ABSTRACT
BACKGROUND: Allergies to cashew are increasing in prevalence, with clinical symptoms ranging from oral pruritus to fatal anaphylactic reaction. Yet, cashew-specific T cell epitopes and T cell cross-reactivity amongst cashew and other tree nut allergens in humans remain uncharacterized. OBJECTIVES: In this study, we characterized cashew-specific T cell responses in cashew-allergic subjects and examined cross-reactivity of these cashew-specific cells towards other tree nut allergens. METHODS: CD154 up-regulation assay was used to determine immunodominance hierarchy among cashew major allergens at the T cell level. The phenotype, magnitude and functionality of cashew-specific T cells were determined by utilizing ex vivo staining with MHC class II tetramers. Dual tetramer staining and proliferation experiments were used to determine cross-reactivity to other tree nuts. RESULTS: CD4(+) T cell responses were directed towards cashew allergens Ana o 1 and Ana o 2. Multiple Ana o 1 and Ana o 2 T cell epitopes were then identified. These epitopes elicited either TH 2 or TH 2/TH 17 responses in allergic subjects, which were either cashew unique epitope or cross-reactive epitopes. For clones that recognized the cross-reactive epitope, T cell clones responded robustly to cashew, hazelnut and/or pistachio but not to walnut. CONCLUSIONS: Phylogenetically diverse tree nut allergens can activate cashew-reactive T cells and elicit a TH 2-type response at an epitope-specific level. CLINICAL RELEVANCE: Lack of cross-reactivity between walnut and cashew suggests that cashew peptide immunotherapy approach may not be most effective for walnut.
