These cytokines induce class switching and production of allergen-specific IgE.43, 44, 45 Primary allergic sensitization (such as a class switch toward IgE production) occurs early in life and leads to T-cell and IgE memory, which can be boosted with repeated allergen contact (secondary immune response).46, 47, 48, 49 Upon contact with a primary food allergen, nonallergic individuals produce allergen-specific IgG and IgA, which do not induce allergic reactions. This evidence concerns the gene IGHE and hypersensitivity reaction disease.