IL13 and atopic asthma: As IL‐18 stimulates T cells to produce increased IFN‐γ, IL‐13 and IL‐5 23, and IL‐13 and IL‐5 are potent Th2 cytokines, which play key pro‐inflammatory role in atopic asthma, it is believed that IL‐18 ought to be a causative factor for asthma.