Dipeptidyl peptidase IV/CD26 in T cell activation, cytokine secretion and immunoglobulin production.

Dipeptidyl peptidase IV (DPPIV/CD26; EC. 3.4.14.5), a widely distributed multifunctional type II plasma membrane glycoprotein, is involved in different biological processes. It is a serine protease associated with uptake and transmembrane transport of proline-containing peptides as well as with processing of physiological active peptides1. As an exopeptidase it cleaves N -terminal dipeptides after proline or alanine residues. Furthermore, an endopeptidase activity of DPPIV has also been reported2. Due to its interaction with proteins of the extracellular matrix (ECM), such as collagen and fibronectin, DPPIV/CD26 can also be considered as a cell adhesion molecule3. The interaction of DPPIV/CD26 with proteins of the ECM has been determined by several binding assays4-6. Although the binding properties of DPPIV/CD26 to proteins of the ECM have been well characterized, the significance of this interaction for its biological function, especially for the immune regulation is still unknown. It has been shown that DPPIV/CD26 plays a crucial role in T cell activation and immune regulation7-10. The expression level of DPPIV/CD26 is tightly regulated during the development of T lymphocytes and its density on the plasma membrane is markedly enhanced after lymphocyte activation.