INDUCTION OF AMINOPEPTIDASE N CD13 ON HUMAN-LYMPHOCYTES AFTER ADHESION TO FIBROBLAST-LIKE SYNOVIOCYTES, ENDOTHELIAL-CELLS, EPITHELIAL-CELLS, AND MONOCYTES/MACROPHAGES/

Aminopeptidase N (APN/CD13) is a transmembrane ectoenzyme occurring on a wide variety of cells. In contrast to monocytes and granulocytes, l ymphocytes of peripheral blood do not express CD13 Ag. However, tumor- infiltrating T cells in renal cell cancer as well as synovial fluid T cells from patients suffering from various forms of arthritis can be C D13 positive. To learn more about expression of CD13 in these tissues, we cocultured lymphocytes with different adherent cell lines. CD13 ex pression was induced in T and B lymphocytes upon adhesion to fibroblas t-like synoviocytes, HUVEC, renal tubular epithelial cells, and monocy tes/macrophages but not always upon interaction with different tumor c ell lines. Induction of APN was rapid, occurring as early as 1 h after coincubation. Expression persisted for >3 days and partially resisted inhibition by cycloheximide. Fixation of adherent cells with paraform aldehyde could not prevent induction of CD13 in lymphocytes. Soluble A PN from human kidneys or placenta could not induce CD13 expression on lymphocytes. Induction of CD13 Ag on lymphocytes required direct cell- to-cell contact as shown in experiments using dual chambers. Lymphocyt es exhibited an induction not only in CD13 protein but also in Ala-pNA -cleaving enzyme activity and in CD13 mRNA. Lymphocytic expression of CD13 represents a potentially increased cellular ability to inactivate inflammatory mediators. Furthermore, CD13 could be involved in adhesi on, in lymphocytic migration, or in the Ag processing of peptides boun d in the groove of MHC class II molecules.