnut allergic subjects. Understanding this T-cell heterogeneity may improve our understanding of disease manifestation.

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Assessment of allergen specific response in humans