Metallothionein (MT) gene expression and cadmium-induced immunotoxicity in hemocytes of the eastern oyster Crassostrea virginica

Metal exposure is known to result in immunotoxicity in bivalve molluscs. To understand the relationship between metallothionein (MT) gene expression and Cd toxicity in oyster hemocytes, methods were developed for quantitative reverse transcription polymerase chain reaction of MT mRNA and selective inhibition of MT expression with antisense phosphorothioate deoxyoligonucleotides (S-ODN). In vitro Cd exposure of hemocytes at sub-cytolethal concentrations up to 15 μM CdCl2 resulted in concentration-dependent increases in MT induction. This upper Cd concentration also corresponded with the first detection of inhibited reactive oxygen intermediate (ROI) generation and lysosomal neutral red retention. Further Cd increases caused a decline in induced MT mRNA, ROI generation, and neutral red retention. Cell viability was not affected until Cd concentrations exceeded 50 μM. Incubation of hemocytes with antisense S-ODN resulted in significant reductions in basal and Cd-induced MT mRNA as well as significant inhibition of ROI production. These findings suggest a protective role for MT at low concentrations of Cd and a functional role for MT in ROI production.