Bogdan C, Vodovotz Y, Paik J, Xie Q W, Nathan C
Beatrice and Samuel A. Seaver Laboratory, Department of Medicine, Cornell University Medical College, New York, NY 10021.
J Immunol. 1993 Jul 1;151(1):301-9.
A nitric oxide synthase (iNOS) inducible by cytokines and microbial products contributes to the cytotoxic and antimicrobial activity of mouse macrophages. Bacterial LPS interacts synergistically with IFN-gamma to induce iNOS when both stimuli are added together. In contrast, we show here that pre-exposure of peritoneal macrophages to low concentrations of LPS suppresses the induction of iNOS when IFN-gamma is added subsequently. Suppression required pretreatment with LPS for at least 8 h and was optimal with LPS concentrations in the range of 50 to 200 pg/ml. Suppression was exerted by smooth and rough forms of LPS from Escherichia coli and by lipid A from Salmonella minnesota, but not by a biologically inactive lipid A from Rhodobacter sphaeorides. Suppression of nitrite accumulation and iNOS enzyme activity by prior exposure of macrophages to LPS could be explained by their markedly decreased content of iNOS protein, as revealed by immunoblot with monospecific anti-iNOS IgG. Messenger RNA for iNOS was affected in a biphasic manner by pretreatment with LPS. Five hours after addition of IFN-gamma, iNOS mRNA levels were unaltered or even enhanced by pretreatment with LPS, but by 24 to 48 h, expression of iNOS mRNA was inhibited strongly enough to account for the reduced levels of iNOS protein. Suppression by LPS did not appear to be mediated by endogenous prostaglandins, transforming growth factor-beta, or TNF-alpha, even though pretreatment with exogenous TNF-alpha was also suppressive. These findings suggest that preactivation of pathways normally contributing to synergistic induction of iNOS may deplete macrophages of factors needed for its expression. Regulation of iNOS in vivo may depend on the relative tempo with which the inflammatory and immune responses evolve.
一种可被细胞因子和微生物产物诱导的一氧化氮合酶（iNOS）有助于小鼠巨噬细胞的细胞毒性和抗菌活性。当同时添加细菌脂多糖（LPS）和干扰素-γ（IFN-γ）这两种刺激物时，它们会协同诱导iNOS。相比之下，我们在此表明，将腹腔巨噬细胞预先暴露于低浓度的LPS会抑制随后添加IFN-γ时iNOS的诱导。这种抑制需要用LPS预处理至少8小时，且在LPS浓度为50至200 pg/ml范围内效果最佳。来自大肠杆菌的光滑型和粗糙型LPS以及来自明尼苏达沙门氏菌的脂多糖A均可发挥抑制作用，但球形红杆菌的无生物学活性的脂多糖A则无此作用。巨噬细胞预先暴露于LPS后对亚硝酸盐积累和iNOS酶活性的抑制作用，可通过免疫印迹法用单特异性抗iNOS IgG检测发现的iNOS蛋白含量显著降低来解释。iNOS的信使核糖核酸（mRNA）受到LPS预处理的双相影响。添加IFN-γ 5小时后，LPS预处理对iNOS mRNA水平无影响甚至使其升高，但到24至48小时，iNOS mRNA的表达被强烈抑制，足以解释iNOS蛋白水平的降低。LPS的抑制作用似乎不是由内源性前列腺素、转化生长因子-β或肿瘤坏死因子-α介导的，尽管外源性肿瘤坏死因子-α预处理也具有抑制作用。这些发现表明，正常情况下有助于iNOS协同诱导的信号通路的预激活可能会耗尽巨噬细胞中iNOS表达所需的因子。体内iNOS的调节可能取决于炎症和免疫反应演变的相对速度。
