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.