Abstract

Exposure to various waterborne contaminants induces altered immune function in fish. Less is known about the immune response during periods of recovery subsequent to chemical exposure. Understanding such immune responses is important when monitoring fish health following exposure to fluctuating concentrations of contaminants in aquatic environments. We have been using copper as a model toxicant since copper concentrations may fluctuate from industrial release or during use as an algicide and chemotherapeutant in aquaculture. Copper-induced immune suppression may compromise the immune system of fish making them more susceptible to disease. Over-stimulation of the immune response, specifically production of reactive oxygen intermediates (ROI) can cause oxidative stress. In the past, experiments from our lab have demonstrated increased production of ROI following acute copper exposure. In order to determine if copper causes a reversible effect on macrophage ROI production, we exposed goldfish (Carassius auratus) to sublethal concentrations of copper (100 ppb) for 4-25 d then allowed them to recover for 0-21 days. The production of intracellular superoxide (O₂-) following stimulation of the respiratory burst with PMA was compared in control and copper treated fish by measuring the reduction of NBT in head kidney macrophages. Fish were either treated continuously with copper or exposed for 96 h then placed in fresh water for recovery. In both groups after 96 h copper exposure, O₂-production was 133% and 129% of control. In the continuously exposed group, O₂-production was 132% (7 d) and 154% (11 d) of control. 02 production in the group that was allowed to recover from the 96 h exposure was 75% (3 d recovery) and 184% (7 d recovery) of control. By days 18 and 25, O₂- production returned to within 12% of control level in both groups. Our results indicate that copper stimulates O₂-production during acute exposure and that at 3 d of recovery a rapid decline (below control level) occurs followed by a rapid rebound at 7 d of recovery. To discern if suppressed O_2-production evident at recovery day 3 is mediated by a humoral factor, we treated macrophages from control animals with serum from control and copper-recovered animals. Preliminary results indicate that serum from copper-recovered animals suppresses O₂-production compared to serum from control animals.

Acknowledgements

This work was supported by a grant from NIEHS T32ES07263.