Abstract
We have determined the effect of altering assay conditions on the observed neutrophil elastase inhibitory capacity in lung secretions from emphysematous patients with normal serum α 1 PI. α 1 PI, ALP and α 2-macroglobulin were detected in all samples. Measurement at low enzyme concentration (< 33.6 nmol/l) caused a 43% reduction in observed neutrophil elastase inhibitory capacity of sputum sol-phase, while inhibition by secretions in buffer without added NaC1 was 20% greater than in the presence of 0.2 mol/l NaCl. Increasing the concentration of the synthetic substrate Suc-[Ala] 3-pNA in the assay from 0.45 mmol/l to 7.2 mmol/l reduced the observed inhibitory capacity by 53% and the use of elastin-fluorescein gave lower results for inhibitory capacity than the Suc-[Ala] 3-pNA (median 0.26 mol neutrophil elastase/mol measured inhibitors (range 0–0.72) with elastin; 1.40 mol neutrophil elastase/mol measured inhibitors (0.80–3.21) with Suc-[Ala] 3-pNA). Assay conditions therefore greatly influence the results. In addition these findings suggest the presence of an additional inhibitor of neutrophil elastase in these secretions.
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