Some properties of human blood monocyte cell lysate neutral proteinase(s)

The proteinase content of highly purified preparations of human peripheral blood monocytes was investigated. Monocyte cell lysates exhibited activity at neutral pH against azocasein, 3H-labelled elastin as well as several synthetic substrates used to detect serine proteinases (EC 3.4.21.-) of human polymorphonuclear leucocytes. The cell lysates also contain at least two acid proteinases. The levels of neutral proteinase activity in monocytes was considerably less than that found in polymorphonuclear leucocytes. The effect of inhibitors on the monocytes neutral proteinases showed them to be of the serine type. Monocytes also solubilized and degraded the type IV collagen found in human glomerular basement membrane at neutral and acid pH. The action of the monocyte proteinase on glomerular basement membrane indicated that their properties were similar but not identical to that of the polymorphonuclear leucocyte serine proteinases. Since monocytes infiltrate the glomerulus in certain forms of immunologically mediated glomerulonephritis, it may well be that monocyte serine proteinases make a contribution to the glomerular damage that occurs.