Vascular injury and lysis of basement membrane in vitro by neutral protease of human leukocytes.

Frozen and thawed granules of human, peripheral-blood leukocytes rapidly produce hemorrhage when injected into animal tissues. The effect is blocked by inhibitors of proteolysis. The granule extract can digest vascular basement membrane in vitro at neutral pH. In addition, basement membranes of blood vessels damaged in vivo by the leukocyte fraction are found to be attenuated when examined by electron microscopy. The proteases of human leukocyte granules differ in several important respects from known lysosomal cathepsins and trypsin-like esterases. Polymorphonuclear neutrophils are a major source of the neutral proteases present in circulating white cells, and release these enzymes during phagocytosis of immune complexes.