Mercuric chloride down‐regulates T cell interferon‐γ Production in Brown Norway but not in Lewis rats; role of glutathione

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Abstract
Injection of a low dose of mercuric chloride into Brown Norway (BN) rats caused a marked decrease in the concanavalin A (ConA)-induced generation of interferon-γ-producing cells (IFN-γ pc) in spleen cell cultures prepared 1 h after mercury administration. A second injection 48 h later caused a further diminution of IFN-γ pc down to 30% of the number generated in splenocyte cultures of phosphate-buffered saline (PBS)-injected controls. Injection of Lewis rats with either one or two doses of HgCl2 revealed no inhibitory effect on splenic IFN-γ production. The presence of the reduced form of glutathione (GSH) in the culture medium was found to be essential in these experiments. In the absence of GSH there was an overall 20-fold reduction of the number of IFN-γ pc in splenocyte cultures of normal or PBS-injected rats, which was further reduced to a 60- to 70-fold-lower level in cultures of rats exposed to HgCl2. This mercury-mediated extra reduction could be fully reversed with an excess (2 mM) of GSH in Lewis but not in BN splenocyte cultures. Since the bivalent Hg2+ ion is known to bind to and inactivate sulfydryl groups of proteins and low molecular weight thiols, most notably GSH, we investigated a possible role for thiols in IFN-γ production. It was found that the generation of IFN-y pc in normal BN and Lewis splenocyte cultures was strongly dependent on GSH or its precursor cysteine in the culture medium. Other thiol compounds were also effective but disulfides were completely inactive. Depletion of intracellular GSH in ConA-stimulated splenocytes by buthionine sulfoximide (BSO), an inhibitor of de novo GSH biosynthesis, strongly inhibited the generation of IFN-γ pc. The inhibitory effect of BSO was not abolished by the addition of interleukin-2 (IL-2), but was mimicked with antibodies directed to the IL-2 receptor. The data stress the importance of GSH in the enhancement of IL-2-mediated IFN-γ production and are most consistent with a model in which mercury interferes with T cell IFN-γ production by affecting the intracellular availability of GSH. The strain-specific susceptibility to mercury-mediated inhibition of IFN-γ production is discussed.