Immunological characterization of onion (Allium cepa) allergy

Abstract

Introduction: Onion (Allium cepa) handling can induce contact dermatitis, rhinoconjunctivitis and asthma. However, only sporadic reports exist on allergic reactions to onion consumption.

Aim: We describe herein a case of a 35-year-old man who had an episode of anaphylaxis following cooked onion ingestion. We evaluated onion-specific IgE, the possible cross-reactivity between onion and peach and lymphocyte proliferation in response to onion.

Material and methods: Specific IgE was evaluated using two techniques: skin test and ImmunoCAP technology. Cross-reactivity between onion and peach was evaluated by IgE-ELISA inhibition test. As for lymphocyte proliferation, blood mononuclear cells were stained with CFSE dye and cultured with an in-house onion extract. Proliferation and phenotype was assessed by flow-cytometry.

Results: The skin test and ImmunoCAP confirmed the IgE-dependent response towards onion. The incubation of the patient serum with increasing concentrations of the peach extract reduced only scarcely (~30%) onion-specific IgE. Interestingly, B cells but not T cells showed proliferation in response to onion extract.

Conclusions: In conclusion, our report shows that cooked onion can induce severe allergic reactions, suggesting the presence of thermostable components. Moreover, we applied for the first time a B-cell-based approach to the diagnosis of food allergy. This latter approach might also be applied to other allergic conditions.

Keywords: IgE-ELISA inhibition; food allergy; lipid transfer proteins; lymphocyte proliferation; onion allergy.

Figure 1

Evaluation of onion-specific IgE. A – Quantitative skin prick tests for a commercially available array of food allergens. B – Quantitative skin prick tests for a commercially available onion extract and semi-purified in-house onion extract; prick tests with raw and cooked onion, raw garlic and M. comosum; C – circulating food allergen-specific IgE, as measured by ImmunoCAP. The Skin Index represents the ratio between the area of the allergen wheal and the area of the exogenous histamine reference wheal

Figure 2

Evaluation of onion cross-reactivity. A – Circulating LTP-specific IgE as measured by ImmunoCAP. B – IgE-ELISA inhibition by onion proteins. Serum of the patient was incubated for 24 h at 4°C with the indicated amount of onion protein from an in-house extract. C – IgE-ELISA inhibition by peach proteins. Serum of the patient was incubated for 24 h at 4°C with the indicated amount of peach protein from an in-house extract. D – All c 3 and Pru p 3 amino acid sequence identity. Vertical lines between the two sequences indicate the identical amino acid residues

Figure 3

Onion-specific B-cell proliferation. A – Gating strategy for CD 19 and CD 3 cells. Representative CD 19+ (B) and CD 3+ (C) cell proliferation assessed by reduction of CFSE intensity for the patient compared to healthy controls. Experiments were done in triplicates