IGHE and allergic disease: The immunological mechanisms of (atopic) allergic diseases, that is, allergic rhinitis, asthma, atopic dermatitis, insect venom allergy, and IgE-mediated food allergy, are characterized by an aberrant type 2 immune response to otherwise harmless allergens and a decrease in allergen-specific regulatory T (Treg) cells that are restored during allergen-specific immunotherapy (AIT), the only causal-oriented treatment known so far.