Of particular importance to allergic disease is the recent recognition of the regulation of helper immune function by two lineages of T helper cells, i.e., Th1 and Th2, by these cytokines.[10] The Th2 hypothesis of allergy considers atopy as a Th2-driven hypersensitivity reaction to allergens of complex genetic and environmental origins, in which the Thl lineage, normally driven by IL-2, TNF, and IFN-γ is deficient, and in which a predominant Th2 response is seen that is driven by IL-4, IL-13, IL-5, and IL-10. This evidence concerns the gene IL5 and allergic disease.