Table 3.

Endogenous protease inhibitors detected in the GI tract

Family	Protease inhibitor	Targeted proteases	Source	Possible sites of action
Serpins	Serpin A1	Trypsin/chymase/tryptase/elastase/proteinase-3/cathepsin G/thrombin/kallikreins	Systemic	M, P
	Serpin A3	Chymotrypsin/chymase/cathepsin G	Systemic	M, P
	Serpin A4	Kallikreins	Systemic	M, P
	Serpin E1	Plasminogen activator	Systemic	M, P
	Serpin C1	Thrombin	Systemic	M, P
Chelonianin	SLPI	Elastase/cathepsin G/trypsin/chymotrypsin/tryptase/chymase	Local	L, M, P, I
	Elafin	Elastase, proteinase-3	Local	L, M, P, I
TIMPs	TIMP-1	MMP-1/MMP-2/MMP-3/MMP-4/MMP-6/MMP-19/ADAM-10/ADAM-17	Systemic and local	M, P
	TIMP-2	MMP-1, MMP-2, MMP-14		M, P
	TIMP-3	Membrane-bound MMPs	Local	M, P
	TIMP-4	MMP-1/MMP-2/MMP-3/MMP-4/MMP-6/MMP-19	Systemic	M, P
	c-IAP2	Caspase-9	Local	I

ADAM, A Disintegrin And Metalloprotease; c-IAP2, cellular inhibitor of apoptosis protein-2; I, intracellular; L, lumen; M, matrix; MMP, matrix metalloproteinases; P, plasma; TIMPs, tissue inhibitors of metalloproteinases; SLPI, secretory leucocyte protease inhibitor.