| Popis: |
In the adult organism, monocytes and macrophages are among the few cell types that can migrate within and between body compartments. To do so, they must have the capacity to clear for themselves a path through the macromolecular barriers of basement membranes and other extracellular matrices. This requires the controlled and localized degradation of matrix proteins by extracellular proteases. Mononuclear phagocytes can produce a number of such enzymes, including collagenolytic, elastinolytic, and gelatinolytic hydrolases (Takemura and Werb 1984). Because they can, directly or indirectly, catalyze the degradation of most components of extracellular matrices, plasminogen activators (PAs) are thought to play a key role in the proteolytic events that accompany the migration of a wide variety of cell types, during ontogeny as well as in pathologic circumstances. Monocytes and macrophages can produce PAs, and the regulation of their PA-dependent proteolytic activity has been a focus of attention in recent years. The findings of a number of investigators converge to suggest that the expression of PA activity is a tightly controlled phenotypic property of human and murine mononuclear phagocytes, and that multiple mechanisms act concurrently to achieve the exquisitely focused and regulated generation of plasmin precisely where and when it is needed to allow cell migration in the context of inflammatory reactions. |
