Dipeptidyl peptidase IV (DP IV), a functional marker of the T lymphocyte system

Dipeptidyl peptidase IV (DP IV; E.C. 3.4.14.5), a plasma membrane structure of human T lymphocytes has been shown to be an important enzyme in the process of activation and proliferation of lymphocytes. In presence of specific inhibitors and antibodies against DP IV different functions of lymphocytes in vitro were found to be impaired. This holds true for mitogen and alloantigen induced DNA synthesis, immunoglobulin production and secretion, and interleukin-2 as well as interferon-gamma production. Studies of mitogen-induced expression of different activation markers (HLA class II antigen, 4F2, Tac) suggested that one of the functions of DP IV lies in overriding the cell cycle restriction point at G1. These data, together with other features of the DP IV, support the notion that this enzyme plays a key role in the modulation of lymphokine action by X-Pro- or X-Ala-directed limited proteolysis. Moreover the high frequency of DP IV susceptible bonds in different growth factors (e.g. IL-1, IL-2) and other biologically active peptides leads to the speculation that this peptidase is of more general significance to the regulation of cell growth.