The degradation of human glomerular basement membrane with purified lysosomal proteinases: evidence for the pathogenic role of the polymorphonuclear leucocyte in glomerulonephritis.

1. Human polymorphonuclear leucocyte elastase and cathepsin G were incubated with preparations of isolated human glomerular basement membrane at neutral pH and 37 degrees C. 2. The ability of these enzymes to degrade glomerular basement membrane was followed by the release of hydroxyproline. Both proteinases released considerable amounts of hydroxyproline. 3. By using Sephadex G-100 it was shown that the solubilized basement membrane fragments appeared as a single peak and had a molecular weight of over 100 000. These proteins after reduction were analysed by sodium dodecyl sulphate-gel electrophoresis to examine their subunit pattern and determine their molecular size. 4. The released basement membrane proteins gave at least four precipitin lines with a rabbit anti-(glomerular basement membrane) antiserum. 5. These results support the concept that polymorphonuclear leucocyte neutral proteinases play an important role in the pathogenesis of glomerulonephritis. 6. At acid pH values cathepsin B also released hydroxyproline from human glomerular basement membrane but the lysosomal carboxyl proteinase, cathepsin D, had no action.