Degradation patterns of HLE ‐ alpha 1 PI complexes in sol and gel phases of tracheobronchial aspirates

Uninhibited activity of human leukocyte elastase (HLE), a serine protease, is detectable in the airways of patients with purulent tracheobronchitis. Uninhibited HLE degrades extracellular matrix proteins and has secretagogue, chemoattractant, and proinflammatory properties. This study assessed the compartmentalization of HLE in the soluble phase (sol) and insoluble phase (gel) of airway secretions. Samples of tracheobronchial aspirates were obtained from patients who were receiving mechanical ventilation. The aspirate samples were separated into sol and gel phases by centrifugation. HLE was eluted from the gel phase fractions using 1 M NaCl to disrupt electrostatic bonds which are hypothesized to play an important role in binding HLE to gel phase. These gel phase extracts and corresponding sol phases were analyzed by chromogenic HLE activity assays, casein zymograms, and immunoblots for HLE and alpha 1 protease inhibitor. Immunoreactive HLE and alpha 1‐PI were detected together in at least six complexes with molecular weights ranging from 30 to 97 kDa. There was less size heterogeneity in complexes containing immunoreactive HLE and alpha‐1‐PI in the gel phase extracts than in the corresponding sol phase samples. The amidolytic activity of HLE was always greater in the extracts, although the total amount of immunoreactive HLE was lower than in the sol phase samples. Immunoblot patterns also indicate that HLE or immunoreactive degradation products of HLE were bound to proteins other than alpha 1‐ PI. Supported by NIH (DE‐10985 and AI‐53524).