Transient inhibition of mixed lymphocyte reactivity by dieldrin in mice.

Dieldrin, a non-aromatic organochlorinated pesticide, was shown to be a potent modulator of the immune system. We had earlier demonstrated that mice treated with a single sublethal dose of dieldrin showed an impaired antibody response and reduced viral restriction mediated by macrophages. These dieldrin-induced immunosuppressive effects were shown to be dose dependent, when administered by the oral or intraperitoneal (i.p.) route. This study was undertaken to investigate the effect of dieldrin on the T-cell immune response. Lymphoid cells from mice injected i.p. 7 days earlier with 36 mg/kg body weight (0.6 LD50) dieldrin were assessed for their ability to recognize a foreign antigen and to proliferate in a mixed lymphocyte reaction (MLR) at 4, 7, 14 and 24 days post-treatment. We have demonstrated a strong but transient inhibition of MLR at 7 days after pesticide exposure. This effect was reversible and could not be attributed to a direct cell cytotoxicity, nor to the modulation of the T-cell ratio in lymphoid organs. Since the mitogen response was not impaired at this time point, we suggest that T-cell ability to recognize a foreign antigen can be altered by dieldrin, but not the proliferative potential of the cells.