Characterization of a low molecular weight anti-elastase isolated from human bronchial secretion

An elastase-specific, low molecular weight inhibitor was isolated from human bronchial secretions that is able to inhibit porcine pancreatic elastase and human granulocyte elastase (Ki = 1.0 X 10(-9) M) but not bovine pancreatic trypsin or human cathepsin G. Under dissociating conditions the inhibitor has a molecular weight of 5000, whereas 10,000 mol. wt. was found for the native protein. The inhibitor was quantified by an enzyme-linked immunosorbent assay using an antiserum prepared in rabbits. In 16 acid-treated sputum samples, the inhibitor was present at concentrations of 1.8 +/- 1.2 microgram/ml (means +/- SD), whereas only trace amounts were detectable in serum. These quantitative results suggest a local production of the inhibitor in the lung.