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. 2015 Apr 17;308(12):L1189–L1201. doi: 10.1152/ajplung.00028.2015

Table 3.

Target substrates, sources, and activity of respiratory antiproteases

Antiproteases in the Respiratory Tract Target Substrates Sources in the Lung Activity
TIMPs MMPs (24) Alveolar epithelial cells, alveolar macrophages, granulocytes (28, 97) Insert reactive ridge NH2-terminal domain into MMP active site, inhibit apoptosis (103, 120)
Serpin Serine and cysteine proteases, caspases, bacteria, viruses (9, 57, 138, 141, 154) Epithelial cells, alveolar macrophages (35, 115, 159) Insert RCL into the active site of the targeted protease, inhibit LPS-induced inflammation, block microbial infection (101, 130)
Trappin/Elafin NE and proteinase-3, enveloped viruses (193) Tracheal epithelial cells, club cells, type II cells, alveolar macrophages (123) Contain WAP domain for antiprotease activity, inhibit viral infection (59, 150, 156, 187)
SLPI NE, cathepsin G, chymase, bacteria, and viruses (62, 184) Epithelial cells, neutrophils, macrophages (48, 121) Contain WAP domain for antiprotease activity, antimicrobial effects due to NH2-terminal domain and high cationicity, block inflammatory cascades, inhibit viral infection (67, 91, 93, 150, 156, 172, 173, 187)

MMPs, matrix metalloproteinases; NE, neutrophil elastase; RCL, reactive center loops; SLPI, secretory leukocyte protease inhibitor; TIMPs, tissue inhibitors of metalloproteinases; WAP, whey acidic protein domain.