An Elastase-Specific Inhibitor from Human Bronchial Mucus. Isolation and Characterization

Abstract

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-TE (identical with the inhibitor HUSI-I [HUSI-I = Human seminal plasma inhibitor] from human seminal plasma or antileucoprotease), another acid-stable inhibitor BSI-E is present in the mucus. This elastase-specific inhibitor exerts inhibitory activity towards porcine pancreatic and human granulocytic elastase but not against trypsin, chymotrypsin or granulocytic cathepsin G; it was isolated by affinity chromatography and its molecular mass and 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.