Sources of fibroblasts in inflammatory bowel disease-associated fibrosis. Fibroblast precursors can derive from intestinal stellate cells (6) or from fully differentiated epithelial or endothelial cells under inflammatory pressure [epithelial- (42) or endothelial-to-mesenchymal transition (EMT) (43)]. Fibrocytes, circulating fibroblast precursors, which express both hematopoietic (CD14, CD45) and mesenchymal (CD34, Col I) cell markers (44), as well as bone marrow stem cells (which replenish intestinal fibroblasts) are recruited to inflamed or injured intestine (6). The role of pericytes, the main origin of fibroblasts in kidney fibrosis (5), has not been investigated in intestinal stricture formation.