METALLOTHIONEIN MESSENGER-RNA INDUCTION AND GENERATION OF REACTIVE OXYGEN SPECIES IN MOLLUSCAN HEMOCYTES EXPOSED TO CADMIUM IN-VITRO

(1) Hemocytes of the oyster Crassostrea virginica were exposed to Cd i n vitro to examine the concomitant induction of metallothionein (MT) m RNA and production of reactive oxygen species (ROS) during the oxidati ve burst response of phagocytic cells. (2) MT mRNA induction was conce ntration-dependent, exhibiting a threshold between 5 and 10 mu M CdCl2 , and an increase at higher Cd concentrations up to a maximum level of 36 mu M CdCl2. Continued increases in the Cd exposure concentrations resulted in declines in the levels of MT mRNA. (3) No significant effe cts of Cd on ROS production were observed at Cd concentrations up to 3 6 mu M CdCl2. However, ROS production decreased in a concentration-dep endent fashion at CdCl2 concentrations from 36 to 356 mu M, the highes t concentration tested. (4) At these higher concentrations of Cd, the concomitant decrease in MT mRNA inducibility and suppression of ROS pr oduction were probably manifestations of the general cytotoxicity of C d. ROS suppression can result in reduced resistance to infectious agen ts, suggesting that Cd is immunotoxic to C. virginica. (C) 1997 Elsevi er Science Inc.