IL4 and chronic obstructive pulmonary disease: Aberrant activities of cytokines participating in the allergic Th2 inflammation cascade, including the upstream epithelial alarmin sensing environmental insults represented by TSLP and downstream mediator and effector types of Th2 cytokines, including IL-4, IL-5, and IL-13, are the leading causes of complex allergic inflammatory diseases, including atopic asthma, COPD, atopic dermatitis, CRSwNP, food allergy, and IBD.