Neutrophil-mediated proteolysis

In this study, we assessed the underlying mechanisms by which proteinases released from activated neutrophils mediate fibronectin degradation. Purified human neutrophils (1 X 10⁶) were incubated for 1 hr with 1 M PMA in the absence or presence of different prateinase inhibitors in 96-well microtiter plates that were coated with¹²⁵I-labeled fibronectin (FN). PMA-activated neutrophils caused 85% of FN to be degraded (versus5% under control conditions). A selective inhibitor of elastase (L658,758), a monoclonal antibody directed against human neutrophilic elastase, and plasma all reduced the: neutrophil-mediated FN degradation by 60%. A monoclonal antibody directed against the neutrophil adhesion glycoprotein CD 11 /CD 18 increased the antiproteoly tic effect of plasma to 70 % but had no effect on the other anti-elastase agents, suggesting that the subjacent space formed by adherent neutrophils restricted to a small degree plasma derived antiproteinases. Agents that blocked cathepsin G or cathepsin G and elastase completely prevented the proteolysis associated with PMA-stimulated neutrophils, suggesting that the actions of elastase may be dependent on the presence of biologically active cathepsin G.Supported by grants from the National Institutes of Health (HL26441) and DK43785 and the Medical Research Council of Canada (MRC). Dr. Paul Kubes is an MRC Scholar.