Regulation of proteolysis at the neutropbil-substrate interface by secretory leukoprotease inhibitor
- Rice GR, Weiss SJ
Degradation of surface-bound fibronectin of the upper respiratory tract by human leucocyte elastase (HLE) was shown to favour colonization of these mucosal surfaces by Gram-negative bacteria. We investigated the degradation of fibronectin by purified HLE and by enzymes released from stimulated human polymorphonuclear leucocytes (PMNs), in the presence of recombinant secretory leucocyte proteinase inhibitor (rSLPI) and alpha 1-proteinase inhibitor (alpha 1-PI), the two main inhibitors of HLE within the airways. Our results show that HLE degraded fibronectin at concentrations as low as 0.2 nM. To inhibit the degradation of fibronectin by pure HLE in an experimental system in which the enzyme was premixed with inhibitor, a twofold molar excess of rSLPI and an equimolar concentration of alpha 1-PI were required. On the other hand, a fivefold molar excess of rSLPI was necessary to inhibit degradation of fibronectin by enzymes released from stimulated neutrophils. In order to estimate the role of oxidants generated by stimulated PMNs in the activation of the inhibitory capacity of rSLPI by stimulated PMNs, we preincubated PMNs with antioxidants such as superoxide dismutase, methionine, catalase or Na-azide prior to stimulation of the cells. Under these conditions, a threefold molar excess of rSLPI over released HLE was required to inhibit the degradation of fibronectin, raising the possibility that either exogenous or endogenous antioxidants in the lung could be important in improving the efficacy of this therapeutic antiprotease. We conclude that a molar excess of rSLPI to HLE is always necessary to inhibit fibronectin degradation by HLE, and that addition of antioxidants partly prevents the inactivation of rSLPI by oxidants released from stimulated PMNs.