In turn, the histamine increases the secretion of Th2 cytokines such as IL-4, IL-5, and IL-13 and inhibits the production of the Th1 cytokines IL-2 and IFN-γ through the upregulation of prostaglandin E2 and nitric oxide (7), thereby exacerbating the allergy. Here, IL4 is linked to Allergy.