Expression and functional role of dipeptidyl peptidase IV (CD26) on human natural killer cells

The expression and functional role of dipeptidyl peptidase IV (DP IV, CD26, EC 3.4.14.5) was studied on human natural killer (NK) cells. Here we show that freshly isolated NK cells do express only low amounts of DP IV. However, after IL-2 stimulation of NK cells (70% purity) surface DP IV expression was significantly increased in a subpopulation (30%) of these cells. Specific DP IV inhibitors (Lys-[Z-(NO2)]-piperidide, Lys-[Z(NO2)]-thiazolidide) and polyclonal antibodies directed against the ectopeptidase suppressed DNA synthesis and cell cycle progression of NK cells. The natural cytotoxic activity of DP IV+ CD56+ cells was found unchanged in comparison to those of DP IV- CD56+ cells. DP IV inhibitors had no effect on the natural cytotoxicity of mononuclear cells. From these data we conclude that DP IV is involved in the regulation of proliferation of NK cells, whereas natural cytotoxicity seems to be regulated independently.