Long-term characteristics of hazelnut allergy in an adjuvant-free mouse model.

BACKGROUND Clinically it is recognized that tree nut allergies such as hazelnut allergy are not usually outgrown. Specific mechanisms underlying the persistence of such food allergies are incompletely understood. Here we studied the natural history and the long-term immune and clinical characteristics of hazelnut allergy in an adjuvant-free mouse model. METHODS BALB/c mice were sensitized to hazelnut protein using a transdermal sensitization protocol that does not use adjuvant. After establishing sensitization, exposure to hazelnut was withdrawn for 3, 5 or 8 months. The fate of circulating IgE antibodies was monitored. Subsequently, mice were given booster exposures and examined for memory IgE antibody and spleen cell IL-4 responses. Clinical characteristics and hypothermia responses upon oral allergen challenge were studied. RESULTS Upon allergen withdrawal, circulating hazelnut-specific IgE antibody levels began to drop. Nevertheless, IgE responses once established remained at significantly high levels for up to 8 months (the last time point studied) despite withdrawal of allergen exposure. Memory IgE responses to booster exposures were robust after 3, 5 or 8 months of allergen withdrawal. Furthermore, significant clinical reactivity to oral hazelnut challenge, and hypothermia responses were demonstrable at each of these time points. Long-lasting spleen cell memory IL-4 responses to hazelnut were detectable in these mice explaining the mechanism of sustenance of IgE responses and clinical sensitization. CONCLUSIONS Hazelnut allergy once established persists for long periods, despite withdrawal of allergen exposure, due to long-lasting, memory IgE and IL-4 responses.