Effects of physiological concentrations of heavy metals both individually and in mixtures on the viability and function of peripheral blood human leukocytes in vitro.

Among environmental contaminants recognized for their toxicity and global distribution, heavy metals are elements known to exert serious ecological consequences. Published experiments on the immunotoxic effects of metals such as methylmercury (MeHg), cadmium (Cd), and lead (Pb) were often conducted at concentrations higher than those present in the environment or those in human blood. In the present study the in vitro effects on human blood of environmentally relevant concentrations of MeHg (33-200 mug/L), Cd (3.1-16 mug/L), and Pb (75-207 mug/L) were assessed individually and in mixtures on the viability and immune competence of peripheral blood leukocytes (PBLs). At MeHg concentrations of 120 and 200 mug/L both lymphocyte proliferation, as measured by [(3)H]thymidine incorporation, and natural killer (NK) cytotoxity activity, as determined by dioctadecyloacarbocyanine, were suppressed. Our results showed an increase of intracellular thiols in lymphocytes and in monocytes at all the concentrations of metals tested. A decrease in the level of metallothionein (MT) was seen in monocytes in presence of Hg at concentration of 120 mug/L and higher. For lymphocytes, a significant increase of MT in groups containing the lower concentrations of Cd, and Hg was noted. In summary, it appears that Hg represents the most toxic metal at environmentally relevant concentrations on human peripheral mononuclear cells. The effects of Hg exposure were greater on lymphocytes and NK cells than on monocytes.