Dietary exposure to low pesticide doses causes long-term immunosuppression in the leopard frog (Rana pipiens)

This study examines the relationship between dietary exposure of pesticides, DDT, and dieldrin and immunosuppression in the northern leopard frog (Rana pipiens). Immune function was measured before, during, and after a 10-week exposure period with the use of both adaptive and innate immunity responses. Exposure to low doses (75 ng/g body wt DDT or 2.1 ng/g dieldrin total dose over the 10 weeks) resulted in significant suppressive effects on antibody production and secondary delayed-type hypersensitivity (DTH). The high doses (750 ng/g DDT and 21 ng/g dieldrin), however, did not affect antibody production, DTH, or oxidative burst in a predictable dose-response manner. The differences in magnitude and direction of the effects of the two dosing regimes were likely due to differences in chemical exposure on the basis of feeding and effectiveness of chemical uptake. The low dose results demonstrated that moderate concentrations of pesticides, frequently observed in the environment, are able to weaken the immune response of R. pipiens.