Abstract
<jats:p>Exposure to copper, one of the prevalent contaminants in aquatic environments, has wide-ranging adverse immunological effects. However, it is unclear if copper induced immune changes are due to alterations in lymphoid tissues or the result of direct immune cell toxicity. Therefore, to understand the mechanistic action of copper immunomodulation, we utilized an emerging immunotoxicologic model, threespine stickleback fish (Gasterosteus aculeatus). We exposed stickleback fish to dietary copper for a period of 14 days and examined its effect on the spleen, including histopathologic changes in splenic architecture and resident melanomacrophage centers (MMC) populations. We found that dietary copper exposure decreases splenic MMC coverage, suggesting copper is suppressing this phagocyte population. We found no histopathological differences between control and copper groups. Quantification of splenic compartments demonstrated that there is no significant difference in red or white pulp between the control and copper groups, suggesting that reduced MMC coverage is not due to the expansion of other splenic regions. Overall, results from this study suggest that copper toxicity leads to melanomacrophage suppression without damaging or altering the splenic secondary immune tissue structure. Future studies should examine the effect of copper on melanomacrophage viability, development, and function to better understand the mechanism behind MMC reduction.</jats:p>