Abstract: Objective  To investigate microglial activation and inflammatory cytokine expression in chronic Toxoplasma gondii infection.  Methods  Thirty mice were randomly divided into chronic T. gondii infection group and normal control group. Each mouse in infection group was infected orally with 30 cysts of the TgCtwh6 strain. Normal group received 0.3 ml normal saline. On the 60th day after infection， immunohistochemical staining was performed to assess the number of microglia and morphological change. The expression of inflammatory cytokines （IL-1β， IL-6， and TNF-α） was measured by RT-PCR. The expression of iNOS was determined by Western blotting and immunofluorescence.  Results  Immunohistochemistry analysis showed that the number of Iba-1 positive cells in the cortex and hippocampus of infection group （16.5±0.8 and 17.9±1.1） was higher than that of the control（8.4±0.2 and 10.3±0.8）（P<0.05）. Iba-1 positive cells （i.e. microglia） had larger cell bodies and ramified morphology. RT-PCR result indicated that mRNA level of IL-1β， IL-6， and TNF-α in infection group （0.862±0.169， 0.407±0.158， and 0.305±0.073） was significantly higher than that of the control （0.149±0.030， 0.037±0.008， and 0.001±0.001）（P<0.05）. The iNOS protein expression in infection group （0.252±0.164） was higher than that of the control（0.0433±0.004）（P<0.05）. Immunofluorescence demonstrated that iNOS protein released by activated microglia.  Conclusion  Chronic T. gondii infection caused micro-glial activation， which up-regulate the level of IL-1β， IL-6， TNF-α， and iNOS.

Key words: Toxoplasma gondii, Chronic infection, Microglia, Inflammatory cytokines