The dipeptidyl peptidase IV, a membrane enzyme involved in the proliferation of T lymphocytes.

Dipeptidyl peptidase IV can be demonstrated in 60% of T lymphocytes from human peripheral blood. As could be shown recently, this enzyme is irreversibly inhibited by N-Ala-Pro-O-(nitrobenzoyl-)hydroxylamine, a substrate analogous enzyme-activated inhibitor of X-Pro-specific peptidases. We found that this inhibitor was able to suppress the proliferation of human lymphocytes stimulated with mitogens or allogeneic cells. Furthermore, after stimulation with pokeweed mitogen the development of lymphocytes containing cytoplasmic immunoglobulins and thiol proteindisulfide oxidoreductase was reduced in the presence of this inhibitor. It is concluded that dipeptidyl peptidase IV is involved or might represent a limiting factor in the process of regulation of T lymphocyte proliferation.