Interaction of polymorphonuclear leukocytes with cartilage in vitro. Catabolic effects of serine proteases and oxygen radicals.

The ability of purified PMN serine proteases as well as oxygen-derived free radicals (ODFR) generated by activated phagocytes to damage cartilage matrix has been thoroughly investigated in vitro. The question in the present study was the extent to which enzymatic and ODFR-mediated mechanisms can contribute to the degradation of bovine cartilage slices by zymosan-stimulated PMN. Tissue destruction as assessed by mechanical parameters of stability as well as by liberation of uronic acids from matrix proteoglycans was not inhibitable by the radical scavengers superoxide dismutase (SOD) and catalase (CAT), while serine protease inhibitors led to a significant reduction of matrix degradation. Thus an enzymatic mechanism may play a major part in PMN-induced cartilage damage. Besides this predominant role of especially serine proteases a direct, non-zymosan-dependent stimulatory effect of cartilage matrix on PMN to release elastase into the incubation medium was detected. Hence an as-yet unknown mechanism of PMN activation is indicated, while unspecific effects by bacterial contamination, complement factors, or endotoxin could be excluded as an explanation for the observed phenomenon.