The electrophoretic mobility of alpha 1-antitrypsin in sputum and its relationship to protease inhibitory capacity, leucocyte elastase concentrations and acute respiratory infection.

The electrophoretic mobility of uncomplexed alpha 1-antitrypsin was studied in the sol phase of sputum from 14 patients with chronic bronchitis. The mobility of alpha 1-antitrypsin in the sputum of each subject was reduced compared to the mobility in serum (mean sputum value = 71.1% of albumin mobility; mean serum value = 78.5% of albumin mobility). This reduction in alpha 1-antitrypsin mobility was most significant in the sputum samples of patients with chest infections which contained free elastolytic activity (mean value in cases where no enzyme activity was found = 74.9%; in cases with enzyme activity = 66.1%, 2P < 0.01). There was a significant inverse relationship between alpha 1-antitrypsin mobility in sputum and concentration of immunoreactive leucocyte elastase (r = -0.739, 2P < 0.01). The addition of trypsin to the sputum samples showed failure to inhibit the enzyme despite the apparant presence of sufficient uncomplexed alpha 1-antitrypsin in these samples, suggesting this alpha 1-antitrypsin was non-functional. Proteolytic enzymes can inactivate alpha 1-antitrypsin with a reduction in its electrophoretic mobility. The results of this study suggest that the alpha 1-antitrypsin in sputum may be inactivated by lysosomal proteases including elastase.