Reduced expression of the inducible nitric oxide synthase after infection with Toxoplasma gondii facilitates parasite replication in activated murine macrophages
Reduced expression of the inducible nitric oxide synthase after infection with Toxoplasma gondii facilitates parasite replication in activated murine macrophages
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DOI：
10.1016/s0020-7519(03)00092-4
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发表时间：
2003-07-30
影响因子：
4
通讯作者：
Gross, U
中科院分区：
文献类型：
--
作者：
Lüder, CGK;Algner, M;Gross, U
活化的鼠巨噬细胞产生一氧化氮被认为是限制专性细胞内寄生虫弓形虫复制的重要机制。在这项研究中，我们描述了弓形虫对一氧化氮产生和诱导型一氧化氮合酶表达的影响，并确定了寄生虫诱导逃避这种潜在效应机制的功能意义。用小鼠无毒弓形虫菌株感染原代骨髓来源的巨噬细胞或单核/巨噬细胞RAW264.7细胞，显着降低了通过干扰素γ或脂多糖或干扰素γ加脂多糖激活诱导的一氧化氮的产生。重要的是，弓形虫对一氧化氮产生的下调使得寄生虫在单独用干扰素-γ或单独脂多糖激活的巨噬细胞中大量复制。此外，通过添加硝普钠来补充内源性一氧化氮至未感染的干扰素-γ-或脂多糖-激活的巨噬细胞中观察到的水平几乎完全消除了弓形虫的复制。尽管弓形虫也部分抑制由干扰素-γ和脂多糖诱导的一氧化氮的旺盛产生，但抑制的程度不足以允许寄生虫在这些协同激活的巨噬细胞中进行细胞内繁殖。干扰素γ、脂多糖和干扰素γ加脂多糖诱导的一氧化氮产生的抑制与诱导型一氧化氮合酶蛋白水平的降低相一致。这种下调需要通过免疫荧光显微镜测定细胞内寄生虫的存在。弓形虫感染 RAW264.7 细胞后，干扰素-y 单独或与脂多糖联合诱导的诱导型一氧化氮合酶转录物也出现剂量依赖性下调。总之，这种逃避策略使得寄生虫能够在被干扰素γ或脂多糖适度激活的巨噬细胞中复制，但不足以逃避被干扰素γ加脂多糖完全激活的巨噬细胞的抗寄生虫活性。一氧化氮的产生及其对寄生虫的部分抑制可能会调节弓形虫病期间的寄生虫-宿主平衡。 (C) 2003 年澳大利亚寄生虫学协会。由 Elsevier Science Ltd 出版。保留所有权利。
Production of nitric oxide by activated murine macrophages is thought to represent an important mechanism to restrict replication of the obligate intracellular parasite Toxoplasma gondii. In this study, we characterised the effect of T. gondii on nitric oxide production and expression of the inducible nitric oxide synthase and determined the functional significance of a parasite-induced evasion of this potential effector mechanism. Infection of primary bone marrow-derived macrophages or monocytic/macrophage RAW264.7 cells with a mouse-avirulent T. gondii strain significantly decreased nitric oxide production that had been induced by activation with either interferon-gamma or lipopolysaccharide or interferon-gamma plus lipopolysaccharide. Importantly, down-regulation of nitric oxide production by T. gondii enabled considerable parasite replication in macrophages activated with interferon-gamma alone or lipopolysaccharide, alone. Furthermore, supplementation of endogenous nitric oxide by addition of sodium nitroprusside to levels as observed in uninfected interferon-gamma- or lipopolysaccharide-activated macrophages almost completely abrogated replication of T. gondii. Although T. gondii also partially inhibited the vigorous nitric oxide production induced by interferon-gamma along with lipopolysaccharide, the magnitude of inhibition did not suffice to allow intracellular propagation of the parasite in these synergistically activated macrophages. Inhibition of interferon-gamma-, lipopolysaccharide- and interferon--y plus lipopolysaccharide-induced nitric oxide production coincided with reduced inducible nitric oxide synthase protein levels. Such down-regulation required the presence of intracellular parasites as determined by immunofluorescence microscopy. Inducible nitric oxide synthase transcripts induced by interferon--y alone or in combination with lipopolysaccharide were also dose-dependently down-regulated after infection of RAW264.7 cells with T gondii. In conclusion, this evasion strategy enables parasite replication in macrophages moderately activated by interferon-gamma or lipopolysaccharide, but does not suffice to evade the anti-parasitic activity of macrophages fully activated by interferon-gamma plus lipopolysaccharide. Nitric oxide production and its partial inhibition by the parasite may modulate the parasite-host equilibrium during toxoplasmosis. (C) 2003 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.