Interleukin (IL)-13/transforming growth factor (TGF)-β signalling pathways. IL-13 signalling via IL-4Rα/IL-13Rα1 occurs via the JAK/STAT6 pathway and can cause increased collagen production from fibroblasts, recruit immune effector cells and enhance chemokine expression. Signalling via IL-13Rα2 in macrophages activates AP-1 inducing TGF-β secretion. Similarly IL-13Rα2 expression can be enhanced by TGF-β in hepatic stellate cells. TGF- β activates two serine/threonine kinase receptors and signals through Smad phosphorylation. TGF-β can also activate mitogen activated protein kinase signalling.