TNF and fibrosis: Regarding bowel wall SWS, it may be possible to evaluate the presence of fibrosis at the time of initial diagnosis.24 Fibrosis results from the activation of mesenchymal cells by TNF-α, TGF-β, vascular growth factor, insulin-like growth factor-1, matrix metalloproteinases, and other mediators released by leukocytes, epithelial and mesenchymal cells, and the gut microbiota.