Figure 2.

Presence of proteases in the GI tract. Trypsin is released in the lumen of the GI tract for digestive purposes, but can also be present deeper into the tissues released from endothelial or epithelial cells. Proteases of the coagulation cascade such as thrombin, factor Xa and VIIa can be released into the lumen or the GI tissues upon tissue damage. When they degranulate, mast cells release massive amounts of tryptase both in the gut lumen and vasculature. Neutrophils present either in the tissues or translocated in the lumen release cathepsin G. Epithelial cells are exposed to bacterial proteases from the luminal side.