TGFB1 and pulmonary fibrosis: Liver fibrosis induced by local transgenic overexpression of IL-13 and signaling through the type II receptor on fibroblasts (including hepatic stellate cells) may be independent of TGFβ.116,315,316 Pulmonary fibrosis induced by similar transgenic overexpression of IL-13 in murine lungs, although induced using a different genetic technique, required TGFβ for fibrosis (Figure 3A).317,318 Why this distinction was observed is currently unclear.