Severe microvascular injury induced by lysosomal releasates of human polymorphonuclear leukocytes. Increase in vasopermeability, hemorrhage, and microthrombosis due to degradation of subendothelial and perivascular matrices.

The purpose of this study was to assess the nature of the lesions in the microcirculation of the dermis of rabbits induced with lysosomal releasates of human polymorphonuclear leukocytes (PMNs). No attempt was made in the studies presented in this publication to deal with the offending agent in the releasate. Four parameters of microvascular injury were quantitated: increase in vascular permeability with 125I-labeled serum albumin, hemorrhage with 59Fe-labeled erythrocytes, accumulation (aggregation) of platelets with 111In-labeled platelets. In one experiment accumulation of 51Cr-PMNs was investigated. The lysosomal releasate induced a rapid increase in vasopermeability, but both hemorrhage and exudate formation peaked 1 hour after intradermal injection. Platelet accumulation was also demonstrable in these lesions, and microthrombosis was a very prominent feature. The microvascular injury, including microthrombosis, could be elicited also in animals rendered leukopenic with nitrogen mustard. Simultaneous injection of prostaglandin E2 with the releasate enhanced the microvascular injury. The morphologic changes in the microcirculation of the rabbit's dermis were assessed in lesions 5 minutes to 5 hours old. Several changes were encountered, primarily in the wall of venules and small veins and to a lesser degree in small arteries and capillaries. Ultrastructurally very early lesions (up to 15 minutes) had gaps or spaces in the endothelium, resembling those induced by mediators such as histamine or bradykinin. Older lesions were different, quite characteristic, and represent the hallmark of these lesions. Lysis and disappearance of vascular basement membrane, of perivascular collagen, and of the internal elastic lamina were a frequent finding, best demonstrable when microthrombi did not abut on vessel walls. Cellular components of vessels (endothelium, pericytes, smooth muscle) showed fragmentation, leading to complete disappearance of cellular elements. These lesions were usually walled off by platelet aggregates and fibrin. At times microthrombi occluded an entire vessel. These changes were interpreted as hemostasis. The mild accumulation of PMNs at the site of injury did not contribute significantly to the microvascular injury. The findings indicate that the unique changes in the microcirculation, not described before, may occur quite frequently, when the microvascular injury is elicited primarily by release of lysosomal constituents by phagocytic or nonphagocytic stimuli. One can conclude that the hallmark of this type of injury is disappearance of basement membrane followed secondarily by disintegration of the vascular wall, followed in turn by hemo