Past studies have focused attention on the lysosomal proteinases of polymorphonuclear leukocytes (PMN) as mediators of vascular injury (1-6). A specific association between the hydrolases in these ceils and selected targets in vessel wails was suggested by Cochrane and Aiken, who showed that acid-cathepsins D and E extracted from rabbit PMN granules could digest vascular basement membrane in vitro (5). As pointed out by these same authors, acid-cathepsinmediated vessel damage presupposes significant lowering of local pH. It remains to be determined whether sufficient acidity can be maintained at the tissueblood interface to permit such reactions to occur in vivo.Recently, evidence has appeared of vascular damage by leukocyte proteinases with neutral pH optima. A neutral mucoproteinase has been detected in rabbit PMN granules (7), and neutral proteinases have been purified from Arthus edema fluid in this species (8). Human neutrophiles are also known to contain neutral proteolytic activity or "leukoprotease" (9-12). We recently reported that extracts of human PMN granules could degrade vascular basement membrane at physiological pH in vitro and in vivo (6). Indeed, a neutral collagenase has been found in human PMN granules (13) and may be responsible for the lysis of vascular basement membranes occurring at physiological pH.The present studies were undertaken to examine the neutral proteinases of human neutrophilic leukocytes for possible activity against elastin. This sialoprotein comprises the elastic lamina and supportive fibers present in the walls of arterial and major venous blood vessels. Such activity, if present, would help account for the development of arterial lesions in PMN-mediated arteritis.Our results show that the granules of human PMN contain neutral elastinolyric activity which can be separated from the collagenolytic activity present in these cells. The data also demonstrate that the properties of elastolysis

The vascular permeability-increasing action of rabbit PMNL lysosomes has been studied in skin and cremaster muscle of the rat. Both an extract of frozen-thawed granules and a cathepsin-free cationic protein fraction of the granules (which had previously been demonstrated to cause leukocyte adhesion and emigration in vivo) induce increased vascular permeability in skin and muscle which resembles that produced by histamine or histamine-liberators with respect to the timing of the response and the predominant type of microvessel affected. Extracts of frozen-thawed lysosomes and the inflammatory lysosomal cationic protein both cause disruption of rat mesenteric mast cells in vitro, whereas a granule-free cytoplasmic fraction of PMN leukocytes and a non-inflammatory cationic protein fraction of the granules do not do so under identical test conditions. The mastocytolytic action of lysosomal materials in vitro is not inhibited in the presence of 10 kallikrein-inhibiting units of trasylol per ml. The mast cell rupturing fraction of PMNL granules (cationic protein) possesses no detectable peroxidase activity or acid-mucopolysaccharase activity. When compared with compound 48/80 on the basis of estimated molecular weight, the lysosomal cationic protein appears to be at least as active as the latter compound with respect to in vitro mastocytolytic potency. Chronic pretreatment of rats with an agent known to reduce tissue mast cell numbers causes marked suppression of the vascular permeability change normally induced in skin and muscle by lysosomal extracts and cationic protein. Similar results are obtained if lysosomal materials are tested in rats pretreated with an antihistaminic. These observations are discussed with respect to the mode of action of PMNL lysosomes in the early and late phases of local tissue-injury reactions.