Effects of cadmium on metallothionein levels in human peripheral blood leukocytes: a comparison with zinc.

Metallothioneins (MT) are low-molecular-weight, cysteine-rich proteins that are induced in response to a variety of chemical stresses and therefore can be used to assess human exposure to environmental agents. In the current study, flow cytometry was used to characterize the basal and cadmium-induced expression of MT in the three major leukocyte populations of human peripheral blood. In the analysis, monocytes were the most sensitive leukocytes to this toxic metal, with significant increases in cellular MT levels being detected at concentrations of cadmium as low as 0.1 microM (24 h). The lymphocyte population also exhibited pronounced treatment-associated elevations in cellular MT, while the granulocyte population was found to be nonresponsive. Although both CdCl2 (3 microM) and ZnCl2 (50 microM) induced MT expression in monocytes to a similar degree and did not affect the expression of this protein in granulocytes, cadmium but not zinc treatment induced dramatic increases in MT levels of lymphocytes. Our results indicate that cellular MT protein levels, as determined by this flow cytometric method, may be used to characterize the differential responsiveness of the major human leukocyte subpopulations to transitional metals. It is evident from the current work that the responsiveness of all peripheral blood leukocyte populations should be analyzed in exposure assessment studies.