Urokinase localization and activity in isolated eosinophils.

Urokinase-type plasminogen activator is implicated in cell invasion and migration. In this study, we provide evidence for the presence of urokinase-type plasminogen activator (3.5 +/- 1.5 ng/mg of cell protein) in isolated peripheral blood eosinophils, in comparison to 6.7 +/- 2.3 ng/mg of protein in neutrophils. Both immunocytochemical and immunogold staining of urokinase-type plasminogen activator on electron microscopy showed its localization in granules of resting cells. Mild stimulation by platelet-activating factor induced a translocation of urokinase-type plasminogen activator from the granules to the cell membrane and a formation of urokinase-type plasminogen activator capping, suggesting a role for urokinase-type plasminogen activator in eosinophil migration. The activation of eosinophils led to the release of factor(s) which, after activation of pro-urokinase-type plasminogen activator, induced an inactivation of generated urokinase-type plasminogen activator. Our results suggest that urokinase-type plasminogen activator is implicated in activated eosinophils invasiveness because the exposure of urokinase-type plasminogen activator is regulated both in space and time.