IL9 and allergic disease: Previous studies have shown that Th1 cells produce interleukin-1 (IL-2) and interferon gamma (IFN-γ), which are involved in cell-mediated inflammation; Th2 cells produce IL-4, IL-6, IL-9, IL-10, and IL-13, which are involved in antibody and allergic reactions, and inhibit Th1 cells from synthesizing proinflammatory cytokines [42].