Response of fish immune cells to in vitro organotin exposures

Abstract

The presence of contaminants in aquatic environments may compromise the health and survival of fish. Many of these compounds are known immunotoxins in mammals; however, relatively little information is available on the immunotoxic responses of fish to these pollutants. Organotins are examples of widespread industrial and agricultural compounds which persist in aquatic environments. In this study, we investigate the effects of tributyltin (TBT) and its dealkylated metabolite dibutyltin (DBT) on fish immune responses. Immune cells were isolated from the spleen and head kidney of juvenile rainbow trout ( Oncorhynchus mykiss) and exposed to 0, 2.5, 50 and 500 ppb of either TBT or DBT. Mitogenesis was quantified by tritiated thymidine incorporation into cells cultured with the mitogens concanavalin A (Con A) or lipopolysaccharide (LPS). No changes in immune function occurred at the lowest organotin dose of 2.5 ppb. Con A-stimulated mitogenesis was significantly suppressed by 85% in spleen cells on exposure to 50 ppb DBT. LPS-stimulated mitogenesis was significantly suppressed by 96% in spleen cells and by 58% in head kidney cells with 50 ppb DBT. The highest concentration of 500 ppb of TBT and DBT inhibited both Con A- and LPS-stimulated mitogenesis by more than 95% in both head kidney and spleen cells. Flow cytometric analysis revealed dose-dependent changes in the cell population profile which correlated with the inhibition of mitogen-stimulated lymphoproliferation. In contrast, natural cytotoxic cell activity was not inhibited by in vitro exposure to either compound, as determined by the lysis of chromium-51-labelled K562 human erythroleukaemia cells and P815 mouse mastocytoma cells. These results show that organotins have both functional and tissue-specific effects on the fish immune system, i.e. spleen ⪢ head kidney tissue and, in general. LPS-responsive ⪢ Con A-responsive leukocytes. In aquatic systems, TBT is considered to be the most toxic organotin compound, and this toxicity decreases with progressive dealkylation to diand mono-organotins. However, our results indicate that DBT is a more potent immunotoxin than TBT, and suggest a need for the reassessment of the potential toxicity of DBT to aquatic organisms.