Th2 lymphocytes play a prominent role in the initiation and progression of allergic disease, including asthma and AD, by releasing IL-4, IL-5, and IL-13, which promote IgE-mediated allergic inflammation, and IFN-γ, a Th1 cytokine secreted by Th1 cells, acts in conjunction with Th2 cytokines in maintaining the chronic inflammatory response in allergic disease, particularly in asthmatic airways (Ngoc et al., 2005). This evidence concerns the gene IFNG and asthma.