Membrane-bound peptidases of lymphocytes: functional implications.

The paper is aimed towards the role of the membrane ecto-enzymes aminopeptidase N (CD13, AP-N) and dipeptidyl peptidase IV (CD26, DP IV) in the immune system. Both peptidases have been identified on T lymphocytes, AP-N also on monocytes and non-T cells. Using enzyme inhibitors and antibodies it has been shown by different groups that DP IV plays a key role in T cell activation and growth. Inhibition studies of our laboratory, using bestatin, actinonin and probestin, also demonstrated an essential role of AP-N in regulation of T cell growth. Moreover, the action of cytokines/lymphokines having DP IV susceptible bonds, as IL-1, IL-2 and IL-6, on lymphocyte proliferation, was found to be suppressed by specific inhibitors of DP IV as well as AP-N. These results are in favour of our hypothesis that DP IV and AP-N, possibly both in a concerted action, are involved in cytokine/lymphokine mediated signalling between immune cells.