Heo Yong, Mondal Tapan K, Gao Donghong, Kasten-Jolly Jane, Kishikawa Hiroko, Lawrence David A
Department of Occupational Health, Catholic University of Daegu, Kyongsan-si, Kyongbuk, Korea 712-702.
Toxicol Sci. 2007 Mar;96(1):92-100. doi: 10.1093/toxsci/kfl182. Epub 2006 Dec 12.
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 (IFNgamma) 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 IFNgamma have not been reported. Here, we assessed the modulation of IFNgamma production at the mRNA and protein levels. Pb did not significantly affect IFNgamma 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 IFNgamma protein in supernatants and cell lysates of antigen-activated T cells in comparison to stimulated controls, suggesting that the lower amounts of IFNgamma released into culture supernatants were not due to a blockage of secretion that gave rise to a cytoplasmic accumulation of IFNgamma. Pb inhibition also was not prevented by addition of zinc or iron. Pb did not enhance protein degradation of IFNgamma, in that lactacystin, an effective blocker of proteosomal proteolysis, did not prevent loss of IFNgamma; additionally, Pb did not accelerate loss of IFNgamma after cycloheximide treatment. Pb did, however, significantly suppress IFNgamma biosynthesis, as investigated using 35S-incorporation in pulse/chase experiments, although it did not suppress total protein synthesis, indicating that Pb selectively inhibits IFNgamma biosynthesis. Thus, Pb appears to selectively interfere with the translation of certain proteins, such as IFNgamma. 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.
已知铅（Pb）会优先抑制1型CD4 +辅助性T细胞（Th1）反应的激活和发展，而它会增强2型CD4 +辅助性T细胞（Th2）反应的发展。体外实验已证明，Th1克隆和DO11.10卵清蛋白转基因（OVA-tg）CD4 + T细胞会抑制干扰素-γ（IFNγ）的产生，体内实验也证明野生型和OVA-tg BALB / c小鼠会出现这种情况；然而，尚未报道铅诱导IFNγ下调的机制。在此，我们在mRNA和蛋白质水平评估了IFNγ产生的调节情况。通过逆转录聚合酶链反应（RT-PCR）、核糖核酸酶保护和实时RT-PCR测量，铅对Th1克隆或活化的脾细胞的IFNγ mRNA表达没有显著影响。然而，与刺激对照组相比，铅确实显著降低了抗原激活的T细胞上清液和细胞裂解物中IFNγ蛋白的量，这表明释放到培养上清液中的IFNγ量较低并非由于分泌受阻导致IFNγ在细胞质中积累。添加锌或铁也不能阻止铅的抑制作用。铅不会增强IFNγ的蛋白质降解，因为蛋白酶体蛋白水解的有效阻断剂乳胞素并不能阻止IFNγ的损失；此外，在环己酰亚胺处理后，铅也不会加速IFNγ的损失。然而，在脉冲/追踪实验中使用35S掺入法研究发现，铅确实显著抑制IFNγ的生物合成，尽管它不会抑制总蛋白质合成，这表明铅选择性地抑制IFNγ的生物合成。因此，铅似乎选择性地干扰某些蛋白质的翻译，例如IFNγ。白细胞介素-12阻断了铅对Th2细胞的优先促进作用，但缺乏信号转导和转录激活因子6（STAT6）并不能阻止铅的偏向作用。因此，铅可能调节独特的调节途径。
