Abstract: 【Abstract】 Objective To observe the changes of CD4⁺CD25⁺ regulatory T cells in the spleen of mice infected with T.gondii. Methods Twenty?鄄eight female C57BL/6 mice were randomly divided into four groups. Three groups of mice were inoculated intraperitoneally with 104 tachyzoites in 200 μl sterile PBS. At 2，4 and 6 days post-infection， the spleens were removed. The expression level of Foxp3 mRNA in splenic CD4+ T cells was quantitated by real-time PCR. The percentage of CD4⁺CD25⁺ regulatory T cells in CD4⁺ T cells was determined by flow cytometry， and the absolute numbers of splenic CD4⁺CD25⁺ regulatory T cells and CD4⁺ T cells were assessed. The fourth group was injected intraperitoneally with 200 μl sterile PBS as control. Results The relative mRNA level of Foxp3 in splenic CD4⁺ T cells at day 4 （1.89±0.23） and day 6 （1.79±0.24） post-infection was significantly higher than control （1.00±0.12）（P＜0.01）. After an initial up-regulation at 2 days post-infection （15.07%±2.73%） （P＜0.05）， the proportion of CD4⁺CD25⁺ regulatory T cells in CD4⁺ T cells at day 4 （24.29%±3.19%） and day 6 （19.80%±2.66%） post-infection was significantly higher than control （11.58%±2.04%） （P＜0.01）. At day 6 post-infection， both the percentage of splenic CD4⁺ T cells in splenocytes（5.49%±1.71%） and absolute number of CD4⁺ T cells （1.71±0.44）×10⁶ greatly decreased（P＜0.01）. Conclusion The proportion of splenic CD4⁺CD25⁺ regulatory T cells in CD4⁺ T cells has been up-regulated following T.gondii infection， which is mainly due to a great reduction of CD4⁺ T cells in the spleen.

Key words: Toxoplasma gondii, CD4⁺CD25⁺ regulatory T cells, Immunosuppression