FN1 and infection: In animals, ECM constituents such as hyaluronan, glycosaminoglycans, and fibronectin form bioactive fragments during infection or injury, which activate PRRs such as Toll-Like Receptors (TLRs) both in non-immune cells (e.g., fibroblast and epithelial cells) and in immune cells (e.g., macrophages and dendritic cells), alerting the immune system of tissue damage and infection, which initiates pathogen clearance and tissue repair [128].