Immunomodulation by heavy metals tested individually or in mixtures in rainbow trout (Oncorhynchus mykiss) exposed in vivo

The objective of this study was to evaluate the effect of heavy metals, at environmentally relevant concentrations, on the immune response of rainbow trout. Trout were exposed for 30 d to cadmium chloride (CdCl2), mercuric ch loride (HgCl2), or zinc chloride (ZnCl2) either individually or in combinat ions: CdCl2/HgCl2, CdCl2/ZnCl2, HgCl2/ZnCl2, or CdCl2/HgCl2/ZnCl2. Followin g the 30-d exposure, parameters of the nonspecific cellular immune response (phagocytosis, respiratory burst, and lymphoblastic proliferation) and of the nonspecific humoral immune response (lysozyme activity and the level of immunoglobulin) were measured. The results obtained indicate that individu ally, all three metals tested induce significant immunomodulations. However , the toxicity of mercury or cadmium is significantly reduced in fish simul taneously exposed to zinc, indicating that a protection is afforded by zinc against cadmium- and mercury-induced immunotoxicity.