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 2 × 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, PBS/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)]mm ³ was significantly smaller than that of control [(9027.46±1362.01)] mm ³ (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.