CD26 is Involved in Regulation of Cytokine Production in Natural Killer Cells

Abstract

Dipeptidyl peptidase IV (DP IV, CD26) is a postproline cleaving enzyme which catalyses the degradation of polypeptides from the N-terminal part. DP IV is expressed on the surface of cells from several tissues. High levels of DP IV activity were found in the brush border membrane of the intestinal epithelium, in the proximal tubulus of the kidney, and in the serum [1,2]. In the immune system, DP IV was observed to be expressed on activated T cells, on activated NK cells, and on activated B lymphocytes [3,4]. DP IV was characterised as a key enzyme in the regulation of activation and proliferation of T lymphocytes. The mitogen- and antigen-induced DNA synthesis was found to be inhibited by specific DP IV inhibitors [5]. Earlier we described the expression of DP IV/CD26 on activated NK cells using enzymatic and immunologic techniques. Moreover, evidence was presented that DP IV is involved in the regulation of DNA synthesis and cell cycle progression, but not in that of the natural cytotoxic activity of NK cells against K 562 cells. The mechanisms of regulation of the DNA synthesis are unclear as yet. In T lymphocytes it could be shown that DP IV inhibitors specifically regulate the cytokine production of these cells and by that means affect the autocrine growth regulation [6]. It was shown that both resting and activated NK cells are capable of cytokine production [7,8]. These cytokines seem to play a role in regulation of NK cell activation as well as in their effector functions [9]. Other authors postulated a link between CD26 expression and apoptosis [10].