Midgut thrombin inhibitor that plays a major role in keeping the midgut microenvironment at low hemostatic and inflammatory tonus (PubMed:18286181, PubMed:26745503). Also inhibits FXIa (F11), kallikrein (KLK1), neutrophil elastase (ELANE) and cathepsin G (CTSG), which play a role in the contact pathway of the coagulation cascade (PubMed:18286181, PubMed:26745503). Also abrogates platelet aggregation by cathepsin G and plasmin, and attenuates tissue factor (F3) pathway inhibitor cleavage by elastase (PubMed:18286181, PubMed:26745503). In vivo, inhibits thrombosis and promotes bleeding in mice (PubMed:26745503). Interacts with host thrombin and trypsin. Expressed in the midgut. The N-terminus is blocked.