The dysfunction of CD4(+)CD25(+) regulatory T cells contributes to the abortion of mice caused by Toxoplasma gondii excreted-secreted antigens in early pregnancy.

Toxoplasma gondii is an opportunistic intracellular parasite that is highly prevalent in human and warm-blooded animals throughout the world, leading to potentially severe congenital infections. Although the abortion caused by T. gondii is believed to be dependent on the timing of maternal infection during pregnancy, the mechanism remains unclear. This study was focused on the effects of T. gondii excreted-secreted antigens on pregnant outcomes and CD4(+)CD25(+) Foxp3(+) regulatory T cells at different stages of pregnancy. The results showed that in mice the frequency and suppressive function of CD4(+)CD25(+) regulatory cells were diminished after injection of T. gondii excreted-secreted antigens at early and intermediate stages of pregnancy. The abortion caused by T. gondii excreted-secreted antigens at early pregnancy could be partly prevented by adoptively transferring of CD4(+)CD25(+) cells from the mice injected with T. gondii excreted-secreted antigens at late pregnancy, but not from the mice with the same treatment at early pregnancy. Furthermore, T. gondii excreted-secreted antigens induced apoptosis of CD4(+)CD25(+) regulatory cells of mice in early and intermediate stages of pregnancy by down-regulating their Bcl-2 expressions and Bcl-2/Bax ratio. This study provides new insights into the mechanism that T. gondii infection is the high risk factor for abortion in early pregnancy.

[Effects of excreted/secreted antigens of Toxoplasma gondii on CD4+ CD25+ Foxp3+ T cells and NK cells of melanoma-bearing mice].

OBJECTIVE: To explore the effects of excreted/secreted antigens (ESA) of Toxoplasma gondii on CD4+CD25+ Foxp3+ T cells and NK cells of melanoma-bearing mice, as well as the tumor growth. METHODS: B16F10 (denoted B16) tumor cells were cultured in complete medium and maintained by serial passage in vitro. The 2x 10(5) B16 tumor cells were injected into the right flank of the mouse to establish the tumor-bearing mice model. Mice were randomly divided into four groups, namely PBS, B16F10, PES/ESA and B16F10/ESA groups after ESA injections. On days 2, 4 and 6 post-ESA injection, the spleens were removed. The percentage of CD4+CD25+ Foxp3+ T cells and NK cells in splenocytes were determined by flow cytometry; the suppression functions of CD4+CD25+ Tregs and the NK cell activity were detected by WST-8 and LDH methods, respectively. The tumor growth of each group was measured. RESULTS: On Days 4 and 6 post-ESA injection, the percentages of CD4+CD25+ Foxp3+ T cells in splenocytes of the B16F10/ESA-injected mice decreased being (1.65 +/- 0.18)% and (1.56 +/- 0.17)%, respectively, and compared with those in the B16-injected mice [(2.47 +/- 0.10)% and (2.82 +/- 0.12)%], there were significant differences (both P values < 0.05). The inhibition of CD4+CD25+ Tregs of the B16F10/ESA-injected mice decreased markedly on Day 4 (50.03%) and Day 6 (50%) compared with those in the control (75.03% and 78.14%) post-ESA injection, there were significant difference (both P values < 0.05). The percentages of NK cells in splenocytes on Day 6 post-ESA injection [(3.58 +/- 0.07)%] was significantly higher than that of control [(2.61 +/- 0.13)%]. The activities of NK cells from B16F10/ESA - injected mice against B16 cells at different effect - to - target cell ratios (5 : 1, 10 :1, 20 : 1), increased significantly being 26.51%, 35.25%, 60.19%, respectively, while compared with those in the control (16.81%, 24.63% and 45.62%), there were significant differences (all P values < 0.05). In addition, the volume of the B16 tumors [(6 208.34 +/- 443.64)]mm3 was significantly smaller than that of control [(9 027.46 +/- 1 362.01)] mm3(P < 0.05) when measured at Day 35 post-tumor innoculation. CONCLUSIONS: T. gondii ESA can downregulate CD4+CD25+Tregs while upregulating NK cells of B16 tumor-bearing mice quantitatively and functionally, therefore plays a role in suppression of tumor growth.

[Changes of CD4+CD25+ T cells in the spleen of mice infected with Toxoplasma gondii].

OBJECTIVE: To observe the changes of CD4+CD25+ regulatory T cells in the spleen of mice infected with T.gondii. METHODS: Twenty-eight female C57BL/6 mice were randomly divided into four groups. Three groups of mice were inoculated intraperitoneally with 10(4) tachyzoites in 200 microl 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 microl 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%+/-l.71%) and absolute number of CD4+ T cells (1.71+/-0.44)x106 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.