Differential regulation of aminopeptidase N (CD13) by transendothelial migration and cytokines on human eosinophils

Aminopeptidase N (CD13) is a cell surface metalloprotease involved in growth regulation, tumor invasion, and down-regulation of regulatory peptides. CD13 expression on eosinophils in bronchoalveolar lavage (BAL) of asthmatics 10 minutes and 18 hours after segmental allergen provocation was significantly increased (+225% to +294%) compared to blood eosinophils. In vitro CD13 expression could be induced on blood eosinophils by transendothelial migration of the cells across interlenkin (IL) 1beta-activated human umbilical cord vein endothelial cells (HUVECs) as well as by the exposure to the cytokines IL-3, IL-5, and granulocyte-macrophage colony-stimulating factor (GM-CSF). The cytokines GM-CSF and IL-5 were significantly less effective in inducing CD13 compared to IL-3. The IL-3-induced expression of CD13 was decreased in the presence of the protein-synthesis inhibitor cycloheximide (-8.8%). Moreover, blocking of CD13 by the protease inhibitors actinonin and bestatin significantly enhanced migration (+40.0% to +80.0%) of eosinophils across HUVEC monolayers. In summary, the data suggest that CD13 is regulated both by the process of transmigration and by the cytokine IL-3. Further, CD13 itself seems to be involved in the process of eosinophil transmigration.