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In vitro immune effects of Pt compounds of occupational and/or environmental importance, or those used in cancer treatment were studied. Spontaneous and PHA-stimulated proliferation of peripheral blood mononuclear cells (PBMC) and in vitro release of TNF-alpha, IFN-gamma, and IL-5 were assessed in presence of high and very low concentrations of Pt salts: 10(-4) and 10(-7) M (NH4)2[PtCl6], (NH4)2[PtCl4], PtCl4, PtCl2, Na2PtI6, and cis-diaminedichloroPt (CisPt). Spontaneous and PHA-stimulated PBMC proliferation were both inhibited by 10(-4) M (NH4)2[PtCl6] and (NH4)2[PtCl4], while only PHA-stimulated proliferation was inhibited by 10(-4) M CisPt, without significant effects of the other Pt salts. TNF-alpha release from PBMC was reduced by 10(-4) M (NH4)2[PtCl6] and INF-gamma release was reduced by 10(-4) and 10(-7) M hexa- and tetrachloroplatinate and 10(-4) M Na2PtI6, but not by other Pt salts. IL-5 release (related to the Th2 immune response) was inhibited by 10(-4) M (NH4)2[PtCl6], (NH4)2[PtCl4] and Na2PtI6, but it was enhanced by both 10(-4) and 10(-7) M PtCl4. PtCl2 did not influence the immune effects. The study shows Pt salts have immune effects and their potency is ranked in the following order: (NH4)2[PtCl6](NH4)2[PtCl4]Na2PtI6 and CisPtPtCl4PtCl2. These results indicate that certain Pt salts affect lymphocyte proliferation and cytokine release. The intracellular mechanisms responsible for such effects have not been identified.