Effect of ziram on natural killer, lymphokine-activated killer, and cytotoxic T lymphocyte activity.

Ziram is a carbamate pesticide, which is widely used throughout the world as a fungicide in agriculture and as an accelerating agent in latex production. In the present study, we investigated the effect of ziram at 0.031-4 μM in vitro on human natural killer (NK) and lymphokine-activated killer (LAK) and murine cytotoxic T lymphocyte (CTL) activity and found that it significantly inhibited all three activities in a concentration-dependent manner. To explore the mechanism of ziram-induced inhibition of NK activity, NK-92MI cells, a human NK cell line, were used. We previously confirmed that NK-92MI cells express CD56, perforin, granzyme (Gr) A, GrB, Gr3/K, and granulysin and are highly cytotoxic to K562 cells in the chromium release assay. NK-92MI cells were treated with ziram at 0.125-4 μM for 4 or 16 h at 37°C in vitro. Then, intracellular levels of perforin, GrA, GrB, Gr3/K, and granulysin were determined by flow cytometry. It was found that ziram significantly reduced Gr3/K, granulysin, perforin, GrA, and GrB levels. The extent of the decrease differed among the proteins, and the order was as follows: Gr3/K > granulysin > perforin, GrA, and GrB. Taken together, these findings suggest the ziram-induced inhibition of NK, LAK, and CTL activities to be at least partially mediated by decreases in the intracellular levels of Gr3/K, granulysin, perforin, GrA, and GrB.