Immunomodulation of human natural killer cell cytotoxic function by triazine and carbamate pesticides.

Triazine (atrazine) and carbamates (maneb, metiram, and ziram) are used as pesticides on a variety of crops around the world. To our knowledge, there have been no studies dealing with the effects of these compounds on human natural killer (NK) cells cytotoxic function. NK cells play a central role in immune defense against tumor development and viral infections. Thus, any agent that interferes with the ability of NK cells to lyse their targets could increase the risk of tumor incidence and/or viral infections. In this study, we examined the effects of atrazine, maneb, metiram, zineb, and ziram on the ability of human NK cells to lyse tumor cells. The compounds were tested in both purified NK cells as well as a cell preparation that contained both T and NK lymphocytes (T/NK cells). Lymphocytes were exposed to the compounds for periods of time ranging from 1 h to 6 days. Exposure of highly purified NK cells to 10 microM atrazine, maneb, or metiram inhibited K562 tumor cell lysis by 63+/-25, 95+/-4, and 50+/-6%, respectively, after a 24 h exposure and by 83+/-21, 70+/-39, and 48+/-41% after a 6-day exposure. Exposure to 2.5 microM ziram for 24 h caused a 99+/-2% decrease in lytic function and at 1 microM for 6 days caused a 96+/-4% decrease. However, when T/NK cells were exposed to atrazine, maneb, or metiram for 24 h only 10 microM atrazine and maneb caused a significant decreases in lytic function (61+/-13 and 38+/-18%) and after 6 days only atrazine was inhibitory (54+/-12%). A 24-h exposure to 2.5-microM ziram caused a 41+/-51% decrease in function, but a 6-day exposure to 1 microM ziram caused no inhibition of lytic function. The results provide evidence of relative toxic potential for the five compounds and the immunomodulatory effects on both T and NK lymphocyte function.