Induction of Macrophage Plasminogen Activator by Endotoxin Stimulation and Phagocytosis

Abstract

The injection of thioglycollate medium into the peritoneal cavity of the mouse induces high levels of macrophage fibrinolytic activity due to the production and secretion of a plasminogen activator, a trypsinlike serine protease, which is absent in unstimulated macrophages. Intraperitoneal injection of endotoxin or mineral oil can stimulate only a fraction (<10%) of the fibrinolytic activity of thioglycollate cells, similar to the partial stimulation (<10%) seen 1–2 days after phagocytosis of latex or SRBC by unstimulated macrophages. The endotoxin-stimulated macrophages contain and release relatively low levels of plasminogen activator, but these primed cells can be triggered to produce and secrete high levels of enzyme, by phagocytosis of latex. Under conditions where the plasminogen activator is induced and secreted, there are no effects on the production and/or release of lysozyme or intracellular acid hydrolases, Discovery of a two-stage procedure for inducing macrophage plasminogen activator made it possible to study the role of cell priming and phagocytosis separately. Endotoxin was a more effective priming agent, weight for weight, than lipid A:BSA complex. Secretion of the plasminogen activator was induced only by thioglycollate, or endotoxin and latex. In situ fibrinolysis was induced by these agents and mineral oil, BCG, and fetal calf serum, in decreasing order of effectiveness. Phagocytosis of latex in all cases except thioglycollate stimulation, increased fibrinolytic activity from three- to sixfold. Latex and a variety of other particles such as M. lysodeikticus, aggregated γ-globulin and immune complexes showed dose-dependent stimulation of fibrinolysis by endotoxin-primed macrophages. Although the initial phagocytic trigger was not specific for the substance employed, the ability to induce a sustained response depended on the persistence of the phagocytized particle within the cell. Fibrinolysis and secretion of plasminogen activator continued at high levels for at least 9 days after uptake of latex, a nondigestible particle, whereas plasminogen activator was secreted only transiently after ingestion of rapidly digested M. lysodeikticus. The induction of plasminogen activator secretion provides a mechanism by which the activated macrophage can exert a selective effect on its extracellular environment.

Elastase secretion by stimulated macrophages. Characterization and regulation.

“…The increased rate of secretion of elastase and collagenase was sustained for at least 13 days after phagocytosis and these secretory rates were maintained equally well in Dulbecco's medium containing 0.2% LH or in Neumann-Tytell medium (Table V) . These data suggest that the control of release of elastase is strongly co-ordinated with the release of collagenase (12) and plasminogen activator (25) . Unstimulated Macrophages* *Average of three experiments in which 1 -2 x 10' cells were plated initially (0 .3 -0.7 mg cell protein finally ; phagocytosis increased the cell protein by 10 to 82%) .…”

“…Induction of their secretion is associated with cell stimulation, for example, by thioglycollate treatment in vivo, and secretion is enhanced by phagocytosis . They are all secreted in parallel over prolonged periods in culture (11,12,25) . As a class, these products can be readily differentiated from other secretory products, such as lysozyme and intracellular acid hydrolases, which are regulated independently (13) .…”

“…Both collagenase and plasminogen activator secretion are regulated by macrophage activation (11,12,25) ; elastase secretion is also controlled by this mechanism. After thioglycollate stimulation the elastase Concn.…”

Degradation of basic protein in myelin by neutral proteases secreted by stimulated macrophages: A possible mechanism of inflammatory demyelination

“…Furthermore, macrophage supernatants plus Pig were effective in degrading BP in brain myelin prepared from the three species tested-cow, cat, and rabbit. In additional experiments, purified BP isolated from myelin was found also to be sensitive to proteolytic degradation by macrophage-conditioned medi- (20)(21)(22)(23), collagenase (16,19,31), and elastase (17). Although the Plg-independent myelinolysis may have been produced directly by one of these proteases, the possible sequential activation of latent enzymes by macrophage-secreted enzymes, as has been demonstrated for a latent collagenase (32), precludes certain identification of the Plg-independent protease activity.…”

“…been established that mouse peritoneal macrophages stimulated by thioglycollate broth or by products of activated lymphocytes secrete several neutral proteases (16)(17)(18)(19), including plasminogen (Plg) activator (20)(21)(22)(23)(24)18). Such extracellular proteases generated from macrophages activated as a consequence of a reaction of sensitized T-lymphocytes with antigen, if capable of degrading myelin proteins, could initiate a process of myelin destruction common to inflammatory and cell-mediated immune reactions occurring in nervous tissue.…”