Mechanisms of IL-13–induced phenotype generation. IL-13 binds to the IL-13 receptor complex made up of IL-4 receptor α (IL-4Rα) and IL-13 receptor α1 (IL-13Rα1). IL-13 also binds to IL-13Rα2, which is a decoy receptor that inhibits IL-13 responses. After binding to the IL-13 receptor complex, IL-13 activates STAT-6 signal transduction pathways. Pathways that involve chemokines, the chemokine receptor CCR2, MMPs, urinary plasminogen activator (UPA), TGF-β1, VEGF, and/or adenosine are then activated, and inflammation, fibrosis, blood vessel alterations, and mucus responses are generated. Each of these pathways is a site against which therapeutic agents can be directed.