Glomerular basement membrane injury by neutrophil and monocyte neutral proteinases.

Human peripheral blood leucocytes known to be present in the glomeruli of patients with certain forms of clinical glomerulonephritis have been investigated for their proteinase content and their ability to degrade glomerular basement membrane (GBM). Polymorphonuclear leucocytes (PMN) and monocytes, but not lymphocytes, contain neutral proteinases which extensively degrade GBM at physiological pH. Inhibitor studies indicate that the enzymes responsible are serine-type proteinases. The relative susceptibilities of the GBM to proteolytic attack showed that the monocyte preparation was considerably more active than the PMN neutral proteinases. The monocyte preparation also showed the ability to degrade GBM at acid pH. Lymphocytes had no effect on GBM either at acid or neutral pH. The possibility that the lysosomal proteinase of monocytes and PMNs are implicated in the damage to the GBM in glomerulonephritis is suggested.