The Th2 cells are critical players in allergy because: (1) IgE antibody responses are Th2 (i.e., IL-4) dependent; (2) IL-5 is critical player in eosinophilia; (3) IL-13 is critical in mucus production and also enhances IgE responses; (4) these cytokines can also be produced by mast cells, basophil and eosinophil that can result in positive feed-back enhancement of chronic allergic reactions such as atopic dermatitis [33]. This evidence concerns the gene IL4 and allergic disease.