Evidence for lipid-associated serine proteases and metalloproteases in human bronchoalveolar lavage fluid.

1. We have investigated the nature of elastase activity in bronchoalveolar lavage samples from healthy cigarette smokers and subjects with emphysema. 2. Initial experiments with pure human leucocyte elastase showed this enzyme to be inhibited by high concentrations (greater than 10 mmol/l) of ethylenediaminetetra-acetate, indicating that results of previous studies of 'metalloelastase' activity in bronchoalveolar lavage were ambiguous. 3. We have nevertheless demonstrated the presence in bronchoalveolar lavage of an elastase with the characteristics of a metalloproteinase, although samples also contained a substantial amount of activity that was sensitive to serine proteinase inhibitors. 4. Fractionation of lavage fluid supernatant by size-exclusion chromatography demonstrated most of the elastase activity to be of molecular mass greater than 300 kDa. Treatment of samples with lipase or detergent caused a reduction in metalloelastase activity and the generation of lower-molecular-mass components (90-100 kDa and 40 kDa) which were predominantly serine elastases. This suggested that the enzymes were associated with lipid.