An elastase-specific inhibitor from human bronchial mucus. Isolation and characterization.

It was shown previously that human bronchial mucus contains an acid-stable proteinase inhibitor directed against trypsin and chymotrypsin, polymorphonuclear granulocyte elastase and cathepsin G. In addition to this well-characterized inhibitor, designated here as BSI-ATE (identical with the inhibitor HUSI-I from human seminal plasma or antileucoprotease), another acid-stable inhibitor BSI-E is present in the mucus which exerts inhibitory activity towards porcine pancreatic and human granulocytic elastase, but not against trypsin, chymotrypsin, or granulocytic cathepsin G. This elastase-specific inhibitor was isolated by affinity chromatography. Its molecular mass and its amino acid composition are very similar to those of BSI-TE. An immunological cross-reactivity between both inhibitor species was not observed. In the mucus of patients suffering from obstructive airway disease the elastase-specific inhibitor is not present in the free form but can be liberated by acidification.