Effect of cytotoxic T-lymphocyte-associated protein 4 on CD4+CD25+ regulatory T cells in murine Schistosomiasis japonica

• Anti-CTLA-4 mAb favors the host to clear S. japonicum.
• Anti-CTLA-4 mAb may bias and enhance Th1-type host immune responses.
• Egg granuloma sizes in anti-CTLA-4 mAb-treated animals were significantly larger.
• Tregs and CTLA-4 may exert synergistic effect on the immune evasion of S. japonicum.

In a previous study we demonstrated that CD4+CD25+ regulatory T cells (Tregs) contributed to the escape of Schistosoma japonicum (S. japonicum) from the host’s immune responses. In this paper, we studied the effect of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) on CD4+CD25+ Tregs in murine Schistosomiasis japonica and its corresponding role in the immune evasion of S. japonicum in mice. The results showed substantial reductions of worm burden and egg production in worm groups treated with anti-CD25 or anti-CTLA-4 monoclonal antibodies (mAb) compared to an infected but untreated control. The reduction effect was even enhanced in an experimental group co-treated with both mAbs. Compared to the control group, the percentage of CD4+CD25+ Tregs was very much lower in the anti-CD25 mAb group as determined by FACS analyses and higher in the anti-CTLA-4 mAb group. ELISA analyses showed that both the anti-CTLA-4 mAb and the co-treated groups had higher levels of cytokines compared to the control group as well as larger egg granuloma sizes as determined by microscopical analyses of liver sections of infected mice. These results suggest that treatment with an anti-CTLA-4 mAb allows the host to clear S. japonicum, but at the cost of elevated pathological damage. The latter indicated a role of CTLA-4 in granuloma formation. Moreover, CD4+CD25+ Tregs and CTLA-4 may exert synergistic effects during immune evasion processes by enhancing Th1-type immune response.