Effect and mechanism of CD4+CD25+ regulatory T cells on protective efficacy of protein vaccine against Schistosoma japonicum in mice

Abstract

To explore the effect and mechanism of CD4+CD25+ Tregs (Tregs) on the protective efficacy of gluthatione-S-transferase (GST) against Schistosoma japonicum in mice. Female BALB/c mice were divided randomly into five groups：a normal control group, an infected control group, an anti-CD25mAb group, a GST immunization group and a combination group with GST immunization and anti-CD25 mAb. The GST group and combination group were injected percutaneously with GST 50 μg each mouse, the other two groups were injected with equal volume PBS. The immunization was performed for 3 times for two-week interval, and 2 weeks after the last immunization, each mouse was challenged with 40 S. japonicum cercaria. Two weeks post-infection, the combination group and anti-CD25 mAb group were injected intraperitoneally with 300 μg antiCD25 mAb each mouse. The mice were succumbed 2 weeks, 3 weeks, 4 weeks and 5 weeks post-infection respectively. The percentages of CD4+CD25+ Tregs in splenocytes of mice were measured with flow cytometer. The levels of IFN-γ, IL-2, IL-4, IL-5 and TGF-β in cell cultural supernatants were determined by sandwich-ELISA after stimulation with Con A. The liver sections were stained with hematoxylin and eosin. The worm burden in the combination group (15.80±2.74) was significantly lower than those of the infected control group (27.78±3.15), anti-CD25 mAb group (21.50±4.21), and GST group (20.84± 6.46). Compared to those of the infected control group, the percentages of CD4+CD25+ Tregs were significantly higher in the GST group, while the percentages of CD4+CD25+ Tregs were significantly lower post-anti-CD25 mAb-administration. Regardless of GST administration, the levels of IFN-γ, IL-2, IL-4 and IL-5 after anti-CD25 mAb were significantly higher than those of the infected control groups. There were no significant differences of egg granuloma and the level of TGF-β between each group. CD4+CD25+ Tregs could be partially blocked by anti-CD25 mAb while Th1 and Th2 type immunization response could be enhanced, which plays a role in improving the protective efficacy of GST against of S. japonicum.