Lüder C G, Giraldo-Velásquez M, Sendtner M, Gross U
Institute of Hygiene and Microbiology, University of Würzburg, Josef-Schneider-Strasse 2, Würzburg, 97080, Germany.
Exp Parasitol. 1999 Sep;93(1):23-32. doi: 10.1006/expr.1999.4421.
The central nervous system (CNS) of the intermediate host plays a central role in the lifelong persistence of Toxoplasma gondii as well as in the pathogenesis of congenital toxoplasmosis and reactivated infection in immunocompromised patients. In order to analyze the parasite-host interaction within the CNS, the host cell invasion, the intracellular replication, and the stage conversion from tachyzoites to bradyzoites was investigated in mixed cultures of dissociated CNS cells from cortices of Wistar rat embryos. Two days post infection (p.i.) with T. gondii tachyzoites, intracellular parasites were detected within neurons, astrocytes, and microglial cells as assessed by double immunofluorescence and confocal microscopy. Quantitative analyses revealed that approximately 10% of neurons and astrocytes were infected with T. gondii, while 30% of the microglial cells harbored intracellular parasites. However, the replication of T. gondii within microglial cells was considerably diminished, since 93% of the parasitophorous vacuoles (PV) contained only one to two parasites which often appeared degenerated. This toxoplasmacidal activity was not abrogated after treatment with NO synthase inhibitors or neutralization of IFN-gamma production. In contrast, 30% of the PV in neurons and astrocytes harbored clearly proliferating parasites with at least four to eight parasites per vacuole. Four days p.i. with tachyzoites of T. gondii, bradyzoites were detected within neurons, astrocytes, and microglial cells of untreated cell cultures. However, the majority of bradyzoite-containing vacuoles were located in neurons. Spontaneous differentiation to the bradyzoite stage was not inhibited after addition of NO synthase inhibitors or neutralization of IFN-gamma. In conclusion, our results indicate that intracerebral replication of T. gondii as well as spontaneous conversion from the tachyzoite to the bradyzoite stage is sustained predominantly by neurons and astrocytes, whereas microglial cells may effectively inhibit parasitic growth within the CNS.
中间宿主的中枢神经系统（CNS）在刚地弓形虫的终身持续性感染以及先天性弓形虫病的发病机制和免疫功能低下患者的再激活感染中起着核心作用。为了分析中枢神经系统内的寄生虫 - 宿主相互作用，在来自Wistar大鼠胚胎皮质的解离中枢神经系统细胞的混合培养物中研究了宿主细胞入侵、细胞内复制以及速殖子向缓殖子的阶段转换。用刚地弓形虫速殖子感染两天后（p.i.），通过双重免疫荧光和共聚焦显微镜评估，在神经元、星形胶质细胞和小胶质细胞内检测到细胞内寄生虫。定量分析显示，约10%的神经元和星形胶质细胞被刚地弓形虫感染，而30%的小胶质细胞含有细胞内寄生虫。然而，刚地弓形虫在小胶质细胞内的复制明显减少，因为93%的寄生泡（PV）仅含有一到两个寄生虫，这些寄生虫通常看起来已退化。在用一氧化氮合酶抑制剂处理或中和γ干扰素产生后，这种杀弓形虫活性并未消除。相比之下，神经元和星形胶质细胞中30%的PV含有明显增殖的寄生虫，每个泡内至少有四到八个寄生虫。用刚地弓形虫速殖子感染四天后，在未处理的细胞培养物的神经元、星形胶质细胞和小胶质细胞内检测到缓殖子。然而，大多数含缓殖子的泡位于神经元中。添加一氧化氮合酶抑制剂或中和γ干扰素后，向缓殖子阶段的自发分化并未受到抑制。总之，我们的结果表明，刚地弓形虫的脑内复制以及从速殖子到缓殖子阶段的自发转换主要由神经元和星形胶质细胞维持，而小胶质细胞可能有效抑制中枢神经系统内的寄生虫生长。
