In allergic diseases, such as asthma, allergic rhinitis, and atopic dermatitis, where well-defined antigens, such as dust mites, grass and weed pollen, pet dander, and mildew, are identified as causative, multiple courses of allergen delivery via subcutaneous or sublingual routes induce a switch from a “Th2-type” response, with dominant production of IL-4 and IL-5, in favor of a “Th1-type” response, with the production of interferon gamma and IL-2 [20]. This evidence concerns the gene IL2 and allergic disease.