D3.279 - SWEET HONEY AND SOUR ALLERGIES: POLLEN-FOOD DEFENSIN CROSS-REACTIVITY - a case series

Plant defensins are small antimicrobial peptides involved in innate plant defense and have recently been recognized as clinically relevant allergens. Due to structural similarity, defensins present in pollens and plant-derived foods, including honey, may induce IgE-mediated cross-reactivity, resulting in pollen–food allergy syndromes with diverse clinical manifestations.

We report a case series of three patients who developed allergic symptoms after ingestion or contact with plant-derived foods containing defensins. The first patient, a 55-year-old man, was sensitized to D. pteronyssinus, ragweed, and birch pollen without clear clinical relevance. Over seven years, he experienced recurrent urticaria and labial angioedema after consuming plant-based foods, as well as a single episode of urticaria after a honey massage.The second patient, a 40-year-old man with allergic rhinitis and bronchial asthma sensitized to birch pollen, reported recurrent pruritus of the forearms and neck over five years, mainly September to August. He also described oral paresthesia after eating apples or peaches and a previous episode of abdominal pain and syncope after honey ingestion.The third patient, a 38-year-old woman, had a history of two anaphylactic reactions—one related to food intake at a social event and another during household cleaning, as well as a remote episode of exercise-induced generalized urticaria 20 years earlier.

All patients underwent molecular allergy assessment using ALEX MADx testing. Birchweed-derived defensins were identified as a shared allergenic component in the second and third patients. In the first patient, specific IgE to birchwood defensins was negative, while birchwood skin prick tests were positive on two occasions. Prick-to-prick testing with honey was performed in the first and third patients and yielded positive results.

This case series highlights plant defensins as key molecular mediators of pollen–food cross-reactivity. Honey represents a clinically relevant and often overlooked source of defensins, capable of inducing allergic reactions through ingestion and skin contact. Improved recognition of honey-related defensin allergy may enhance diagnostic accuracy and management of pollen-associated food allergies.