Evaluation of the immunotoxicity of herbicide simazine in mice

Simazine is one of the most predominant herbicides used in agricultural applications for a long time. Since very few data are available concerning the influence of simazine on the immune system, immunotoxicity of the simazine was examined in mice following a exposure to the herbicide. Animals (5 mice/group) were gavaged with a dose of 300 or 600 mg/kg of simazine in 0.5% carboxymethyl cellulose for 4 weeks. Body weight of animal was affected at 1-4 weeks after the herbicide exposure. While exposure to the herbicide resulted in some marked fluctuations in weight of the spleen, thymus and adrenal gland at 1-4 weeks, lung, kidney, or liver weight was not changed. Splenocytes isolated from simazine-treated mice were used to evaluate the blastogenesis. A marked suppression of proliferation was observed at 1-4 weeks. Furthermore, the number of plaque-froming cells (PFC) was decreased at 2-4 weeks after exposure to simazine. However, a marked increase was noted in the number of PFC at 3 weeks after exposure to 600 mg/kg. In addition, antitumoral activity of macrophages and NK cell cytotoxicity were suppressed in simazine-treated mice. The inhibitory effect of simazine on TNF-α production in macrophages was observed at 1-4 weeks and NO production was decreased at 4 weeks only. Furthermore, expousre to simazine inhibited the production of CFU-GM, suggesting that simazine suppress the formation of colonies by hematopoietic stem cells. Taken together, these findings suggest that treatment with doses of simazine at or above maximum tolerated dose may result in the suppression of immune function, including antibody production, macrophage function, NK cell activity, and the CFU-GM production.