ENZYMATIC-ACTIVITY OF CD26 (DIPEPTIDYLPEPTIDASE IV) IS NOT REQUIRED FOR ITS SIGNALING FUNCTION IN T-CELLS

CD26 is a proteolytic enzyme (dipeptidylpeptidase IV) expressed on the T cell surface that defines an alternative activation signal for huma n T lymphocytes. Crosslinking of CD26 via monoclonal antibodies trigge rs proliferation and cytotoxicity in preactivated T cells. In this stu dy, we used,highly specific competitive and irreversible inhibitors of dipeptidylpeptidase IV to study the role of the enzymatic activity in activation of CD26-transfected T cells as well as of CD26-expressing normal human T cell clones. These inhibitors at concentrations that bl ocked up to 95 % of the enzymatic activity, did not specifically inhib it T cell activation neither via TCR/CD3 nor via CD26 itself. This dem onstrates that the enzymatic activity of CD26 is not required for its T cell activating properties.