Comparative analysis of the ability of leucocytes, endothelial cells and platelets to degrade the subendothelial basement membrane: evidence for cytokine dependence and detection of a novel sulfatase.

The subendothelial basement membrane (BM) is regarded as an important barrier to the entry of leucocytes into inflammatory sites. This study compares the ability of leucocytes, platelets and endothelial cells (EC) to degrade a [35SO4]-labelled subendothelial extracellular matrix (ECM) and assesses the effect of PMA and various pro-inflammatory cytokines on this degradative activity. The different products of degradation, identified by fast protein liquid chromatography (FPLC) gel filtration chromatography, were indicative of protease, endoglycosidase (heparanase) and exoglycosidase and/or sulfatase activity. In terms of ECM degradation, EC and platelets were the most active, with PMA stimulation further enhancing the degradative activity of these two cell types. Platelets exhibited predominantly heparanase activity whereas the EC degradation products suggested a range of enzymic activities, namely proteases, heparanases and sulfatases. Interestingly, EC in suspension expressed these three enzymic activities whereas confluent EC monolayers only exhibited sulfatase activity, suggesting that the former situation might represent an angiogenic response. In the case of leucocytes, neutrophils and lymphocytes degraded the ECM to a much greater extent than monocytes. Each cell type also differed in the predominant enzymic activities it expressed, for example, heparanase activity by lymphocytes, protease activity by neutrophils and sulfatase activity by monocytes. Furthermore, PMA stimulation was shown to have differential effects on these enzymic activities. Some pro-inflammatory cytokines were found to be cell-type specific in their effects on ECM degradation. Thus, IL-1 + TNF enhanced neutrophil and EC degradation of the ECM but inhibited lymphocyte ECM degradation. In contrast, the chemokine IL-8 enhanced ECM degradation by neutrophils, lymphocytes and EC. Of particular interest was the unique sulfatase activity expressed by EC and monocytes which was induced in EC by TNF + IL-1 and IL-8, whereas in monocytes the sulfatase activity was exclusively induced by the chemokine monocyte chemotactic and activating factor (MCAF). Collectively, the results of this study show that leucocytes differ markedly in the enzymes they express to degrade the BM during extravasation and that PMA and cytokines are cell-type specific in their induction of hydrolytic enzyme activity. These results also indicate that EC may play an important role, not only in the recruitment of leucocytes, but also via sulfatase activity in the preparation of vascular BM for leucocyte extravasion.