Allergen-specific IgG show distinct patterns in persistent and transient food allergy

Background: Immediate food-allergic reactions are IgE-mediated, but many individuals with detectable allergen-specific IgE do not react to the food. Allergen-specific IgG may interfere with allergen-IgE interaction and/or through intracellular inhibitory signalling to suppress mast cell and basophil response to food allergens. We aimed to understand the role of allergen-specific IgG in food allergy and natural tolerance. Methods: IgG and IgG isotypes specific to peanut, cow's milk and egg were measured using ImmunoCAP and ELISA respectively in samples of children with suspected food allergies. Expression of IgE and IgG and their receptors and expression of activation markers following allergen stimulation were measured on basophils and mast cells by flow cytometry, with and without blockade of Fc gamma RII alpha or Fc gamma RII beta receptors. Results: The levels of peanut-specific IgG, IgG1, IgG2, IgG3 and IgG4 in ELISA were higher in peanut-allergic than in non-peanut-allergic children. No difference in allergen-specific IgG isotypes was observed between allergic and non-allergic children to milk or egg, except for milk-specific IgG4 that was higher in non-cow's milk-allergic than in cow's milk-allergic children. Basophils and LAD2 cells expressed IgG receptors, but IgG and IgA were not detected on the surface of either cell type and blocking Fc gamma RII alpha or Fc gamma RII beta did not modify basophil or mast cell activation in response to allergen in allergic or tolerant children. Conclusion: Allergen-specific IgG patterns were distinct in persistent (peanut) versus transient (milk and egg) food allergies. We found no evidence that Fc gamma RII alpha or Fc gamma RII beta receptors affect allergen-induced activation of mast cells and basophils in food allergy or natural tolerance.