Studies on the action of dimethoate on the immune system.

The actions of the organophosphorous insecticide dimethoate (0.0-dimethyl S-(N-methylcarbamoylmethyl)phosphorodiothioate) on the immune response of mice and rats were studied. There was a decrease of lymphocytes to at 50% of normal. The weights of the thymus and spleen were diminished and the production of antibodies was reduced. 72 h after administration all the parameters measured had returned to normal. Histological examinations show a reduction of the cortex of the thymus and disruption of the thymocytes. The number of rosettes forming cells in rats was reduced after dimethoate. The actions seen after dimethoate administration are identical with the effects observed after glucocorticoid application. These results suggest an indirect depression of the immune system by dimethoate producing a release of glococorticoids.