TLR9 is important for protection against intestinal damage and for intestinal repair.

Toll-like receptors (TLRs) are innate receptors critical for host defense, and play a role in normal biological processes. For example, host DNA, a TLR9 ligand, stimulates epithelial repair following skin wounding. TLR signaling also plays a crucial role in regulating intestinal homeostasis. We therefore asked whether TLR9 is important for intestinal wound repair using a dextran sulfate sodium (DSS)-induced intestinal damage and repair model. We showed that TLR9-deficient mice are more susceptible to DSS, and exhibited delayed wound repair at both the clinical and histologic levels. TLR9-deficient mice showed reduced gene expression of hairy enhancer of split 1, an intestinal progenitor cell differentiation factor, and vascular endothelial growth factor, a growth factor important for epithelial cell restitution. Therefore, we conclude that TLR stimulation may play a normal role in regulating intestinal homeostasis and could potentially be a novel therapeutic target to enhance intestinal wound repair in inflammatory bowel diseases.