ToxSci Advance Access originally published online on December 12, 2006
Toxicological Sciences 2007 96(1):92-100; doi:10.1093/toxsci/kfl182
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Posttranscriptional Inhibition of Interferon-Gamma Production by Lead
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* Department of Occupational Health, Catholic University of Daegu, Kyongsan-si, Kyongbuk, Korea 712-702
Laboratory of Clinical and Experimental Endocrinology and Immunology, Wadsworth Center, New York State Department of Health, Albany, New York 12201
1 To whom correspondence should be addressed at Laboratory of Clinical and Experimental Endocrinology and Immunology, Wadsworth Center, New York State Department of Health, PO Box 509, Albany, NY 12201-0509. Fax: (518)-474-1412. E-mail: david.lawrence{at}wadsworth.org.
Received September 29, 2006; accepted November 1, 2006
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Abstract |
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Lead (Pb) is known to preferentially suppress the activation and development of type-1 CD4+ helper T cell (Th1) responses, whereas it enhances the development of type-2 CD4+ helper T cell (Th2) responses. The inhibition of interferon-gamma (IFN
) production has been demonstrated in vitro with a Th1 clone and DO11.10 ovalbumin-transgenic (OVA-tg) CD4+ T cells, and in vivo with wild-type and OVA-tg BALB/c mice; however, the mechanisms responsible for the Pb-induced downregulation of IFN have not been reported. Here, we assessed the modulation of IFN production at the mRNA and protein levels. Pb did not significantly affect IFN mRNA expression by a Th1 clone or activated splenocytes, as measured by reverse transcriptase–polymerase chain reaction (RT-PCR), ribonuclease protection, and real-time RT-PCR. However, Pb did significantly lower the amount of IFN protein in supernatants and cell lysates of antigen-activated T cells in comparison to stimulated controls, suggesting that the lower amounts of IFN released into culture supernatants were not due to a blockage of secretion that gave rise to a cytoplasmic accumulation of IFN. Pb inhibition also was not prevented by addition of zinc or iron. Pb did not enhance protein degradation of IFN, in that lactacystin, an effective blocker of proteosomal proteolysis, did not prevent loss of IFN; additionally, Pb did not accelerate loss of IFN after cycloheximide treatment. Pb did, however, significantly suppress IFN biosynthesis, as investigated using 35S-incorporation in pulse/chase experiments, although it did not suppress total protein synthesis, indicating that Pb selectively inhibits IFN biosynthesis. Thus, Pb appears to selectively interfere with the translation of certain proteins, such as IFN. IL-12 blocked Pb's preferential promotion of Th2 cells, but absence of STAT6 did not prevent the Pb skewing. Thus, Pb may modulate unique regulatory pathways.