LAUSR

Amphibian populations are decreasing world-wide, and pollution is a contributing factor. Polychlorinated biphenyls (PCBs) are a class of persistent organic pollutants known to exert immunotoxicity. To assess impacts of PCBs on frogs, we exposed Lithobates pipiens tadpoles to a diet of PCB-126 (0 to 5 ng PCB-126/g wet food) through metamorphic climax. Post-metamorphic frogs were immunized with keyhole limpet hemocyanin (KLH) and production of KLH-specific IgY, as well as total IgY and IgM, were measured (Trial I). A second larval study (0 and 7.3 ng PCB-126/g wet food) was performed to investigate whether PCB altered antigenic responses in prometamorphic tadpoles (GS 36-39), and to measure innate immune response of post-metamorphic frogs (Trial II). With larval PCB-126 exposure, both KLH-specific IgY levels and complement activity were reduced. Because post-metamorphic frogs carried a body burden of PCB-126 (≤ 2.4 ng/g), we wanted to determine if the effect on immune response was due to larval exposure or the resulting body burden as frogs. To test this, we reared tadpoles under control conditions (no PCB), and limited PCB exposure to post-metamorphosis only by injecting 2-week old frogs with 10 ng PCB-126/g (Trial III). The resulting body burden (3.4 ng/g) was similar to frogs in Trial I, but we no longer detected suppression of KLH-specific IgY or hemolytic activity. These results suggest life-stage specific immune responses; however, because we administered PCB-126 differently between trials, it is premature to conclude that these differences are intrinsically life-stage dependent and further study is warranted. Regardless, this study demonstrated a long-lasting effect of larval PCB-126 exposure that persisted through metamorphosis and suppressed frog immunity. This article is protected by copyright. All rights reserved.