IL13 and pulmonary fibrosis: IL-13 has been demonstrated in certain studies to induce fibrosis by boosting autocrine CTGF signaling in fibroblasts and inducing the pro-fibrotic transcription factor Snail, although IL-4 has not been proven to activate similar pathways. In numerous animal models of pulmonary fibrosis, IL-13 is considered to be more pro-fibrotic than IL-4.