The effect of exposure to a commercial 2,4-D formulation during gestation on the immune response in CD-1 mice

Pregnant CD-1 mice were administered a commercial 2,4-dichlorophenoxyacetic acid (2,4-D) formulation on days 6-16 days of gestation, in drinking water at concentrations ranging from 0 to 1.0% of the formulated product, equivalent to approximately 0-650 mg/kg per day expressed as the amine derivative. The effect of 2,4-D on immune function was evaluated in offspring 7 weeks after birth. The dams tolerated repeated 2,4-D exposure in drinking water without difficulty. The offspring exhibited decreased body weight with minor reductions in the kidney weights in the 0.1 and 1.0% 2,4-D treatment groups. A generalized suppression of lymphocyte stimulation by concanavalin A (Con A) was observed at high dose of commercial 2,4-D formulation (1.0%). Cytometric studies of the lymphocyte subpopulations demonstrated an increased relative count of B cells and reduced T cytotoxic or suppressor cells in the 1.0% formulation. The humoral immune response, antibody production against sheep red blood cells and peritoneal macrophage phagocytic function, were not altered by 2,4-D. Since the immune alterations in the offspring were observed many weeks after exposure, it appears as though 2,4-D exposure during gestation causes permanent changes in cell types associated with immune function. Since 2,4-D is not considered a persistent chemical, it is unlikely that 2,4-D residues are contributing significantly to the observed immune alterations. The immune alterations were observed only in the higher treatment groups. Therefore, the impact on human and animal health from an immune perspective, which would be encountered following normal application in the environment, would be minimal.