Acid-Stable Low Molecular Mass Proteinase Inhibitors in Human Lung Lavage

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Abstract
An acid-stable, low molecular mass proteinase inhibitor, bronchial mucus proteinase inhibitor (BMPI), has been isolated from sputum and partially characterised. A single band with a modal molecular mass of 18,700 was observed following SDS-polyacrylamide gel electrophoresis BMPI inhibited human leukocyte elastase, cathepsin G, trypsin and chymotrypsin, but not porcine pancreatic elastase. Although BMPI had a molecular mass close to the similarly isolated inhibitor of Girard et al. (Girard, F. Tournier, J. M., Polu, J. M. and Sadoul, P. (1980), Bull Eur. Physiopathol Respir. 16 (Suppl.) 237-245), and although it showed immunological cross reactivity to the low molecular mass inhibitor of Kramps et al. (Kramps, J. A. Franken, C., Meyer, C.J.L.M. and Dijkman, J. H. (1981) J. Histochem. Cytochem 29, 712-719), it was found to have an amino-acid profile different to any previously described inhibitor. BMPI was detectable in bronchoalveolar lavage fluid collected from healthy and diseased human lungs. The median molar ratio of BMPI/.alpha.1-proteinase inhibitor (.alpha.1PI) observed in these lavage samples was 0.7, which is generally higher than those derived from the data of other authors. This suggests that BMPI is a different protein to those previously described, although its exact relationship to other low molecular mass proteinase inhibitors remains to be determined.