Reduced expression of dipeptidyl peptidase (DPP) IV in peripheral blood T lymphocytes of oral cancer patients.

To investigate the mechanism of decrease of serum DPP IV activity in oral cancer patients, we analyzed the expression of DPP IV in peripheral blood T lymphocytes of oral cancer patients and healthy subjects. Consequently, serum DPP IV activity was found to correlate significantly with the number of peripheral blood lymphocytes (PBL), T lymphocytes and CD26 (identified as DPP IV)+ T lymphocytes in healthy subjects, and the number of PBL and CD26+ T lymphocytes in cancer patients. However, the numbers of PBL and T lymphocytes were significantly less in cancer patients than in healthy subjects. Although the number of CD26+ T lymphocytes was somewhat greater in cancer patients than in healthy subjects, serum DPP IV activity was significantly lower in cancer patients. DPP IV activity and amount of CD26 in T lymphocyte plasma membranes were much less in cancer patients than in healthy subjects. These findings suggest that a decrease in the number of T lymphocytes and the small amount of DPP IV in their plasma membrane may contribute to the decrease of serum DPP IV activity in cancer patients.